Organic flow-equalizing wood fiber-based composite material as well as preparation method and application thereof

Abstract

The invention discloses an organic flow-equalizing wood fiber-based composite material and a preparation method and application thereof.The preparation method comprises the following steps that S1, after a wood material and polyhydric alcohol are mixed, acid treatment and alkali treatment are conducted in sequence, and polyhydric alcohol lignin is obtained; s2, dissolving and mixing polyol lignin and a polymer base material to obtain a uniform solution, so as to obtain a flow equalizing agent pre-polymerized solution; s3, mixing the flow equalizing agent prepolymerization liquid with the wood flour subjected to colloid milling, adding a cross-linking agent, and kneading; and S4, carrying out hot-pressing polymerization on the uniformly kneaded material to obtain the wood fiber-based composite material. The prepared organic solvent flow equalizing agent reduces fiber aggregation and endows wood fibers with uniform fluidity through the activity characteristic of polyol lignin and the rheological behavior of a polymer base material, so that the processability and quality of a wood fiber composite material are remarkably improved.

Description

Technical Field

[0001] The present invention relates to wood fiber composites, and specifically, to an organic flow-equalizing wood fiber-based composite material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the increasingly high global environmental protection calls and the fashion of green consumption, people generally have formed such a concept: loving trees, cherishing wood, while enjoying wood and being keen on using wood products. Therefore, in the case of increasingly scarce wood resources, wood fiber composites have become particularly in short supply. Currently, in the international market, the demand for wood fibers has become strong accordingly. The reason why the status of wood fibers has been continuously rising in the international market is mainly that the growth trend of the market demand for composites made with wood fibers as the main raw material is extremely rapid. Wood fibers are widely used in thermosetting polymers, and the hot sales of thermosetting composites globally have continuously increased the demand for reinforcing fillers and fiber-reinforced products. In addition, natural wood fibers are much cheaper than industrial fibers (such as glass fibers, etc.) as reinforcing materials, and are convenient to obtain, light in weight, and can also change the processing performance and surface appearance of materials. The above-mentioned many factors have made wood fibers popular and favored by producers and market consumers internationally.

[0003] However, since the wood fiber surface contains a large number of polar hydroxyl groups, the interfacial bonding force with hydrophobic organic substrates is poor, which easily leads to problems such as poor dispersibility and fiber aggregation during the processing, affecting the mechanical properties and processing stability of the composite material.

[0004] Existing modification technologies mostly use methods such as surface treatment, adding interfacial modifiers, or using adhesives to improve the dispersibility and fluidity of wood fibers, but these methods usually have problems of poor environmental protection or complex production. For example, formaldehyde-containing urea-formaldehyde resins and isocyanate adhesives are effective, but may pose potential hazards to the environment and health. Therefore, it is particularly important to develop a non-toxic, environmentally friendly, and efficient flow-equalizing agent. Summary of the Invention

[0005] Aiming at the current problems of poor environmental protection and complex production in wood fiber modification, the present invention provides an organic flow-equalizing wood fiber-based composite material, a preparation method thereof, and an application thereof. By forming a stable interfacial bond between the active groups of polyol lignin, wood fibers, and polymer substrates, the dispersibility and processing performance of wood fibers are significantly improved.

[0006] To achieve the above object, on the one hand, the present invention provides a preparation method of an organic flow-equalizing wood fiber-based composite material, which includes the following steps: S1, mixing the wood material with the polyol, and then subjecting the mixture to acid treatment and alkali treatment in sequence to obtain polyol lignin; S2, dissolving and mixing the polyol lignin and the polymer substrate into a uniform solution to obtain a prepolymer solution of a flow leveling agent; S3. Mix the prepolymerized liquid of the equalizing agent with the wood powder after rubber grinding, add the cross-linking agent and knead; treat the wood powder through the rubber grinding process, effectively destroy the cell wall structure of the wood fiber while achieving particle refinement, and significantly increase the specific surface area and the exposure of the surface reactive sites. During the rubber grinding process, high-speed rotary shearing and impact energy transfer promote the improvement of the surface energy and pore structure reconstruction of the wood fiber, and its dense structure gradually loosens, the internal cavity is activated, and microcracks and channels are generated on the surface, thereby forming a porous and roughened new surface morphology, which has both physical refinement and microstructure regulation functions, and increases the specific surface area and reactive sites of the wood powder.

[0007] S4, subjecting the evenly kneaded materials to hot-pressing polymerization to obtain a wood fiber-based composite material.

[0008] The present invention prepares polyol lignin by acid-base treatment, combines it with a polymer substrate to form a flow equalizer, and then obtains a wood fiber composite material by hot pressing and melt polymerization. The polyol lignin of the present invention can form a stable interface bond (such as hydroxyl, phenolic hydroxyl, ether group, etc.) with wood fiber and polymer substrate through hydrogen bonds, covalent bonds and π-π interactions of its active groups (hydroxyl, phenolic hydroxyl, ether group, etc.). Figure 1 As shown, Figure 1Shows a schematic diagram of the three-dimensional cross-linked structure in the material of the present invention. This structure is composed of polymer segments as the basic skeleton, and is synergistically constructed by various interaction forces such as hydrogen bonding, π-π stacking, and covalent cross-linking to form a stable three-dimensional network system. In the figure, the connection relationship between molecules is intuitively shown in the form of ball-and-stick. Among them, the brown balls represent functional molecules or cross-linking points, and the blue lines represent polymer chains or force paths. The overall structure reflects the orderliness, interconnectivity of the micro-structure of the material in the present invention and the construction basis for enhancing its performance, significantly improving the dispersibility and interfacial compatibility of wood fibers, and improving the overall processing performance of the composite system. During the hot pressing process, the polymer substrate cross-links with polyol lignin under the action of a cross-linking agent to form a three-dimensional network structure. This network is composed of chemical cross-linking points between the main chains and intermolecular hydrogen bonds and π-π interactions, and has certain rigid-flexible synergistic characteristics. Rigid covalent bonds (irreversible covalent connections C–C, C–O) provide structural support and load transfer paths, significantly enhancing the tensile strength of the composite material; flexible interaction forces (reversible non-covalent interactions provided by hydrogen bonds, π-π bonds, etc.) play a buffering and energy-consuming role during the stress process, improving the toughness and impact resistance of the material. The three-dimensional network structure also restricts the free movement of molecular segments, effectively improving the dimensional stability and durability of the material. The hot melt plasticity of the flow improver ensures the uniform flow of the composite material during the hot pressing forming process, and is suitable for processing complex molds. The composite material of the present invention has a high density, high strength, excellent water resistance, and at the same time avoids the toxic components in traditional adhesives, meets the environmental protection requirements, and is suitable for fields such as packaging materials, functional coatings, and structural reinforcement materials.

[0009] Preferably, in step S1, the polyol is one or more of polyethylene glycol, glycerol, and sugar alcohol; the mass ratio of the wood material to the polyol is 1:(4 - 6).

[0010] Specifically, in step S1, the acid treatment is: adding 0.03 - 0.05 wt% (mass ratio of the whole system, the same below) of concentrated sulfuric acid, and stirring at 130 - 150 °C for 1 - 2 hours; and / or The alkali treatment is: after cooling to room temperature, adding 0.01 - 0.03 wt% of a strong alkali solution (such as sodium hydroxide, potassium hydroxide) and continuing to stir for 1 - 3 hours.

[0011] Preferably, in step S2, the polymer substrate needs to have the following characteristics: 1. Good compatibility with lignin, and can form a homogeneous substance with polyol lignin; 2. Have a certain viscosity for easy kneading; 3. Have a certain thermal stability during hot pressing. It can be one of butylene terephthalate - adipate, lactic acid, or caprolactone, and its mass fraction is 10 - 20 wt%, and the mass fraction of polyol lignin is 20 - 30 wt%.

[0012] Preferably, in step S3, the wood powder is one or more of poplar wood powder, coconut shell silk fiber, cotton fiber, and mahogany wood powder, with a particle size of 100-120 mesh, a refining time of the wood powder of 0.5-6 hours, and a refining speed maintained at about 5000 rpm; the mass ratio of the wood powder to the pre-polymer solution of the flow equalizer is (6-7):(3-4).

[0013] Preferably, in step S3, the cross-linking agent is N,N'-methylenebisacrylamide, polyethylene glycol diacrylate PEGDA or ethylene glycol dimethacrylate EGDMA, and its mass fraction is 0.5-0.6 wt%.

[0014] Specifically, in step S3, the kneading is: kneading at room temperature for 0.5-2 hours.

[0015] Specifically, in step S4, the hot pressing is: the temperature is 80-120 °C, the pressure is 10-30 MPa, and the time is 1-3 hours.

[0016] The second aspect of the present invention provides a wood fiber-based composite material prepared by the above preparation method.

[0017] The third aspect of the present invention provides the application of the above wood fiber-based composite material in the preparation of furniture, building materials or molds.

[0018] Through the above technical solutions, the present invention achieves the following beneficial effects: 1. The organic solvent flow equalizer prepared by the present invention reduces fiber aggregation and imparts uniform fluidity to wood fibers through the active characteristics of polyol lignin and the rheological behavior of the polymer substrate, thereby significantly improving the processability and quality of wood fiber composites.

[0019] 2. The composite material prepared in the present invention has good thermoplasticity, is suitable for complex mold forming, and significantly improves the processing performance and application breadth of the material.

[0020] 3. The wood fiber composite material prepared by the present invention does not rely on toxic adhesives, meets environmental protection requirements, and the design of introducing a cross-linked network improves the density, strength, water resistance and chemical resistance of the composite material, and has a wider application prospect. Description of the Drawings

[0021] Figure 1 is a three-dimensional network structure diagram of the wood fiber composite material of the present invention; Figure 2 is the tensile property test result of the wood fiber composite material prepared in the examples and comparative examples; Figure 3 is the specific strength result of the wood fiber composite material prepared in the examples and comparative examples; Figure 4Test results of the tensile property changes of the wood fiber composites prepared in the examples and comparative examples. Detailed implementation manners

[0022] The following details the specific implementation manners of the present invention. It should be understood that the specific implementation manners described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0023] Example 1 S1. Mix dry wood chips with polyethylene glycol at a mass ratio of 1:5, add 0.04 wt% of concentrated sulfuric acid, and stir at 140 °C for 1.5 hours to complete the preliminary modification. Through this acid treatment process, polyol groups are introduced, significantly enhancing the activity of hydroxyl groups in lignin, thereby improving its solubility and chemical reactivity. After cooling to room temperature, add 0.02 wt% of sodium hydroxide aqueous solution and continue stirring for 2 hours to further enhance the chemical stability and processing performance of lignin. Subsequently, perform solid-liquid separation through a Buchner funnel, adjust the obtained liquid to pH 1 with sulfuric acid, and add deionized water to precipitate to obtain a solid. Dry and grind the precipitate to finally obtain modified ethylene glycol lignin.

[0024] S2. Put poplar wood powder into a colloid mill and mill it for 45 minutes, then filter out the wood powder with a mesh size of 120. Dry the coconut shell fiber in an oven at 105 °C for later use. Dissolve the modified ethylene glycol lignin (25 wt%) prepared in S1 in dimethylformamide and stir evenly; at the same time, dissolve terephthalic acid-butylene glycol adipate (15 wt%) in dimethylformamide at room temperature. After the two solutions are evenly mixed, stir evenly to form a homogeneous flow agent prepolymer solution.

[0025] S3. Mix the homogeneous flow agent prepolymer solution with the milled poplar wood powder and coconut shell fiber at a mass ratio of 6:4, add 0.5 wt% of N,N'-methylenebisacrylamide as a crosslinking agent, and knead at room temperature for 1 hour using a kneader to obtain an initial composite material. Place the initial composite material in a hot press and hot press it at 120 °C and 20 MPa for 2 hours, and then dry it in a vacuum oven at 100 °C under vacuum conditions for 1 hour to finally obtain the wood fiber composite material.

[0026] Example 2 S1. Mix dry wood chips with glycerol at a mass ratio of 1:4, add 0.03 wt% of concentrated sulfuric acid, and stir at 130 °C for 2 hours to complete the preliminary modification. After cooling to room temperature, add 0.01 wt% of potassium hydroxide aqueous solution and continue stirring for 1 hour to further enhance the chemical stability and processing performance of lignin. Subsequently, perform solid-liquid separation through a Buchner funnel, adjust the obtained liquid to pH 1 with sulfuric acid, and add deionized water to precipitate to obtain a solid. Dry and grind the precipitate to finally obtain modified glycerol lignin.

[0027] S2. Put the mahogany wood powder into a glue mill and grind it for 30 minutes, then filter out the wood powder with a mesh size of 100. Dissolve the modified glycerol lignin (30 wt%) prepared in S1 in dimethylformamide and stir evenly; at the same time, dissolve lactic acid (20 wt%) in dimethylformamide at room temperature. After the two solutions are evenly mixed, stir evenly to form a flow agent prepolymer solution.

[0028] S3. Mix the flow agent prepolymer solution with the ground mahogany wood powder at a mass ratio of 6:4, add 0.6 wt% of polyethylene glycol diacrylate as a crosslinking agent, and knead at room temperature for 0.5 hours using a kneader to obtain an initial composite material. Place the initial composite material in a hot press and hot press it at 100 °C and 20 MPa for 1 hour, then dry it in a vacuum oven at 100 °C under vacuum conditions for 1 hour to finally obtain a wood fiber composite material.

[0029] Example 3 S1. Mix the dry wood chips and sugar alcohol at a mass ratio of 1:6, add 0.05 wt% of concentrated sulfuric acid, and stir at 150 °C for 1 hour to complete the preliminary modification. After cooling to room temperature, add 0.03 wt% of sodium hydroxide aqueous solution and continue to stir for 3 hours to further improve the chemical stability and processing performance of lignin. Subsequently, perform solid-liquid separation through a Buchner funnel, adjust the obtained liquid to pH 1 with sulfuric acid, and add deionized water to precipitate to obtain a solid. Dry and grind the precipitate to finally obtain modified sugar alcohol lignin.

[0030] S2. Put the mahogany wood powder into a glue mill and grind it for 3 hours, then filter out the wood powder with a mesh size of 120. Dry the cotton fibers in an oven at 105 °C for standby. Dissolve the modified sugar alcohol lignin (30 wt%) prepared in S1 in dimethylformamide and stir evenly; at the same time, dissolve caprolactone (10 wt%) in dimethylformamide at room temperature. After the two solutions are evenly mixed, stir evenly to form a flow agent prepolymer solution.

[0031] S3. Mix the flow agent prepolymer solution with the ground mahogany wood powder and cotton fibers at a mass ratio of 6:4, add 0.5 wt% of ethylene glycol dimethacrylate as a crosslinking agent, and knead at room temperature for 1 hour using a kneader to obtain an initial composite material. Place the initial composite material in a hot press and hot press it at 80 °C and 30 MPa for 2 hours, then dry it in a vacuum oven at 100 °C under vacuum conditions for 1 hour to finally obtain a wood fiber composite material.

[0032] Example 4 S1. Mix the dry wood chips with polyethylene glycol at a mass ratio of 1:5, add 0.04 wt% concentrated sulfuric acid, and stir at 140 °C for 1.5 hours to complete the preliminary modification. After cooling to room temperature, add 0.02 wt% sodium hydroxide aqueous solution and continue stirring for 2 hours to further improve the chemical stability and processing performance of lignin. Subsequently, perform solid-liquid separation through a Buchner funnel, adjust the obtained liquid to pH 1 with sulfuric acid, and add deionized water to precipitate to obtain a solid. Dry and grind the precipitate to finally obtain modified ethylene glycol lignin.

[0033] S2. Put the poplar wood powder into a colloid mill and grind it for 6 hours, then filter out the wood powder with a mesh size of 120. Dissolve the modified ethylene glycol lignin (25 wt%) prepared in S1 in dimethylformamide and stir evenly; at the same time, dissolve terephthalic acid-butylene adipate (15 wt%) in dimethylformamide at room temperature. After the two solutions are evenly mixed, stir evenly to form a flow agent prepolymer solution.

[0034] S3. Mix the flow agent prepolymer solution, the ground poplar wood powder and coconut shell fiber in a mass ratio of 7:3, add 0.6 wt% N,N'-methylenebisacrylamide as a crosslinking agent, and knead at room temperature for 2 hours with a kneader to obtain an initial composite material. Place the initial composite material in a hot press and hot press it at 120 °C and 10 MPa for 3 hours, then dry it in a vacuum oven at 100 °C under vacuum conditions for 1 hour to finally obtain a wood fiber composite material.

[0035] Comparative Example 1 Other conditions are the same as in Example 1, except that in step S1: add 0.04 wt% concentrated sulfuric acid to the dry wood chips and stir at 140 °C for 1.5 hours to complete the preliminary modification. After cooling to room temperature, add 0.02 wt% sodium hydroxide aqueous solution and continue stirring for 2 hours. Subsequently, perform solid-liquid separation through a Buchner funnel, adjust the obtained liquid to pH 1 with sulfuric acid, and add deionized water to precipitate to obtain a solid. Dry and grind the precipitate to finally obtain lignin.

[0036] Comparative Example 2 Other conditions are the same as in Example 1, except that the wood powder is sanded: mix the wood powder and deionized water at a mass ratio of 1:3 evenly, and then add it to a wet sand mill. Add zirconia grinding beads with a diameter of 0.5 mm to the sanding chamber, set the grinding speed to 5000 rpm, and continuously sand for 2 hours in the circulation mode. After grinding, filter out the grinding beads.

[0037] Comparative Example 3 Other conditions are the same as in Example 1, except that terephthalic acid-butylene adipate is omitted.

[0038] Performance Test The tensile properties of the materials prepared in Examples 1 - 4 and Comparative Examples 1 - 3 were tested separately, and in combination with the density of the materials, the specific strength was calculated. Also, the changes in mechanical properties of Examples 1 - 4 and Comparative Examples 1 - 3 under certain environments were tested.

[0039] Tensile properties: The tensile properties of the materials were measured using a microcomputer mechanical testing machine. According to the measurement results of the tensile test, the tensile strength of the materials was calculated. The specific method was as follows: Place the prepared material between the fixtures and use a microcomputer mechanical testing machine to measure its tensile strength. The specific test results are shown in Table 1 and Figure 2 as follows. It can be seen from Table 1 and Figure 2 that the tensile strength of the wood fiber composites prepared from Examples 1 - 4 was 19.3 ± 4.2 MPa, while the tensile strength of the materials prepared from Comparative Examples 1 - 3 was only 12.7 ± 1.3 MPa.

[0040] Specific strength: By combining the density of their respective materials, the specific strength of each material can be calculated. The specific calculation results are shown in Table 1 and Figure 3 as follows. The specific strength of the wood fiber composites prepared from Examples 1 - 4 was 13.8 ± 3 Mpa / g·cm 3 , while the specific strength of the wood fiber composites prepared from Comparative Examples 1 - 3 was 9.9 ± 1.3 Mpa / g·cm 3 , indicating that the wood fiber composites prepared from Examples 1 - 4 can withstand more loads under the same mass.

[0041] Tensile property changes: Examples 1 - 4 and Comparative Examples 1 - 3 were placed in a thermo - hygrostat. Using the GB / T 2918 standard (25°C, RH = 65%), they were cultured for 48 h, and the changes in their tensile properties at 1 h, 12 h, 24 h, and 48 h were tested to observe the water resistance of the materials. The specific test results are shown in Table 1 and Figure 4 as follows. It can be seen from Table 1 and Figure 4 that the tensile properties of the examples decreased slightly (16 - 30%), while those of the comparative examples decreased significantly (40 - 63%), indicating that the water resistance of the composites in the comparative examples was poor.

[0042] Table 1 Performance test results

[0043] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above - mentioned embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0044] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0045] In addition, any combinations can be made among various different embodiments of the present invention, as long as they do not violate the idea of the present invention, and they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing an organic uniform flow type wood fiber-based composite material, characterized in that: The steps include: S1, mixing the wood material with the polyol, and then subjecting the mixture to acid treatment and alkali treatment in sequence to obtain polyol lignin; S2, dissolving and mixing the polyol lignin and the polymer substrate into a uniform solution to obtain a prepolymer solution of a flow leveling agent; S3, mixing the prepolymerized liquid of the equalizing agent with the wood powder after rubber grinding, adding a cross-linking agent and kneading; S4, subjecting the evenly kneaded materials to hot-pressing polymerization to obtain a wood fiber-based composite material.

2. The preparation method according to claim 1, characterized in that In step S1, the polyol is one or more of polyethylene glycol, glycerol, and sugar alcohol; the mass ratio of the wood material to the polyol is 1:(4-6).

3. The preparation method according to claim 1, characterized in that In step S1, the acid treatment is: adding 0.03-0.05 wt% concentrated sulfuric acid and stirring at 130-150° C. for 1-2 hours; and / or The alkali treatment comprises: adding 0.01-0.03 wt % of a strong alkali solution after cooling to room temperature and continuing stirring for 1-3 hours.

4. The preparation method according to claim 1, characterized in that In step S2, the polymer substrate is one of butylene terephthalate-adipate, lactic acid or caprolactone, and the mass fraction thereof is 10-20 wt%, and the mass fraction of polyol lignin is 20-30 wt%.

5. The preparation method according to claim 1, characterized in that: In step S3, the wood powder is one or more of poplar wood powder, coconut shell fiber, cotton fiber, and mahogany wood powder, and its particle size is 100-120 mesh. The wood powder colloid grinding time is 0.5-6 hours. The mass ratio of the wood powder to the equalizing agent prepolymer liquid is (6-7): (3-4).

6. The preparation method according to claim 1, characterized in that: In step S3, the cross-linking agent is N,N'-methylenebisacrylamide, polyethylene glycol diacrylate or ethylene glycol dimethacrylate, and its mass fraction is 0.5-0.6wt%.

7. The preparation method according to claim 1, characterized in that: In step S3, the kneading is: kneading at room temperature for 0.5-2 hours.

8. The preparation method according to claim 1, characterized in that In step S4, the hot pressing is performed at a temperature of 80-120° C., a pressure of 10-30 MPa, and a time of 1-3 hours.

9. The wood fiber-based composite material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the wood fiber-based composite material according to claim 9 in preparing furniture or building materials.

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