Superstrong wood film and method for making same

Abstract

The application discloses a super-strong wood film and a preparation method thereof. The wood film has a dense structure composed of nanofibers of wood cell walls and regenerated cellulose. The nanofiber bundles are uniformly distributed in cell cavities, and each nanofiber bundle is surrounded by regenerated cellulose. The preparation method comprises the following steps: wood flake is immersed in a lignin removal solution for sufficient reaction, then wood fibers are treated by using a chemical solution, and after sufficient perfusion reaction, the wood film is washed with water, naturally dried and shrunk to obtain the super-strong wood film. The super-strong wood film prepared by using the "top-down" rule has multiple superior performances: high mechanical strength (the tensile strength along the grain is 600-900 MPa), good optical performance, strong flexibility, length and width splicing treatment can be realized, the strength of the wood film after splicing basically remains unchanged, and the separation phenomenon does not occur at the bonding part.

Description

Technical Field

[0001] This invention relates to an ecological material and its preparation method, and more particularly to an ultra-strong wood film and its preparation method. Background Technology

[0002] Thin film materials are a type of high-tech material widely used in various industrial fields, including but not limited to plastic films, metal films, glass films, and ceramic films. As a crucial material form, thin film materials possess numerous superior properties, such as high light transmittance, high strength, high toughness, high plasticity, high barrier properties, and high thermal insulation. These outstanding properties have led to their widespread application in industries such as construction and transportation, aerospace, medical building materials, energy, and electronics, resulting in rapid global development. However, the aforementioned types of thin film materials suffer from problems such as high cost, difficulty in degradation, and severe waste pollution. Especially in recent years, environmental issues have garnered significant attention from all sectors of society. Therefore, finding alternatives to existing thin film materials and developing new, fully biodegradable, environmentally friendly, renewable, low-cost, and high-performance thin film materials has significant scientific and social value.

[0003] Natural fiber materials, especially wood, as a renewable resource with excellent physical and mechanical properties, exhibit a complex hierarchical structure and an ordered fiber structure, giving them outstanding mechanical strength, tensile strength, and biocompatibility. Nanofibers in the hierarchical structure of wood are considered a new generation of high-performance fibers, with theoretical strength on par with carbon fiber and glass fiber. They are also transparent, lightweight, and environmentally friendly, meaning that the performance of natural materials like wood has significant potential for improvement in fields such as aerospace, medical care, and transportation, while simultaneously meeting the requirements of sustainable development. Current technologies mostly employ a "bottom-up" approach to prepare wood films, utilizing wood cell dissolution and regeneration processes, employing methods such as filtration, molding, and self-assembly to prepare wood cellulose into films. These wood films are isotropic and highly transparent, but their preparation steps are cumbersome, especially the process of dissolving wood macromolecules into nanoscale cellulose, which is complex and difficult to achieve large-scale industrial production. Furthermore, they suffer from low mechanical strength and high brittleness, making them difficult to mold. Meanwhile, conventional film materials cannot achieve high strength while sacrificing transparency. For example, CN 117901219 A discloses a wood-based film in which a mixture of plant fibers is coated on the surface of wood chips after lignin removal, resulting in a wood-based film with low transparency. Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide an ultra-strong wood film that combines high strength and excellent optical properties; the present invention also aims to provide a method for preparing the aforementioned ultra-strong wood film.

[0005] Technical solution: The super-strong wood film of the present invention has a dense structure composed of nanofibers of wood cell walls and regenerated cellulose. The nanofiber bundles are evenly distributed in the cell cavity, and each nanofiber bundle is surrounded by regenerated cellulose. The wood cells are in the shape of "solid" columns.

[0006] Preferably, the thickness of the ultra-strong wood film is 10~200μm, and the density is 1.4~1.8 g·cm³. -3 The lignin content is 10%~90%.

[0007] Preferably, the tensile strength parallel to the grain of the ultra-strong wood film is 600-900 MPa. This high-strength wood film is obtained by treating wood chips with a chemical reagent to partially remove lignin, causing fiber swelling, followed by thorough infusion of a cellulose solution and natural drying and shrinkage. After the fiber swelling treatment, the fibers are uniformly dispersed throughout the cell cavities, and large pores essentially disappear. At this point, a certain distance is created between the fibers, and individual wood cells appear as porous columnar units. Further infusion of cellulose solution fills the uniformly distributed cell cavities, surrounding the nanofiber bundles within the cavities. This significantly increases the hydrogen bond density between cellulose chains, resulting in a strengthening and toughening effect, achieving a breakthrough improvement in the mechanical properties of the wood film. After further drying under certain conditions, the wood cells shrink, the film thickness decreases, and the strength is further enhanced.

[0008] Preferably, the ultra-strong wood film can be spliced ​​in both length and width. In particular, when spliced ​​in a flat joint manner, the strength of the wood film remains basically unchanged, and there is no separation at the adhesive joint.

[0009] Preferably, the transparency of the ultra-strong wood film can reach up to 90%, and the haze is 50-90%. After the lignin is removed from the wood chips, a certain amount of lignin still exists, which contains a large number of chromophores, causing the resulting wood film to absorb light in the visible light region (400-800nm). At the same time, this absorption is wavelength selective. For example, in the visible light region (400-800nm), as the wavelength increases, the absorption capacity decreases and the transparency increases accordingly.

[0010] To prepare the aforementioned ultra-strong wood film, the present invention provides the following preparation method:

[0011] (1) The wood veneer is immersed in treatment solution A and heated to obtain natural wood with lignin removal content of 10% to 90%; the treatment solution A is at least one of strong alkali solution, hydrogen peroxide solution, sodium hypochlorite solution, and sodium hydroxide / sodium sulfite solution.

[0012] (2) The treated wood veneer is immersed in treatment solution B. After the reaction is complete, the large pores such as vessels and cell cavities in the wood microstructure "disappear", and the fibers are dispersed in the entire space and have certain gaps between each other. The treatment solution B is at least one of the following: alkali / urea mixed solution, lithium chloride / NN dimethylacetamide solution, N-methylmorpholine-N-oxide solution, ionic solution, and copper ammonia solution.

[0013] (3) The wood slabs obtained in step (2) are infused with C treatment solution. The infusion solution fills the gaps between wood cells. After infusion, the wood slabs are subjected to natural drying and self-shrinkage treatment to obtain an ultra-strong wood film. The C treatment solution is at least one of cellulose powder solution, ramie cellulose solution, and cotton cellulose solution.

[0014] Preferably, in step (1), the temperature at which the wood veneer reacts fully in treatment solution A is 50℃~100℃, and the time is between 30min~10h. The purpose of this process is to partially remove lignin and hemicellulose, thereby creating a certain space within the wood cell walls and interstices, providing an active area for the subsequent swelling of the wood fibers within the cell cavities and the regeneration of the injected nanocellulose solution.

[0015] Preferably, in step (2), the wood fibers are first activated and then swollen. Under the swelling effect of the chemical reagent, the fibers that were originally gathered on the wood cell wall move towards the cell axis and are then evenly dispersed throughout the cell cavity. Larger pores in the wood, such as vessels and cell cavities, "disappear," and a certain distance is created between the fibers. Individual wood cells become columnar units with gaps. Different types of swelling solutions can be used for this step to fully react. The mass ratio of lithium chloride to N / N dimethylacetamide solution in the lithium chloride / NN dimethylacetamide solution should be 1:9 to 1:10. The reaction time for partially lignin-removed natural wood in the B treatment solution is 30 min to 24 h.

[0016] Preferably, in step (3), the swollen wood slabs are fully infused with the C treatment solution. Nanoscale cellulose solution molecules fill the gaps between wood fibers. After washing with water, the cellulose is regenerated in situ. The regenerated cellulose tightly surrounds the nanofiber bundles dispersed in the wood cell cavities, significantly increasing the hydrogen bond density between cellulose chains and enhancing cohesion, thereby achieving a breakthrough improvement in the mechanical properties of the wood film. The concentration of the C treatment solution is between 0.1% and 10%. The infusion time is between 10 min and 24 h. Vacuuming and filtration are used during the infusion process to accelerate the infusion speed and increase the infusion degree. Subsequently, after drying under natural conditions, the wood cells shrink, the film thickness decreases, and the strength is further enhanced.

[0017] Preferably, the type of wood includes, but is not limited to, coniferous or broadleaf wood.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The super-strong wood film has both high strength and superior optical properties. The tensile strength along the grain of the super-strong wood film is 600~900MPa, the transparency is 10~90%, and the haze is 50~90%. It has broad application prospects in mechanical construction, structural engineering, electronic components and other fields; (2) The super-strong wood film is swollen after partial removal of lignin, so that the fibers are evenly dispersed in the whole space. After the nanocellulose solution is injected, the cellulose fibers are regenerated in the gaps between the wood fibers and the fibers of natural wood. The elements entangle with each other, synergistically increasing the hydrogen bond density between cellulose chains, forming a solid and dense microstructure. The three preparation steps work together to significantly improve the strength and optical properties of the wood film; (3) The wood film can achieve an increase in length parallel to the fiber growth direction and a increase in width perpendicular to the fiber growth direction. After splicing, the strength of the wood film remains basically unchanged and there will be no separation at the bonding part; (4) The raw materials are widely available, green and environmentally friendly, and low in cost. The operation steps are simple and time-consuming and energy-saving, making the preparation of this invention highly operable and enabling large-scale industrial production. Attached Figure Description

[0019] Figure 1 This is a photograph of the ultra-strong wood film prepared in Example 1;

[0020] Figure 2 This is a scanning electron microscope cross-sectional image of the ultra-strong wood film prepared in Example 1, perpendicular to the fiber direction.

[0021] Figure 3 The image shows a scanning electron microscope (SEM) cross-sectional image of the vascular bundles parallel to the fiber direction of the ultra-strong wood film prepared in Example 1.

[0022] Figure 4 This is a tensile stress-strain curve of the ultra-strong wood film prepared in Example 1;

[0023] Figure 5 This is a schematic diagram of the ultra-strong wood film prepared in Example 1, which can be spliced ​​in length and width.

[0024] Figure 6 This is a comparison image showing the transparency of the ultra-strong wood film prepared in Example 1. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0026] Example 1

[0027] The preparation method of the super-strong wood film is as follows:

[0028] (1) Natural calcined wood was rotary cut to obtain wood veneer, which was then immersed in sodium hydroxide / sodium sulfite aqueous solution (10wt% sodium hydroxide, 5wt% sodium sulfite), heated at 90℃ for 5h, and then placed in 10wt% hydrogen peroxide solution at 50℃ for 1h to obtain natural wood with lignin partially removed.

[0029] (2) The above-mentioned natural wood with lignin removed was immersed in NN dimethylacetamide solution. After the pretreatment, it was placed in an environment of 140℃ for 0.5h to fully react. Then, it was cooled to 80℃ and a certain amount of lithium chloride was added for heat preservation treatment for 2h. The mass ratio of lithium chloride to NN dimethylacetamide solution was 1:10.

[0030] (3) The wood veneer obtained in step (2) is infused with a 1% cellulose powder solution. This process is carried out under vacuum (vacuum degree of 50MPa) for 2 hours. After washing and drying, an ultra-strong wood film can be obtained.

[0031] The prepared ultra-strong wood film is shown in the following figure. Figure 1 As shown, Figure 2-3 The images show scanning electron microscope (SEM) cross-sectional images of the ultra-strong wood-based film, taken perpendicular to and parallel to the fiber direction. They reveal a dense structure composed of nanofibers from the wood cell walls and regenerated cellulose. Nanofiber bundles are uniformly distributed within the cell cavities, each surrounded by regenerated cellulose, resulting in solid columnar wood cells. The wood film has a thickness of 25 μm and a tensile strength parallel to the grain of 724 MPa (see [link to relevant documentation]). Figure 4 Its density is 1.65 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 87%, and the tensile strength along the grain is increased by 13 times; for example... Figure 5 The length (5a) and width (5b) of the wood film can be increased by using a flat splicing method, while the tensile strength of the spliced ​​wood film should not be less than 95% of that of the original wood film; such as Figure 6 As shown, the transparency of the wood film can reach up to 83%; the haze is 55%.

[0032] Example 2

[0033] Natural poplar wood was rotary-cut into thin wood veneers, which were then immersed in a sodium hydroxide / sodium sulfite aqueous solution (5 wt% sodium hydroxide, 2 wt% sodium sulfite) and heated at 70°C for 8 hours. Following this, the veneers were placed in a 30 wt% hydrogen peroxide solution at 60°C for 0.5 hours. The wood veneers were then immersed in an N,N dimethylacetamide solution, and after pretreatment, the solution was placed at 100°C for 5 hours to react fully. The temperature was then lowered to 60°C, and a certain amount of lithium chloride was added for heat treatment for 4 hours. The resulting wood veneers were then impregnated with a 3% ramie cellulose solution under vacuum (20 MPa) for 5 hours. After washing and drying, a super-strong wood film was obtained. This wood film had a thickness of 35 μm, a tensile strength parallel to the grain of 697 MPa, and a density of 1.51 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 79%, and the tensile strength along the grain is increased by 12 times. The length and width of the wood film can be increased by using a flat splicing method, while the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 84%, and the haze is 63%.

[0034] Example 3

[0035] Natural pine wood was rotary-cut into thin wood veneers, which were then immersed in a 2 mol / L sodium hydroxide solution and heated at 80°C for 8 hours. The wood veneers were then immersed in a 1-methyl-3-methylimidazolium hydrochloride ion solution, and after pretreatment, placed at 60°C for 1 hour to react fully. The resulting wood veneers were then impregnated with a 2% cotton cellulose solution and filtered for 3 hours. After washing and drying, a super-strong wood film was obtained. This wood film had a thickness of 42 μm, a tensile strength parallel to the grain of 676 MPa, and a density of 1.50 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 82%, and the tensile strength along the grain is increased by 12.2 times. The length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 76%, and the haze is 83%.

[0036] Example 4

[0037] Natural calcite wood was rotary-cut into thin wood veneers, which were then immersed in a 20 wt% hydrogen peroxide solution at 70°C for 30 min. The wood veneers were then immersed in a sodium hydroxide-urea aqueous solution (alkali to urea to water mass ratio of 7:12:81) and, after pretreatment, placed at -12°C for 10 h to react fully. The resulting wood veneers were then impregnated with a 3% cellulose powder solution under vacuum (80 MPa) for 7 h. Finally, the veneers were washed and dried to obtain a super-strong wood film. This wood film has a thickness of 43 μm, a tensile strength parallel to the grain of 815 MPa, and a density of 1.72 g / cm³. 3Compared to natural linden wood chips, the thickness is reduced by 86%, and the tensile strength along the grain is increased by 14.8 times. The length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 86%, and the haze is 49%.

[0038] Example 5

[0039] Natural calcite wood was rotary-cut into thin wood veneers, which were then immersed in a 7 wt% sodium hypochlorite solution at 80°C for 2 hours. The wood veneers were then immersed in a 5 wt% copper sulfate, 2 wt% sodium hydroxide, and 12 wt% concentrated ammonia solution, mixed thoroughly, stirred continuously, and treated at room temperature for 1 hour. The resulting wood veneers were then impregnated with a 2% cellulose powder solution, and this process was carried out by vacuum filtration for 5 hours. After washing and drying, a super-strong wood film was obtained. The wood film had a thickness of 41 μm, a tensile strength parallel to the grain of 751 MPa, and a density of 1.66 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 90%, and the tensile strength along the grain is increased by 13.2 times; the length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film; the transparency of the wood film can reach up to 79%; the haze is 45%.

[0040] Example 6

[0041] Natural poplar wood was rotary-cut into thin wood veneers, which were then immersed in a sodium hydroxide / sodium sulfite aqueous solution (10 wt% sodium hydroxide, 4 wt% sodium sulfite) and heated at 85°C for 12 hours. The wood veneers were then immersed in a sodium hydroxide-urea aqueous solution (alkali to urea to water mass ratio of 7:12:81) and, after pretreatment, placed at -18°C for 6 hours to react fully. The resulting wood veneers were then impregnated with a 2% cotton cellulose solution under vacuum (60 MPa) for 10 hours. Finally, the veneers were washed and dried to obtain a super-strong wood film. This wood film has a thickness of 34 μm, a tensile strength parallel to the grain of 827 MPa, and a density of 1.66 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 83%, and the tensile strength along the grain is increased by 15 times. The length and width of the wood film can be increased by using a flat splicing method, while the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 80%, and the haze is 51%.

[0042] Example 7

[0043] Natural calcite wood was rotary-cut into thin wood sheets, which were then immersed in a 20 wt% hydrogen peroxide solution at 70°C for 3 hours. The wood sheets were then immersed in an 85 wt% N-methylmorpholine-N-oxide solution and thoroughly stirred, reacting at 120°C for 2 hours. The resulting wood sheets were then impregnated with a 2% cellulose powder solution and simultaneously vacuum-treated (30 MPa) for 5 hours. After washing and drying, a super-strong wood film was obtained. This wood film had a thickness of 33 μm, a tensile strength parallel to the grain of 653 MPa, and a density of 1.68 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 87%, and the tensile strength along the grain is increased by 11.8 times. The length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 82%, and the haze is 59%.

[0044] Example 8

[0045] Natural pine wood was rotary-cut into thin wood veneers, which were then immersed in a 12 wt% sodium hypochlorite solution at 90°C for 1.5 hours. The wood veneers were then immersed in an N,N dimethylacetamide solution, and after pretreatment, placed in an environment at 150°C for 5 hours to react fully. The temperature was then lowered to 100°C, and a certain amount of lithium chloride was added for heat treatment for 3 hours. The resulting wood veneers were then infused with a 1% ramie cellulose solution and simultaneously vacuum-treated (at a vacuum degree of 40 MPa) for 2 hours. After washing and drying, a super-strong wood film was obtained. This wood film had a thickness of 30 μm, a tensile strength parallel to the grain of 735 MPa, and a density of 1.75 g / cm³. 3 Compared to natural linden wood chips, the thickness is reduced by 89%, and the tensile strength along the grain is increased by 13.4 times. The length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 78%, and the haze is 83%.

[0046] Example 9

[0047] Natural poplar wood was rotary-cut into thin wood veneers, which were then immersed in a 3 mol / L sodium hydroxide solution and heated at 50°C for 24 hours. The wood veneers were then immersed in a sodium hydroxide-urea aqueous solution (alkali to urea to water mass ratio of 7:12:81) and, after pretreatment, placed at -12°C for 5 hours to react fully. The resulting wood veneers were then impregnated with a 1% cellulose powder solution, and this process was performed by vacuum filtration for 10 hours. After washing and drying, a super-strong wood film was obtained. This wood film had a thickness of 35 μm, a tensile strength parallel to the grain of 751 MPa, and a density of 1.45 g / cm³. 3Compared to natural linden wood chips, the thickness is reduced by 84%, and the tensile strength along the grain is increased by 13.7 times. The length and width of the wood film can be increased by using a flat splicing method, and the tensile strength of the spliced ​​wood film is not less than 95% of that of the original wood film. The transparency of the wood film can reach up to 83%, and the haze is 51%.

Claims

1. A super-strong wood film, characterized in that, It has a dense structure composed of nanofibers from wood cell walls and regenerated cellulose, with nanofiber bundles uniformly distributed in the cell cavities, and each nanofiber bundle surrounded by regenerated cellulose; the preparation method of the ultra-strong wood film includes the following steps: The wood veneer is immersed in treatment solution A to remove lignin. Treatment solution A is at least one of strong alkali solution, hydrogen peroxide solution, sodium hypochlorite solution, and sodium hydroxide / sodium sulfite solution. The treated wood veneer is immersed in treatment solution B for swelling treatment, wherein treatment solution B is at least one of the following: alkali / urea mixed solution, lithium chloride / NN dimethylacetamide solution, N-methylmorpholine-N-oxide solution, ionic solution, and copper ammonia solution; The wood slabs obtained after swelling treatment are fully infused with C treatment solution. The infusion solution fills the intercellular spaces of the wood cells. After washing and drying, an ultra-strong wood film can be obtained. The C treatment solution is at least one of cellulose powder solution, ramie cellulose solution, and cotton cellulose solution.

2. The ultra-strong wood film according to claim 1, characterized in that, The wood-based film has a thickness of 10–200 μm and a density of 1.4–1.8 g·cm³. -3 .

3. The ultra-strong wood film according to claim 1, characterized in that, The tensile strength of wood film along the grain is 600~900MPa.

4. The ultra-strong wood film according to claim 1, characterized in that, It can be spliced ​​in length and width, and the strength of the spliced ​​wood film is not less than 95% of the original.

5. The ultra-strong wood film according to claim 1, characterized in that, The transparency of the wood film can reach up to 90%, and the haze is 50-90%.

6. The ultra-strong wood film according to claim 1, characterized in that, The wood veneer was treated in treatment solution A at a temperature of 50℃~100℃ for a time of 30min~10h.

7. The ultra-strong wood film according to claim 1, characterized in that, The treated wood veneers were allowed to react fully in the B-treatment solution for 30 min to 24 h.

8. The ultra-strong wood film according to claim 1, characterized in that, The mass concentration of the C-treated solution is between 0.1% and 10%, and the treatment time is between 1 hour and 24 hours.

9. The ultra-strong wood film according to claim 1, characterized in that, The injection is carried out using vacuuming or filtration.

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