Preparation method of damp-heat aging resistant wheat straw / polyvinyl chloride composite material

Abstract

The invention discloses a preparation method of a damp-heat aging resistant wheat straw / polyvinyl chloride composite material. Wheat straw and polyvinyl chloride are used as main raw materials, a plasma treatment technology is adopted for the wheat straw to enhance the hydrophilicity of the surface of the straw, the surface roughness of the straw is improved through laser etching, an interface modifier is introduced to improve the interface compatibility between the straw and a polyvinyl chloride matrix, the treated wheat straw is mixed with the polyvinyl chloride, and the mixture is prepared. And the composite material is prepared through single-screw melt extrusion. According to the invention, the service life of the composite material in a humid and hot environment is prolonged, and an efficient solution is provided for application of the wood-plastic composite material in an aging environment.

Description

Technical Field The present invention belongs to the technical field of composite materials, and particularly relates to a preparation method of a wheat straw / polyvinyl chloride composite material resistant to damp heat aging. Background Art

[0002] In recent years, with the increasing prominence of resource and environmental issues, the research and development of sustainable development materials have received extensive attention. Among them, wood-plastic composite materials have been widely used in the fields of industry, construction, and environmental protection due to their high strength, light weight, and versatility. Especially, polymer matrix composites reinforced with crop straw plant fibers have become an important raw material for replacing traditional synthetic polymer materials due to their low density, low cost, renewable nature, and good biodegradability. However, due to the natural hydrophilicity of plant fibers, there are interfacial incompatibility problems between them and the hydrophobic polymer matrix, which not only reduces the mechanical properties of the composite material but also causes the performance of the material to decline easily in a damp heat environment, thus limiting its actual application range.

[0003] Plasma treatment is a technology for modifying the surface of materials using low-temperature plasma. For plant fibers such as wheat straw, plasma treatment generates highly reactive ions, free radicals, and electrons through activated gases under low-pressure or atmospheric pressure conditions, which undergo physical or chemical reactions with the straw surface. This treatment can clean the surface, remove impurities, introduce polar functional groups, and change the microstructure of the fiber, thus significantly improving the interfacial bonding between wheat straw and the polymer matrix. This technology does not require chemical reagents and a large amount of water resources, avoiding the generation of chemical waste liquids and solid wastes, and meeting the requirements of sustainable development.

[0004] Laser etching is a technology for precisely processing and modifying the surface of materials using a laser beam with a high energy density. Laser etching can remove surface impurities, adjust the surface structure, and introduce functional microtopographies on the surface of plant fibers such as wheat straw through the thermal effect and photochemical reaction of the laser with the material surface. Laser etching can not only clean the straw surface but also precisely control the micro-roughness and chemical composition of the straw surface, thus improving the interfacial bonding performance with the polymer matrix. Laser etching mainly acts on the straw surface and has little impact on the internal structure, being able to enhance the interfacial bonding force while retaining the mechanical properties of the fiber itself.

[0005] Chemical pretreatment is to modify plant fibers using chemical reagents, aiming to change the surface characteristics of the fibers, remove impurities, and enhance their compatibility with the matrix. Commonly used chemical treatment methods include alkali treatment, acid treatment, esterification, etherification, etc. Among them, alkali treatment is the most common, usually using alkaline solutions such as hydrogen peroxide to treat the straw, which can remove lignin, hemicellulose, and other impurities on the straw surface, expose the cellulose fibers, and thus improve its surface activity and mechanical properties.

[0006] Inorganic filler modification involves introducing inorganic materials (such as inorganic salts, metal oxides, silicates, calcium carbonate, bentonite, etc.) into plant fibers to improve the surface properties of the fibers as a reinforcing phase and enhance the interfacial bonding force with the polymer matrix, thereby optimizing the performance of the composite material. Common inorganic fillers include silica, alumina, titanium dioxide, talc powder, calcium carbonate, etc., and are usually modified by directly mixing with plant fibers, filling, copolymerization, or surface treatment.

[0007] Single-screw extruders are processing equipment widely used in industries such as plastics, rubber, and food. They heat, mix, and melt materials through the rotation of the screw and extrude them into a shape using a die. The machine is usually equipped with precise temperature control and pressure control systems, which can accurately adjust the temperature and pressure according to the requirements of different materials, thus ensuring the uniform plasticization of the material and the high quality of the product.

[0008] Long-term service in a humid and hot environment will damage the structure of wood-plastic composites, thereby reducing their performance and accelerating their aging. Therefore, it is of great significance to develop a preparation method for wood-plastic composites with resistance to humid and hot aging. Summary of the Invention

[0009] To address the deficiencies in the above-mentioned existing technologies, the present invention provides a preparation method for wheat straw / polyvinyl chloride composites with resistance to humid and hot aging. This method pre-treats wheat straw fibers through plasma and laser etching to modify their surface properties, modifies wheat straw with chemical reagents to change the surface characteristics of the fibers and combines them with inorganic fillers, avoiding the aggregation phenomenon of wheat straw fibers, and significantly improving the interfacial compatibility between wheat fibers and polyvinyl chloride, thereby enhancing the physical and mechanical properties of the composite material. By optimizing the treatment method of wheat straw fibers, the stability of the composite material in a humid and hot environment is further improved, ensuring its excellent resistance to humid and hot aging during long-term use.

[0010] The technical solution of the present invention is as follows: A preparation method for wheat straw / polyvinyl chloride composites with resistance to humid and hot aging, characterized by comprising the following steps: Step 1: Using wheat straw as the raw material, rinse and dry the wheat straw with distilled water; Step 2: Physical pre-treatment process: Place the wheat straw obtained in Step 1 in a high-frequency electric field, excite gas under low-pressure conditions, and perform plasma treatment; Step 3: Physical pre-treatment process: Use a laser beam with a high energy density to scan and etch the surface of the wheat straw treated in Step 2, and perform laser scanning etching treatment; Step 4: Chemical pre-treatment process: React the wheat straw treated in Step 3 with hydrogen peroxide in proportion, then filter and wash to obtain the chemically pre-treated wheat straw; Step Five, Crushing Process: Dry and crush the wheat straw after the treatment in Step Four to obtain wheat straw powder; Step Six, Additive Modification: Mix the inorganic filler with an appropriate amount of solvent, stir evenly, then add the treated wheat straw powder and stir. Remove the solvent by evaporation or drying to obtain a mixture of pigment and straw powder; Step Seven, Mixing Process: Using the method of high-energy ball milling, stir the mixture obtained in Step Six with polyvinyl chloride, stabilizer, and coupling agent in proportion; Step Eight, Melt Extrusion Process: Extrude and mold the mixture obtained in Step Seven in a single-screw extruder.

[0011] Further, in Step One, the ratio of wheat straw to distilled water is 100 g:500 ml - 100 g:1000 ml; the drying time is 4 h - 6 h.

[0012] Further, the gas in Step Two is at least one of air, nitrogen, and oxygen, the gas flow rate is 50 - 200 sccm, and the plasma treatment time for wheat straw is 5 - 30 min.

[0013] Further, the laser beam type in Step Three is CO2 laser; the laser power is 10 w - 50 w; the scanning speed is 2 - 5 mm / s; the etching depth is 30 - 50 µm.

[0014] Further, in Step Four, the concentration of hydrogen peroxide used is 1% - 5%, the ratio of wheat straw to hydrogen peroxide is 100 g:1 L - 100 g:1.5 L, stir at room temperature for 12 - 24 h, then filter and wash with distilled water. The ratio of wheat straw to distilled water is 100 g:500 ml - 100 g:1000 ml.

[0015] Further, the drying time of the wheat straw in Step Five is 4 h - 6 h; after crushing, pass through a 100-mesh sieve to obtain the wheat straw powder.

[0016] Further, the inorganic filler in Step Six is at least one of iron oxide pigment, carbon black, and titanium dioxide; the solvent is water or alcohol; the ratio of inorganic filler, solvent, and wheat straw powder is 3 g - 6 g:500 ml:100 g.

[0017] Further, the ball mill type in Step Seven is a planetary ball mill; the ball milling time is 1 h - 2 h, stop and cool for 5 minutes every 30 min to control the temperature; the ratio of the mixture obtained in Step Six to polyvinyl chloride, stabilizer, and coupling agent is 50:50:4:3.

[0018] Further, in Step 8, the rotational speed of the single-screw extruder is 20 rpm, and the temperatures of the feeding zone, compression zone, homogenization zone, and die head zone are 160 °C - 180 °C, 180 °C - 190 °C, 190 °C - 200 °C, and 200 °C - 210 °C, respectively.

[0019] The present invention uses processes such as plasma process, laser etching treatment process, and chemical reagent treatment process to treat wheat straw. The plasma and laser etching treatment processes increase the surface roughness of plant fibers, modify their surface properties, and improve surface energy; the chemical reagent treatment reduces the hydroxyl content and surface polarity of the fibers, enhancing the compatibility between natural fibers and the matrix, thereby producing high-quality composite materials resistant to wet and heat aging. Inorganic filler filling enhances the interfacial bonding force between wheat straw and the matrix by filling the pores between them and optimizes the properties of the composite materials, greatly improving the service life of the composite materials in a wet and heat aging environment.

[0020] After being treated by the method of the present invention, the overall structure of the straw fibers is less affected. By precisely controlling the parameters of the treatment process, the physical and chemical properties of the fiber surface can be optimized at the microscopic level, thereby improving the interfacial bonding force between plant fibers and the plastic matrix, and further enhancing the overall mechanical properties, durability, and stability of the composite materials. Inorganic filler filling can effectively enhance the mechanical properties, thermal stability, and corrosion resistance of wheat straw / polymer composite materials, etc. This technology broadens the application fields of plant fiber-reinforced composite materials and provides technical support for the development of green, environmentally friendly, and high-performance composite materials.

[0021] The beneficial effects of the present invention are as follows: 1. The present invention overcomes the deficiencies that wheat straw is prone to self-aggregation and has poor compatibility with the polymer matrix polyvinyl chloride by pre-treating wheat straw, improves the compatibility between wheat straw and the polyvinyl chloride matrix, and enhances the interfacial properties between wheat straw and polyvinyl chloride. Plasma and laser etching are green and pollution-free processing methods, which conform to the current trend of environmental protection production.

[0022] 2. The present invention reduces the dimensional changes of wheat straw / polyvinyl chloride composite materials due to humidity changes or thermal expansion by adding inorganic fillers. Especially in high-humidity and high-temperature environments, filling inorganic fillers can effectively reduce the expansion and contraction of materials, improve their dimensional stability, and enable them to show stability in more application scenarios. Description of the Drawings

[0023] Figure 1 are the test results of color difference changes and impact performance of Example 1, Example 2, and Comparative Examples 1 - 4; Figure 2 is the microscopic morphology of the impact fracture surface of the composite material in Comparative Example 1; Figure 3 is the microscopic morphology of the impact fracture surface of the composite material in Comparative Example 2; Figure 4 is the microscopic morphology of the surface of the composite material in Comparative Example 1; Figure 5 is the microscopic morphology of the surface of the composite material in Comparative Example 2. Specific Embodiments

[0024] The present invention will be further described below through specific examples. The following description is merely exemplary and does not limit its content.

[0025] In the following embodiments, all raw materials can be purchased from the market. Embodiment

[0026] Prepare a moisture and heat resistant wheat straw / polyvinyl chloride composite material according to the following method. The steps are as follows: a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a blast drying oven at 60 °C and dry for 4 h; b. Plasma pretreatment process: Place the dried wheat straw in a high-frequency electric field, and introduce 50 sccm of oxygen under low-pressure conditions for plasma treatment for 5 min; c. Laser etching pretreatment process: Use a 10 w CO2 laser beam to scan and etch the surface of the wheat straw at a speed of 2 mm / s to obtain wheat straw with an etching depth of 30 µm; d. Chemical pretreatment process: Dissolve 3% hydrogen peroxide in 1 L of distilled water, then immerse 100 g of wheat straw in 1 L of hydrogen peroxide, and stir at room temperature for 12 h. After filtering the hydrogen peroxide solution, wash the wheat straw with 500 ml of distilled water; e. Place the wheat straw in a blast drying oven at 60 °C and dry for 6 h, then crush it with an ultrafine pulverizer and pass through a 100-mesh standard sieve to obtain wheat straw powder; f. Dissolve 6 g of iron oxide red pigment in 500 ml of distilled water, stir evenly with a glass rod, then add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; g. Use a planetary ball mill to mix the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent and attapulgite in a ratio of 50:50:4:3 for 1 hour, and stop the machine to cool for 5 minutes after mixing for 30 minutes; f. Place the well - mixed blend in a single - screw extruder with a rotational speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone, and die head zone are 160 °C, 180 °C, 190 °C, and 200 °C respectively. After high - temperature extrusion, the obtained product is a rectangular plate. Example

[0027] Prepare a moisture - and heat - resistant aged wheat straw / polyvinyl chloride composite material according to the following method. The steps are as follows: a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a 60 °C blast drying oven and dry for 4 h; b. Plasma pretreatment process: Place the dried wheat straw in a high - frequency electric field, and introduce 50 sccm of oxygen under low - pressure conditions for 5 min of plasma treatment; c. Laser etching pretreatment process: Use a 10 - w CO2 laser beam to scan - etch the surface of the wheat straw at a speed of 2 mm / s to obtain wheat straw with an etching depth of 30 µm; d. Chemical pretreatment process: Dissolve 3% hydrogen peroxide in 1 L of distilled water, then immerse 100 g of wheat straw in 1 L of hydrogen peroxide and stir at room temperature for 12 h. After filtering the hydrogen peroxide solution, wash the wheat straw with 500 ml of distilled water; e. Place the wheat straw in a 60 °C blast drying oven and dry for 6 h, then crush it with an ultra - fine crusher and pass through a 100 - mesh standard sieve to obtain wheat straw powder; f. Dissolve 6 g of carbon black pigment in 500 ml of distilled water, stir well with a glass rod, then add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; g. Use a planetary ball mill to mix the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent, and attapulgite in a ratio of 50:50:4:3 for 1 h. Stop the machine and cool for 5 min after mixing for 30 min; f. Place the well - mixed blend in a single - screw extruder with a rotational speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone, and die head zone are 160 °C, 180 °C, 190 °C, and 200 °C respectively. After high - temperature extrusion, the obtained product is a rectangular plate.

[0028] Comparative Example 1 a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a 60 °C blast drying oven and dry for 4 h; b. Crush the wheat straw with an ultrafine grinder and pass it through a 100-mesh standard sieve to obtain wheat straw powder; c. Dissolve 6 g of iron oxide red pigment in 500 ml of distilled water. After stirring evenly with a glass rod, add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; d. Use a planetary ball mill to mix for 1 h according to the ratio of the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent and attapulgite clay of 50:50:4:3. Stop the machine and cool for 5 min after mixing for 30 min; e. Place the uniformly mixed material in a single-screw extruder with a rotational speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone and die head zone are 160 °C, 180 °C, 190 °C and 200 °C respectively. After high-temperature extrusion, the obtained product is a rectangular plate.

[0029] Comparative Example 2 a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a 60 °C blast drying oven and dry for 4 h; b. Plasma pretreatment process: Place the dried wheat straw in a high-frequency electric field, and excite 50 sccm of oxygen under low-pressure conditions for 5 min of plasma treatment; c. Crush the wheat straw with an ultrafine grinder and pass it through a 100-mesh standard sieve to obtain wheat straw powder; d. Dissolve 6 g of iron oxide red pigment in 500 ml of distilled water. After stirring evenly with a glass rod, add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; e. Use a planetary ball mill to mix for 1 h according to the ratio of the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent and attapulgite clay of 50:50:4:3. Stop the machine and cool for 5 min after mixing for 30 min; f. Place the uniformly mixed material in a single-screw extruder with a rotational speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone and die head zone are 160 °C, 180 °C, 190 °C and 200 °C respectively. After high-temperature extrusion, the obtained product is a rectangular plate.

[0030] Comparative Example 3 a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a 60 °C blast drying oven and dry for 4 h; b. Laser etching pretreatment process: Use a 10 w CO2 laser beam to scan and etch the surface of wheat straw at a speed of 2 mm / s to obtain wheat straw with an etching depth of 30 µm; c. Crush the wheat straw with an ultrafine grinder and pass it through a 100-mesh standard sieve to obtain wheat straw powder; Dissolve 6 g of iron oxide red pigment in 500 ml of distilled water, stir evenly with a glass rod, then add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; d. Use a planetary ball mill to mix for 1 h according to the ratio of the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent and attapulgite clay of 50:50:4:3. Stop the machine and cool for 5 min after mixing for 30 min; e. Place the uniformly mixed material in a single-screw extruder with a rotation speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone and die head zone are 160 °C, 180 °C, 190 °C and 200 °C respectively. After high-temperature extrusion, the obtained product is a rectangular plate.

[0031] Comparative Example 4 a. Immerse 100 g of wheat straw in 500 ml of distilled water and stir with a glass rod for 10 min. After filtering off the distilled water, place the wheat straw in a blast drying oven at 60 °C for 4 h; b. Chemical pretreatment process: Dissolve 3% hydrogen peroxide in 1 L of distilled water, then immerse 100 g of wheat straw in 1 L of hydrogen peroxide and stir at room temperature for 12 h. After filtering the hydrogen peroxide solution, wash the wheat straw with 500 ml of distilled water; c. Crush the wheat straw with an ultrafine grinder and pass it through a 100-mesh standard sieve to obtain wheat straw powder; Dissolve 6 g of iron oxide red pigment in 500 ml of distilled water, stir evenly with a glass rod, then add 100 g of wheat straw powder and stir for 2 h. After stirring evenly, filter the distilled water with filter paper to obtain a mixture of iron oxide red pigment and wheat straw powder; d. Use a planetary ball mill to mix for 1 h according to the ratio of the mixture of iron oxide red pigment and wheat straw powder, polyvinyl chloride, stabilizer, coupling agent and attapulgite clay of 50:50:4:3. Stop the machine and cool for 5 min after mixing for 30 min; e. Place the uniformly mixed material in a single-screw extruder with a rotation speed of 20 rpm. The temperatures of the feeding zone, compression zone, homogenization zone and die head zone are 160 °C, 180 °C, 190 °C and 200 °C respectively. After high-temperature extrusion, the obtained product is a rectangular plate.

[0032] To better illustrate the present invention, the heat and humidity aging tests were carried out on the heat and humidity aging-resistant wheat straw / polyvinyl chloride composites obtained in Examples 1 and 2 and Comparative Examples 1 to 4 by using the standard test methods in the industry to verify the color stability of the composites prepared by the technical method of the present invention. The instrument used for the aging test was a heat and humidity aging test chamber, and the test conditions were set as follows: the temperature of the heat and humidity aging chamber was 60 °C, during which the volume of distilled water in the heat and humidity aging chamber was kept unchanged, and the color change of the tested material was measured after 480 h of cumulative aging.

[0033] The performance verification of the composites in the above examples and comparative examples was carried out as follows: Color difference change test The color change of the composite material was detected according to the CIE 1976 L﹡a﹡b﹡ chromaticity space, and the chromaticity of the composite material before aging was used as the standard value. The calculation formula of the color difference value (ΔE) of the composite material is shown in Equation (1).

[0034] (1) In Equation (1): ΔL is the difference in color lightness; Δa is the difference in color red (Δa > 0) / green (Δa < 0); Δb is the difference in color yellow (Δb > 0) / blue (Δb < 0).

[0035] Impact strength test The specimen test was carried out with reference to GB / T1043.1-2008. The specimen size was 80 mm × 10 mm × 4 mm, the pendulum energy was 1 J, and a G-P01 type simply supported beam impact testing machine (Chrony (Beijing) Instrument Co., Ltd.) was used for the test. The test results of 5 tests were recorded and the average value was obtained. Conclusion:

[0036] Conclusion 1: The test results of the color difference change and impact performance of the products in Example 1, Comparative Example 1 and 4 by using the standard test methods in the industry are as Figure 1 , Figure 2 and Figure 3 shown. After heat and humidity aging, the mechanical properties of the wheat straw / polyvinyl chloride composite are not as good as those of the pretreated wheat straw / polyvinyl chloride composite, indicating that the wheat straw can extend the service life of the wheat straw / polyvinyl chloride composite in a heat and humidity environment after pretreatment.

[0037] Conclusion 2: It can be seen from Figure 4 and 5 that the color difference change of the composite material prepared by the technical method of the present invention is small and more stable during heat and humidity aging.

[0038] Conclusion 3: The present invention provides a method for preparing a wheat straw / polyvinyl chloride composite resistant to hydrothermal aging by subjecting wheat straw to plasma, laser etching and chemical pretreatment, and combining inorganic filler to fill the wheat straw / polyvinyl chloride interface. By modifying the surface of wheat straw, polar functional groups are introduced and the microstructure of the fiber is changed, thereby improving the interfacial bonding between wheat straw and [the relevant material]. At the same time, the use of inorganic filler to fill the pores between wheat straw and polyvinyl chloride matrix successfully improves the compatibility between the two, enhances the mechanical properties, color stability and surface morphology of the wheat straw / polyvinyl chloride composite during the hydrothermal aging process, and expands its application range in humid and hot environments.

[0039] Matters not covered by the present invention are well-known technologies.

[0040] The above embodiments of the present invention are only examples for illustrating the present invention, rather than limitations on the specific implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above examples. It is impossible to give detailed examples of all implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A preparation method of a wheat straw / polyvinyl chloride composite material resistant to damp heat aging, characterized in that It includes the following steps: Step 1: Using wheat straw as raw material, rinse and dry the wheat straw with distilled water; Step 2: Physical pretreatment process: Place the wheat straw obtained in Step 1 in a high-frequency electric field, excite gas under low-pressure conditions, and perform plasma treatment; Step 3: Physical pretreatment process: Use a laser beam with high energy density to scan and etch the surface of the wheat straw treated in Step 2, and perform laser scanning etching treatment; Step 4: Chemical pretreatment process: React the wheat straw treated in Step 3 with hydrogen peroxide in proportion, then filter and wash to obtain chemically pretreated wheat straw; Step 5: Crushing process: Dry and crush the wheat straw treated in Step 4 to obtain wheat straw powder; Step 6: Additive modification: Mix inorganic filler with an appropriate amount of solvent, stir evenly, then add the treated wheat straw powder and stir, and remove the solvent by evaporation or drying to obtain a mixture of pigment and straw powder; Step 7: Mixing process: Using the method of high-energy ball milling, stir the mixture obtained in Step 6 with polyvinyl chloride, stabilizer, and coupling agent in proportion; Step 8: Melt extrusion process: Extrude and mold the mixture obtained in Step 7 in a single-screw extruder.

2. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 1, the ratio of wheat straw to distilled water is 100 g:500 ml - 1000 ml; the drying time is 4 h - 6 h.

3. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 2, the gas is at least one of air, nitrogen, and oxygen, the gas flow rate is 50 - 200 sccm, and the plasma treatment time for wheat straw is 5 - 30 min.

4. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 3, the type of laser beam is CO2 laser; the laser power is 10 w - 50 w; the scanning speed is 2 - 5 mm / s; the etching depth is 30 - 50 µm.

5. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 4, the concentration of hydrogen peroxide used is 1% - 5%, the ratio of wheat straw to hydrogen peroxide is 100g:1L - 100g:1.5L, stir at room temperature for 12 - 24h, then filter and wash with distilled water, and the ratio of wheat straw to distilled water is 100g:500ml - 100g:1000ml.

6. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 5, the drying time of the wheat straw is 4h - 6h; after crushing, pass through a 100-mesh sieve to obtain the wheat straw powder.

7. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 6, the inorganic filler is at least one of iron oxide pigment, carbon black, and titanium dioxide; the solvent is water or alcohol; the ratio of inorganic filler, solvent, and wheat straw powder is 3 - 6 g:500 ml:100 g.

8. The preparation method of a moisture and heat resistant aging wheat straw / polyvinyl chloride composite material according to claim 1, characterized in that: In Step 7, the type of ball mill is a planetary ball mill; the ball milling time is 1 - 2 hours, stop and cool for 5 minutes every 30 minutes to control the temperature; the ratio of the mixture obtained in Step 6 to polyvinyl chloride, stabilizer, and coupling agent is 50:50:4:

3.

9. The preparation method of a wheat straw / polyvinyl chloride composite material resistant to damp heat aging according to claim 1, characterized in that: In Step 8, the rotation speed of the single-screw extruder is 20 rpm, and the temperatures of the feeding zone, compression zone, homogenization zone, and die head zone are 160 ℃ - 180 ℃, 180 ℃ - 190 ℃, 190 ℃ - 200 ℃, 200 ℃ - 210 ℃ respectively.

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