Unidirectional wood fiber paper and preparation method therefor, unidirectional wood fiber paper prepreg and preparation method therefor, and wood fiber paper-reinforced composite material

Abstract

The present invention provides unidirectional wood fiber paper. The unidirectional wood fiber paper is formed shrinking, in at least one direction, a unidirectional wood veneer from which some substances have been removed; said some substances include lignin and hemicellulose; the thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm; and the apparent thickness of the unidirectional wood fiber paper under a planar pressure of not greater than 0.005 MPa does not exceed four times the average thickness of the unidirectional wood fiber paper. Compared with the prior art, the unidirectional wood fiber paper provided in the present invention is thin, has excellent mechanical properties and anisotropy, and is made of 100% pure natural materials; moreover, the shrinkage of the unidirectional wood fiber paper achieves a densification effect on the unidirectional wood fiber paper in the thickness direction, and also enhances the transverse bonding strength and compactness of the unidirectional wood fiber paper, thereby reducing transverse cracking of the unidirectional wood fiber paper.

Description

Unidirectional wood fiber paper and preparation method thereof, unidirectional wood fiber paper prepreg and preparation method thereof, wood fiber paper reinforced composite material

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on February 6, 2024, with application number 2024101716440 and invention name “A wood fiber reinforced material, its preparation method and application”, parts of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of fiber-reinforced composite materials, and in particular relates to unidirectional wood fiber paper and a preparation method thereof, a unidirectional wood fiber paper prepreg and a preparation method thereof, and a wood fiber paper reinforced composite material and a preparation method thereof. Background Art

[0003] The plant fiber prepreg market is one of the emerging markets in the composite materials sector. With growing demand for sustainable materials and increasing environmental awareness, plant fiber prepregs are gaining increasing attention across multiple industries. However, compared to traditional synthetic fibers, the production cost of plant fiber prepregs remains relatively high, and their performance is inferior to that of man-made fibers, hindering their market adoption. A major reason for this is that natural plant fibers, especially high-performance hemp, are short (centimeter-sized). Producing continuous plant fiber prepregs (several meters or even longer) requires a complex production process. For example, the production of high-performance hemp fiber prepregs currently requires several steps: harvesting, degumming, breaking, carding, hackling, modification, drying, laying, and resin impregnation. These steps involve numerous mechanical processes, which inevitably damage the fiber's strength. Furthermore, the numerous steps contribute to high costs.

[0004] Wood fibers, a type of plant fiber, are relatively long. Theoretically, longer plant fibers can be obtained, but their performance needs to be improved. In the past decade or so, industry and academics have proposed several publicly available technologies for improving wood performance. They discovered that chemically treating wood to remove a certain amount of lignin increases its compressibility. Further unidirectional pressure (through the thickness) on the wood can produce a wood structure with excellent mechanical properties. However, existing technologies are difficult to directly apply to the production and processing of unidirectional veneer prepregs: First, current chemical treatment of wood is still at the laboratory principle stage, and the cycle required to achieve a high lignin removal ratio is long and energy-intensive; second, current public technologies actually treat and process thicker wood boards. When the thickness of the treated unidirectional wood is low to a certain extent (e.g., ≤0.8 mm, hereinafter referred to as unidirectional veneer), the chemically treated unidirectional veneer is prone to transverse cracking and poor transverse mechanical properties in the compression direction. Existing technologies have not yet found a solution to this problem; third, after chemical treatment, unidirectional veneer is very prone to wrinkles during the drying and dehydration process (thick wood boards generally do not have this problem). Therefore, it is also necessary to consider how to quickly drain moisture from the wood while densifying it and ensuring the flatness of the wood. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a unidirectional wood fiber paper with excellent mechanical properties and high flatness and its preparation method, a unidirectional wood fiber paper prepreg and its preparation method, a wood fiber paper reinforced composite material and its preparation method.

[0006] The present invention provides a unidirectional wood fiber paper, which is formed by shrinking a unidirectional wood veneer with some substances removed in at least one direction;

[0007] The partial substances include lignin and hemicellulose;

[0008] The thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm;

[0009] The apparent thickness of the unidirectional wood fiber paper under a plane pressure of no more than 0.005 MPa is no more than 4 times the average thickness of the unidirectional wood fiber paper.

[0010] Preferably, the unidirectional wood fiber paper comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended along a single direction as a whole at a microscopic level.

[0011] Preferably, the density of the unidirectional wood fiber paper is 0.8-1.5 g / cm 3 ;

[0012] And / or, the surface density of the unidirectional wood fiber paper is 20 to 400 g / m 2 ;

[0013] And / or, the tensile strength of the unidirectional wood fiber paper parallel to the wood fiber direction is 150-1000 MPa.

[0014] Preferably, the thickness of the unidirectional wood fiber paper is 0.03 to 0.6 mm;

[0015] And / or, the Young's modulus of the unidirectional wood fiber paper parallel to the wood fiber direction is 20 to 80 GPa.

[0016] Preferably, the thickness of the unidirectional veneer is less than or equal to 0.8 mm;

[0017] And / or, the decomposition of the shrinkage force includes lateral shrinkage and thickness shrinkage.

[0018] Preferably, the unidirectional veneer from which some substances have been removed is shrunk in at least two directions;

[0019] The shrinkage includes transverse shrinkage and thickness shrinkage;

[0020] The shrinkage force directions of the transverse shrinkage and the thickness shrinkage are intersecting.

[0021] Preferably, the unidirectional veneer from which some substances have been removed comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at a microscopic level;

[0022] The shrinkage force of the transverse shrinkage is a force in the horizontal direction of the unidirectional veneer, and is a force that intersects with the extension direction of the wood fibers and / or fiber bundles in the plane; and / or, the shrinkage force of the thickness shrinkage is a force in the vertical direction of the unidirectional veneer;

[0023] The horizontal force and the vertical force are each independently an originally applied force, and / or a force formed after synthesis or decomposition of forces.

[0024] Preferably, the apparent thickness of the unidirectional wood fiber paper when pressed flat at a pressure of 0.005 MPa is no more than 3 times the average thickness of the unidirectional wood fiber paper;

[0025] And / or, all and / or part of the unidirectional wood fiber paper has a smooth plastic feel;

[0026] And / or, when the thickness of the unidirectional wood fiber paper is less than 0.15 mm, the light transmittance of all and / or part of the unidirectional wood fiber paper is 2% to 70%.

[0027] Preferably, the weight loss of the unidirectional veneer after removing some substances is 10% to 60% relative to the unidirectional veneer;

[0028] And / or, the shrinkage rate of the transverse shrinkage is 2% to 40%; the shrinkage rate of the thickness shrinkage is 20% to 90%.

[0029] The present invention also provides a method for preparing unidirectional wood fiber paper, comprising the following steps:

[0030] S1) chemically modifying the unidirectional veneer to obtain the unidirectional veneer with some substances removed;

[0031] S2) shrinking the unidirectional veneer from which some substances have been removed in at least one direction to obtain unidirectional wood fiber paper;

[0032] The decomposition of the shrinkage force includes lateral shrinkage and thickness shrinkage.

[0033] Preferably, the thickness of the unidirectional veneer is 0.05 to 0.8 mm;

[0034] And / or, the surface density of the unidirectional veneer is 20 to 450 g / m 2 ;

[0035] And / or, the chemical modification in S1) is carried out in a closed high-pressure system; the target temperature of the chemical modification is 100-150° C.; the target pressure of the chemical modification is 0.07-1.9 MPa; and the residence time of the chemical modification at the target temperature / pressure is 1-12 hours;

[0036] Alternatively, the chemical modification is carried out under normal pressure; the residence time of the chemical modification at the target temperature / pressure is 24 to 72 hours; the temperature of the chemical modification is the boiling temperature of water at normal pressure;

[0037] And / or, after chemical modification, the reaction solution is cooled to obtain unidirectional veneer with some substances removed.

[0038] Preferably, the modification liquid for chemical modification in step S1) comprises an alkaline substance, a sulfonating agent and water;

[0039] The pH value of the modified liquid is 12 to 14;

[0040] The concentration of the alkaline substance in the modified solution is 0.01 to 5 kg / L;

[0041] The alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and potassium bicarbonate;

[0042] The concentration of the sulfonating agent in the modified solution is 0.01 to 5 kg / L;

[0043] The sulfonating agent in the modified liquid is selected from one or more of sulfite, chlorosulfonic acid, hydroxymethylsulfonate, sulfuryl chloride and aminosulfonic acid;

[0044] And / or, the material ratio of the unidirectional veneer to the chemically modified modifying liquid is 4.6 to 184 cm3 :1L;

[0045] And / or, the mass of the unidirectional veneer from which some substances are removed is reduced by 10% to 60% compared with the mass of the unidirectional veneer.

[0046] Preferably, the unidirectional veneer is placed in a material frame for chemical modification;

[0047] The material frame includes a frame body, a partition and a frame cover; the partition is arranged in the frame body; the side walls of the frame body, the bottom of the frame body, the partition and the frame cover are all provided with holes.

[0048] Preferably, the material frame is a cylindrical material frame; the number of the partitions is multiple; and the multiple partitions are arranged in concentric circles within the frame.

[0049] Preferably, the material frame is a rectangular parallelepiped material frame; the number of the partitions is multiple; and the multiple partitions are arranged in parallel in the material frame.

[0050] Preferably, the shrinkage process includes a lateral shrinkage process and a thickness shrinkage process; the force of the lateral shrinkage process and the force of the thickness shrinkage process intersect.

[0051] Preferably, the transverse shrinkage treatment is selected from applying external mechanical force in the transverse direction and / or spontaneous shrinkage due to dehydration;

[0052] The external mechanical force applied in the transverse direction intersects in the plane with the extending direction of the wood fibers and / or fiber bundles of the unidirectional veneer from which some substances have been removed.

[0053] Preferably, applying the external mechanical force in the transverse direction is specifically: using a film material that can produce transverse contraction, sticking it on the surface of the unidirectional veneer from which some substances have been removed, applying pressure, and then removing the film material;

[0054] and / or, roller-rubbing the unidirectional veneer with some of the material removed;

[0055] and / or, applying transverse pressure to the unidirectional veneer with some of the material removed.

[0056] Preferably, the pressure of the external mechanical force applied in the lateral direction is 0.001 to 1.5 MPa;

[0057] and / or, the temperature of the transverse shrinkage treatment is 15° C. to 150° C.;

[0058] And / or, the time of the transverse shrinkage treatment is 1 second to 4 minutes.

[0059] Preferably, the thickness shrinking comprises performing a hot pressing treatment under negative pressure conditions;

[0060] The pressure of the hot pressing treatment is 0.1 to 60 MPa;

[0061] And / or, the temperature of the hot pressing treatment is 50°C to 150°C;

[0062] And / or, the heat pressing treatment time is 0.5 to 20 minutes.

[0063] Preferably, the thickness shrinkage is performed under single sheet or stacking conditions; the number of stacked layers is 2 to 20 sheets;

[0064] The pressure of thickness shrinkage under the stacking condition is 0.1 to 60 MPa.

[0065] Preferably, the shrinkage rate of the transverse shrinkage treatment is 2% to 40%;

[0066] And / or, the shrinkage rate of the thickness shrinkage is 20% to 90%.

[0067] Preferably, the splicing is performed before or after the shrinkage treatment;

[0068] The splicing is specifically as follows: marking the splicing outline on the unidirectional veneer with some materials removed or the wood fiber paper after shrinkage treatment, and then splicing the corresponding parts.

[0069] The present invention also provides a method for preparing unidirectional wood fiber paper, comprising the following steps:

[0070] A1) chemically modifying the unidirectional veneer to obtain the unidirectional veneer from which some substances have been removed;

[0071] A2) shrinking and leveling the unidirectional veneer from which some substances have been removed in at least one direction to obtain unidirectional wood fiber paper;

[0072] The leveling process is to perform flat hot pressing in a negative pressure exhaust environment.

[0073] Preferably, during the leveling process, an exhaust channel is provided on the double contact surface or the single contact surface of the unidirectional wood fiber paper.

[0074] Preferably, the pressure of the plane hot pressing is 0.01 to 2 MPa;

[0075] And / or, the leveling treatment time is 0.1 to 4 minutes;

[0076] And / or, the temperature of the leveling treatment is 40°C to 150°C.

[0077] Preferably, the flattening treatment is selected from one or more of a blister treatment and a negative pressure hot pressing treatment;

[0078] And / or, the moisture content of the unidirectional wood fiber paper is less than or equal to 10%.

[0079] Preferably, the shrinkage treatment includes a transverse shrinkage treatment and a thickness shrinkage treatment;

[0080] The thickness shrinkage treatment is to apply mechanical pressure in the thickness direction;

[0081] The mechanical pressure applied in the thickness direction is 0.01 to 80 MPa;

[0082] And / or, the thickness shrinkage treatment time is 0.1 to 3 minutes;

[0083] And / or, the temperature of the thickness shrinkage treatment is 15°C to 150°C.

[0084] The present invention also provides a unidirectional wood fiber paper prepreg, comprising the unidirectional wood fiber paper and a high molecular polymer layer attached to at least one surface of the unidirectional wood fiber paper.

[0085] Preferably, the mass of the high molecular polymer layer is 5% to 85% of the mass of the unidirectional wood fiber paper prepreg;

[0086] And / or, the thickness ratio of the high molecular polymer layer to the unidirectional wood fiber paper is 5:1 to 0.05:1;

[0087] And / or, the surface density of the unidirectional wood fiber paper prepreg is 30 to 500 g / m 2 ;

[0088] And / or, the thickness of the unidirectional wood fiber paper prepreg is 0.03-0.7 mm.

[0089] Preferably, the polymer layer comprises a thermoplastic polymer and / or a thermosetting polymer;

[0090] The weight of the polymer layer is 5 to 200 g / m 2 .

[0091] The present invention also provides a method for preparing a unidirectional wood fiber paper prepreg, comprising the following steps:

[0092] The high molecular polymer is transferred to at least one surface of the unidirectional wood fiber paper to obtain a unidirectional wood fiber paper prepreg; the transfer method is selected from one or more of laminating, printing, impregnation and coating.

[0093] The present invention also provides a wood fiber paper reinforced composite material, comprising multiple layers of the above-mentioned unidirectional wood fiber paper;

[0094] The adjacent unidirectional wood fiber papers are bonded together by high molecular polymer.

[0095] Preferably, the tensile strength of the wood fiber paper reinforced composite material is 130 to 1000 MPa;

[0096] and / or, the flexural strength of the wood fiber paper reinforced composite material is 130 to 1000 MPa;

[0097] And / or, the Young's modulus of the wood fiber paper reinforced composite material is 12 to 75 GPa.

[0098] Preferably, the thickness of a single layer of wood fiber paper in the wood fiber paper reinforced composite material is 0.02 to 0.6 mm;

[0099] and / or, the wood fiber paper reinforced composite material has distinct layers in the longitudinal section;

[0100] And / or, the volume fraction of the wood fiber paper in the wood fiber paper reinforced composite material is 40% to 99%.

[0101] Preferably, at least one surface of the wood fiber paper reinforced composite material is provided with a waterproof polymer layer.

[0102] The present invention also provides a method for preparing a wood fiber paper reinforced composite material, comprising the following steps:

[0103] The unidirectional wood fiber paper is stacked, glued, and cured to obtain a wood fiber paper reinforced composite material;

[0104] Alternatively, the unidirectional wood fiber paper prepregs are stacked and cured to obtain a wood fiber paper reinforced composite material.

[0105] The present invention also provides a shrinkage method for unidirectional veneer, wherein the unidirectional veneer is subjected to shrinkage treatment in at least one direction; the decomposition of the shrinkage force includes transverse shrinkage and thickness shrinkage.

[0106] Preferably, the unidirectional veneer is first chemically treated to remove some substances and then subjected to shrinkage treatment in at least one direction.

[0107] Preferably, the shrinkage includes lateral shrinkage and thickness shrinkage; the shrinkage force directions of the lateral shrinkage and thickness shrinkage intersect.

[0108] Preferably, the unidirectional veneer comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at a microscopic level;

[0109] The shrinkage force of the transverse shrinkage is a force in the horizontal direction of the unidirectional veneer, and is a force that intersects with the extension direction of the wood fibers and / or fiber bundles of the unidirectional veneer in the plane; and / or, the shrinkage force of the thickness shrinkage is a force in the vertical direction of the unidirectional veneer;

[0110] The horizontal force and the vertical force are independently the originally applied forces, and / or are forces formed after the synthesis or decomposition of forces.

[0111] Preferably, the thickness shrinking comprises performing a hot pressing treatment under negative pressure conditions;

[0112] The pressure of the hot pressing treatment is 0.1 to 60 MPa;

[0113] And / or, the temperature of the hot pressing treatment is 50°C to 150°C;

[0114] And / or, the heat pressing treatment time is 0.5 to 20 minutes.

[0115] The present invention also provides a wooden hollow tube, which is formed from the above-mentioned unidirectional wood fiber paper, the above-mentioned unidirectional wood fiber paper prepreg or the above-mentioned wood fiber paper reinforced composite material.

[0116] The present invention provides unidirectional wood fiber paper, which is formed by shrinking unidirectional wood bark in at least one direction after removing a portion of its material; the portion includes lignin and hemicellulose; the thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm; and the apparent thickness of the unidirectional wood fiber paper under a planar pressure of no more than 0.005 MPa is no more than four times the average thickness of the unidirectional wood fiber paper. Compared with the prior art, the unidirectional wood fiber paper provided by the present invention is thin, has excellent mechanical properties, exhibits anisotropy, and is composed of 100% pure natural materials. Furthermore, shrinkage not only densifies the unidirectional wood fiber paper in the thickness direction, but also increases its transverse bonding strength and compactness, thereby reducing transverse cracking of the unidirectional wood fiber paper.

[0117] Furthermore, the present invention provides a unidirectional wood fiber paper prepreg similar to the fiber prepregs (such as glass fiber prepregs and carbon fiber prepregs) in the conventional composite materials industry, which makes the product more applicable. In addition, the raw material of the unidirectional wood fiber prepreg is high-performance unidirectional wood fiber paper, which is green and environmentally friendly. Moreover, it is only necessary to stack multiple unidirectional wood fiber paper prepregs and apply less pressure to obtain the product, which is easy to use.

[0118] Furthermore, the present invention provides a wood fiber paper reinforced composite material, which has distinct layers and high mechanical properties.

[0119] Furthermore, the surface of the wood fiber paper reinforced composite material provided by the present invention is a polymer with waterproof performance, which can make the wood fiber paper reinforced composite material have higher waterproof performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] FIG1 is a microscopic image of the unidirectional wood fiber paper provided by the present invention;

[0121] FIG2 is a physical picture of the unidirectional wood fiber paper provided by the present invention;

[0122] FIG3 is a schematic diagram of the preparation process of the unidirectional wood fiber paper provided by the present invention;

[0123] FIG4 is a schematic structural diagram of a material frame for a vertical reactor provided by the present invention;

[0124] FIG5 is a schematic diagram of placing the unidirectional veneer provided by the present invention in a vertical reactor;

[0125] FIG6 is a schematic structural diagram of a material frame for a horizontal reactor provided by the present invention;

[0126] FIG7 is a schematic diagram of placing the unidirectional veneer provided by the present invention in a horizontal reactor;

[0127] FIG8 is a physical diagram of cracks generated by unidirectional shrinkage in the thickness direction provided by the present invention;

[0128] FIG9 is a schematic diagram of the collapse and contraction of the spontaneously transversely contracting wood fiber paper tube provided by the present invention;

[0129] FIG10 is a physical diagram of the spontaneous lateral shrinkage of the unidirectional wood fiber paper provided by the present invention;

[0130] FIG11 is a schematic diagram of a continuous hot pressing process of hot rolling rollers provided by the present invention;

[0131] FIG12 is a schematic diagram of a continuous hot pressing process performed by a continuous flat press provided by the present invention;

[0132] FIG13 is a schematic diagram of continuous hot pressing processing with a belt press provided by the present invention;

[0133] FIG14 is a schematic diagram of splicing unidirectional wood fiber paper provided by the present invention;

[0134] FIG15 is a schematic diagram of flattening by blister packaging according to the present invention;

[0135] FIG16 is a preparation process of the unidirectional wood fiber paper prepreg provided by the present invention;

[0136] FIG17 is a schematic diagram of a single-sided lamination operation according to the present invention;

[0137] FIG18 is a schematic diagram of preparing unidirectional wood fiber paper prepreg by the doctor blade method provided by the present invention;

[0138] FIG19 is a schematic diagram showing the principle of preparing a wood fiber paper reinforced composite material from the unidirectional wood fiber paper prepreg provided by the present invention;

[0139] FIG20 is a schematic cross-sectional view of a wood fiber paper reinforced composite material provided by the present invention;

[0140] FIG21 is a schematic diagram of preparing a wood fiber paper reinforced composite material with waterproof properties from the unidirectional wood fiber paper prepreg provided by the present invention;

[0141] FIG22 is a schematic diagram of a process for preparing a wood fiber paper reinforced composite material from unidirectional wood fiber paper provided by the present invention;

[0142] FIG23 is a physical picture of the wooden hollow tube provided by the present invention;

[0143] FIG24 is a photograph of the unidirectional veneer obtained in Example 1 of the present invention in a wet state with some substances removed;

[0144] FIG25 is a graph showing the spontaneous transverse shrinkage of the unidirectional veneer with some material removed in Example 1 of the present invention;

[0145] FIG26 is a graph showing a tensile stress-strain test along the fiber direction of the unidirectional wood fiber paper obtained in Example 1 of the present invention;

[0146] FIG27 is a photo of the unidirectional veneer in Comparative Example 1 of the present invention, which shrinks only in the thickness direction after chemical treatment;

[0147] FIG28 is a photograph of unidirectional wood fiber paper prepared with different overlap widths in Example 10 of the present invention;

[0148] FIG29 is a top view of the wood fiber reinforced epoxy resin-based composite material obtained in Example 11 of the present invention;

[0149] FIG30 is a side view of the wood fiber reinforced epoxy resin-based composite material obtained in Example 11 of the present invention;

[0150] FIG31 is a transmittance test chart of the unidirectional wood fiber paper obtained in Example 15 of the present invention. DETAILED DESCRIPTION

[0151] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0152] The present invention provides a unidirectional wood fiber paper, which is formed by shrinking a unidirectional wood veneer with part of its material removed in at least one direction; the part of its material includes lignin and hemicellulose; the thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm; the thickness of the unidirectional wood fiber paper is less than the thickness of the unidirectional wood veneer; and the apparent thickness of the unidirectional wood fiber paper under a plane pressure not greater than 0.005 MPa is no more than 4 times the average thickness of the unidirectional wood fiber paper.

[0153] According to the present invention, the unidirectional wood fiber paper preferably includes wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at the microscopic level. Specifically, greater than or equal to 70% of the wood fibers and / or fiber bundles are arranged or extended in a single direction at the microscopic level. More specifically, greater than or equal to 80% of the wood fibers and / or fiber bundles are arranged or extended in a single direction at the microscopic level. See Figure 1, which is a microscopic photograph of the unidirectional wood fiber paper.

[0154] In composite materials, unidirectional refers to the fact that all or most fibers extend in a single, relatively parallel direction; this can also be referred to as non-patterned. Because the wood fiber paper provided herein differs from conventional composite fiber fabrics, it lacks the characteristic characteristics of individual fibers. However, in its microstructure, wood fiber paper comprises continuous wood fibers connected by naturally occurring chemical components found in natural wood, resulting in a macroscopically uniform physical form of a single sheet. The arrangement of these continuous fibers conforms to the definition of unidirectional in conventional composite materials, and therefore is referred to as unidirectional wood fiber paper in this invention.

[0155] According to the present invention, the tensile strength of the unidirectional wood fiber paper parallel to the wood fiber direction is preferably 150-1000 MPa. Optionally, the tensile strength of the unidirectional wood fiber paper parallel to the wood fiber direction is 150 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa or a range between any two of the above values; the Young's modulus of the unidirectional wood fiber paper parallel to the wood fiber direction is preferably 20-80 GPa. Optionally, the Young's modulus of the unidirectional wood fiber paper parallel to the wood fiber direction is 20 GPa, 25 GPa, 30 GPa, 35 GPa, 40 GPa, 45 GPa, 50 GPa, 55 GPa, 60 GPa, 65 GPa, 70 GPa, 75 GPa, 80 GPa or a range between any two of the above values. Such wood fiber paper has good tensile strength and deformation resistance.

[0156] The unidirectional wood fiber paper provided by the present invention has high flatness. Specifically, the apparent thickness of the unidirectional wood fiber paper under a plane pressure of no more than 0.005 MPa is no more than 4 times the average thickness of the unidirectional wood fiber paper.

[0157] More specifically, the apparent thickness of the unidirectional wood fiber paper when pressed flat under a pressure of 0.005 MPa is preferably no more than three times the average thickness of the unidirectional wood fiber paper.

[0158] And those skilled in the art can understand that the apparent thickness is related to pressure. The greater the pressure, the smaller the apparent thickness, and the smaller the multiple between the apparent thickness and the average thickness. Therefore, the description of flatness can also be equivalent to the above description.

[0159] In a specific embodiment provided by the present invention, the flatness test method is as follows: unidirectional wood fiber paper is placed between two planar objects. Pressure is applied to the two surfaces so that the unidirectional wood fiber paper receives a relatively small flat pressure. The flat wood fiber paper tends to conform to the pressure-applying surfaces. The difference between the highest and lowest points of the compressed unidirectional wood fiber paper is the apparent thickness of the unidirectional wood fiber paper. The average thickness of the unidirectional wood fiber paper is the average thickness of the unidirectional wood fiber paper measured at different locations on the paper using a micrometer.

[0160] According to the present invention, the unidirectional wood fiber paper is formed by chemically modifying the unidirectional wood veneer to remove some substances and shrink in at least one direction; the present invention uses natural unidirectional wood to produce unidirectional wood fiber paper, and the fibers of the unidirectional wood grow along the longitudinal direction of the trunk. The fibers are arranged tightly and uniformly, forming a parallel straight line feature. Using unidirectional wood as raw material eliminates the harvesting, degumming (Retting), breaking (Breaking), carding (Scutching), combing (Hackling), and laying arrangement processes required for the currently common hemp fibers, and directly achieves the purpose of continuous, unidirectionally arranged plant fibers, which can greatly save the cost of prepreg manufacturing and improve the excellent performance of wood fiber prepregs through chemical treatment of wood and subsequent operations. In the present invention, the thickness of the unidirectional veneer is less than or equal to 0.8 mm, and can further be 0.05 to 0.8 mm. Optionally, the thickness of the unidirectional veneer can be 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 1 mm, or a range between any two of the above values. In the embodiment provided by the present invention, a unidirectional veneer with a thickness of 0.28 mm is specifically used as an example for illustration; the surface density of the unidirectional veneer is preferably 20 to 450 g / m 2 , more preferably 70 to 200 g / m 2 ; Optionally, the surface density of the unidirectional veneer is 20g / m 2 , 50g / m 2 , 70g / m 2 , 80g / m 2 , 90g / m 2 , 100g / m 2 , 110g / m 2 , 120g / m 2 , 130g / m 2 , 150g / m 2 , 180g / m 2, 200g / m 2 , 250g / m 2 , 280g / m 2 , 300g / m 2 , 320g / m 2 、350g / m 2 , 400g / m 2 , 420g / m 2 , 450g / m 2 Or the range between any two of the above values; generally speaking, the thicker the unidirectional veneer, the greater the surface density; the greater the surface density, the greater the thickness, and the greater the thickness leads to greater rigidity of the material, thereby making the material have better sound insulation.

[0161] According to the present invention, the weight loss of the unidirectional veneer after removing some substances relative to the unidirectional veneer is preferably 10% to 60%; optionally, the weight loss of the unidirectional veneer after removing some substances relative to the unidirectional veneer is 10%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range between any two of the above values; the partial substances include lignin and hemicellulose.

[0162] According to the present invention, the decomposition of the shrinkage in at least one direction includes lateral shrinkage and thickness shrinkage.

[0163] In a specific embodiment provided by the present invention, the shrinkage in at least one direction is specifically shrinkage in at least two directions; the shrinkage includes lateral shrinkage and thickness shrinkage; and the shrinkage force directions of the lateral shrinkage and thickness shrinkage intersect.

[0164] In a specific embodiment provided by the present invention, the shrinkage is bidirectional shrinkage; the bidirectional shrinkage includes transverse shrinkage and thickness shrinkage, that is, the unidirectional veneer with part of the material removed is formed into unidirectional wood fiber paper through bidirectional shrinkage.

[0165] In a specific embodiment provided by the present invention, the shrinkage rate of the transverse shrinkage is preferably 2% to 40%; optionally, the shrinkage rate of the transverse shrinkage is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range between any two of the above values; as the transverse shrinkage rate increases, the tensile strength and modulus of the unidirectional wood fiber paper perpendicular to the fiber direction tend to increase, so it can be selected according to needs.

[0166] In a specific embodiment provided by the present invention, the shrinkage rate of the thickness shrinkage is preferably 20% to 90%, more preferably 20% to 86%; optionally, the shrinkage rate of the thickness shrinkage is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, 90% or a range between any two of the above values; a higher thickness shrinkage rate means a thinner unidirectional wood fiber paper, and its tensile strength and tensile modulus in the fiber direction tend to increase, and can be selected according to needs.

[0167] In a specific embodiment provided by the present invention, the directions of the shrinkage forces of the lateral shrinkage and the thickness shrinkage intersect with each other; and the angle of the intersection is preferably 60° to 90°.

[0168] In a specific embodiment provided by the present invention, the unidirectional veneer with some substances removed includes wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at the microscopic level, and the force intersects with the extension direction of the wood fibers and / or fiber bundles within the plane; the intersection within the plane also belongs to the direction perpendicular to the fiber direction at the macroscopic level; the shrinkage force of the lateral shrinkage is the force in the horizontal direction of the unidirectional veneer; and / or, the shrinkage force of the thickness shrinkage is the force in the vertical direction of the unidirectional veneer; the horizontal force and the vertical force are each independently the original applied force, and / or, are the forces formed after the synthesis or decomposition of the forces.

[0169] The thickness and density of the unidirectional wood fiber paper obtained by shrinking in at least two directions will change; the thickness of the unidirectional wood fiber paper is less than the thickness of the unidirectional veneer, preferably 10% to 80% of the thickness of the unidirectional veneer. Optionally, the thickness of the unidirectional wood fiber paper can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% of the thickness of the unidirectional veneer, or a range between any two of the above values.

[0170] In a specific embodiment provided by the present invention, the thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm; optionally, the thickness of the unidirectional wood fiber paper is 0.01 mm, 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm or a range between any two of the above values.

[0171] In a specific embodiment provided by the present invention, the density of the unidirectional wood fiber paper is 0.8-1.5 g / cm 3 ; Optionally, the density of the unidirectional wood fiber paper is 0.8g / cm 3, 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 Or the range between any two of the above values.

[0172] In a specific embodiment provided by the present invention, the surface density of the unidirectional wood fiber paper is 20 to 400 g / m 2 Optionally, the surface density of the unidirectional wood fiber paper is 20g / m 2 , 25g / m 2 , 30g / m 2 , 40g / m 2 , 50g / m 2 , 60g / m 2 , 70g / m 2 , 80g / m 2 , 90g / m 2 , 100g / m 2 , 110g / m 2 , 120g / m 2 , 130g / m 2 , 150g / m 2 , 160g / m 2 , 170g / m 2 , 180g / m 2 , 190g / m 2 , 200g / m 2 , 220g / m 2 , 250g / m 2 , 280g / m 2 , 300g / m 2 , 320g / m 2 、350g / m 2 , 380g / m 2 , 400g / m 2 Or the range between any two of the above values.

[0173] According to the present invention, the raw material of the unidirectional wood fiber paper is natural wood, which is 100% natural material.

[0174] According to the present invention, the size of the unidirectional wood fiber paper can theoretically be spliced ​​to an infinite width and length. Specifically, the length of a single unspliced ​​unidirectional wood fiber paper is preferably 0.1 to 5 m, more preferably 0.1 to 3 m; the width of the single unspliced ​​unidirectional wood fiber paper is preferably 0.01 to 1 m.

[0175] According to the present invention, the water content of the unidirectional wood fiber paper is preferably below 10 wt %; the unidirectional wood fiber paper does not wrinkle when placed at room temperature.

[0176] According to the present invention, all and / or part of the unidirectional wood fiber paper has a smooth plastic feel; further, when the thickness of the unidirectional wood fiber paper is less than 0.15 mm, some areas thereof have a light-transmitting effect. Specifically, the light transmittance of all and / or part of the unidirectional wood fiber paper is preferably 2% to 70%; see Figure 2, which is a physical picture of the unidirectional wood fiber paper provided by the present invention.

[0177] The present invention also provides a method for preparing the above-mentioned unidirectional wood fiber paper, comprising the following steps: S1) chemically modifying the unidirectional veneer to obtain the unidirectional veneer with some substances removed; S2) shrinking the unidirectional veneer with some substances removed in at least one direction to obtain the unidirectional wood fiber paper; the shrinkage force decomposition includes lateral shrinkage and thickness shrinkage.

[0178] Referring to FIG3 , FIG3 is a schematic diagram of the preparation process of the unidirectional wood fiber paper provided by the present invention.

[0179] The present invention has no particular limitation on the sources of all raw materials, and any commercially available raw materials may be used.

[0180] In the present invention, the unidirectional veneer can be any unidirectional veneer known to those skilled in the art, without particular limitation. Examples include, but are not limited to, walnut, oak, basswood, rosewood, ebony, teak, rosewood, catalpa, ebony, cherry, cork, poplar, beech, cedarwood, pine, maple, and ash. Unidirectional veneer is natural, avoiding the environmentally unfriendly effects of artificial engineered wood, which is often doped with excessive amounts of polymers and can cause structural separation during subsequent chemical reactions. Natural veneer is environmentally friendly, with cellulose, hemicellulose, and lignin cross-linked within the naturally formed structure, maintaining structural integrity during subsequent chemical reactions. Unidirectional veneer has a relatively regular fiber arrangement, with virtually all fibers oriented in the same direction, and the surface texture also oriented in the same direction, resulting in a highly anisotropic veneer. Unidirectional veneer is chosen over veneers with other fiber orientations because subsequent processing can result in significant internal stress release. Unidirectional veneer maintains better overall dimensional consistency and is less prone to defects. During the subsequent chemical reaction process, some substances in the wood will be removed from the structure, which will cause the wood to have internal stress of shrinkage after the reaction. Since the removed substances are mainly concentrated between the wood fibers, the internal stress release of the unidirectional veneer after the chemical reaction will be concentrated in one direction, and the veneer will also shrink uniformly from the outside to the inside in a direction perpendicular to the wood fibers, so that the veneer is not prone to defects. If other non-unidirectional veneers with irregular fiber arrangement are used, the internal stress release will be in different directions, and it is easy for excessive internal stress to occur in local areas, resulting in defects such as fractures, resulting in waste. The thickness of the unidirectional veneer is less than or equal to 0.8 mm; in the embodiment provided by the present invention, a unidirectional veneer with a thickness of 0.28 mm is specifically used as an example for explanation; the maximum surface size of the unidirectional veneer is preferably 3000×500 mm, and any size can be obtained by cutting within this size range; the surface density of the unidirectional veneer is preferably 20 to 450 g / m 2 .

[0181] The unidirectional veneer is chemically modified to obtain the unidirectional veneer with some substances removed; the pH value of the chemically modified modification liquid is preferably 12-14; the chemically modified modification liquid preferably comprises an alkaline substance, a sulfonating agent and water; the alkaline substance is an alkaline substance well known to those skilled in the art and is not particularly limited. In the present invention, it preferably comprises but is not limited to one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and potassium bicarbonate; the concentration of the alkaline substance in the modification liquid is preferably 0.01-5 kg / L, more preferably 0.05-3 kg / L, and even more preferably 0.1-2 kg / L; in some embodiments provided by the present invention, the concentration of the alkaline substance in the modification liquid is specifically 0.1 kg / L, 0.05 kg / L or 0.145 kg / L ; The sulfonating agent is any sulfonating agent well known to those skilled in the art, and is not particularly limited. In the present invention, it preferably includes but is not limited to one or more of sulfite, chlorosulfonic acid, hydroxymethylsulfonate, sulfuryl chloride and aminosulfonic acid; the sulfite is preferably sodium sulfite; the concentration of the sulfonating agent in the modifying liquid is preferably 0.01 to 5 kg / L, more preferably 0.01 to 3 kg / L, and even more preferably 0.01 to 1 kg / L; in some embodiments provided by the present invention, the concentration of the sulfonating agent in the modifying liquid is specifically 0.05 kg / L, 0.075 kg / L or 0.072 kg / L; the concentration of the sulfonating agent in the modifying liquid can be increased accordingly as the volume of the reaction solution increases, thereby compensating for the reduced mass transfer caused by the increase in the scale of the chemical reaction. The volume of the modified liquid can be any volume, depending on the production requirements and the specifications of the reactor equipment, including but not limited to 500mL, 2L, 4L, 20L, 100L, 500L, 1000L, 2000L, 5000L, 8000L, 10000L, etc.; the material ratio of the unidirectional veneer to the chemically modified modified liquid is preferably 4.6 to 184cm 3: 1L. The higher the material ratio, the higher the single reaction output, so it is generally necessary to maximize the material ratio of the reaction. However, the difficulty of mass transfer and the problem of excessive material accumulation in the reactor must also be considered. During the reaction, the alkaline substance will react with the lignin, hemicellulose, and cellulose in the unidirectional veneer. For example, if the alkaline substance is sodium hydroxide and the sulfonating agent is sodium sulfite, hemicellulose may react with sodium hydroxide to form sodium hemicellulose (as shown in Reaction Equation 1), and lignin may react with sodium hydroxide and sodium sulfite to form sodium lignin sulfonate (as shown in Reaction Equations 2 and 3). The byproducts of these reactions will separate from the unidirectional veneer structure and dissolve or suspend in the reaction solution. If the material ratio is too high, the reaction mass transfer efficiency is reduced, and the reaction byproducts are difficult to evenly disperse in the system. This will lead to a decrease in the reaction rate in local areas, resulting in a decrease in the uniformity of the properties of the unidirectional veneer after the reaction, affecting the stability of subsequent processes and the performance of the final product. Moreover, the problem of excessive material accumulation in the reactor will increase the friction between the unidirectional veneer and the internal structure of the reactor during the reaction, causing damage to the unidirectional veneer.

[0182] For small-scale reactions below 5L, the mass transfer and heat transfer in the system are relatively easy, and the amount of one-way veneer is relatively small, so the whole piece of veneer can be curled and attached to the wall of the reaction device. For reactions above 5L, due to the large scale of the reaction, the mass transfer and heat transfer rate in the system is reduced, and the amount of one-way veneer is large, so the one-way veneer needs to be pre-layered and placed in the reactor. At the same time. The need to increase pre-layering can maximize the use of the internal space of the reactor and evenly arrange the one-way veneer throughout the reactor. In addition, through this partitioning, the one-way veneer in a single area can also be controlled to a certain number, reducing the damage to the one-way veneer caused by mutual friction and improving the mass transfer effect. The one-way veneer is preferably placed in a material frame for chemical modification; the material frame includes a frame, a partition and a frame cover; the partition is arranged in the frame; the side walls of the frame, the bottom of the frame, the partition and the frame cover are all provided with holes. In a specific embodiment provided by the present invention, the material frame is a cylindrical material frame; the number of the partitions is multiple; the multiple partitions are arranged in a concentric circle manner in the frame, and can be arranged along the same interval or along different intervals. In a specific embodiment provided by the present invention, the material frame is a rectangular material frame; the number of the partitions is multiple; the multiple partitions are arranged in parallel in the material frame, and can be arranged along the same interval or along different intervals. In the present invention, the one-way veneer can be pre-layered using upper and lower stacked material frames, see Figures 4 and 5. Figure 4 is a structural schematic diagram of a material frame for a vertical reactor, and Figure 5 is a schematic diagram of the placement of the one-way veneer in a vertical reactor, where 1 is the one-way veneer, 3 is the vertical reactor, and the main structure of the material frame is composed of a mesh plate with a certain number of holes. The diameter of the hole should not be too small, which will affect the mass transfer effect, nor should it be too large, which will cause scratches on the veneer and reduce the structural strength. Generally, the diameter of the hole ranges from 3 to 5 mm, and the overall hole density is 4×10 5 ~3.5×10 5 pcs / m 3, depending on the actual working conditions and equipment conditions. The thickness of the corresponding mesh plate must meet the requirement that the frame itself can maintain structural stability after loading the material. Generally, a 1 to 5 mm thick plate is selected according to the size of the material frame. The single-layer height is mainly determined by the width of the processed veneer, generally between 10 and 30 cm. The outermost radius and the innermost radius of the material frame are determined by the specific reactor structure and the amount of material. The intervals in the frame are not equidistant. Generally, the distance increases from the inside to the outside. The specific increase depends on the thickness and quantity of the veneer. The basic standard of this design is that it is convenient to operate when loading the veneer and will not damage the veneer. Figure 6 is a structural schematic diagram of the material frame for the horizontal reactor provided by the present invention. The overall appearance size of the material frame is determined by the structure of the horizontal reactor, the single-layer height is determined by the material width, and the thickness is determined by the material loading amount and the size of the material frame. The material frame needs to be designed as a porous structure. The diameter of the holes is generally in the range of 3 to 5 mm, and the overall hole density is 6.8×10 5 ~5.0×10 5 pcs / m 3 . The internal partition adopts a perforated plate with a thickness of 2mm. The partition distance should be equidistant, and the distance value is 1 to 5cm higher than the width of the veneer. Allow the material to migrate freely in and out of the material frame, and the size of the hole should be as large as possible, so that the unidirectional veneer can be effectively layered without affecting mass transfer. The material frame needs to be designed to be close to the inner diameter of the reactor, so that the stacked multi-layer material frame can maximize the use of the space in the reactor. The material of the material frame needs to be alkali-resistant and temperature-resistant. Figure 7 is a schematic diagram of the placement of unidirectional veneer in a horizontal reactor, where 1 is unidirectional veneer and 2 is a horizontal reactor.

[0183] The reactor can be vertical or horizontal, and any heating method can be used, as long as the temperature accuracy within the system can be controlled within ±10°C. For large-volume reactors, additional stirring, solution reflux, overall reactor rotation, and external circulation pumps can be used to improve mass transfer. In the present invention, there are two options for the reaction temperature and pressure of the chemical modification: one is to heat to the boiling state of water at normal pressure, but this method requires an additional condensation reflux module, which increases the reaction energy consumption a lot. In addition, the reaction time at normal pressure, that is, the residence time at the target temperature / pressure, is 24 to 72 hours to ensure that the reaction is complete. In some embodiments provided by the present invention, the reaction time at normal pressure can be specifically 48 hours. Another option is to heat to a temperature exceeding the boiling point of water in a closed high-pressure system, that is, the target temperature is preferably 100 to 150°C, more preferably 110 to 150°C, more preferably 120 to 130°C, and most preferably 125°C, forming the entire system into a high-pressure system, so that there is no need to add a condensation reflux module, and the reaction time, that is, the residence time, can be reduced to 1 to 12 hours to complete the reaction, more preferably 3 to 10 hours, more preferably 4 to 8 hours, and most preferably 5 to 8 hours, which can greatly reduce the energy consumption of the reaction and reduce the process cost of the chemical reaction. In addition, the pumping capacity of the material pump is 1.4 to 3.5 t / h. The optimal reaction temperature depends on the wood species and the scale of the reactor. Different wood species will have slightly different temperature windows due to different chemical compositions. Generally, the larger the scale of the reactor, the higher the reaction temperature is to compensate for the reduction in mass transfer and heat transfer. Generally, the higher the reaction temperature, the faster the reaction rate. However, since cellulose will gradually hydrolyze starting at 150°C, and the mechanical properties of cellulose are relatively high and need to be retained as much as possible, the reaction temperature needs to be set below 150°C. In some embodiments provided by the present invention, the temperature of the chemical modification in the closed high-pressure system, that is, the target temperature, is specifically 125°C, 116°C or 130°C; in some embodiments provided by the present invention, the target time of the chemical modification in the closed high-pressure system is specifically 6h, 8h or 6.5h; when the chemical modification is carried out in a closed high-pressure system, the target pressure of the chemical modification is preferably 0.07~1.9MPa; the present invention has no special restrictions on the heating rate of the chemical modification. The specific chemical modification can be carried out under normal pressure or in a closed high-pressure system at a heating rate of 0.2~5°C / min, more preferably 0.5~5°C / min. In some embodiments provided by the present invention, the heating rate can be specifically 3°C / min, 2.5°C / min, 5°C / min, 2°C / min, 0.5°C / min or 0.2°C / min; when the temperature of the system reaches and stabilizes at the target temperature, the reaction in the closed high-pressure system needs to stay at the target temperature for 1 to 12 hours or under normal pressure conditions needs to stay at the target temperature for 24 to 72 hours, and then start to cool down.Because the modified unidirectional veneer reforms its intermolecular hydrogen bonds and begins crystallization during the cooling process, the cooling method can significantly impact the final performance. If the cooling rate is too rapid, the molecular chains of the unidirectional veneer, which has been partially degraded, will be prematurely fixed, intermolecular forces will not be fully established, resulting in low crystallinity and larger crystal particles, all of which will negatively impact performance. Therefore, in the present invention, after the chemical modification is completed, the reaction solution is preferably subjected to heat exchange with an external environment at room temperature to slowly cool it down. This cooling method can promote the establishment of intermolecular forces while simultaneously achieving crystals with high crystallinity and larger grain size. Specifically, the cooling method includes water cooling or air cooling, and more specifically, the cooling method includes indirect water cooling, indirect air cooling, or direct water cooling. The cooling rate is preferably 0.2-10°C / min, more preferably 1-10°C / min. In some embodiments provided herein, the cooling rate is specifically 0.2°C / min, 1°C / min, 0.5°C / min, 2°C / min, or 3°C / min.

[0184] After cooling to operating temperature (e.g., 60°C), the partially debonded veneer is preferably washed and dried. Specifically, the reactor is opened to remove the partially debonded veneer, or the material frame containing the partially debonded veneer is removed. The obtained material is then placed in water for cleaning, or the material frame containing the material is placed in water for cleaning. Cleaning removes residual chemicals on the surface and simultaneously reacts sodium cellulose that may have formed during the reaction back into cellulose, thereby maintaining the natural chemical composition of the wood. Multiple rounds of cleaning can be performed depending on the material. After cleaning, the material is dried to obtain the unidirectional veneer with some substances removed. The material can be dried naturally or placed in an oven for accelerated drying. The mass of the unidirectional veneer with some substances removed is reduced by 10% to 60% compared to the unidirectional veneer, and further reduced by 35% to 55%. In some embodiments provided by the present invention, the mass of the unidirectional veneer with some substances removed is specifically reduced by 50%, 42%, 46.8%, 49.1%, 49% or 48.2% compared to the unidirectional veneer.

[0185] During the chemical modification process, the mass of unidirectional veneer decreases by 10% to 60%, creating numerous voids in its microstructure. These voids impart excellent plastic deformation properties to the depleted veneer, allowing it to be easily compressed to a smaller size under external forces. This decrease in mass is also due to the significant removal of lignin and hemicellulose from the veneer, resulting in an increase in the proportion of cellulose in the overall composition. Since cellulose possesses the best mechanical properties of the three main components of unidirectional veneer, this adjustment in proportion offers potential for material enhancement. Unmodified wood has relatively poor plastic deformation properties. Significant plastic deformation of unmodified wood generally requires 2 to 24 hours of steam heating and humidification to achieve sufficient softening. The shrinkage densification process is a critical step, requiring the material to achieve volume compression in a short period of time, requiring excellent plastic deformation properties, which are not readily apparent in unmodified wood. Furthermore, the chemically treated material must maintain its morphology intact and flat, requiring controlled reaction progress during the chemical reaction. If the reaction is excessive, the veneer will form a large number of wrinkles and cannot be leveled; if the reaction is insufficient, the veneer will have a low degree of unidirectional compression and the mechanical properties of the densified material will be poor.

[0186] In the present invention, after chemical modification of the unidirectional veneer, the removal ratio of lignin is 20% to 80%, and the removal ratio of hemicellulose is 30% to 80%. Specifically, within the temperature and time range of the chemical modification provided by the present invention, the removal ratios of hemicellulose and lignin are roughly positively correlated with the temperature and time.

[0187] The partially dematerialized unidirectional veneer is subjected to a shrinkage treatment in at least one direction; this shrinkage, through force decomposition, includes transverse shrinkage and thickness shrinkage. Transverse shrinkage and thickness shrinkage refer to shrinkage in both the transverse direction and the thickness direction perpendicular to the fiber direction of the unidirectional wood fiber paper, thereby producing a densification effect. The number of shrinkage treatments can be selected based on the direction of the force, as long as the force decomposition can actually achieve transverse (horizontal) and vertical (thickness) shrinkage.

[0188] In a specific embodiment of the present invention, the shrinkage process includes both transverse shrinkage and thickness shrinkage, i.e., bidirectional shrinkage. The forces of the transverse shrinkage process and the thickness shrinkage process intersect. Bidirectional shrinkage of the wood fiber paper can be achieved by separate devices, or by a single device simultaneously or alternately shrinking in both directions.

[0189] When the thickness of the processed raw unidirectional veneer is less than 0.8mm, transverse shrinkage is necessary. Within this thinner thickness range, the cellulose density and the distribution of lignin and hemicellulose in the transverse direction at any location in the unidirectional veneer are uneven, while the distribution of the reaction medium during chemical or biological treatment is relatively more uniform. If there is less cellulose in a certain transverse area and more lignin and hemicellulose are removed, chemical modification will inevitably cause a large loss of connecting substances in some areas, and the cellulose structure in this area will fall apart. Unidirectional shrinkage in the thickness direction will easily cause cracks in this area due to the lack of the necessary transverse connecting force, as shown in Figure 8.

[0190] According to the present invention, the transverse shrinkage treatment is preferably to apply external mechanical force and / or dehydration spontaneous shrinkage in the transverse direction; the application of external mechanical force in the transverse direction intersects with the direction of extension of the wood fibers and / or fiber bundles of the unidirectional veneer from which part of the material has been removed.

[0191] Among them, the method of applying external mechanical force in the transverse direction is a method well known to those skilled in the art, and there is no special limitation. Basically, any method can be applied as long as the parameters such as pressure meet the process requirements. For example, a membrane material that can produce transverse shrinkage is attached to the surface of a one-way veneer with some substances removed and pressure is applied, and then the membrane material is removed; when the transverse shrinkage of the membrane material is controlled, the friction between the membrane and the surface of the one-way veneer with some substances removed will drive the transverse shrinkage of the one-way veneer with some substances removed; in this process, the tension of the membrane material affects the degree of transverse shrinkage, and it is specifically preferred to control the tension of the membrane material to achieve an equivalent transverse shrinkage pressure of 0.001 to 1.5 MPa, more preferably 0.01 to 1.5 MPa; optionally, the tension of the membrane material is controlled to achieve an equivalent transverse shrinkage pressure of 0.001 MPa, 0.002 MPa, 0.005 MPa, 0.01 MPa, 0.05 MPa, 0.08 MPa, 0.1 MPa, 0.2 MPa, 0.5 MPa, 0.8MPa, 1.0MPa, 1.2MPa, 1.4MPa, 1.5MPa or a range between any two of the above values; at the same time, the friction force exerted on the surface of the one-way veneer with some substances removed away from the membrane material will also affect the lateral shrinkage of the one-way veneer with some substances removed. Therefore, the lower the roughness of the contact surface of the one-way veneer with some substances removed away from the membrane material, the better. Specifically, it is preferred to contact with a surface with a surface roughness less than or equal to Ra6.3. Optionally, the roughness of the contact surface is Ra0.0063, Ra0.025, Ra0.05, Ra0.1, Ra0.2, Ra0.4, Ra0.8, Ra1.6, Ra3.2 or Ra6.3; in addition, the external force can also be achieved by mechanical force, such as roller rubbing, direct pressure and the like. The pressure of the external mechanical force applied in the lateral direction is preferably 0.001 to 1.5 MPa, more preferably 0.01 to 1.5 MPa; optionally, the pressure of the external mechanical force applied in the lateral direction is 0.001 MPa, 0.002 MPa, 0.005 MPa, 0.01 MPa, 0.05 MPa, 0.08 MPa, 0.1 MPa, 0.2 MPa, 0.5 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.4 MPa, 1.5 MPa or a range between any two of the above values.

[0192] Transverse shrinkage can also be achieved through spontaneous forces within the unidirectional veneer, a process known as dehydration-induced shrinkage. Thinner wood fiber paper undergoes spontaneous transverse shrinkage during dehydration, as shown in Figure 9, which illustrates the collapse and shrinkage of the lumen of wood fiber paper during spontaneous transverse shrinkage. This is due to the removal of some of the lignin and hemicellulose supporting the lumen from the chemically modified veneer, resulting in a large number of voids in the microstructure that are easily filled with water. Furthermore, since cellulose is the dominant component in the continuous veneer, its chemical structure contains numerous hydroxyl groups, making it a hydrophilic material, which facilitates the entry of water molecules into the microstructure voids. During dehydration, water is removed from these voids, which disappear due to capillary forces. The distance between the cellulose microfibrils is rapidly shortened, and hydrogen bonds between the microfibrils are reestablished. This structural contraction and chemical bond formation produce the effect of spontaneous transverse shrinkage. Macroscopically, the wood fiber paper develops wrinkles, with a reduced transverse width and increased density, as shown in Figure 10.

[0193] In the present invention, the transverse shrinkage can be carried out at room temperature or at high temperature. The specific temperature of the transverse shrinkage treatment is preferably 15°C to 150°C, more preferably 25°C to 130°C; optionally, the temperature of the transverse shrinkage treatment is 20°C, 25°C, 30°C, 50°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or a range between any two of the above values; the time of the transverse shrinkage treatment is preferably 1s to 4min; optionally, the time of the transverse shrinkage treatment is 1s, 10s, 30s, 1min, 2min, 3min, 4min or a range between any two of the above values; after the transverse shrinkage treatment, the shrinkage rate is preferably 2% to 40% compared with the unidirectional veneer raw material; optionally, the shrinkage rate of the transverse shrinkage is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range between any two of the above values.

[0194] In a specific embodiment provided by the present invention, the lateral shrinkage treatment is specifically spontaneous lateral shrinkage, specifically: the unidirectional veneer with some substances removed is dried in a wet state to spontaneously achieve a spontaneous lateral shrinkage effect. After one or more spontaneous lateral shrinkages, the unidirectional veneer with some substances removed is filled with water again, and the lateral shrinkage perpendicular to the fiber direction is obvious, and the lateral tensile performance is improved.

[0195] Normal wood boards can be densified by hot pressing after being softened with steam, but this densification process requires applying relatively high pressure to the wood boards for a long time. For the unidirectional veneer in the present invention, the veneer is relatively thin, and the veneer is prone to cracking when directly hot pressed, and the densification effect obtained is also limited. After chemical modification, the veneer's mass decreases by 35% to 55%, and a large number of cavities are formed inside. Moreover, since the chemical cost removed is mainly hydrophobic lignin, the hydrophilicity of the unidirectional veneer obtained by modification and removing some substances is significantly improved. The internal cavities will be quickly filled with water molecules, and the overall structure will become soft, which can be easily densified by natural water loss. The densification process has low energy consumption and short time, which is conducive to mass production.

[0196] This spontaneous lateral shrinkage process can even completely eliminate the need for external mechanical forces. Modified unidirectional veneer with some material removed can also achieve spontaneous lateral shrinkage through a microstructural hydration-dehydration process, also known as wood keratinization. This process occurs because the chemically modified wood microstructure contains numerous voids, which are easily filled with water. Furthermore, since cellulose is the dominant component in the continuous veneer, its chemical structure contains numerous hydroxyl groups, making it a hydrophilic material, which also facilitates the entry of water molecules into the microstructural voids. During this hydration process, the voids between the cellulose microfibrils expand significantly. During the subsequent drying process, water is removed from these voids, which disappear due to capillary forces. The distance between the cellulose microfibrils is rapidly shortened, and hydrogen bonds between the microfibrils are re-established. This structural contraction and chemical bonding results in spontaneous lateral shrinkage, which is particularly pronounced in the lateral direction of the veneer, perpendicular to the fiber axis, where the densification effect is most pronounced.

[0197] According to the present invention, the spontaneous transverse shrinkage process can achieve the densification effect completely through the chemical and physical changes that spontaneously form during the drying process of the modified unidirectional veneer with some substances removed. Specifically, the spontaneous transverse shrinkage is to dry the unidirectional veneer with some substances removed in a wet state, that is, the spontaneous transverse shrinkage includes water filling treatment and dehydration treatment; the water filling treatment makes the unidirectional veneer with some substances removed in a wet state; the water filling treatment preferably makes the moisture content 60-120wt%; optionally, the water filling treatment makes the moisture content 60wt%, 80wt%, 100wt%, 120wt% or the range between any two of the above values; the dehydration treatment is natural drying and / or heating drying; when the dehydration treatment is carried out by natural drying in an environment, the humidity of the environment for natural drying is preferably less than 50%RH, otherwise after drying The structure of the unidirectional veneer with some substances removed still retains a lot of moisture; the use of heating and drying for dehydration treatment can shorten the dehydration treatment time, thereby shortening the process time, and the unidirectional veneer with some substances removed can be dried to a moisture content of less than 10wt%, and the densification effect will be better; the dehydration treatment is preferably to make the moisture content 2-20wt%; optionally, the dehydration treatment makes the content rate 2wt%, 5wt%, 10wt%, 15wt%, 20wt% or a range between any two of the above values; the present invention has no special requirements for the drying temperature and drying time of the spontaneous transverse shrinkage process, as long as the target moisture content can be finally reached. The process of spontaneous transverse shrinkage can be one time, or it can be repeated 2-10 times, more preferably repeated 2-6 times. The process of repeated spontaneous transverse shrinkage is to refill the unidirectional veneer with some substances removed with water after a round of spontaneous transverse shrinkage, and then perform the same spontaneous transverse shrinkage process. Repeated spontaneous transverse shrinkage can lead to greater densification of the material. This is because the spontaneous transverse shrinkage process is uncontrollable, so the intermolecular forces in the partially delaminated unidirectional veneer structure may not be fully established after a single round of spontaneous transverse shrinkage. After one or more spontaneous transverse shrinkages, the partially delaminated unidirectional veneer will shrink slightly in width perpendicular to the fiber direction when refilled with water. This strengthens the transverse fiber bonding, indicating that some irreversible transverse shrinkage densification has occurred.

[0198] According to the present invention, the thickness shrinkage treatment involves applying mechanical pressure in the thickness direction. Specifically, any method capable of applying external mechanical pressure in the thickness direction of the chemically treated veneer to cause shrinkage in the veneer, and where parameters such as pressure meet the process requirements, is generally applicable. Applicable equipment includes, but is not limited to, flatbed presses, blister presses, hot presses, cold presses, continuous flatbed presses, and continuous belt presses. By applying external mechanical pressure, the veneer is flattened and thinned in the thickness direction due to the force, squeezing out excess moisture and producing a smooth, dense, unidirectional wood fiber paper with a moisture content below 30%. Furthermore, the thickness shrinkage treatment can be performed on a single sheet or in a stack. This process is more efficient when performed on multiple sheets. Depending on the process, the number of stacks is preferably 2 to 30 sheets per stack, more preferably 3 to 20 sheets per stack. The pressure of the thickness shrinkage treatment is preferably 0.01 to 80 MPa; under the condition of stacking, the pressure of the thickness shrinkage is preferably 0.1 to 60 MPa, more preferably 3 to 10 MPa; optionally, the pressure of the thickness shrinkage treatment is 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 8 MPa, 10 MPa, 12 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa or a range between any two of the above values; according to the calculation formula of pressure and area, under the condition of a certain required pressure, the more stacks of one-way veneer with some substances removed, the greater the gauge pressure of the press. If a press is used, it should also be considered that the one-way veneer with some substances removed will be easily broken by the instantaneous high pressure, so the pressure needs to be slowly increased to the target pressure. The thickness shrinkage treatment can be carried out at room temperature or at a high temperature. The specific process temperature range is preferably 15 to 150°C, more preferably 25 to 130°C. Optionally, the temperature of the thickness shrinkage treatment is 15°C, 25°C, 35°C, 50°C, 80°C, 100°C, 120°C, 130°C, 150°C, or a range between any two of the above values. In order to reduce process costs, the time of the thickness shrinkage treatment (only to achieve a densification effect) is preferably 0.1 to 3 minutes. Optionally, the time of the thickness shrinkage treatment is 0.1 min, 0.5 min, 1 min, 2 min, 3 min, or a range between any two of the above values. Carrying out the treatment at a high temperature will shorten the process time, but will also increase equipment costs.

[0199] In a specific embodiment provided by the present invention, the thickness shrinkage treatment is performed by roller pressing; specifically, a pair of counter-rotating hot rolling rollers are used for continuous hot pressing, as shown in Figure 11, which is a schematic diagram of continuous hot pressing processing by hot rolling rollers, wherein 6 is a unidirectional veneer with some materials removed, and 7 is a pair of counter-rotating hot rolling rollers; the force direction of the unidirectional wood fiber paper is not fixed during rolling, but is decomposed into the transverse direction or thickness direction after the force is decomposed.

[0200] In a specific embodiment provided by the present invention, the thickness shrinkage treatment is carried out using a continuous flat press for continuous hot pressing, as shown in Figure 12. Figure 12 is a schematic diagram of continuous hot pressing of a continuous flat press, wherein 6 is a unidirectional veneer with some material removed, 8 is a flat press, and 9 is a driving roller.

[0201] In a specific embodiment provided by the present invention, the thickness shrinkage treatment is performed using a belt press for continuous hot pressing, as shown in Figure 13, which is a schematic diagram of continuous hot pressing using a belt press, wherein 6 is a unidirectional veneer with some material removed, and 10 is a belt press.

[0202] In the present invention, the lateral shrinkage treatment and thickness shrinkage treatment will result in different process times and process times depending on the different processes used. It can be multiple times or a single time, can be performed alternately or simultaneously, and ultimately the process operation time and operation times are designed to achieve the target parameters.

[0203] The effect of the biaxial shrinkage treatment is mainly reflected in the reduction of the moisture content and thickness of the unidirectional veneer after some substances have been removed. After the biaxial shrinkage treatment, the thickness of the unidirectional veneer raw material is thinned from the original 0.05-0.8 mm to a thickness of less than or equal to 0.6 mm; the thickness of the veneer treated with biaxial shrinkage is preferably 10% to 80% of the thickness of the unidirectional veneer; the moisture content of the veneer washed and soaked after chemical modification is preferably reduced to less than 30% after the biaxial shrinkage treatment, and more preferably reduced to 20% to 30%.

[0204] The present invention adopts a bidirectional shrinkage process to achieve densification in thickness and transverse (width) directions of unidirectional wood fiber paper through external or spontaneous physical effects. Transverse shrinkage can increase the transverse bonding force and compactness of unidirectional wood fiber paper, avoiding transverse cracking of unidirectional wood fiber paper; shrinkage in the thickness direction can increase the compactness of unidirectional wood fiber paper and improve the performance of unidirectional wood fiber paper; through simultaneous or sequential shrinkage in two directions, a significant improvement in the performance of unidirectional wood fiber paper can be achieved. Further combined with temperature control, the unidirectional wood fiber paper can be quickly shrunk and densified while being quickly dehydrated, avoiding the occurrence of wrinkles and transverse cracks. The bidirectional shrinkage process proposed by the present invention can generally be completed within 5 minutes, and the process efficiency is high.

[0205] In a specific embodiment provided by the present invention, the thickness shrinkage includes hot pressing under negative pressure conditions; by performing hot pressing under negative pressure conditions, thickness shrinkage and flattening and dehydration of unidirectional wood fiber paper can be achieved simultaneously; the pressure of the hot pressing treatment is preferably 0.1-60 MPa, more preferably 0.1-15 MPa; optionally, the pressure of the hot pressing treatment is 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.5 MPa, 1 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa or a range between any two of the above values; the flow rate under the negative pressure condition is preferably 50-500 L / min; optionally, the The flow rate under the negative pressure condition is 50 L / min, 80 L / min, 100 L / min, 150 L / min, 200 L / min, 250 L / min, 300 L / min, or a range between any two of the above values; the temperature of the hot pressing treatment is preferably 50°C to 150°C; optionally, the temperature of the hot pressing treatment is 50°C, 80°C, 100°C, 120°C, 130°C, 150°C, or a range between any two of the above values; the time of the hot pressing treatment is preferably 0.5 to 20 minutes; optionally, the time of the hot pressing treatment is 0.5 minutes, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 8 minutes, 10 minutes, 12 minutes, 15 minutes, 18 minutes, 20 minutes, or a range between any two of the above values. If the thickness shrinkage treatment is achieved only by hot pressing under negative pressure conditions, the time required is longer due to the lower pressure.

[0206] In the present invention, splicing is performed before or after the bidirectional shrinkage treatment according to the requirements for the size of the unidirectional wood fiber paper. The flatness of the wood fiber paper after the bidirectional shrinkage treatment is improved and the moisture content is reduced. However, due to the size limitations of the veneer raw materials, the veneer used for chemical treatment is discontinuous. In order to meet the requirements of use, the wood fiber paper needs to be connected to make different sizes. When used, it can also be cut according to actual needs and then used to prepare products of different sizes. The whole size can theoretically be spliced ​​to an infinite width and length. The length of the unidirectional wood fiber paper used for splicing is preferably 0.1 to 5m, and the width is preferably 0.01 to 1m. In the present invention, the splicing of unidirectional wood fiber paper can be between two sheets or between multiple sheets, mainly ensuring that the size of the spliced ​​wood fiber paper meets the requirements. The splicing specifically involves marking the splicing outline on the unidirectional veneer with some substances removed or the wood fiber paper after bidirectional shrinkage treatment, and then splicing the corresponding parts. More specifically, before splicing, the splicing parts are first designed on the unidirectional veneer with some substances removed or the wood fiber paper after shrinkage treatment to be spliced, mainly by marking their respective splicing outlines. Then, some splicing techniques are used to connect the multiple scattered unidirectional veneer with some substances removed or the wood fiber paper after shrinkage treatment to form a large-sized unidirectional wood fiber paper. After splicing, the thickness of the wood fiber paper at the splicing part is about 0.08 to 0.12 mm.

[0207] In the present invention, the unidirectional wood fiber paper can be spliced ​​in a partial area overlap manner, as shown in the upper figure in FIG14 , or can be spliced ​​in a non-area overlap manner, as shown in the lower figure in FIG14 .

[0208] In the present invention, the splicing process may be one or more of glue splicing, glue line seam splicing, wet extrusion splicing and film splicing.

[0209] In a specific embodiment provided by the present invention, glue splicing can be used. Specifically, glue is applied to the overlapping portion of one of the debonded unidirectional veneer or shrunk wood fiber paper sheets to be spliced, and then the overlapping portion of the other debonded unidirectional veneer or shrunk wood fiber paper is pressed against it. In this way, the overlapping portions of the two debonded unidirectional veneer or shrunk wood fiber paper sheets are spliced ​​together after the glue cures, thereby increasing the size of the continuous wood fiber paper. Because the overlapping portion is thicker than the other portions of the two debonded unidirectional veneer or shrunk wood fiber paper sheets, pressure can be applied to the overlapping portion to reduce its thickness and improve the thickness uniformity of the entire wood fiber paper sheet.

[0210] In a specific embodiment provided by the present invention, glue line splicing can be used. Specifically, the contours of the debonded unidirectional veneer or shrunken wood fiber paper to be spliced ​​are designed to fit perfectly together. The contours of the two debonded unidirectional veneers or shrunken wood fiber papers to be spliced ​​are then aligned together. Glue line is then moved back and forth along the two aligned contours. The glue line adheres to the surfaces of the unidirectional wood fiber papers, and the glue line is continuous, thereby fixing the positions of the two debonded unidirectional veneers or shrunken wood fiber papers, thereby achieving the purpose of splicing the unidirectional wood fiber papers. To improve the strength of the splicing, on the one hand, the number of glue lines connecting the two debonded unidirectional veneers or shrunken wood fiber papers can be increased during the splicing process. On the other hand, the two sides of the debonded unidirectional veneers or shrunken wood fiber papers can be spliced ​​together. The advantage of glue seams is that there is no overlapping of two unidirectional wood fiber papers during seams. Instead, the size of the wood fiber paper can be increased simply by fitting the contours, so that the thickness of the wood fiber paper at the seams remains basically consistent with that at other parts.

[0211] In a specific embodiment provided by the present invention, wet extrusion splicing can be adopted. Specifically: the method of wet extrusion splicing is similar to glue splicing, but glue is not used, and only water is used. Water is applied to the overlapping parts of the one-way veneer with some substances removed or the wood fiber paper after shrinkage treatment to make them wet, and then the overlapping parts are stacked together, and a large plane pressure (≥5MPa) is applied thereto, supplemented by heating and drying, until the wood fiber paper is dry and adhered together to achieve the purpose of splicing. The one-way veneer with some substances removed or the wood fiber paper after shrinkage treatment in a wet state has a soft texture. Under the action of large pressure, the textures of the two pieces of one-way veneer with some substances removed or the wood fiber paper after shrinkage treatment are tightly pressed together, and they adhere to each other to the point of hydrogen bonding. This pressure is maintained until the wood fiber paper is dry, thereby fixing this bonding force and completing the splicing. The advantage of wet extrusion splicing is that it well maintains the natural properties of wood fiber paper. It can easily produce wood fiber paper of any size and width. After the subsequent process of lamination / pre-impregnation, continuous prepregs of unlimited sizes can theoretically be produced.

[0212] In one specific embodiment of the present invention, a film-laminated splicing method can be employed. Specifically, a continuous adhesive film is selected based on the desired large size. Smaller unidirectional wood fiber papers are then pressed against the film. Through the film's connection, the smaller unidirectional wood fiber papers are spliced ​​together, achieving the goal of increasing the size. The type of adhesive film can be selected as needed; a thin layer of felt mixed with glue can also be used to create a homemade prepreg. The principle is to attach a film layer to connect the smaller unidirectional wood fiber papers. This method can theoretically produce continuous prepregs of unlimited size.

[0213] The present invention also provides another method for preparing unidirectional wood fiber paper, comprising the following steps: A1) chemically modifying unidirectional veneer to obtain unidirectional veneer with some substances removed; A2) shrinking and leveling the unidirectional veneer with some substances removed in at least one direction to obtain unidirectional wood fiber paper; the leveling treatment is flat hot pressing under a negative pressure exhaust environment.

[0214] The shrinkage treatment in step A1) and step A2) is the same as described above and will not be repeated here. Specifically, the thickness shrinkage treatment in the shrinkage treatment in step A2) does not include the above-mentioned hot pressing treatment under negative pressure conditions.

[0215] The veneer after shrinkage treatment can be dehydrated more efficiently and quickly through leveling treatment, while achieving relatively good flatness during the dehydration process to obtain unidirectional wood fiber paper; the effect of leveling is mainly reflected in quickly and efficiently improving the flatness of the wood fiber paper and reducing the moisture content to obtain dry and flat unidirectional wood fiber paper.

[0216] According to the present invention, more specifically, the moisture content of the obtained unidirectional wood fiber paper can be made less than or equal to 10 wt % through the leveling treatment.

[0217] According to the present invention, exhaust channels are provided on the double contact surfaces or single contact surface of the unidirectional wood fiber paper during the leveling process. Specifically, it can be implemented using various types of equipment such as a heatable negative pressure membrane press, a vacuum hot press, etc., such as a vacuum hot press with multiple exhaust channels. The characteristic of the leveling process is that the processing process can be heated, and at the same time, exhaust channels are directly provided on both sides or one side of the pressed wood fiber paper, so that water vapor can be discharged. Generally, the pressure in the leveling process will be significantly lower than the pressure used in thickness shrinkage, because if the pressure is too high, the exhaust rate of water vapor will be reduced, which will reduce the leveling efficiency. When using the leveling process, the pressure is selected with the purpose of preventing the unidirectional wood fiber paper from generating wrinkles during the drying process. The pressure used in the leveling process is 0.01 to 2 MPa. Optionally, the pressure is 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, or any range between the above two values. The heating temperature is 40°C to 150°C. Optionally, the heating temperature is 40°C, 50°C, 70°C, 80°C, 100°C, 120°C, 150°C, or any range between the above two values. By properly setting the exhaust channel on the contact surface of the unidirectional wood fiber paper, leveling can be completed within 0.1 to 4 minutes. Optionally, the leveling time is 0.1 minute, 0.5 minute, 1 minute, 2 minutes, 3 minutes, 4 minutes, or any range between the above two values.

[0218] The present invention also provides a wood fiber paper prepreg, comprising the above-mentioned unidirectional wood fiber paper and a high molecular polymer layer attached to at least one surface of the unidirectional wood fiber paper.

[0219] According to the present invention, the polymer in the polymer layer can be any thermosetting resin and / or thermoplastic resin known to those skilled in the art, without particular limitation. In the present invention, the thermosetting resin can specifically be one or more of epoxy resin, unsaturated polyester, polybutadiene resin, phenolic resin, and cross-linkable polyurethane; the thermoplastic resin can specifically be a hot melt adhesive-grade polymer such as polyamide, polylactic acid, polyurethane, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, or copolyester.

[0220] According to the present invention, the mass of the high molecular polymer layer is preferably 5% to 85% of the mass of the unidirectional wood fiber paper prepreg.

[0221] According to the present invention, the unidirectional wood fiber paper prepreg comprises unidirectional wood fiber paper; a high molecular polymer layer is provided on one side and / or both sides of the unidirectional wood fiber paper.

[0222] According to the present invention, the thickness ratio of the high molecular polymer layer to the unidirectional wood fiber paper is preferably 5:1 to 0.05:1.

[0223] According to the present invention, the surface density of the unidirectional wood fiber paper prepreg is preferably 30 to 500 g / m 2 .

[0224] According to the present invention, the thickness of the unidirectional wood fiber paper prepreg is preferably 0.03 to 0.7 mm.

[0225] According to the present invention, the weight of the polymer layer is preferably 5 to 200 g / m 2 .

[0226] The present invention also provides a method for preparing a unidirectional wood fiber paper prepreg, comprising the following steps: transferring a high molecular polymer to at least one surface of the above-mentioned unidirectional wood fiber paper to obtain a unidirectional wood fiber paper prepreg; the transfer method is selected from one or more of lamination, impregnation and coating.

[0227] In a specific embodiment provided by the present invention, the transfer method is lamination, specifically: the unidirectional wood fiber paper and the polymer adhesive film are passed through an automatic laminating machine with a double-sided heating function, the polymer in a molten state at high temperature and the unidirectional wood fiber paper are infiltrated into each other under the action of roller pressure, and then a single-layer sheet-like unidirectional wood fiber paper prepreg with a surface polymer layer is obtained.

[0228] In a specific embodiment provided by the present invention, the preparation process of the unidirectional wood fiber paper prepreg is shown in Figure 16, specifically as follows: prepare 2 rolls of polymer adhesive film with the same width as the unidirectional wood fiber paper, and fix them on the upper and lower film roll sleeves of the automatic laminating machine respectively. Open the paper feed platen and the heating rubber roller protective cover, pass the ends of the polymer adhesive film on the upper and lower sleeves through the upper and lower traction rollers respectively, and overlap and cover the surface of a pair of heated rubber rollers of the laminating machine flatly to ensure that the two ends of the film are aligned. Install the paper feed platen and the heating roller protective cover, and adjust the positioner on the platen to the same width according to the width of the wood fiber paper. Turn on the power of the automatic laminating machine and select the working mode as hot lamination. According to the type and gram weight of the polymer adhesive film to be covered, set the corresponding rubber roller heating temperature and select the appropriate laminating speed gear, and start the double rubber roller preheating. After the upper and lower rubber rollers are preheated to the specified temperature, the unidirectional wood fiber paper to be laminated is fed from the paper feed platen into the space between the heated rollers, where it is kept flat and aligned with the upper and lower polymer adhesive films. The motor is then turned on to operate the rubber rollers, which pass the unidirectional wood fiber paper and the two layers of polymer adhesive film through the heated rollers. During this process, the polymer adhesive film, where it contacts the heated rollers, undergoes a series of heating, melting, impregnation, and pressing steps, completing the lamination process. The lamination rate and gap between the heated rollers can be adjusted to ensure a smooth and continuous lamination process, achieving the desired lamination conditions.

[0229] In another specific embodiment provided by the present invention, the operating mode can be changed from the upper and lower double-sided lamination mode to a single-sided lamination mode with upper roller heating and lower roller film placement and lamination, depending on actual needs. That is, by turning off the double-roll preheating button, the machine automatically switches to upper roller heating. The polymer adhesive film reel on the lower film reel sleeve is pulled out, passed through the lower traction roller, and fed together with the unidirectional wood fiber paper to be coated to the middle of the running roller pair. A series of heating, melting, impregnation, and pressing processes are completed in sequence, thereby completing the single-sided lamination process of the wood fiber paper and obtaining a unidirectional wood fiber paper prepreg. A schematic diagram of the preparation process is shown in Figure 17, which is a schematic diagram of the single-sided lamination process.

[0230] According to the present invention, the high molecular polymer adhesive film can be a lamellar thermoplastic polymer adhesive film or a thermosetting polymer adhesive film.

[0231] To be more specific, the types of lamellar thermoplastic polymer adhesive films include: continuous web or thin layer film materials based on hot melt adhesive grade polymers such as polyamide, polylactic acid, polyurethane, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, copolyester, and so on; and spunlace non-woven fabrics, needle-punched non-woven fabrics, spunbond non-woven fabrics, and meltblown non-woven fabrics based on thermoplastic polymers such as polypropylene, polyamide, polylactic acid, polyester, and viscose fiber.

[0232] More specifically, the types of thermosetting polymer adhesive films include: continuous thin layer film materials with thermosetting polymer prepolymers such as epoxy resin, unsaturated polyester, polybutadiene resin, phenolic resin, cross-linkable polyurethane as the matrix.

[0233] According to the present invention, the specification of the high molecular polymer adhesive film is: the selected width range is 10 to 5000 mm.

[0234] More specifically, the weight range of the thermoplastic polymer adhesive film is preferably 5 to 200 g / m 2 , more preferably 5 to 80 g / m 2 , more preferably 10 to 60 g / m 2 , most preferably 10 to 50 g / m 2 .

[0235] More specifically, the weight range of the thermosetting polymer adhesive film is preferably 5 to 200 g / m 2 , more preferably 5 to 120 g / m 2 , more preferably 10 to 100 g / m 2 .

[0236] More specifically, the heating temperature of the rubber roller is preferably 70-170°C, more preferably 80-160°C, and even more preferably 110-150°C.

[0237] More specifically, the coating rate is preferably 0.6 to 2.4 m / min, more preferably 0.6 to 2.0 m / min, and even more preferably 0.9 to 1.8 m / min.

[0238] Functional additives such as flame retardants and anti-hygroscopic agents may be added to the thermosetting / thermoplastic polymer system used for the above-mentioned coating to impart flame retardancy and anti-hygroscopicity properties to the prepreg.

[0239] In a specific embodiment provided by the present invention, the transfer method is dipping and / or coating, and in this case, the high molecular polymer is liquid.

[0240] More specifically, the unidirectional wood fiber paper prepreg is prepared according to the following steps: the unidirectional wood fiber paper is passed through (e.g., by rollers) a resin tank to be coated / impregnated and immersed below the liquid surface, and continuously conveyed to the scraper on the right side so that a specific thickness of polymer remains on the surface of the unidirectional wood fiber paper. See Figure 18, which is a schematic diagram of the preparation of unidirectional wood fiber paper prepreg by the coating and scraping method. The polymer in this step should generally be a single-component curing system with a slow curing speed at room temperature. It should generally be ensured that it will not fail when stored at room temperature / low temperature for 3 months, and can be cured within a few hours after being heated to the use temperature. The polymer can be a thermosetting polymer prepolymer such as epoxy resin, unsaturated polyester, polybutadiene resin, phenolic resin, cross-linked polyurethane, etc.

[0241] The present invention also provides a wood fiber paper reinforced composite material, comprising multiple layers of the above-mentioned unidirectional wood fiber paper; adjacent unidirectional wood fiber papers are bonded by a high molecular polymer.

[0242] The types of polymers between adjacent wood fiber papers can be the same or different. More specifically, the surfaces of the unidirectional wood fiber papers on both surfaces of the wood fiber paper reinforced composite material are preferably provided with a waterproof polymer layer to improve the waterproofness of the wood fiber paper reinforced composite material.

[0243] According to the present invention, the tensile strength of the wood fiber paper reinforced composite material is preferably 130 to 1000 MPa, more preferably 150 to 1000 MPa.

[0244] According to the present invention, the bending strength of the wood fiber paper reinforced composite material is preferably 130 to 1000 MPa.

[0245] According to the present invention, the Young's modulus of the wood fiber paper reinforced composite material is preferably 12 to 75 GPa, more preferably 12 to 60 GPa.

[0246] According to the present invention, the proportion of bio-based components or natural components in the wood fiber paper reinforced composite material is preferably 50% to 100%.

[0247] According to the present invention, the volume fraction of the wood fiber paper in the wood fiber paper reinforced composite material is preferably 50% to 95%.

[0248] According to the present invention, the wood fiber paper reinforced composite material has common unidirectional texture characteristics of natural wood.

[0249] According to the present invention, the thickness direction of the cut surface of the wood fiber paper reinforced composite material is a laminated structure; the longitudinal section of the wood fiber paper reinforced composite material has distinct layers; since pressure needs to be applied during the molding process of the wood fiber paper reinforced composite material, the thickness of the unidirectional wood fiber paper in the wood fiber paper reinforced composite material is thinner than the thickness of the unidirectional wood fiber paper in the raw material, preferably 0.02 to 0.6 mm.

[0250] According to the present invention, the density of the wood fiber paper reinforced composite material is preferably 0.8 to 1.5 g / cm 3 .

[0251] In a specific embodiment provided by the present invention, a waterproof polymer layer is provided on at least one surface of the wood fiber paper reinforced composite material.

[0252] The present invention also provides a method for preparing a wood fiber paper reinforced composite material, comprising the following steps: stacking and curing the above-mentioned unidirectional wood fiber paper prepreg to obtain a wood fiber paper reinforced composite material; or stacking, gluing and curing the above-mentioned unidirectional wood fiber paper to obtain a wood fiber paper reinforced composite material.

[0253] See FIG19 , which is a schematic diagram showing the principle of preparing a wood fiber paper reinforced composite material from a unidirectional wood fiber paper prepreg.

[0254] In the present invention, the curing molding method of the unidirectional wood fiber paper prepreg can adopt the conventional method used for composite molding, including but not limited to the autoclave method, vacuum bag pressing method, mold pressing method, etc.; further, the wood fiber paper prepreg can be cut into the required shape and size according to the external size characteristics of the part, and then stacked and cured to obtain a wood fiber paper reinforced composite material.

[0255] In a specific embodiment provided by the present invention, the wood fiber paper reinforced composite material is prepared according to the following steps: the unidirectional wood fiber paper prepreg is cut into the required shape and size, placed in a mold according to the ply design, the prepreg is heated and pressurized, and then cooled and the workpiece is taken out to obtain the required laminated structure. Specifically, the unidirectional wood fiber paper prepreg can be flexibly placed in the mold according to the ply design requirements; using the mold, the obtained wood fiber paper reinforced composite material can contain complex geometric features such as planes, curved surfaces, inclined surfaces, arc surfaces, and cylindrical surfaces, see Figure 20, which is a schematic cross-sectional view of the wood fiber paper reinforced composite material; the pressurization can be applied by any one or more of hydraulic pressure, vacuum, compressed air, etc., and the heating can be applied by any one or more of electric heating, electromagnetic heating, thermal radiation, etc.

[0256] In another specific embodiment provided by the present invention, the unidirectional wood fiber paper prepregs on the upper and lower surfaces and / or the unidirectional wood fiber paper prepregs on the upper and lower surface sublayers of the wood fiber paper reinforced composite material are preferably unidirectional wood fiber paper prepregs coated with a waterproof polymer on both sides, and the other internal layers still use unidirectional wood fiber paper prepregs coated with a polymer on one side. After molding, the outer side of the laminated structure already has a waterproof polymer layer of a certain thickness, which can effectively block water absorption. See Figure 21, which is a schematic diagram of preparing a wood fiber paper reinforced composite material with waterproof performance from unidirectional wood fiber paper prepregs; the waterproof polymer is a waterproof polymer well known to those skilled in the art. The water-based polymer is not particularly limited and can be a common thermosetting polymer system such as epoxy resin, polyurethane, polyester, phenolic resin, acrylic resin, etc., or a thermoplastic polymer system such as polyethylene, polypropylene, copolyolefin, polyamide, polylactic acid, acrylonitrile-butadiene-styrene copolymer, polyurethane, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polymethacrylate, copolyester, etc.; the thickness of the waterproof polymer coated in the unidirectional wood fiber paper prepreg coated with the waterproof polymer on both sides is preferably between 0.001 and 1 mm, more preferably between 0.005 and 0.5 mm, and can be simply prepared by the above-mentioned lamination or dipping method.

[0257] In the present invention, in addition to the unidirectional wood fiber paper prepreg, the unidirectional wood fiber paper also has good manufacturability and can be formed into parts using methods commonly used in the field of composite materials, such as hand lay-up molding, resin transfer molding, vacuum-assisted resin transfer molding, compression molding, and vacuum bag pressing. Unlike the unidirectional wood fiber paper prepreg, a polymer must be coated or brushed on the unidirectional wood fiber paper by machine or by hand before molding. The polymer is the same as described above and will not be repeated here. See Figure 22, which is a schematic diagram of the process of preparing wood fiber paper reinforced composite materials from unidirectional wood fiber paper.

[0258] After preparing high-performance unidirectional wood fiber paper, the present invention creates a unidirectional wood fiber paper prepreg through a laminating / impregnation process, simplifying subsequent use and essentially resembling the use of prepreg in composite material molding. Multiple sheets of unidirectional wood fiber paper prepreg are simply stacked together, then placed in a mold with minimal pressure. Once the resin cures, the prepreg is shaped to create the desired part, thereby creating a wood fiber paper-reinforced composite material.

[0259] The present invention also provides a wooden hollow tube formed from the aforementioned unidirectional wood fiber paper, the aforementioned unidirectional wood fiber paper prepreg, or the aforementioned wood fiber paper reinforced composite material. See FIG23 , which is a physical image of the wooden hollow tube.

[0260] The molding process of the wood fiber paper reinforced composite material and wooden hollow tube provided by the present invention is to cut each layer of unidirectional wood fiber paper and / or unidirectional wood fiber paper prepreg into corresponding sizes and shapes, and then stack them according to the design drawings. During the stacking process, the materials need to be simultaneously formed into three-dimensional features, such as being attached to a pre-processed mold surface or wrapped / coated on the surface of a core rod mold. Finally, the polymer is cured and demolded to complete the structural molding of the wood fiber paper reinforced composite material or wooden hollow tube. And because the raw materials used in the present invention are unidirectional wood fiber paper and / or unidirectional wood fiber paper prepreg, it has the ability to mold and form complex structures.

[0261] The present invention also provides a method for shrinking unidirectional veneer, wherein the unidirectional veneer is subjected to shrinkage treatment in at least one direction; the decomposition of the shrinkage force includes transverse shrinkage and thickness shrinkage.

[0262] The unidirectional veneer is the same as described above and will not be described in detail here.

[0263] In a specific embodiment provided by the present invention, the unidirectional veneer is first subjected to a chemical treatment to remove some substances, and then subjected to a shrinkage treatment in at least one direction. The chemical treatment method is the same as described above and will not be repeated here.

[0264] In a specific embodiment provided by the present invention, the shrinkage includes lateral shrinkage and thickness shrinkage; the shrinkage force directions of the lateral shrinkage and thickness shrinkage intersect.

[0265] Specifically, the unidirectional veneer comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are microscopically arranged or extend in a single direction as a whole; the lateral shrinkage force is a horizontal force acting within the unidirectional veneer and intersecting the in-plane extension direction of the wood fibers and / or fiber bundles; and / or the thickness shrinkage force is a vertical force acting within the unidirectional veneer; the horizontal and vertical forces are each independently original forces, and / or are forces formed through force synthesis or decomposition. The lateral shrinkage and thickness shrinkage are the same as described above and will not be further elaborated here.

[0266] In the present invention, unless otherwise specified, the pressure referred to refers to the pressure exerted on the unidirectional veneer and the unidirectional wood fiber paper.

[0267] To further illustrate the present invention, the following describes in detail the present invention, in combination with embodiments, to provide a unidirectional wood fiber paper and a preparation method thereof, a unidirectional wood fiber paper prepreg and a preparation method thereof, and a wood fiber paper reinforced composite material and a preparation method thereof.

[0268] The reagents used in the following examples are all commercially available.

[0269] Example 1 (Lateral and thickness sequential shrinkage process)

[0270] 1) Chemical treatment

[0271] First, prepare the reaction solution with a total solution volume of 100L. The reactor is a vertical reactor (with an external circulation pump), and the material frame of the vertical reactor proposed by the present invention is used to load the unidirectional veneer for chemical treatment. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and unidirectional basswood veneer with a thickness of 0.28mm are mixed at a material ratio of 0.49m 2 The reaction vessel was placed in a reactor under a pressure of 125°C. The reactor was heated to 125°C, placing the entire internal system under high pressure. After maintaining the target temperature and pressure for 6 hours, the temperature was lowered to ambient temperature and pressure. The reactor was then opened and the partially dematerialized unidirectional veneer was removed. The partially dematerialized veneer was then washed with water to complete the chemical modification process. See Figure 24, which shows a photograph of the partially dematerialized unidirectional veneer in its wet state. The weight of the resulting partially dematerialized unidirectional veneer was reduced by 50%.

[0272] 2) Spontaneous lateral contraction

[0273] Take a 10cm wide piece of partially debonded unidirectional veneer obtained in step 1). Place the veneer in an oven and heat it to 80°C. After 2-3 minutes, the veneer reaches a dry state and exhibits significant transverse shrinkage perpendicular to the fiber direction, with the apparent width reduced by 50% and noticeable wrinkling. Even after re-immersion in water and expansion, the width does not fully recover, indicating that some irreversible transverse shrinkage has occurred. See Figure 25, which shows the spontaneous transverse shrinkage of the partially debonded unidirectional veneer.

[0274] 3) Shrinkage and leveling in the thickness direction

[0275] The transversely shrunk veneer (raw material thickness of about 0.28 mm) obtained in step 2) is shrunk in the thickness direction using a vacuum hot press in a wet state, with a pressure of 6 MPa, a compression time of 0.5 minutes, and a temperature of 110°C. The pressure needs to rise slowly during the compression process to prevent the veneer from being crushed by excessive impact. The compression direction is perpendicular to the thickness direction of the veneer fibers. Due to the chemical modification in step 1) that removes most of the hemicellulose and lignin, the pore structure of the wood is fully opened, and the hydroxyl groups on the surface of the hydrophilic cellulose are induced to form new hydrogen bonds during the process of water infiltration and extrusion. Therefore, adjacent wood fibers are tightly bonded to obtain a dense veneer with greatly enhanced mechanical properties. After shrinking in the thickness direction, the thickness of the veneer is reduced to about 0.08 mm, and the moisture content is 20%. Then, negative pressure was turned on and additional positive pressure was added (the pressure in the thickness direction of the wood fiber paper was about 0.5 MPa), the flow rate was about 150 L / min, the temperature was still 110 degrees Celsius, and it was maintained for 4 minutes to obtain dry and flat unidirectional wood fiber paper. There were very few cracks, with a probability of less than 5%. The average thickness of the unidirectional wood fiber paper was 0.08 mm. According to the flatness test method described in the instructions, the wood fiber paper was placed between two smooth and flat glass plates, and a small plane pressure of about 4500 Pa was applied to the glass surface. The gap between the glass plates was measured (considering that the glass plates were not completely flat, the gap was the maximum apparent thickness of the highest and lowest points of the wood fiber paper) and was between 0.15 and 0.2 mm. The average moisture content was 4%, and the final width was about 30% smaller than that of the wet veneer after chemical treatment. Based on the plastic tensile testing standard GB / T1040.1-2006, mechanical tensile testing was conducted on the paper. The wood fiber paper strips were 4 mm wide and stretched at a rate of 2 mm / min. The resulting tensile curve is shown in Figure 26, which shows the tensile stress-strain curve along the fiber direction of the unidirectional wood fiber paper. Figure 26 shows an average breaking strength of 381 MPa and an average elastic modulus of 32 GPa. The tensile strength perpendicular to the fiber direction was 8.7 MPa, and the tensile modulus was 1.74 GPa.

[0276] Comparative Example 1 (shrinkage in thickness direction only)

[0277] The chemical treatment was the same as in Example 1. Without the transverse shrinkage step, the chemically treated wet veneer (10 cm wide) was directly shrunk in the thickness direction using a vacuum hot press, with the pressure remaining at 6 MPa and the compression time at 0.5 minutes. As in Example 1, negative pressure was then applied with additional positive pressure (the pressure in the thickness direction of the wood fiber paper was approximately 0.5 MPa), with a flow rate of approximately 150 L / min and the temperature remaining at 110 degrees Celsius for 4 minutes. Upon opening the press, cracks were observed in some of the wood fiber paper, with a probability of approximately 40%. The average thickness was 0.07 mm, thinner than the transversely shrunk veneer, and the width remained essentially unchanged. See Figure 27, which shows a photo of the chemically treated veneer subjected only to thickness shrinkage. Mechanical tensile testing revealed the following tensile properties for the resulting wood fiber paper: an average tensile strength of 348 MPa and an average tensile modulus of 30 GPa in the fiber direction; a tensile strength of 4.8 MPa and a tensile modulus of 1.1 GPa perpendicular to the fiber direction.

[0278] The average parameters and properties of the unidirectional wood fiber papers obtained in Example 1 and Comparative Example 1 from the same batch and specification of wood fiber papers are shown in Table 1 below.

[0279] Table 1 Average parameters and properties of unidirectional wood fiber paper

[0280] Example 2 (lateral shrinkage method)

[0281] The chemical treatment is the same as that in Implementation Case 1. Different methods are used for transverse shrinkage, but the thickness compression method is the same: the wood fiber paper is placed on a smooth metal table with a surface roughness of Ra1.6, and a cover plate is placed on top. The cover plate is made of a pre-tensioned silicone soft film. The tension is perpendicular to the fiber direction of the wood fiber paper, and the tightness is adjustable. A pressure of about 0.5 MPa is applied to the cover plate to make the film close to the wood fiber paper to generate pressure. In the process of releasing the tension of the silicone film, the wood fiber paper shrinks laterally under the action of friction. In this case, the equivalent shrinkage pressures of approximately 0.002 MPa, 0.2 MPa and 1.2 MPa are achieved by controlling the tension of the silicone mold. The thickness shrinkage rate and transverse shrinkage rate of the wood fiber paper obtained in this comparative example were tested, and then its tensile mechanical properties were tested. The results are shown in Table 2.

[0282] Table 2 Table 1 Average parameters and properties of unidirectional wood fiber paper

[0283] Example 3 (Thickness Shrinkage Method and Pressure Comparison)

[0284] The chemical treatment and transverse shrinkage methods are exactly the same as those in Example 1, and the thickness compression adopts the roller pressing method. By adjusting the gap between the rollers, the effect of adjusting the pressure in the thickness direction can be achieved, as shown in Figure 11. During the rolling process, the wood fiber paper is subjected to a combined force composed of pressure and friction in the thickness direction, and the combined force is in the direction shown by the dotted line in the figure. The component force (pressure) in the thickness direction can make the wood fiber paper have a better shrinkage effect. In this comparative example, the last gap between the rollers is set to 0.07mm, and the average thickness of the wood fiber paper after compression is 0.08mm. The tensile properties of the wood fiber paper were tested, and the results are shown in Table 3.

[0285] Table 3 Average parameters and properties of unidirectional wood fiber paper obtained by different thickness shrinkage methods

[0286] To compare the effects of pressure on thickness shrinkage, veneer materials of the same specifications as in Example 1 were selected. The chemical treatment, transverse shrinkage method, and thickness shrinkage method were identical to those in Example 1, with the only difference being that the thickness shrinkage pressure was 0.02 MPa, compared to 6 MPa in Example 1. Furthermore, to compare the thickness shrinkage effect under higher pressures, unidirectional veneer materials of the same specifications were selected. The chemical treatment and transverse shrinkage methods were the same as in Example 1, but a higher pressure of 18 MPa was used for thickness compression. The wood fiber paper was then flattened using a vacuum press equipped with an exhaust channel. The flattening parameters were a pressure of 0.2 MPa, a temperature of 110°C, and a vacuum pump flow rate of approximately 150 L / min for 1 minute. The parameters of the unidirectional wood fiber paper obtained by the above process are shown in Table 4 below.

[0287] Table 4 Average parameters and properties of unidirectional wood fiber paper obtained under different thickness shrinkage conditions

[0288] Example 4 (Compression Direction Order)

[0289] The chemical treatment was the same as in Example 1, the thickness compression method was the same, and the transverse shrinkage method was the same as in Example 2. The difference was that thickness compression was performed first, followed by transverse shrinkage. For details, see above. The thickness shrinkage-first method also produced excellent wood fiber paper. The performance test results are shown in Table 5.

[0290] Table 5 Average parameters and properties of unidirectional wood fiber paper

[0291] The chemical treatments in Examples 5 to 9 are different from those in Example 1, but the other processes are the same.

[0292] Example 5

[0293] First, prepare the reaction solution with a total solution volume of 20L. The reactor is a vertical reactor, and the unidirectional veneer can be placed directly against the wall of the reactor for reaction. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and the unidirectional veneer of basswood with a thickness of 0.28mm are mixed at a temperature of 0.29m. 2 The materials were placed in a reactor at a ratio of 1 / L. The reactor was heated to 125°C, creating a high-pressure state within the entire system. After maintaining the target temperature and pressure for 6 hours, the reactor was cooled to ambient temperature and pressure within the system. The reactor was then opened and the partially debonded unidirectional veneer was removed. The debonded veneer was then washed and the chemical modification process was completed. The resulting debonded veneer had a mass reduction of 42.0%.

[0294] Example 6

[0295] First, prepare the reaction solution with a total solution volume of 100L. The reactor is a vertical reactor (with an external circulation pump), and the material frame of the vertical reactor proposed by the present invention is used to load the unidirectional veneer for chemical treatment. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and the unidirectional veneer of basswood with a thickness of 0.28mm are mixed at a temperature of 0.12m. 2 The materials were placed in a reactor at a ratio of 1 / L. The reactor was heated to 125°C, creating a high-pressure state within the entire system. After maintaining the target temperature and pressure for 4 hours, the reactor was cooled to ambient temperature and pressure. The reactor was then opened and the partially debonded unidirectional veneer was removed. The debonded veneer was then washed and the chemical modification process was completed. The resulting debonded veneer had a mass reduction of 46.8%.

[0296] Example 7

[0297] First, prepare the reaction solution with a total solution volume of 100L. The reactor is a vertical reactor (with an external circulation pump), and the material frame of the vertical reactor proposed by the present invention is used to load the unidirectional veneer for chemical treatment. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and the unidirectional basswood veneer with a thickness of 0.28mm are mixed with 0.12m 2The materials were placed in a reactor at a ratio of 1000 ppm to 1000 ppm. The reactor was heated to 125°C, creating a high-pressure state within the entire system. After maintaining the target temperature and pressure for 5 hours, the reactor was cooled to ambient temperature and pressure. The reactor was then opened and the partially debonded unidirectional veneer was removed. The debonded veneer was then washed and the chemical modification process was completed. The resulting modified unidirectional veneer had a mass reduction of 49.1%.

[0298] Example 8

[0299] First, prepare the reaction solution with a total solution volume of 3T. The reactor is a vertical reactor (with an external circulation pump), and the material frame of the vertical reactor proposed by the present invention is used to load the unidirectional veneer for chemical treatment. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and the unidirectional basswood veneer with a thickness of 0.28mm are mixed with 0.25m 2 The materials were placed in a reactor at a ratio of 1 / L. The reactor was heated to 125°C, placing the entire internal system under high pressure. After maintaining the target temperature and pressure for 5 hours, the reactor was cooled to ambient temperature and pressure. The reactor was then opened and the partially debonded unidirectional veneer was removed. The debonded veneer was then washed and the chemical modification process was completed. The resulting debonded veneer had a mass reduction of 49.0%.

[0300] Example 9

[0301] First, prepare the reaction solution with a total solution volume of 3T. The reactor is a horizontal reactor (with an external circulation pump), and the material frame of the horizontal reactor proposed by the present invention is used to load the one-way veneer for chemical treatment. Sodium hydroxide and sodium sulfite are dissolved in water. The concentration of sodium hydroxide in the reaction solution is 100g / L, the concentration of sodium sulfite is 50g / L, and the pH value of the reaction solution is 14. Then the reaction solution and the one-way basswood veneer with a thickness of 0.28mm are mixed with 0.37m 2 The materials were placed in a reactor at a ratio of 1 / L. The reactor was heated to 125°C, creating a high-pressure state within the entire system. After maintaining the target temperature and pressure for 5 hours, the reactor was cooled to ambient temperature and pressure. The reactor was then opened and the partially debonded unidirectional veneer was removed. The debonded veneer was then washed and the chemical modification process was completed. The resulting debonded veneer had a mass reduction of 48.2%.

[0302] The unidirectional veneers obtained in Examples 5 to 9 from which some substances were removed were subsequently treated according to the method of Example 1 to obtain unidirectional wood fiber paper. The tensile properties of the unidirectional wood fiber paper in the fiber direction were tested, and the results are shown in Table 6.

[0303] Table 6 Performance test results of unidirectional wood fiber paper obtained in Examples 5 to 9

[0304] Example 10

[0305] The entire process is the same as in Example 1, except that a splicing process is added.

[0306] The width of the unidirectional veneer raw material was 15 cm. The same chemical treatment method as in Example 1 was used to obtain partially debonded unidirectional veneer. The debonded veneer was then wet-jointed at its edges, with an overlap width of 2 mm to 6 mm. The same shrinking process as in Example 1 was then used to produce unidirectional wood fiber paper with a width equal to the overlap width of two sheets of unidirectional wood fiber paper, as shown in Figure 28 . Figure 28 shows photographs of unidirectional wood fiber paper produced with different overlap widths.

[0307] Transverse tensile testing of unidirectional wood fiber paper with a 2.6mm overlap width revealed a transverse tensile strength of 0.67 kN / m, exceeding the 0.57 kN / m strength of unjoined unidirectional wood fiber paper prepared by the same method. This indicates that the overlapped sections of the wood fiber paper are tightly bonded after complete drying. Mechanical tensile testing along the fiber direction revealed an average breaking strength of 347 MPa and an average elastic modulus of 32 GPa. This method can produce wide-width unidirectional wood fiber paper.

[0308] Example 11

[0309] The surface of the unidirectional wood fiber paper obtained in Example 1 was coated with epoxy resin (the pure resin had a tensile strength of 60 MPa and a Young's modulus of 3 GPa after curing) to obtain an epoxy-wood fiber paper prepreg. The epoxy-wood fiber paper prepreg was then laid unidirectionally and vacuum-baked at 80°C for 1 hour until the epoxy resin was completely cured, resulting in a wood fiber-reinforced epoxy resin-based composite material, wherein the volume percentage of the wood fiber reinforcement was 90%.

[0310] Figure 29 is a top view of the wood fiber reinforced epoxy resin-based composite material obtained in Example 11. Figure 30 is a side view of the wood fiber reinforced epoxy resin-based composite material obtained in Example 11.

[0311] The mechanical properties of the wood fiber reinforced composite material obtained in Example 8 were tested according to GB / T 1499-2005 Test Method for Flexural Properties of Fiber Reinforced Plastics, and the results showed that the flexural strength was 349 MPa and the Young's modulus was 29 GPa.

[0312] Example 12

[0313] The unidirectional wood fiber paper obtained in Example 1 was coated with a film having a thickness of 0.02 mm and a surface density of 23 g / m2 The PA-wood fiber paper prepreg is compounded with a polyamide (PA) hot melt adhesive web film to obtain a PA-wood fiber paper prepreg, which is single-sided composite thermoplastic film. The prepreg is unidirectionally laid in the direction of wood fiber reinforcement to form a structure in which wood fiber paper and coated PA layers are alternately stacked. Then, a pressure of 0.6 MPa is applied at 130°C to form the PA to a molten low viscosity state, so that the wood fiber is impregnated. After 10 minutes, it is cooled to room temperature and the PA solidifies to obtain a wood fiber reinforced polyamide-based composite material.

[0314] The mechanical properties of the wood fiber reinforced composite material obtained in Example 9 were tested according to GB / T1499-2005 Test Method for Flexural Properties of Fiber Reinforced Plastics. The results showed that the flexural strength was 363 MPa, the Young's modulus was 31 GPa, and the density was 1.30 g / cm 3 .

[0315] Example 13

[0316] The chemical treatment was the same as in Example 1. The post-treatment was also essentially the same as in Example 1, differing only in the pressure. The chemically treated veneer of this example was subjected to one transverse shrinkage, with the pressure during thickness shrinkage set at 10 MPa. Mechanical tensile testing of the resulting unidirectional wood fiber paper revealed an average breaking strength of 519 MPa and an average elastic modulus of 37 GPa.

[0317] Example 14

[0318] The chemical treatment was identical to that in Example 4, and the post-treatment was identical to that in Example 1, with the only difference being the pressure applied during the transverse contraction process. During the transverse contraction process, a shrinkable soft film was used to apply a transverse contraction force to the wood fiber paper. Two conditions were tested, corresponding to equivalent pressures of 0.1 MPa and 0.5 MPa, respectively. The mechanical properties of the resulting unidirectional wood fiber paper were measured, and the results are shown in Table 7.

[0319] Table 7 Performance test results of the unidirectional wood fiber paper obtained in Example 14

[0320] Example 15

[0321] The transmittance of some unidirectional wood fiber paper samples (transverse shrinkage pressure 0.1 MPa) in Example 14 was measured, and the transmittance was 11.0%. The test results are shown in FIG31 .

[0322] Example 16

[0323] The wood fiber paper obtained in Example 10 was dip-coated to prepare an epoxy-wood fiber paper prepreg (tensile strength of 60 MPa and Young's modulus of 3 GPa after pure resin curing). The prepreg was then unidirectionally laid and vacuum-baked at 80°C for 1 hour until the epoxy resin was completely cured, yielding a wood fiber-reinforced epoxy resin-based composite material, wherein the volume percentage of the wood fiber reinforcement was 90%.

[0324] The mechanical properties of the wood fiber reinforced composite material obtained in Example 16 were tested according to GB / T 1499-2005 Test Method for Flexural Properties of Fiber Reinforced Plastics, and the results showed that the flexural strength was 394 MPa and the flexural elastic modulus was 34 GPa.

[0325] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A unidirectional wood fiber paper, characterized in that: The unidirectional wood fiber paper is formed by shrinking the unidirectional wood veneer with some substances removed in at least one direction; The partial substances include lignin and hemicellulose; The thickness of the unidirectional wood fiber paper is less than or equal to 0.6 mm; The apparent thickness of the unidirectional wood fiber paper under a plane pressure of no more than 0.005 MPa is no more than 4 times the average thickness of the unidirectional wood fiber paper.

2. The unidirectional wood fiber paper according to claim 1, characterized in that: The unidirectional wood fiber paper includes wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended along a single direction as a whole in a microscopic sense.

3. The unidirectional wood fiber paper according to claim 2, characterized in that: The density of the unidirectional wood fiber paper is 0.8-1.5 g / cm 3 ; And / or, the surface density of the unidirectional wood fiber paper is 20 to 400 g / m 2 ; And / or, the tensile strength of the unidirectional wood fiber paper parallel to the wood fiber direction is 150-1000 MPa.

4. The unidirectional wood fiber paper according to claim 2, characterized in that: The thickness of the unidirectional wood fiber paper is 0.03-0.6 mm; And / or, the Young's modulus of the unidirectional wood fiber paper parallel to the wood fiber direction is 20 to 80 GPa.

5. The unidirectional wood fiber paper according to claim 1, characterized in that: The thickness of the unidirectional veneer is less than or equal to 0.8 mm; And / or, the decomposition of the shrinkage force includes lateral shrinkage and thickness shrinkage.

6. The unidirectional wood fiber paper according to claim 1, characterized in that: The unidirectional veneer from which some substances have been removed shrinks in at least two directions; The shrinkage includes transverse shrinkage and thickness shrinkage; The shrinkage force directions of the transverse shrinkage and the thickness shrinkage are intersecting.

7. The unidirectional wood fiber paper according to claim 6, characterized in that: The unidirectional veneer with some substances removed comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at a microscopic level; The shrinkage force of transverse shrinkage is a force in the horizontal direction of the unidirectional veneer, and intersects with the extension direction of the wood fibers and / or fiber bundles in the plane; and / or, the shrinkage force of the thickness shrinkage is a unidirectional force in the vertical direction of the veneer; The horizontal force and the vertical force are each independently an originally applied force, and / or a force formed after synthesis or decomposition of forces.

8. The unidirectional wood fiber paper according to claim 6, characterized in that: The apparent thickness of the unidirectional wood fiber paper when pressed flat under a pressure of 0.005 MPa is no more than 3 times the average thickness of the unidirectional wood fiber paper; And / or, all and / or part of the unidirectional wood fiber paper has a smooth plastic feel; And / or, when the thickness of the unidirectional wood fiber paper is less than 0.15 mm, the light transmittance of all and / or part of the unidirectional wood fiber paper is 2% to 70%.

9. The unidirectional wood fiber paper according to claim 6, characterized in that: The weight loss of the unidirectional veneer after removing some of the substances is 10% to 60% relative to the unidirectional veneer; And / or, the shrinkage rate of the transverse shrinkage is 2% to 40%; the shrinkage rate of the thickness shrinkage is 20% to 90%.

10. A method for preparing unidirectional wood fiber paper, characterized in that: The following steps are involved: S1) chemically modifying the unidirectional veneer to obtain the unidirectional veneer with some substances removed; S2) shrinking the unidirectional veneer from which some substances have been removed in at least one direction to obtain unidirectional wood fiber paper; The decomposition of the shrinkage force includes lateral shrinkage and thickness shrinkage.

11. The preparation method according to claim 10, characterized in that: The thickness of the unidirectional veneer is 0.05-0.8 mm; And / or, the surface density of the unidirectional veneer is 20 to 450 g / m 2 ; And / or, the chemical modification in S1) is carried out in a closed high-pressure system; the target temperature of the chemical modification is 100-150° C.; the target pressure of the chemical modification is 0.07-1.9 MPa; and the residence time of the chemical modification at the target temperature / pressure is 1-12 hours; Alternatively, the chemical modification is carried out under normal pressure; the residence time of the chemical modification at the target temperature / pressure is 24 to 72 hours; the temperature of the chemical modification is the boiling temperature of water at normal pressure; And / or, after chemical modification, the reaction solution is cooled to obtain unidirectional veneer with some substances removed.

12. The preparation method according to claim 10, characterized in that The chemically modified solution in step S1) comprises an alkaline substance, a sulfonating agent and water; The pH value of the modified liquid is 12 to 14; The concentration of the alkaline substance in the modified solution is 0.01 to 5 kg / L; The alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and potassium bicarbonate; The concentration of the sulfonating agent in the modified solution is 0.01 to 5 kg / L; The sulfonating agent in the modified liquid is selected from one or more of sulfite, chlorosulfonic acid, hydroxymethylsulfonate, sulfuryl chloride and aminosulfonic acid; And / or, the material ratio of the unidirectional veneer to the chemically modified modifying liquid is 4.6 to 184 cm 3 :1L; And / or, the mass of the unidirectional veneer from which some substances are removed is reduced by 10% to 60% compared with the mass of the unidirectional veneer.

13. The preparation method according to claim 10, characterized in that The unidirectional veneer is placed in a material frame for chemical modification; The material frame includes a frame body, a partition and a frame cover; the partition is arranged in the frame body; the side walls of the frame body, the bottom of the frame body, the partition and the frame cover are all provided with holes.

14. The preparation method according to claim 13, characterized in that The material frame is a cylindrical material frame; there are multiple partitions; and the multiple partitions are arranged in a concentric circle manner within the frame.

15. The preparation method according to claim 13, characterized in that The material frame is a rectangular parallelepiped material frame; there are multiple partitions; and the multiple partitions are arranged in parallel in the material frame.

16. The preparation method according to claim 10, characterized in that The shrinkage process includes a transverse shrinkage process and a thickness shrinkage process; the force of the transverse shrinkage process and the force of the thickness shrinkage process intersect.

17. The preparation method according to claim 16, characterized in that The transverse shrinkage treatment is selected from applying external mechanical force in the transverse direction and / or spontaneous shrinkage due to dehydration; The external mechanical force applied in the transverse direction intersects in the plane with the extending direction of the wood fibers and / or fiber bundles of the unidirectional veneer from which some substances have been removed.

18. The preparation method according to claim 17, characterized in that: The external mechanical force applied in the transverse direction is specifically: using a film material that can produce transverse contraction, sticking it on the surface of the unidirectional veneer from which some substances have been removed, applying pressure, and then removing the film material; and / or, roller-rubbing the unidirectional veneer with some of the material removed; and / or, applying transverse pressure to the unidirectional veneer with some of the material removed.

19. The preparation method according to claim 17, characterized in that The pressure of the external mechanical force applied in the lateral direction is 0.001 to 1.5 MPa; and / or, the temperature of the transverse shrinkage treatment is 15° C. to 150° C.; And / or, the time of the transverse shrinkage treatment is 1 second to 4 minutes.

20. The preparation method according to claim 16, characterized in that The thickness shrinkage includes heat pressing under negative pressure; The pressure of the hot pressing treatment is 0.1 to 60 MPa; And / or, the temperature of the hot pressing treatment is 50°C to 150°C; And / or, the heat pressing treatment time is 0.5 to 20 minutes.

21. The preparation method according to claim 16, characterized in that The thickness shrinkage is carried out under the condition of single sheet or stacking; the number of layers of the stacking is 2 to 20 sheets; The pressure of thickness shrinkage under the stacking condition is 0.1 to 60 MPa.

22. The preparation method according to claim 10, characterized in that The shrinkage rate of the transverse shrinkage treatment is 2% to 40%; And / or, the shrinkage rate of the thickness shrinkage is 20% to 90%.

23. The preparation method according to claim 10, characterized in that Splicing is performed before or after shrinkage treatment; The splicing is specifically as follows: marking the splicing outline on the unidirectional veneer with some materials removed or the wood fiber paper after shrinkage treatment, and then splicing the corresponding parts.

24. A method for preparing unidirectional wood fiber paper, characterized in that: The following steps are involved: A1) chemically modifying the unidirectional veneer to obtain the unidirectional veneer from which some substances have been removed; A2) shrinking and leveling the unidirectional veneer from which some substances have been removed in at least one direction to obtain unidirectional wood fiber paper; The leveling process is to perform flat hot pressing in a negative pressure exhaust environment.

25. The preparation method according to claim 24, characterized in that During the leveling process, exhaust channels are provided on the double contact surfaces or the single contact surface of the unidirectional wood fiber paper.

26. The preparation method according to claim 24, characterized in that The pressure of the plane hot pressing is 0.01 to 2 MPa; And / or, the leveling treatment time is 0.1 to 4 minutes; And / or, the temperature of the leveling treatment is 40°C to 150°C.

27. The preparation method according to claim 24, characterized in that The flattening treatment is selected from one or more of a blister treatment and a negative pressure hot pressing treatment; And / or, the moisture content of the unidirectional wood fiber paper is less than or equal to 10%.

28. The preparation method according to claim 24, characterized in that The shrinkage treatment includes a transverse shrinkage treatment and a thickness shrinkage treatment; The thickness shrinkage treatment is to apply mechanical pressure in the thickness direction; The mechanical pressure applied in the thickness direction is 0.01 to 80 MPa; And / or, the thickness shrinkage treatment time is 0.1 to 3 minutes; And / or, the temperature of the thickness shrinkage treatment is 15°C to 150°C.

29. A unidirectional wood fiber paper prepreg, characterized in that: The invention comprises the unidirectional wood fiber paper according to any one of claims 1 to 9 or the unidirectional wood fiber paper prepared by the preparation method according to any one of claims 10 to 28, and a high molecular polymer layer attached to at least one surface of the unidirectional wood fiber paper.

30. The unidirectional wood fiber paper prepreg according to claim 29, characterized in that: The mass of the high molecular polymer layer is 5% to 85% of the mass of the unidirectional wood fiber paper prepreg; And / or, the thickness ratio of the high molecular polymer layer to the unidirectional wood fiber paper is 5:1 to 0.05:1; And / or, the surface density of the unidirectional wood fiber paper prepreg is 30 to 500 g / m 2 ; And / or, the thickness of the unidirectional wood fiber paper prepreg is 0.03-0.7 mm.

31. The unidirectional wood fiber paper prepreg according to claim 29, characterized in that: The high molecular polymer layer includes a thermoplastic polymer and / or a thermosetting polymer; The weight of the polymer layer is 5 to 200 g / m 2 .

32. A method for preparing a unidirectional wood fiber paper prepreg, characterized in that: The following steps are involved: A high molecular weight polymer is transferred to at least one surface of the unidirectional wood fiber paper according to any one of claims 1 to 9 or the unidirectional wood fiber paper prepared by the preparation method according to any one of claims 10 to 28 to obtain a unidirectional wood fiber paper prepreg; the transfer method is selected from one or more of lamination, printing, impregnation and coating.

33. A wood fiber paper reinforced composite material, characterized in that: Comprising multiple layers of the unidirectional wood fiber paper according to any one of claims 1 to 9 or the unidirectional wood fiber paper prepared by the preparation method according to any one of claims 10 to 28; The adjacent unidirectional wood fiber papers are bonded together by high molecular polymer.

34. The wood fiber paper reinforced composite material according to claim 33, characterized in that: The wood fiber paper reinforced composite material has a tensile strength of 130 to 1000 MPa; and / or, the flexural strength of the wood fiber paper reinforced composite material is 130 to 1000 MPa; And / or, the Young's modulus of the wood fiber paper reinforced composite material is 12 to 75 GPa.

35. The wood fiber paper reinforced composite material according to claim 33, characterized in that: The thickness of a single layer of wood fiber paper in the wood fiber paper reinforced composite material is 0.02 to 0.6 mm; and / or, the wood fiber paper reinforced composite material has distinct layers in the longitudinal section; And / or, the volume fraction of the wood fiber paper in the wood fiber paper reinforced composite material is 40% to 99%.

36. The wood fiber paper reinforced composite material according to claim 33, characterized in that: At least one surface of the wood fiber paper reinforced composite material is provided with a waterproof polymer layer.

37. A method for preparing a wood fiber paper reinforced composite material, characterized in that: The following steps are involved: The unidirectional wood fiber paper according to any one of claims 1 to 9 or the unidirectional wood fiber paper prepared by the preparation method according to any one of claims 10 to 28 is stacked, sizing and cured to obtain a wood fiber paper reinforced composite material; Alternatively, the unidirectional wood fiber paper prepreg according to any one of claims 29 to 31 or the unidirectional wood fiber paper prepreg prepared by the preparation method according to claim 32 is stacked and cured to obtain a wood fiber paper reinforced composite material.

38. A method for shrinking unidirectional veneer, characterized in that: The unidirectional veneer is subjected to shrinkage treatment in at least one direction; the decomposition of the shrinkage force includes transverse shrinkage and thickness shrinkage.

39. The method according to claim 38, characterized in that The unidirectional veneer is firstly subjected to a chemical treatment to remove some substances, and then subjected to a shrinkage treatment in at least one direction.

40. The method according to claim 38, wherein The shrinkage includes lateral shrinkage and thickness shrinkage; the shrinkage force directions of the lateral shrinkage and thickness shrinkage intersect.

41. The method according to claim 40, wherein The unidirectional veneer comprises wood fibers and / or fiber bundles; the wood fibers and / or fiber bundles are arranged or extended in a single direction as a whole at a microscopic level; The shrinkage force of the transverse shrinkage is a force in the horizontal direction of the unidirectional veneer, and is a force that intersects with the extension direction of the wood fibers and / or fiber bundles of the unidirectional veneer in the plane; and / or, the shrinkage force of the thickness shrinkage is a unidirectional force in the vertical direction of the veneer; The horizontal force and the vertical force are independently the originally applied forces, and / or are forces formed after the synthesis or decomposition of forces.

42. The method according to claim 40, wherein The thickness shrinkage includes heat pressing under negative pressure; The pressure of the hot pressing treatment is 0.1 to 60 MPa; And / or, the temperature of the hot pressing treatment is 50°C to 150°C; And / or, the heat pressing treatment time is 0.5 to 20 minutes.

43. A wooden hollow tube, characterized in that: It is formed by the unidirectional wood fiber paper described in any one of claims 1 to 9, the unidirectional wood fiber paper prepared by the preparation method of any one of claims 10 to 28, the unidirectional wood fiber paper prepreg described in any one of claims 29 to 31, the unidirectional wood fiber paper prepreg prepared by the preparation method of claim 32, the wood fiber paper reinforced composite material described in any one of claims 33 to 36, or the wood fiber paper reinforced composite material prepared by the preparation method of claim 37.

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