High-hydrophobicity polylactic acid modified wood-based composite material as well as preparation method and application thereof

Abstract

The invention relates to a high-hydrophobicity polylactic acid modified wood-based composite material as well as a preparation method and application thereof, and belongs to the technical field of modified wood-based composite materials. In order to solve the problem of insufficient permeability of a bio-based material in existing chemical modification, the invention provides a preparation method of a high-hydrophobicity polylactic acid modified wood-based composite material, a porous wood frame structure is prepared from a wood-based material sheet, and a lactide and stearic acid composite solution is fully permeated into wood pores by adopting a negative pressure impregnation technology to prepare the high-hydrophobicity polylactic acid modified wood-based composite material. Polylactic acid is synthesized through an in-situ polymerization reaction, and a fatty acid material with low surface energy is introduced on the basis of in-situ synthesis of the polylactic acid, so that the polylactic acid modified wood-based composite material with both mechanical properties and a hydrophobic effect is realized. The polylactic acid modified wood-based composite material prepared by the invention has high hydrophobic self-cleaning performance and excellent weather resistance, can keep good hydrophobic and moisture-proof effects in various extreme environments, and is suitable for the fields of moisture-proof floors, exterior wall decoration or furniture manufacturing.

Description

Technical Field

[0001] The present invention belongs to the technical field of modified wood-based composites, and particularly relates to a highly hydrophobic polylactic acid modified wood-based composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of the green building materials industry, the application of modified wood-based furniture in interior decoration has become increasingly widespread. Such furniture not only retains the natural beauty and warm texture of traditional wooden products, but also overcomes many limitations of natural wood through scientific and technological means, meeting the comprehensive requirements of modern homes for aesthetics, durability, and environmental protection. However, the inherent hygroscopicity of wood itself and its insufficient mechanical properties limit its high-end applications. Especially in a humid and hot environment, untreated wood is prone to chemical degradation reactions, which not only greatly reduces its dimensional stability, affects the overall beauty and service life of furniture, but also further weakens its mechanical properties, resulting in poor performance of furniture in terms of load-bearing and durability.

[0003] Currently, the modification technology of wood-based composites still faces two major problems. One is that traditional physical modification is difficult to balance mechanical enhancement and environmental protection requirements; the other is that although chemical modification provides more possibilities for the comprehensive improvement of wood properties, such as impregnation treatment with bio-based materials such as polylactic acid and stearic acid in order to achieve breakthroughs in enhancing the water resistance and corrosion resistance of wood, these macromolecular materials do not match the pore structure of wood itself, resulting in low impregnation efficiency and difficulty in uniformly penetrating into the interior of wood, thus seriously affecting the modification effect. This problem not only increases production costs, but also becomes one of the main bottlenecks for the large-scale industrialization of green modification technology. Summary of the Invention

[0004] To solve the problem of insufficient permeability of bio-based materials in existing chemical modification, the present invention provides a highly hydrophobic polylactic acid modified wood-based composite material, a preparation method thereof, and an application thereof.

[0005] The technical solution of the present invention:

[0006] A preparation method of a highly hydrophobic polylactic acid modified wood-based composite material, the steps are as follows:

[0007] Step 1, prepare a porous wood framework structure:

[0008] Perform delignification treatment on the wood-based material flakes, wash them to neutral, perform solvent replacement with tert-butanol solution, and then perform freeze-drying treatment to obtain a porous wood framework structure;

[0009] Step 2, prepare a highly hydrophobic polylactic acid modified wood-based composite material:

[0010] Immerse the porous wood framework structure obtained in Step 1 into a mixed solution of L-lactide and stearic acid, and complete the first-stage vacuum melt impregnation treatment at a certain temperature; then ventilate the impregnation system and add an organotin catalyst, fully stir and then re-vacuum to complete the second-stage impregnation treatment, then ventilate the impregnation system again and add N,N'-diisopropylcarbodiimide catalyst, and after re-vacuuming, raise the temperature of the impregnation system by 5 °C to complete the third-stage impregnation treatment to obtain a highly hydrophobic polylactic acid modified wood-based composite material.

[0011] Further, the wood-based material in Step 1 is balsa wood, poplar wood, Chinese fir, radiata pine or basswood; the delignification treatment is to place the wood-based material thin slices in a reaction system prepared from sodium chlorite, acetic acid and deionized water, and continuously stir and react in a water bath at 70-80 °C for 6.5-7.5 h. The mass-volume ratio of the wood-based material thin slices, sodium chlorite, acetic acid and deionized water is 10 g: 3-4 g: 2-3 mL: 300-350 mL, and 3-4 g of sodium chlorite and 2-3 mL of acetic acid are added every hour during the reaction.

[0012] Further, when performing solvent replacement with the tert-butanol solution in Step 1, the volume concentration of the tert-butanol solution increases in gradients of 25%, 50%, 75% and 100% in sequence, and the replacement time for each concentration of tert-butanol solution is 100-120 min; the freeze-drying treatment is carried out at -50 °C under a vacuum of 100-200 Pa for 10-14 h.

[0013] Further, the volume ratio of L-lactide and stearic acid in Step 2 is 10:1-3, and the first-stage vacuum melt impregnation treatment is carried out at 130-150 °C and -0.06 to -0.10 MPa for 30-40 min.

[0014] Further, the organotin catalyst in Step 2 is stannous octoate catalyst, and the addition amount of the organotin catalyst is 0.1-0.5% of the volume of the mixed solution of L-lactide and stearic acid; the second-stage impregnation treatment is carried out at 130-150 °C and -0.06 to -0.10 MPa for 30-40 min.

[0015] Further, the addition amount of the N,N'-diisopropylcarbodiimide catalyst in Step 2 is 0.1-0.5% of the volume of the mixed solution of L-lactide and stearic acid; the third-stage impregnation treatment is carried out at 135-155 °C and -0.06 to -0.10 MPa for 2-2.5 h.

[0016] Further, during the third-stage impregnation treatment in Step 2, the ventilation and vacuum pumping operations are repeated every 30 min.

[0017] A highly hydrophobic polylactic acid modified wood-based composite material prepared by the preparation method of the present invention has a water contact angle of 140-150 °.

[0018] Application of the highly hydrophobic polylactic acid modified wood-based composite material described in the present invention in the fields of moisture-proof floors, exterior wall decoration or furniture manufacturing.

[0019] Furthermore, the moisture-proof bottom surface includes floors supporting underfloor heating systems, paving for outdoor platforms in alpine regions, or moisture-proof floor systems for cold chain logistics warehouses.

[0020] Advantages of the present invention:

[0021] The highly hydrophobic polylactic acid modified wood-based composite material provided by the present invention uses a negative pressure impregnation technique to fully penetrate a composite solution of lactide and stearic acid into the pores of wood, synthesizes polylactic acid through an in-situ polymerization reaction, and introduces a fatty acid material with a low surface energy on the basis of the in-situ synthesis of polylactic acid, thereby realizing a polylactic acid modified wood-based composite material with both mechanical properties and hydrophobic effects. The preparation method of the highly hydrophobic polylactic acid modified wood-based composite material of the present invention breaks through the technical bottleneck in the field of hydrophobic modification of wood-based materials, and avoids the high energy consumption brought by multi-step impregnation modification by in-situ synthesis of lactic acid.

[0022] The polylactic acid modified wood-based composite material prepared by the present invention belongs to an environment-friendly material, has high hydrophobic self-cleaning performance and excellent weather resistance, can maintain a good hydrophobic and moisture-proof effect in a variety of extreme environments, and is particularly suitable for application scenarios in harsh environments such as floors supporting underfloor heating systems, paving for outdoor platforms in alpine regions, and moisture-proof floor systems for cold chain logistics warehouses. Description of the drawings

[0023] Figure 1 Appearance morphology photos of balsa wood raw materials, porous wood frame structures, and modified wood-based composite materials in Example 1;

[0024] Figure 2 Scanning electron microscope photos of balsa wood raw materials, porous wood frame structures, and modified wood-based composite materials in Example 1;

[0025] Figure 3 Water contact angle detection photos of the modified wood-based composite material in Example 1;

[0026] Figure 4 Self-cleaning test result diagrams of balsa wood and the modified wood-based composite material in Example 1;

[0027] Figure 5 Self-cleaning test result diagrams of the porous wood frame structure and the modified wood-based composite material in Example 1;

[0028] Figure 6Graph of the sandpaper wear test results of the modified wood-based composite material in Example 1;

[0029] Figure 7 Graph of the ultraviolet aging test results of the modified wood-based composite material in Example 1;

[0030] Figure 8 Graph of the ultrasonic treatment test results of the modified wood-based composite material in Example 1;

[0031] Figure 9 Graph of the acid and alkali resistance treatment test results of the modified wood-based composite material in Example 1;

[0032] Figure 10 Graph of the mechanical property test results of the modified wood-based composite material in Example 1. Detailed implementation manners

[0033] The technical solutions of the present invention will be further described below in conjunction with the embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0034] Example 1

[0035] This example provides a highly hydrophobic polylactic acid modified wood-based composite material and a preparation method thereof.

[0036] The preparation method of the highly hydrophobic polylactic acid modified wood-based composite material in this example is as follows:

[0037] Step 1: Prepare a porous wood framework structure:

[0038] Place 10 g of balsa wood flakes with a size of 10 mm×10 mm and a thickness of 2 mm into a reaction system prepared with 3.75 g of sodium chlorite, 2.5 mL of acetic acid and 325 mL of deionized water, and continuously stir and react at 75 °C in a water bath for 7 h. During the reaction, 3.75 g of sodium chlorite and 2.5 mL of acetic acid are added every hour.

[0039] After the reaction was terminated, deionized water was used to thoroughly rinse to remove residual chemical reagents, and the obtained wood-based material was washed with distilled water until neutral. Solvent replacement was carried out using a tert-butanol solution, and the volume concentrations of the tert-butanol solution were increased in gradients of 25%, 50%, 75%, and 100% in sequence. The replacement time for each concentration of the tert-butanol solution was 100 min. Finally, freeze-drying was carried out in a freeze-dryer under vacuum conditions of -50 °C and 100 - 200 Pa for 12 h to obtain a porous wood framework structure.

[0040] Step 2. Preparation of highly hydrophobic polylactic acid-modified wood-based composite material:

[0041] The porous wood framework structure obtained in Step 1 was immersed in a mixed solution of L-lactide and stearic acid with a volume ratio of 10:2, and the first-stage vacuum melting impregnation treatment was carried out in a vacuum oven at 140 °C and -0.08 MPa vacuum for 30 min.

[0042] Subsequently, the oven was ventilated, and 0.2% of the volume of the mixed solution of L-lactide and stearic acid, that is, 50 μL of stannous octoate catalyst, was added to the composite solution and stirred well. The vacuum was restored to -0.08 MPa for the second-stage impregnation treatment for 30 min.

[0043] Then, the oven was ventilated again, and 0.2% of the volume of the mixed solution of L-lactide and stearic acid, that is, 50 μL of N,N'-diisopropylcarbodiimide catalyst, was added. The system was evacuated to -0.08 MPa and then heated to 145 °C for continuous reaction for 2 h. During this period, the ventilation and vacuum pumping operations were repeated every 30 min to improve the impregnation effect. Finally, the reaction product was taken out of the oven and cooled to room temperature to obtain the highly hydrophobic polylactic acid-modified wood-based composite material.

[0044] Example 2

[0045] This example provides a highly hydrophobic polylactic acid-modified wood-based composite material and a preparation method thereof.

[0046] The preparation method of the highly hydrophobic polylactic acid-modified wood-based composite material in this example is as follows:

[0047] Step 1. Preparation of porous wood framework structure:

[0048] 10 g of poplar wood flakes with a size of 10 mm × 10 mm and a thickness of 2 mm were placed in a reaction system prepared with 3.75 g of sodium chlorite, 2.5 mL of acetic acid, and 325 mL of deionized water, and continuously stirred and reacted in a water bath at 75 °C for 7 h. During the reaction, 3.75 g of sodium chlorite and 2.5 mL of acetic acid were replenished every hour.

[0049] After the reaction was terminated, the residual chemical reagents were thoroughly rinsed off with deionized water, and the obtained wood-based material was washed with distilled water until neutral. Solvent replacement was carried out using tert-butanol solution, and the volume concentrations of the tert-butanol solution were increased in gradients of 25%, 50%, 75%, and 100% in sequence. The replacement time for each concentration of tert-butanol solution was 110 min. Finally, it was freeze-dried in a freeze dryer under vacuum conditions of -50 °C and 100 - 200 Pa for 12 h to obtain a porous wood framework structure.

[0050] Step 2: Preparation of highly hydrophobic polylactic acid modified wood-based composite material:

[0051] The porous wood framework structure obtained in Step 1 was immersed in a mixed solution of L-lactide and stearic acid with a volume ratio of 10:1, and the first-stage vacuum melting impregnation treatment was carried out in a vacuum oven at 130 °C and -0.06 MPa vacuum for 40 min.

[0052] Subsequently, the oven was ventilated, and 0.3% of the volume of the mixed solution of L-lactide and stearic acid, that is, 75 μL of stannous octoate catalyst, was added to the composite solution and stirred well. The vacuum was restored to -0.06 MPa for the second-stage impregnation treatment for 40 min.

[0053] Then, the oven was ventilated again, and 0.3% of the volume of the mixed solution of L-lactide and stearic acid, that is, 75 μL of N,N'-diisopropylcarbodiimide catalyst, was added. The system was evacuated to -0.06 MPa and then heated to 135 °C for continuous reaction for 2 h. During this period, the ventilation and vacuum pumping operations were repeated every 30 min to improve the impregnation effect. Finally, the reaction product was taken out of the oven and cooled to room temperature to obtain the highly hydrophobic polylactic acid modified wood-based composite material.

[0054] Example 3

[0055] This example provides a highly hydrophobic polylactic acid modified wood-based composite material and its preparation method.

[0056] The preparation method of the highly hydrophobic polylactic acid modified wood-based composite material in this example is as follows:

[0057] Step 1: Preparation of porous wood framework structure:

[0058] 10 g of Chinese fir thin slices with a size of 10 mm × 10 mm and a thickness of 2 mm were placed in a reaction system prepared with 3.75 g of sodium chlorite, 2.5 mL of acetic acid, and 325 mL of deionized water, and continuously stirred and reacted in a water bath at 75 °C for 7 h. During the reaction, 3.75 g of sodium chlorite and 2.5 mL of acetic acid were added every hour.

[0059] After the reaction was terminated, the residual chemical reagents were thoroughly rinsed off with deionized water, and the obtained wood-based material was washed with distilled water until neutral. Solvent replacement was carried out using tert-butanol solution, and the volume concentrations of the tert-butanol solution increased gradually in gradients of 25%, 50%, 75%, and 100%. The replacement time for each concentration of tert-butanol solution was 120 min. Finally, freeze-drying was carried out in a freeze-dryer under vacuum conditions of -50 °C and 100 - 200 Pa for 12 h to obtain a porous wood framework structure.

[0060] Step 2: Preparation of highly hydrophobic polylactic acid modified wood-based composite material:

[0061] The porous wood framework structure obtained in Step 1 was immersed in a mixed solution of L-lactide and stearic acid with a volume ratio of 10:3, and the first-stage vacuum melting impregnation treatment was carried out in a vacuum oven at 150 °C and a vacuum condition of -0.10 MPa for 30 min.

[0062] Subsequently, the oven was ventilated, and 0.1% of the volume of the mixed solution of L-lactide and stearic acid, that is, 25 μL of stannous octoate catalyst, was added to the composite solution and stirred well. The vacuum was restored to -0.10 MPa for the second-stage impregnation treatment for 30 min.

[0063] Then, the oven was ventilated again, and 0.1% of the volume of the mixed solution of L-lactide and stearic acid, that is, 25 μL of N,N'-diisopropylcarbodiimide catalyst, was added. The system was evacuated to -0.10 MPa and then heated to 155 °C for continuous reaction for 2 h. During this period, the ventilation and vacuum pumping operations were repeated every 30 min to improve the impregnation effect. Finally, the reaction product was taken out of the oven and cooled to room temperature to obtain the highly hydrophobic polylactic acid modified wood-based composite material.

[0064] Example 4

[0065] This example provides a highly hydrophobic polylactic acid modified wood-based composite material and its preparation method.

[0066] The preparation method of the highly hydrophobic polylactic acid modified wood-based composite material in this example is as follows:

[0067] Step 1: Preparation of porous wood framework structure:

[0068] 10 g of radiata pine flakes with a size of 10 mm × 10 mm and a thickness of 2 mm were placed in a reaction system prepared with 3.75 g of sodium chlorite, 2.5 mL of acetic acid, and 325 mL of deionized water, and continuously stirred and reacted in a 75 °C water bath for 7 h. During the reaction, 3.75 g of sodium chlorite and 2.5 mL of acetic acid were added every hour.

[0069] After the reaction was terminated, the residual chemical reagents were thoroughly rinsed off with deionized water, and the obtained wood-based material was washed with distilled water until neutral. Solvent replacement was carried out using tert-butanol solution, and the volume concentrations of the tert-butanol solution were increased in gradients of 25%, 50%, 75% and 100% in sequence. The replacement time for each concentration of tert-butanol solution was 100 min. Finally, freeze-drying was carried out in a freeze dryer under vacuum conditions of -50 °C and 100 - 200 Pa for 12 h to obtain a porous wood framework structure.

[0070] Step 2. Preparation of highly hydrophobic polylactic acid modified wood-based composite material:

[0071] The porous wood framework structure obtained in Step 1 was immersed in a mixed solution of L-lactide and stearic acid with a volume ratio of 10:2, and the first-stage vacuum melting impregnation treatment was carried out in a vacuum oven at 135 °C and -0.08 MPa vacuum for 35 min.

[0072] Subsequently, the oven was ventilated, and 0.2% of the volume of the mixed solution of L-lactide and stearic acid, that is, 50 μL of stannous octoate catalyst, was added to the composite solution and stirred well. Then, the vacuum was restored to -0.08 MPa for the second-stage impregnation treatment for 35 min.

[0073] Then, the oven was ventilated again, and 0.2% of the volume of the mixed solution of L-lactide and stearic acid, that is, 50 μL of N,N'-diisopropylcarbodiimide catalyst, was added. The system was evacuated to -0.08 MPa and then heated to 140 °C for continuous reaction for 2 h. During this period, the ventilation and vacuum pumping operations were repeated every 30 min to improve the impregnation effect. Finally, the reaction product was taken out of the oven and cooled to room temperature to obtain the highly hydrophobic polylactic acid modified wood-based composite material.

[0074] Example 5

[0075] This example provides a highly hydrophobic polylactic acid modified wood-based composite material and its preparation method.

[0076] The preparation method of the highly hydrophobic polylactic acid modified wood-based composite material in this example is as follows:

[0077] Step 1. Preparation of porous wood framework structure:

[0078] 10 g of basswood flakes with a size of 10 mm × 10 mm and a thickness of 2 mm were placed in a reaction system prepared with 3.75 g of sodium chlorite, 2.5 mL of acetic acid and 325 mL of deionized water, and continuously stirred and reacted in a water bath at 75 °C for 7 h. During the reaction, 3.75 g of sodium chlorite and 2.5 mL of acetic acid were added every hour.

[0079] After the reaction was terminated, the residual chemical reagents were thoroughly rinsed off with deionized water, and the obtained wood-based materials were washed with distilled water until neutral. Solvent replacement was carried out using tert-butanol solution, and the volume concentrations of the tert-butanol solution were increased in gradients of 25%, 50%, 75% and 100% in sequence. The replacement time for each concentration of tert-butanol solution was 120 min. Finally, freeze-drying was carried out in a freeze dryer under vacuum conditions of -50 °C and 100 - 200 Pa for 12 h to obtain a porous wood framework structure.

[0080] Step 2. Preparation of highly hydrophobic polylactic acid modified wood-based composite material:

[0081] The obtained porous wood framework structure in Step 1 was immersed in a mixed solution of L-lactide and stearic acid with a volume ratio of 10:2, and the first-stage vacuum melting impregnation treatment was carried out in a vacuum oven at 145 °C and -0.08 MPa vacuum for 30 min;

[0082] Subsequently, the oven was ventilated, and 0.3% of the volume of the mixed solution of L-lactide and stearic acid, that is, 75 μL of stannous octoate catalyst, was added to the composite solution and stirred well. The vacuum was restored to -0.08 MPa for the second-stage impregnation treatment for 30 min;

[0083] Then, the oven was ventilated again, and 0.3% of the volume of the mixed solution of L-lactide and stearic acid, that is, 75 μL of N,N'-diisopropylcarbodiimide catalyst, was added. The system was evacuated to -0.08 MPa and then heated to 150 °C for continuous reaction for 2 h. During this period, the ventilation and vacuum pumping operations were repeated every 30 min to improve the impregnation effect. Finally, the reaction product was taken out of the oven and cooled to room temperature to obtain the highly hydrophobic polylactic acid modified wood-based composite material.

[0084] 1. Examine the appearance and microscopic morphology of the highly hydrophobic polylactic acid modified wood-based composite material prepared by the present invention.

[0085] (1) Compare the appearance morphology of balsa wood raw material, porous wood framework structure and the modified wood-based composite material prepared in Example 1. The results are as Figure 1 shown. After delignification treatment, the morphology of the balsa wood sample changed and the color became white. Subsequently, after impregnation modification, the morphology of the composite material was close to that of the original balsa wood sample, maintaining the framework structure of the porous wood.

[0086] (2) Compare the microscopic morphology of balsa wood raw material, porous wood framework structure and the modified wood-based composite material prepared in Example 1. The results are as Figure 2 shown. The balsa wood surface has a rich pore structure. After delignification treatment, the removal of lignin makes the pore structure larger, while the internal pores of the modified wood-based composite material are filled with polylactic acid and stearic acid, generating a rough surface structure with hydrophobic effect.

[0087] II. Investigate the hydrophobicity and self - cleaning effect of the highly hydrophobic polylactic acid - modified wood - based composite prepared by the present invention.

[0088] (1) Detect the water contact angle of the modified wood - based composite prepared in Example 1. The results are as Figure 3 shown. The water contact angle of the modified wood - based composite is 143.87 °.

[0089] (2) Lay a layer of bamboo powder and sand on the surfaces of the inclined balsa wood flakes and the modified wood - based composite prepared in Example 1 respectively. Drop water on the bamboo powder and sand respectively, and observe whether the bamboo powder and sand slide down with the water droplets.

[0090] The results are as Figure 4 shown. Neither the bamboo powder nor the sand on the surface of the balsa wood flakes has changed, while both the bamboo powder and the sand on the surface of the modified wood - based composite prepared by the present invention slide down with the water droplets, proving that the highly hydrophobic polylactic acid - modified wood - based composite has self - cleaning performance.

[0091] (3) Drop methyl red solution on the surfaces of the inclined porous wood frame structure and the modified wood - based composite prepared in Example 1 respectively, or lay methyl red powder and drop water on the surface of the material with methyl red powder laid, and observe whether there is residual methyl red solution or methyl red powder on the surfaces of the porous wood frame structure and the modified wood - based composite.

[0092] The results are as Figure 5 shown. There is residual methyl red solution and methyl red powder on the surface of the porous wood frame structure; while there is no residual methyl red solution on the surface of the modified wood - based composite, and the methyl red powder also slides down with the water droplets without forming residues, indicating that the highly hydrophobic polylactic acid - modified wood - based composite has self - cleaning performance.

[0093] III. Investigate the stability of the hydrophobic property of the highly hydrophobic polylactic acid - modified wood - based composite prepared by the present invention.

[0094] (1) Sandpaper abrasion test: Use 1000 - mesh sandpaper. On the surface of the modified wood - based composite prepared in the example, linearly abrade the sample surface with a 50 - g weight as a constant pressure, and record the number of abrasion times or time. After abrasion, measure the change in the water contact angle of the surface of the modified wood - based composite through a contact angle measuring instrument.

[0095] The results are as Figure 6 shown. The water contact angle of the surface of the modified wood - based composite only drops from 143.83° to 134.82°. After abrasion, the modified wood - based composite still maintains high hydrophobicity.

[0096] (2)UV aging test: The surface of the modified wood-based composite material was irradiated with ultraviolet light at a wavelength of 365 nm, the irradiation distance was 10 cm, and the irradiation time was recorded. After ultraviolet light irradiation, the change in the water contact angle on the surface of the modified wood-based composite material was measured by a contact angle measuring instrument.

[0097] The results are as Figure 7 shown. The water contact angle on the surface of the modified wood-based composite material only decreased from 143.67° to 138.05°. After ultraviolet light irradiation, the modified wood-based composite material still maintained high hydrophobicity.

[0098] (3)Ultrasonic treatment test: The modified wood-based composite material was treated with ultrasonic waves at a power of 120 W, and the treatment time was recorded. After ultrasonic treatment, the change in the water contact angle on the surface of the modified wood-based composite material was measured by a contact angle measuring instrument.

[0099] The results are as Figure 8 shown. The water contact angle on the surface of the modified wood-based composite material only decreased from 143.87° to 126.65°. After ultrasonic treatment, the modified wood-based composite material still maintained high hydrophobicity.

[0100] (4)Acid and alkali resistance treatment test: The modified wood-based composite material was immersed in acidic or alkaline solutions with pH values of 2, 4, 6, 8, 10, or 12, respectively. When the immersion time was 2 h and 4 h, the change in the water contact angle on the surface of the modified wood-based composite material was measured by a contact angle measuring instrument.

[0101] The results are as Figure 9 shown. After treatment with different pH acidic or alkaline solutions, the decrease in the water contact angle on the surface of the modified wood-based composite material was within 3°. After acid and alkali treatment for different times, the modified wood-based composite material still maintained high hydrophobicity.

[0102] From the above analysis, it can be seen that the highly hydrophobic polylactic acid-modified wood-based composite material prepared by the present invention has excellent weather resistance and can maintain good hydrophobic and moisture-proof effects in various extreme environments.

[0103] IV. Examine the mechanical properties of the highly hydrophobic polylactic acid-modified wood-based composite material prepared by the present invention.

[0104] A universal testing machine (CMT-5504, MTS Systems, China) was used to conduct a mechanical compression test at a crosshead speed of 2 mm / min. After compression of 60%, the compressive strength of the material was tested at the end.

[0105] The results are as Figure 10 shown. The maximum compressive strength of the highly hydrophobic polylactic acid-modified wood-based composite material was greatly improved compared with balsa wood, and its mechanical properties meet the application conditions in floors and other occasions.

Claims

1. A preparation method of a highly hydrophobic polylactic acid modified wood-based composite material, characterized in that, The steps are as follows: Step 1. Prepare a porous wood framework structure: The wood-based material flakes are subjected to delignification treatment and then washed to neutrality, solvent-exchanged with a tert-butanol solution, and then freeze-dried to obtain a porous wood framework structure; Step 2. Prepare a highly hydrophobic polylactic acid-modified wood-based composite material: The porous wood framework structure obtained in Step 1 is immersed in a mixed solution of L-lactide and stearic acid, and the first-stage vacuum melting impregnation treatment is completed at a certain temperature; then, the impregnation system is aerated and an organotin catalyst is added, and after sufficient stirring, the vacuum is re-evacuated to complete the second-stage impregnation treatment. Then, the impregnation system is aerated again and an N,N'-diisopropylcarbodiimide catalyst is added. After evacuating the vacuum again, the temperature of the impregnation system is increased by 5 °C to complete the third-stage impregnation treatment, and a highly hydrophobic polylactic acid-modified wood-based composite material is obtained.

2. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 1, wherein The wood-based material described in Step 1 is balsa wood, poplar, Chinese fir, radiata pine or basswood; the delignification treatment is to place the wood-based material flakes in a reaction system prepared from sodium chlorite, acetic acid and deionized water, and continuously stir and react in a water bath at 70-80 °C for 6.5-7.5 h. The mass-volume ratio of the wood-based material flakes, sodium chlorite, acetic acid and deionized water is 10 g: 3-4 g: 2-3 mL: 300-350 mL, and 3-4 g of sodium chlorite and 2-3 mL of acetic acid are added per hour during the reaction process.

3. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 1 or 2, characterized in that, When the solvent exchange is carried out with the tert-butanol solution in Step 1, the volume concentration of the tert-butanol solution increases in gradients of 25%, 50%, 75% and 100% in turn, and the replacement time of each concentration of tert-butanol solution is 100-120 min; the freeze-drying treatment is carried out at -50 °C and 100-200 Pa under vacuum for 10-14 h.

4. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 3, characterized in that, The volume ratio of L-lactide and stearic acid described in Step 2 is 10: 1-3, and the first-stage vacuum melting impregnation treatment is carried out at 130-150 °C and -0.06--0.10 MPa for 30-40 min.

5. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 4, characterized in that, The organotin catalyst described in Step 2 is stannous octoate catalyst, and the addition amount of the organotin catalyst is 0.1-0.5% of the volume of the mixed solution of L-lactide and stearic acid; The second-stage impregnation treatment is carried out at 130-150 °C and -0.06--0.10 MPa for 30-40 min.

6. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 5, characterized in that, The addition amount of the N,N'-diisopropylcarbodiimide catalyst described in Step 2 is 0.1-0.5% of the volume of the mixed solution of L-lactide and stearic acid; the third-stage impregnation treatment is carried out at 135-155 °C and -0.06--0.10 MPa for 2-2.5 h.

7. The preparation method of a highly hydrophobic polylactic acid modified wood-based composite material according to claim 6, characterized in that During the third-stage impregnation treatment described in Step 2, the ventilation and vacuum evacuation operations are repeated every 30 min.

8. A highly hydrophobic polylactic acid modified wood-based composite material prepared by the preparation method according to any one of claims 1-7, characterized in that, The water contact angle is 140-150 °.

9. Application of a highly hydrophobic polylactic acid-modified wood-based composite material as described in claim 8 in the fields of moisture-proof floors, exterior wall decoration or furniture manufacturing.

10. The application according to claim 9, wherein The moisture-proof bottom surface includes floors supporting underfloor heating systems, paving of outdoor platforms in alpine regions or moisture-proof floor systems in cold chain logistics warehouses.

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