Green cross-linked polyvinyl acetal porous powder and preparation method and application thereof

Abstract

The application discloses green cross-linked polyvinyl acetal porous powder and a preparation method and application thereof, and relates to the technical field of polymer materials. The green cross-linked polyvinyl acetal porous powder is prepared by heterogeneous cross-linking reaction of polyvinyl acetal porous powder and a bio-based cross-linking agent in a green solvent, wherein the polyvinyl acetal porous powder is prepared by acetal reaction of polyvinyl alcohol and an aldehyde compound under the action of an acid catalyst. The bio-based cross-linking agent derived from natural oil or sugar is used to replace the traditional chemical synthetic cross-linking agent, and the green solvent system of gamma-valerolactone / ethanol is used to replace the traditional volatile organic solvent, so that VOC emission and the use of toxic substances are avoided from the source, the VOC content is only 12-15 g / L, the green cross-linked polyvinyl acetal porous powder has good environmental friendliness, and meanwhile, has excellent solvent resistance and low-temperature flexibility, and can be widely applied in the fields of flexible electronic packaging materials, green powder coatings, environment-friendly adhesives and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a green cross-linked polyvinyl acetal porous powder, its preparation method, and its application. Background Technology

[0002] Polyvinyl acetal materials, such as polyvinyl butyral, are widely used in adhesives, ceramic binders, coatings, and interlayer films for safety glass due to their excellent substrate adhesion, compatibility, and organic solvent solubility.

[0003] To further improve the adhesion and solvent resistance of polyethylene acetal materials, existing technologies generally employ crosslinking modification by introducing crosslinking functional groups. However, existing crosslinking modification methods still have significant shortcomings. On the one hand, traditional methods often use chemically synthesized crosslinking agents such as maleic anhydride and glycidyl methacrylate, and the reaction solvents are often volatile organic solvents (VOCs) such as hexane and methyl ethyl ketone. This not only easily causes environmental pollution during the production process but also poses risks to human safety. At the same time, the residual chemical crosslinking agents and organic solvents are difficult to completely remove, affecting the subsequent application of the product. On the other hand, traditional crosslinked polyethylene acetal products have poor low-temperature flexibility and are prone to brittleness and deformation in low-temperature environments, failing to meet the low-temperature mechanical performance requirements of materials in emerging fields such as flexible electronics and green chemicals.

[0004] Therefore, developing a cross-linked polyvinyl acetal porous powder that uses green raw materials and environmentally friendly processes, and has excellent solvent resistance and low-temperature flexibility, has become an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a green cross-linked polyethylene acetal porous powder, its preparation method, and its applications. This green cross-linked polyethylene acetal porous powder is prepared by a heterogeneous cross-linking reaction between polyethylene acetal porous powder and a bio-based cross-linking agent in a green solvent. This invention uses a bio-based cross-linking agent to replace the traditional chemically synthesized cross-linking agent and a mixed solvent of γ-valerol and ethanol to replace the volatile organic solvent, thus solving the problems of high VOC emissions and insufficient low-temperature flexibility of existing cross-linked polyethylene acetal materials. It can be widely applied to high-end application scenarios such as flexible electronic packaging and green powder coatings.

[0006] The technical solution provided by this invention is as follows: This invention provides a method for preparing green cross-linked polyvinyl acetal porous powder, comprising the following steps: (1) Preparation of porous polyvinyl acetal powder Polyvinyl alcohol is dissolved in water by stirring to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is slowly cooled to -10~30℃, C2-C6 aldehyde compounds and acid catalysts are added, and the reaction is carried out by keeping it at the temperature for 0.5-5 hours. After aging, the mixture is cooled, washed with water and dried to obtain polyvinyl acetal porous powder. The average particle size of the polyethylene acetal porous powder is 30-1000 μm and the bulk density is 0.12-0.50 g / mL, to ensure that the particle size and bulk density of the polyethylene acetal porous powder are suitable for the subsequent heterogeneous crosslinking reaction.

[0007] Heterogeneous crosslinking reaction The porous polyvinyl acetal powder obtained in step (1) is dispersed in a green solvent, and then a bio-based crosslinking agent and catalyst are added to carry out a heterogeneous crosslinking reaction. Post-processing The reaction solution from step (2) was filtered, the filter residue was washed with water and dried to obtain green cross-linked polyvinyl acetal porous powder.

[0008] Preferably, the degree of polymerization of the polyvinyl alcohol in step (1) is 500-2000 and the degree of alcoholysis is ≥98%; the mass ratio of polyvinyl alcohol to water in step (1) is (3-15):100.

[0009] Preferably, the C2-C6 aldehyde compound in step (1) is n-butyraldehyde, propionaldehyde, isobutyraldehyde or pentanal, and the acid catalyst is hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid or oxalic acid; preferably, the concentration of hydrochloric acid is 10-20wt%.

[0010] Preferably, in step (2), the green solvent is a mixture of γ-valerolactone and ethanol, with a weight ratio of γ-valerolactone to ethanol of (70:30)-(90:10). The mixture of γ-valerolactone and ethanol ensures the solubility of the bio-based crosslinking agent while not dissolving the polyvinyl acetal porous powder and the product powder, thus achieving a heterogeneous reaction. In step (2), the mass ratio of polyvinyl acetal porous powder to green solvent is (15-30):100.

[0011] Preferably, the bio-based crosslinking agent is selected from at least one of glycidyl linoleate, diglycidyl gluconate, or glycidyl linolenic acid; the mass ratio of the bio-based crosslinking agent to the porous polyvinyl acetal powder is (5-15):100.

[0012] The selected bio-based crosslinking agent is derived from natural oils or sugars, has abundant reactive epoxy groups, and the long carbon chains in the molecular structure can improve the flexibility of the product.

[0013] Preferably, the catalyst is triethylamine, tripropylamine, tributylamine, diisopropylethylamine, or pyridine; the molar ratio of the catalyst to the bio-based crosslinking agent is (5-10):100.

[0014] Preferably, in step (1), the stirring and dissolving temperature is 80-100℃, the stirring and dissolving time is 1-4 hours, the aging temperature is 40-80℃, and the aging time is 1-6 hours; in step (2), the heterogeneous cross-linking reaction temperature is 30-50℃ to avoid thermal decomposition of the bio-based cross-linking agent, and the time is 3-8 hours to ensure that the cross-linking functional groups are fully introduced; in step (3), washing with water 3-5 times can effectively remove residual catalyst and unreacted bio-based cross-linking agent.

[0015] Preferably, the green cross-linked polyethylene acetal porous powder has an average particle size of 50-500 μm, a bulk density of 0.15-0.40 g / mL, and a water content ≤2.0wt%; the monomer unit of the cross-linked polyethylene acetal contains at least one cross-linking functional group selected from ester bonds or ether bonds. The ester bond cross-linking functional group is formed by the reaction of the hydroxyl group of the vinyl alcohol unit in the polyethylene acetal with the epoxy group in the bio-based cross-linking agent, and the ether bond cross-linking functional group is formed by the reaction of the hydroxyl group of the vinyl alcohol unit in the polyethylene acetal with the epoxy group in the bio-based cross-linking agent. The cross-linking functional group is derived from the bio-based cross-linking agent, and the molar ratio of the cross-linking functional group to the -CH2-CH2- unit in the main chain of the cross-linked polyethylene acetal is (5-15):100.

[0016] Based on the same inventive concept, the present invention provides a green cross-linked polyethylene acetal porous powder, wherein the green cross-linked polyethylene acetal porous powder is prepared by any of the preparation methods described above.

[0017] Based on the same inventive concept, this invention provides the application of a green cross-linked polyethylene acetal porous powder as described in any of the preceding claims in flexible electronic packaging materials, green powder coatings, or environmentally friendly adhesives.

[0018] Based on the same inventive concept, this invention provides a flexible electronic packaging material comprising the aforementioned green cross-linked polyethylene acetal porous powder, a plasticizer, and a cross-linking initiator; the green cross-linked polyethylene acetal porous powder content is 5-15 wt%, the plasticizer content is 1-5 wt%, and the cross-linking initiator content is 0.01-0.5 wt%; the flexible electronic packaging material, after being immersed in ethanol at 50°C for 2 hours, exhibits a solvent residue rate ≥85% and an elongation at break ≥15% at -20°C, meeting the requirements for solvent resistance and low-temperature flexibility of the packaging material.

[0019] Based on the same inventive concept, the present invention provides a green powder coating comprising the aforementioned green cross-linked polyethylene acetal porous powder, wherein the average particle size of the green cross-linked polyethylene acetal porous powder is ≤200μm and the water content is ≤1.5wt%; the green powder coating, after being coated and then cured by UV irradiation or heat, forms a coating with low VOC emissions and excellent solvent resistance.

[0020] The beneficial effects of this invention are: This invention uses a bio-based crosslinking agent derived from natural oils or sugars to replace the traditional chemically synthesized crosslinking agent, and a γ-valerol / ethanol green solvent system to replace the traditional volatile organic solvent, eliminating VOC emissions and the use of toxic substances at the source. The resulting product has a VOC content of only 12-15 g / L, which meets the requirements of green chemistry and sustainable development. Furthermore, the resulting green crosslinked polyethylene acetal porous powder has excellent solvent resistance and low-temperature flexibility, with a solvent residue rate of ≥89% and an elongation at break of ≥17% at -20℃, effectively solving the problems of insufficient low-temperature flexibility and poor environmental performance of traditional products.

[0021] The preparation method of the present invention is an optimization of the existing production process of porous polyvinyl acetal powder. It only requires the replacement of the crosslinking agent and solvent system, without the need to reconstruct the production equipment. It has strong process compatibility. At the same time, the post-processing steps are simple, without the need for complex purification processes, resulting in high production efficiency and controllable production costs. It has good prospects for large-scale industrial production.

[0022] The green cross-linked polyethylene acetal porous powder prepared by this invention can be widely used in flexible electronic packaging materials, green powder coatings, environmentally friendly adhesives and other fields, and is especially suitable for high-end application scenarios such as flexible electronics and low VOC coatings. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. It should be noted that, unless otherwise specified, all chemical reagents involved in this invention are purchased through commercial channels.

[0024] It should be noted that the specific manufacturers and models of the raw materials involved in this invention are merely examples listed to illustrate the embodiments of this invention, and should not be construed as limiting the scope of protection of this invention. The scope of protection of this invention covers all materials that meet the structural and performance requirements described, and should not be limited by the specific suppliers or product models listed in the embodiments. Example

[0025] A method for preparing a green cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 330g of polyvinyl alcohol (degree of polymerization 1700, degree of alcoholysis 98%) and 4050g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 10℃, and 192g of n-butyraldehyde and 270mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 150 minutes to carry out the acetal reaction. Then the temperature was raised to 50℃ for aging for 120 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 120 μm, and the bulk density is 0.22 g / mL. (2) Heterogeneous crosslinking reaction Add 900g of γ-valerol and 100g of ethanol to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 20g of glycidyl linoleate and 1.2g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 35°C and carry out the heterogeneous cross-linking reaction for 5 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed four times with 2L of distilled water, and then vacuum dried at 80°C until the water content was 1.2wt%, to obtain green cross-linked polyvinyl acetal porous powder. Example

[0026] A method for preparing a green cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 330g of polyvinyl alcohol (degree of polymerization 1700, degree of alcoholysis 98%) and 4050g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 10℃, and 192g of n-butyraldehyde and 270mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 150 minutes to carry out the acetal reaction. Then the temperature was raised to 50℃ for aging for 120 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 120 μm, and the bulk density is 0.22 g / mL. (2) Heterogeneous crosslinking reaction Add 850g γ-valerol and 150g ethanol to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 15g of diglycidyl gluconate and 0.9g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 40°C and carry out the heterogeneous cross-linking reaction for 4 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed four times with 2L of distilled water, and then vacuum dried at 80℃ until the water content was 1.0wt% to obtain green cross-linked polyvinyl acetal porous powder. Example

[0027] A method for preparing a green cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 275g of polyvinyl alcohol (degree of polymerization 1000, degree of alcoholysis 98%) and 3375g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 5℃, and 160g of n-butyraldehyde and 225mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 180 minutes to carry out the acetal reaction. Then the temperature was raised to 60℃ for aging for 240 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 80 μm, and the bulk density is 0.18 g / mL. (2) Heterogeneous crosslinking reaction Add 900g of γ-valerol and 100g of ethanol to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 18g of glycidyl linoleate and 1.0g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 38°C and carry out the heterogeneous cross-linking reaction for 6 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed five times with 2L of distilled water, and then vacuum dried at 80°C until the water content was 1.5wt% to obtain green cross-linked polyvinyl acetal porous powder.

[0028] Comparative Example 1 A method for preparing cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 330g of polyvinyl alcohol (degree of polymerization 1700, degree of alcoholysis 98%) and 4050g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 10℃, and 192g of n-butyraldehyde and 270mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 150 minutes to carry out the acetal reaction. Then the temperature was raised to 50℃ for aging for 120 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 120 μm, and the bulk density is 0.22 g / mL. (2) Crosslinking reaction Add 900g hexane and 100g methyl ethyl ketone to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 15g of maleic anhydride and 1.0g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 25°C and carry out the crosslinking reaction for 5 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed four times with 2L of distilled water, and then vacuum dried at 80℃ until the water content was 1.8wt% to obtain cross-linked polyvinyl acetal porous powder.

[0029] Compared to Example 1, this comparative example uses maleic anhydride, a traditional chemically synthesized crosslinking agent, as the crosslinking agent, and hexane and methyl ethyl ketone, as the reaction solvents.

[0030] Comparative Example 2 A method for preparing cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 330g of polyvinyl alcohol (degree of polymerization 1700, degree of alcoholysis 98%) and 4050g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 10℃, and 192g of n-butyraldehyde and 270mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 150 minutes to carry out the acetal reaction. Then the temperature was raised to 50℃ for aging for 120 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 120 μm, and the bulk density is 0.22 g / mL. (2) Crosslinking reaction Add 900g hexane and 100g methyl ethyl ketone to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 20g of glycidyl linoleate and 1.2g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 35°C and carry out the cross-linking reaction for 5 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed four times with 2L of distilled water, and then vacuum dried at 80°C until the water content was 1.6wt% to obtain cross-linked polyvinyl acetal porous powder.

[0031] Compared to Example 1, this comparative example uses conventional organic volatile solvents hexane and methyl ethyl ketone as the reaction solvent.

[0032] Comparative Example 3 A method for preparing cross-linked polyvinyl acetal porous powder includes the following steps: (1) Preparation of porous polyvinyl acetal powder 330g of polyvinyl alcohol (degree of polymerization 1700, degree of alcoholysis 98%) and 4050g of deionized water were added to a 5L glass container and stirred at 120rpm at 95℃ for 2 hours to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution was slowly cooled to 10℃, and 192g of n-butyraldehyde and 270mL of 20% hydrochloric acid were added. The mixture was kept at this temperature for 150 minutes to carry out the acetal reaction. Then the temperature was raised to 50℃ for aging for 120 minutes. The mixture was then cooled to room temperature, washed with water until neutral, and dried to obtain a porous polyvinyl acetal powder. The average particle size of the polyvinyl acetal porous powder is 120 μm, and the bulk density is 0.22 g / mL. (2) Crosslinking reaction Add 900g of γ-valerol and 100g of ethanol to a 2L separable flask, mix well, and then add 200g of the polyvinyl acetal porous powder obtained in step (1), 15g of glycidyl methacrylate and 0.9g of triethylamine in sequence under stirring. After the addition is complete, heat the system to 40°C and carry out the crosslinking reaction for 4 hours. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed four times with 2L of distilled water, and then vacuum dried at 80℃ until the water content was 1.4wt% to obtain cross-linked polyvinyl acetal porous powder.

[0033] Compared to Example 1, this comparative example uses glycidyl methacrylate, a traditional chemically synthesized crosslinking agent.

[0034] Performance testing: (1) Crosslinking functional group content: using 1H-NMR was performed at 80℃ using dimethyl sulfoxide-d6 as the solvent.

[0035] (1) Particle size and bulk density: The bulk density was determined by using a laser particle size analyzer (SALD2200) according to JIS K6721.

[0036] (3) Solvent resistance: After soaking in ethanol at 50°C for 2 hours, the residual rate was calculated (residual rate = weight after drying / initial weight × 100%).

[0037] (4) Low temperature flexibility: Tensile test was conducted at -20℃, and the elongation at break was measured (elongation at break = (length at break - original length) / original length × 100%).

[0038] (5) VOC emissions: VOC content was determined in accordance with GB / T 23986-2009.

[0039] The cross-linked polyethylene acetal porous powders prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the above test methods. The test results are shown in Table 1.

[0040] Table 1 Performance Test Results

[0041] As shown in Table 1, the green cross-linked polyethylene acetal porous powders prepared in Examples 1-3 of this invention exhibit solvent resistance with a solvent residue rate of 89-94%, which is comparable to, or even better than, the cross-linked polyethylene acetal porous powders prepared in Comparative Examples 1-3. Regarding low-temperature flexibility, their elongation at break at -20℃ is 17-20%, significantly better than Comparative Examples 1 and 3. Comparative Examples 1 and 3, due to the use of chemically synthesized cross-linking agents, show significantly insufficient low-temperature flexibility, indicating that the long carbon chain structure in the bio-based cross-linking agent plays a crucial role in improving the product's flexibility. Regarding environmental friendliness, the VOC content of the green cross-linked polyethylene acetal porous powder prepared in Examples 1-3 is only 12-15 g / L, which is much lower than that of Comparative Examples 1 and 2. Comparative Examples 1 and 2 use traditional hexane / methyl ethyl ketone volatile organic solvents, resulting in serious VOC emissions exceeding the standard and extremely poor environmental performance. This indicates that the γ-valerol / ethanol mixed solvent system has excellent environmental performance. Therefore, the cross-linked polyethylene acetal porous powders prepared in Comparative Examples 1-3 are difficult to adapt to the needs of flexible electronic packaging materials and green powder coatings.

[0042] In summary, this invention successfully prepared a green cross-linked polyvinyl acetal porous powder with excellent solvent resistance, good low-temperature flexibility, and excellent environmental performance through the synergistic effect of bio-based cross-linking agents and green solvents. This effectively solves the problem of balancing environmental protection and performance in existing technologies. It can be widely used in flexible electronic packaging materials, green powder coatings, environmentally friendly adhesives, and other fields. It is particularly suitable for the current urgent needs of the electronics industry for flexible and environmentally friendly materials, as well as the low VOC emission requirements of the coating industry. In addition, the preparation method is simple, does not require the reconstruction of production equipment, and has good process compatibility and industrialization prospects.

[0043] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a green cross-linked polyvinyl acetal porous powder, characterized in that, Includes the following steps: (1) Preparation of porous polyvinyl acetal powder Polyvinyl alcohol is dissolved in water by stirring to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is slowly cooled to -10~30℃, C2-C6 aldehyde compounds and acid catalysts are added, and the reaction is carried out by keeping it at the temperature for 0.5-5 hours. After aging, the mixture is cooled, washed with water and dried to obtain polyvinyl acetal porous powder. The average particle size of the porous polyethylene acetal powder is 30-1000 μm, and the bulk density is 0.12-0.50 g / mL. (2) Heterogeneous crosslinking reaction The porous polyvinyl acetal powder obtained in step (1) is dispersed in a green solvent, and then a bio-based crosslinking agent and catalyst are added to carry out a heterogeneous crosslinking reaction. (3) Post-processing The reaction solution from step (2) was filtered, the filter residue was washed with water and dried to obtain green cross-linked polyvinyl acetal porous powder.

2. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, The degree of polymerization of the polyvinyl alcohol in step (1) is 500-2000 and the degree of alcoholysis is ≥98%; the mass ratio of polyvinyl alcohol to water in step (1) is (3-15):

100.

3. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, The C2-C6 aldehyde compounds mentioned in step (1) are n-butyraldehyde, propionaldehyde, isobutyraldehyde or pentanal, and the acid catalyst is hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid or oxalic acid.

4. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, In step (2), the green solvent is a mixture of γ-valerolactone and ethanol, with a mass ratio of γ-valerolactone to ethanol of (7:3)-(9:1); in step (2), the mass ratio of polyvinyl acetal porous powder to green solvent is (15-30):

100.

5. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, The bio-based crosslinking agent is selected from at least one of glycidyl linoleate, diglycidyl gluconate, or glycidyl linolenic acid; the mass ratio of the bio-based crosslinking agent to the porous polyvinyl acetal powder is (5-15):

100.

6. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, The catalyst is triethylamine, tripropylamine, tributylamine, diisopropylethylamine, or pyridine; the molar ratio of the catalyst to the bio-based crosslinking agent is (5-10):

100.

7. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, In step (1), the temperature for stirring and dissolving is 80-100℃ and the time is 1-4 hours; the temperature for maturation is 40-80℃ and the maturation time is 1-6 hours; in step (2), the temperature for heterogeneous cross-linking reaction is 30-50℃ and the time is 3-8 hours.

8. The method for preparing a green cross-linked polyvinyl acetal porous powder according to claim 1, characterized in that, The green cross-linked polyethylene acetal porous powder has an average particle size of 50-500 μm, a bulk density of 0.15-0.40 g / mL, and a water content of ≤2.0wt%.

9. A green cross-linked polyvinyl acetal porous powder, characterized in that, The green cross-linked polyethylene acetal porous powder is prepared by a method for preparing green cross-linked polyethylene acetal porous powder according to any one of claims 1-8.

10. The application of the green cross-linked polyvinyl acetal porous powder as described in claim 9 in flexible electronic packaging materials, green powder coatings, or environmentally friendly adhesives.

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