Phenolic plastic based on PCB edge material modification and preparation method thereof

Abstract

The application discloses phenolic plastic based on PCB line board offcut modification and a preparation method thereof, and belongs to the technical field of plastics. The typical hazardous waste PCB line board offcut generated in the electronic manufacturing industry is directly used as a functional reinforcing filler for high-value reuse. Not only is the reduction and harmless treatment of electronic hazardous waste achieved, but also the inherent short-cut glass fiber reinforcing phase and the epoxy resin matrix inside are used to realize the rigid reinforcement of the phenolic plastic. At the same time, a large amount of bio-based raw materials are introduced into the formula, so that the product has partial biodegradation characteristics, significantly reduces the carbon emission and environmental load of the product in the whole life cycle, and meets the green and low-carbon industrial development direction. The thermal expansion microspheres with thorny structures on the surface further strengthen the rigidity of the matrix structure on one hand, and assist in forming a uniform closed cell structure by foaming on the other hand, thereby effectively passivating the crack propagation path.

Description

Technical Field

[0001] This invention belongs to the field of plastics technology, specifically to phenolic plastics modified from PCB circuit board scraps and their preparation method. Background Technology

[0002] With the rapid iteration and large-scale development of the electronics and information industry, the output of printed circuit boards (PCBs), as the core carrier components of electronic devices, has continued to climb, resulting in an explosive growth in PCB scrap. Statistics show that by the end of 2025, the global annual waste circuit board production exceeded 6 million tons, with China accounting for approximately 35% of the global total, reaching about 2.1 million tons. PCB scrap, as the main waste generated during the cutting, drilling, and milling processes, accounts for more than 15% of the total waste circuit boards and continues to grow at an average annual rate of over 5%, making it one of the largest and most difficult categories of electronic waste to process.

[0003] Phenolic plastics, as thermosetting polymers, are produced by the condensation reaction of phenol and formaldehyde. They possess excellent heat resistance, electrical insulation, flame retardancy, dimensional stability, and cost advantages, and are widely used in various industrial fields such as electronics, automotive manufacturing, building insulation, and friction materials. In recent years, China's phenolic resin industry has developed steadily. By 2025, domestic production capacity will reach 2.3 million tons, with an output of approximately 1.95 million tons, making China the world's largest producer and consumer. However, traditional phenolic plastics have significant performance shortcomings, including high brittleness, poor impact toughness, and susceptibility to cracking and poor molding performance during processing, which limits their application expansion in high-end fields.

[0004] To improve the mechanical and processing properties of phenolic plastics, existing technologies commonly employ the addition of fillers for modification. Common fillers include wood flour, mica, glass fiber, and calcium carbonate. However, these traditional fillers are either too expensive, significantly increasing the production cost of phenolic plastics, or have poor compatibility with the phenolic resin matrix, resulting in limited modification effects and making it difficult to simultaneously achieve the dual goals of performance improvement and cost control.

[0005] Therefore, in response to the technical pain points of low resource utilization rate and difficult environmental disposal of existing PCB circuit board scraps, as well as the high cost and poor modification effect of traditional phenolic plastic modified fillers, this paper proposes to develop a phenolic plastic based on PCB circuit board scrap modification and its preparation method. This will enable high-value resource utilization of PCB scraps, while improving the comprehensive performance of phenolic plastics and reducing production costs. This has significant environmental significance, economic value and industrial application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide phenolic plastics modified from PCB circuit board scraps and their preparation method. This invention directly reuses typical hazardous waste PCB circuit board scraps generated in the electronics manufacturing industry as functional reinforcing fillers, achieving not only the reduction and harmless disposal of electronic hazardous waste, but also, through the inherent short-cut glass fiber reinforcement phase and epoxy resin matrix, providing rigid reinforcement to the phenolic plastics. Simultaneously, the formulation incorporates a large amount of bio-based raw materials, giving the product partial biodegradability, significantly reducing carbon emissions and environmental burden throughout the product's life cycle, aligning with the green and low-carbon industrial development direction.

[0007] The objective of this invention can be achieved through the following technical solutions: The preparation method of phenolic plastic based on PCB circuit board scrap includes the following steps: Step 1: Citric acid and epoxidized soybean oil undergo a condensation reaction involving ring-opening of epoxy groups and esterification of carboxyl groups to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0008] Step 2: Using hexadecyltrimethylammonium bromide as a template and urea as an auxiliary agent, silica is grown in situ on the surface of thermally expandable microspheres through a hydrolysis-condensation reaction of tetraethyl orthosilicate, thus constructing a spiky micromorphology and obtaining spiky thermally expandable microspheres.

[0009] Step 3: Phenolic resin prepolymer is synthesized by phenol-formaldehyde condensation reaction. Spiky thermally expandable microspheres are introduced for blending modification to obtain modified phenolic resin prepolymer.

[0010] Step 4: Using modified phenolic resin prepolymer as the main body, combined with PCB circuit board scraps as inorganic / organic solid waste filler and reinforcing phase, and citric acid-epoxidized soybean oil oligomer solution interface toughening, phenolic plastic based on PCB circuit board scrap modification is obtained.

[0011] Furthermore, the specific preparation steps of the citric acid-epoxidized soybean oil oligomer solution are as follows: Citric acid and deionized water are added to a reaction vessel and stirred for 12-15 minutes at 20-25℃ and 500-600 r / min. Then, epoxidized soybean oil is added, and the mixture is heated to 95-100℃ and reacted under nitrogen protection in a sealed environment for 1-2 hours. Glycerol is then added as a solvent, and the mixture is stirred for another 11 minutes to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0012] Furthermore, the ratio of citric acid, deionized water, epoxidized soybean oil, and glycerin is 80-90g: 125-130mL: 140-150g: 42-45g.

[0013] Furthermore, the specific preparation steps for the spiky thermally expandable microspheres are as follows: Hexadecyltrimethylammonium bromide, urea, thermally expandable microspheres, and deionized water were added to a reaction vessel and stirred for 30-40 minutes at 20-25°C and 500-600 r / min. Then, isopropanol and tetraethyl orthosilicate were added, and stirring was continued for another 30-40 minutes. The mixture was then heated to 60-70°C and reacted for 16-18 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and dried under vacuum at 60-70°C for 1-2 hours to obtain spiky thermally expandable microspheres.

[0014] Furthermore, the ratio of hexadecyltrimethylammonium bromide, urea, thermally expandable microspheres, deionized water, isopropanol, and tetraethyl orthosilicate is 120-130g: 120-140g: 18-20g: 800-900mL: 160-180mL: 40-60mL.

[0015] Furthermore, the specific preparation steps of the modified phenolic resin prepolymer are as follows: A 30-32% (w / w) formaldehyde solution, ammonium dihydrogen phosphate, phenol, spiky thermally expandable microspheres, and deionized water A are added to a reaction vessel and stirred at 50-55℃ and 500-600 r / min for 1-2 h. Then, a 1-3% (w / w) sodium hydroxide solution is added, and the reaction continues for 1-2 h. The mixture is then heated at 95-100℃ for 1-2 h. The product is cooled to 60-80℃, and the pH is adjusted to neutral with a 1-2 mol / L hydrochloric acid solution. The product is then dehydrated by vacuum distillation at a vacuum degree of 0.092-0.095 MPa. The product is then placed in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B and stirred at 3000-4000 r / min for 20-30 min. The mixture is then transferred to a mold and polycondensed at 60-70℃ to form a modified phenolic resin prepolymer.

[0016] Furthermore, the ratio of formaldehyde solution, ammonium dihydrogen phosphate, phenol, spiky thermally expandable microspheres, deionized water A, sodium hydroxide solution, Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B is 700-900mL: 120-122g: 800-900g: 15-20g: 5000-6000mL: 100-120mL: 10-12mL: 140-180mL: 40-50mL: 100-110mL.

[0017] Furthermore, the specific preparation steps for phenolic plastics modified from PCB circuit board scraps are as follows: PCB circuit board scraps, starch, glycerol, modified phenolic resin prepolymer, and deionized water are added to a reactor and stirred for 35 minutes at 60-70℃ and 500-600 rpm. Then, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 are added and stirred until homogeneous. The mixture is stirred for 1-2 hours at 50-60℃ and 500-600 rpm, sealed, and stored at 20-25℃ for 24-26 hours. The mixture is then transferred to a mixer and heated and plasticized at 155-158℃. The plasticized material is extruded using a twin-screw extruder and then pelletized using a pelletizer to obtain phenolic plastic modified from PCB circuit board scraps.

[0018] Furthermore, the ratio of PCB circuit board scraps, starch, glycerin, modified phenolic resin prepolymer, deionized water, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 is 20-30g: 35-40g: 2-4g: 70-80g: 200-220mL: 3-5g: 3-5g: 45-48g: 6-8g.

[0019] The beneficial effects of this invention are: 1. This invention directly reuses typical hazardous waste PCB circuit board scraps generated in the electronics manufacturing industry as functional reinforcing fillers, achieving high-value reuse. This not only reduces and harmlessly disposes of electronic hazardous waste, but also utilizes the inherent short-cut glass fiber reinforcement phase and epoxy resin matrix to achieve rigid reinforcement of phenolic plastics. At the same time, the formula introduces a large amount of bio-based raw materials, giving the product some biodegradable characteristics, significantly reducing carbon emissions and environmental burden throughout the product's life cycle, which aligns with the green and low-carbon industrial development direction.

[0020] 2. This invention uses chopped glass fibers naturally present in PCB circuit board scraps as a high-strength inorganic rigid phase, significantly improving the material's tensile strength, flexural modulus, and creep resistance. The thermally expandable microspheres with a spiky surface further strengthen the rigidity of the matrix structure through a rigid framework, and also assist in foaming to form a uniform closed-cell structure, effectively blunting crack propagation paths. Simultaneously, the long, flexible fatty chains introduced by the citric acid-epoxidized soybean oil oligomer efficiently absorb impact energy through the flexible phase, solving the industry pain points of traditional phenolic plastics' high brittleness and poor impact resistance, achieving comprehensive optimization of the material's mechanical properties.

[0021] 3. In this invention, the spiky structure on the surface of the spiky thermal expansion microspheres also has a highly efficient char-forming catalytic function. At high temperatures, it can catalyze the formation of a dense and continuous ceramicized oxygen-barrier carbon layer on the substrate, effectively blocking the heat transfer and combustible gas release pathways. The nitrogen element in the phenolic system forms a nitrogen-phosphorus-silicon synergistic flame retardant system with the phosphorus and silicon components in the system, which greatly improves the limiting oxygen index of the material and significantly reduces the smoke density and the release of toxic and harmful gases during the combustion process. Its fire resistance performance can meet the stringent application requirements of flame retardancy, low smoke, and low toxicity in the fields of building materials, automotive interiors, etc.

[0022] 4. This invention constructs a multi-interpenetrating cross-linked network structure by coordinating and cross-linking hydroxyl groups in borax with starch and phenolic resin, which significantly improves the thermal decomposition temperature and heat distortion temperature of the material and optimizes the heat resistance and dimensional stability of the material. The spiky thermally expandable microspheres are uniformly dispersed in the multi-interpenetrating cross-linked network to form a rigid reinforcing phase, which can not only further enhance the mechanical properties of the matrix, but also effectively block ultraviolet rays, delay the photo-oxidative aging process of the matrix, and significantly extend the long-term service life of the material. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: A method for preparing phenolic plastics modified from PCB circuit board scraps, comprising the following steps: S1: Add 80g of citric acid and 125mL of deionized water to the reaction vessel and stir for 12min at 20℃ and 500r / min. Then add 140g of epoxidized soybean oil, heat to 95℃, and react in a sealed manner for 1h under nitrogen protection. Then add 42g of glycerol as a dissolving solution and continue stirring for 11min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0025] S2: Add 120g hexadecyltrimethylammonium bromide, 120g urea, 18g thermally expandable microspheres and 800mL deionized water to a reaction vessel, stir for 30min at 20℃ and 500r / min, then add 160mL isopropanol and 40mL tetraethyl orthosilicate, continue stirring for 30min, heat to 60℃, continue the reaction for 16h, filter, wash the filter cake twice with deionized water, and vacuum dry at 60℃ for 1h to obtain spiky thermally expandable microspheres.

[0026] S3: Add 700 mL of 30% formaldehyde solution, 120 g of ammonium dihydrogen phosphate, 800 g of phenol, 15 g of spiky thermally expandable microspheres, and 5000 mL of deionized water A to a reaction vessel. Stir at 50℃ and 500 r / min for 1 h. Then add 100 mL of 1% sodium hydroxide solution and continue the reaction for 1 h. Heat at 95℃ for 1 h. Cool the product to 60℃ and adjust the pH to neutral with 1 mol / L hydrochloric acid solution. Dehydrate by vacuum distillation at 0.092 MPa. Place the product in a mixed solution of 10 mL Tween 80, 140 mL of n-pentane, 40 mL of concentrated sulfuric acid, and 100 mL of deionized water B. Stir at 3000 r / min for 20 min. Transfer the mixture to a mold and polycondense at 60℃ to form a modified phenolic resin prepolymer.

[0027] S4: Add 20g of PCB circuit board scrap, 35g of starch, 2g of glycerol, 70g of modified phenolic resin prepolymer and 200mL of deionized water to a reactor and stir for 35min at 60℃ and 500r / min. Then add 3g of borax, 3g of stearic acid, 45g of citric acid-epoxidized soybean oil oligomer solution and 6g of Tween 80, stir and mix evenly, stir for 1h at 50℃ and 500r / min, seal and store at 20℃ for 24h, then transfer to a mixer and heat and plasticize at 155℃. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain phenolic plastic modified from PCB circuit board scrap.

[0028] Example 2: A method for preparing phenolic plastics modified from PCB circuit board scraps, comprising the following steps: S1: Add 85g of citric acid and 127.5mL of deionized water to the reactor and stir for 13.5min at 22.5℃ and 550r / min. Then add 145g of epoxidized soybean oil, heat to 97.5℃, and react in a sealed environment under nitrogen protection for 1.5h. Then add 43.5g of glycerol as a dissolving solution and continue stirring for 11min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0029] S2: 125g of hexadecyltrimethylammonium bromide, 130g of urea, 19g of thermally expandable microspheres and 850mL of deionized water were added to a reaction vessel and stirred for 35min at 22.5℃ and 550r / min. Then, 170mL of isopropanol and 50mL of tetraethyl orthosilicate were added and stirred for another 35min. The mixture was then heated to 65℃ and reacted for 17h. After filtration, the filter cake was washed three times with deionized water and dried under vacuum at 65℃ for 1.5h to obtain spiky thermally expandable microspheres.

[0030] S3: Add 800 mL of 31% formaldehyde solution, 121 g of ammonium dihydrogen phosphate, 850 g of phenol, 17.5 g of spiky thermally expandable microspheres, and 5500 mL of deionized water A to a reactor. Stir at 52.5 °C and 550 r / min for 1.5 h. Then add 110 mL of 2% sodium hydroxide solution and continue the reaction for 1.5 h. Heat at 97.5 °C for 1.5 h. Cool the product to 70 °C and adjust the pH to neutral with 1.5 mol / L hydrochloric acid solution. Distill under reduced pressure at 0.0935 MPa to remove water. Place the product in a mixed solution of 11 mL Tween 80, 160 mL of n-pentane, 45 mL of concentrated sulfuric acid, and 105 mL of deionized water B. Stir at 3500 r / min for 25 min. Transfer the mixture to a mold and polycondense at 65 °C to form a modified phenolic resin prepolymer.

[0031] S4: Add 25g of PCB circuit board scrap, 37.5g of starch, 3g of glycerol, 75g of modified phenolic resin prepolymer and 210mL of deionized water to a reactor and stir for 35min at 65℃ and 550r / min. Then add 4g of borax, 4g of stearic acid, 46.5g of citric acid-epoxidized soybean oil oligomer solution and 7g of Tween 80, stir and mix evenly, stir for 1.5h at 55℃ and 550r / min, seal and store at 22.5℃ for 25h. Then transfer to a mixer and heat and plasticize at 156.5℃. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain phenolic plastic modified from PCB circuit board scrap.

[0032] Example 3: A method for preparing phenolic plastics modified from PCB circuit board scraps, comprising the following steps: S1: Add 90g of citric acid and 130mL of deionized water to the reaction vessel, stir for 15min at 25℃ and 600r / min, then add 150g of epoxidized soybean oil, heat to 100℃, and react in a sealed manner for 2h under nitrogen protection. Then add 45g of glycerol as a dissolving solution and continue stirring for 11min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0033] S2: Add 130g hexadecyltrimethylammonium bromide, 140g urea, 20g thermally expandable microspheres and 900mL deionized water to a reaction vessel, stir for 40min at 25℃ and 600r / min, then add 180mL isopropanol and 60mL tetraethyl orthosilicate, continue stirring for 40min, heat to 70℃, continue the reaction for 18h, filter, wash the filter cake 4 times with deionized water, and vacuum dry at 70℃ for 2h to obtain spiky thermally expandable microspheres.

[0034] S3: Add 900 mL of 32% formaldehyde solution, 122 g of ammonium dihydrogen phosphate, 900 g of phenol, 20 g of spiky thermally expandable microspheres, and 6000 mL of deionized water A to a reactor. Stir at 55 °C and 600 r / min for 2 h. Then add 120 mL of 3% sodium hydroxide solution and continue the reaction for 2 h. Heat at 100 °C for 2 h. Cool the product to 80 °C and adjust the pH to neutral with 2 mol / L hydrochloric acid solution. Distill under reduced pressure at 0.095 MPa to remove water. Place the product in a mixed solution of 12 mL Tween 80, 180 mL of n-pentane, 50 mL of concentrated sulfuric acid, and 110 mL of deionized water B. Stir at 4000 r / min for 30 min. Transfer the mixture to a mold and polycondense at 70 °C to form a modified phenolic resin prepolymer.

[0035] S4: Add 30g of PCB circuit board scrap, 40g of starch, 4g of glycerol, 80g of modified phenolic resin prepolymer and 220mL of deionized water to a reactor and stir for 35min at 70℃ and 600r / min. Then add 5g of borax, 5g of stearic acid, 48g of citric acid-epoxidized soybean oil oligomer solution and 8g of Tween 80, stir and mix evenly, stir for 2h at 60℃ and 600r / min, seal and store at 25℃ for 26h, then transfer to a mixer and heat and plasticize at 158℃. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain phenolic plastic modified from PCB circuit board scrap.

[0036] Comparative Example 1: Based on Example 3, the citric acid-epoxidized soybean oil oligomer solution in step S4 was omitted.

[0037] Comparative Example 2: Based on Example 3, the spiky thermally expandable microspheres in step S4 were removed.

[0038] Comparative Example 3: Based on Example 3, the scraps of the PCB circuit board in step S4 are discarded.

[0039] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the results are shown in Table 1: Table 1 Performance Test Table of Phenolic Plastics Modified from PCB Scrap

[0040] As shown in Table 1, in Comparative Example 1, the material's bending strength and compressive strength decreased significantly after losing the flexible toughening phase, and its brittleness increased significantly. Its impact and bending resistance were extremely poor, and it was prone to brittle fracture under stress, failing to meet the mechanical requirements for product molding and service. This completely failed to address the industry pain point of high brittleness in traditional phenolic plastics. While this oligomer can alleviate the internal stress during phenolic resin curing, its removal increases the material's dimensional change rate, leading to internal stress concentration during curing and service, causing molding defects such as warping and cracking, and compromising product dimensional accuracy. This oligomer can significantly improve the melt flowability of the phenolic system and optimize the mixing and extrusion plasticizing effects. However, its removal results in high melt viscosity and difficulty in plasticizing, making it prone to melt fracture, surface pitting, and broken strips during extrusion, thus making it unsuitable for large-scale continuous production.

[0041] In Comparative Example 2, the silicon-based spiky structure on the surface of the microspheres can catalyze the formation of a dense, ceramicized oxygen-barrier carbon layer at high temperatures. Simultaneously, it forms a nitrogen-phosphorus-silicon synergistic flame-retardant system with the nitrogen and phosphorus components within the system. Removing this structure results in a decrease in the limiting oxygen index of the material, preventing the formation of an effective oxygen-barrier carbon layer at high temperatures. This leads to a significant increase in combustion smoke density and the release of toxic and harmful gases, completely failing to meet the stringent requirements for high flame retardancy, low smoke, and low toxicity in building materials, automotive interiors, and other fields. The microspheres, on the one hand, strengthen the matrix rigidity through their spiky rigid framework, and on the other hand, assist in foaming to form a uniform closed-cell structure to passively inhibit crack propagation. Removing this structure further reduces the material's compressive strength and flexural strength, resulting in severely insufficient matrix rigidity. Under stress, the material is prone to plastic deformation, and the lack of a closed-cell structure to buffer stress further exacerbates its brittleness.

[0042] In Comparative Example 3, the inherent short-cut glass fibers within the PCB scrap are the core inorganic rigid reinforcing phase, significantly improving the material's flexural and compressive strength and creep resistance. Removing these fibers reduces the material's flexural and compressive strength, significantly decreasing matrix rigidity and deformation resistance. This makes it unable to withstand long-term loads, leading to creep deformation and breakage, compromising the product's load-bearing capacity and structural stability. The short-cut glass fibers effectively limit the curing shrinkage and thermal expansion of the phenolic matrix, improving dimensional stability. Removing them increases the material's dimensional change rate and significantly increases molding shrinkage, making the product prone to dimensional deviations and warping. This fails to meet the dimensional accuracy requirements of precision products, negates the environmental value of electronic waste resource recovery, and significantly increases the raw material cost of replacing the reinforcing filler, resulting in a significant decrease in the product's market competitiveness.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing phenolic plastics based on PCB circuit board scraps, characterized in that, Includes the following steps: Step 1: Citric acid and epoxidized soybean oil undergo a condensation reaction involving ring-opening of epoxy groups and esterification of carboxyl groups to obtain a citric acid-epoxidized soybean oil oligomer solution. Step 2: Using hexadecyltrimethylammonium bromide as a template and urea as an auxiliary agent, silica is grown in situ on the surface of thermally expandable microspheres through a hydrolysis-condensation reaction of tetraethyl orthosilicate, thus constructing a spiky micromorphology and obtaining spiky thermally expandable microspheres. Step 3: Phenolic resin prepolymer is synthesized by phenol-formaldehyde condensation reaction. Spiky thermally expandable microspheres are introduced for blending modification to obtain modified phenolic resin prepolymer. Step 4: Using modified phenolic resin prepolymer as the main body, combined with PCB circuit board scraps as inorganic / organic solid waste filler and reinforcing phase, and citric acid-epoxidized soybean oil oligomer solution interface toughening, phenolic plastic based on PCB circuit board scrap modification is obtained.

2. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 1, characterized in that, The specific preparation steps of the citric acid-epoxidized soybean oil oligomer solution are as follows: Citric acid and deionized water are added to a reaction vessel and stirred for 12-15 minutes at 20-25℃ and 500-600 r / min. Then, epoxidized soybean oil is added, and the mixture is heated to 95-100℃ and reacted under nitrogen protection in a sealed environment for 1-2 hours. Glycerol is then added as a solvent, and the mixture is stirred for another 11 minutes to obtain a citric acid-epoxidized soybean oil oligomer solution.

3. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 2, characterized in that, The ratio of citric acid, deionized water, epoxidized soybean oil, and glycerin is 80-90g: 125-130mL: 140-150g: 42-45g.

4. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 1, characterized in that, The specific preparation steps for the spiky, thermally expandable microspheres are as follows: Hexadecyltrimethylammonium bromide, urea, thermally expandable microspheres, and deionized water were added to a reaction vessel and stirred for 30-40 minutes at 20-25°C and 500-600 r / min. Then, isopropanol and tetraethyl orthosilicate were added, and stirring was continued for another 30-40 minutes. The mixture was then heated to 60-70°C and reacted for 16-18 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and dried under vacuum at 60-70°C for 1-2 hours to obtain spiky thermally expandable microspheres.

5. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 4, characterized in that, The ratio of hexadecyltrimethylammonium bromide, urea, thermally expandable microspheres, deionized water, isopropanol, and tetraethyl orthosilicate is 120-130g: 120-140g: 18-20g: 800-900mL: 160-180mL: 40-60mL.

6. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 1, characterized in that, The specific preparation steps of the modified phenolic resin prepolymer are as follows: A 30-32% (w / w) formaldehyde solution, ammonium dihydrogen phosphate, phenol, spiky thermally expandable microspheres, and deionized water A are added to a reaction vessel and stirred at 50-55℃ and 500-600 r / min for 1-2 h. Then, a 1-3% (w / w) sodium hydroxide solution is added, and the reaction continues for 1-2 h. The mixture is then heated at 95-100℃ for 1-2 h. The product is cooled to 60-80℃, and the pH is adjusted to neutral with a 1-2 mol / L hydrochloric acid solution. The product is then dehydrated by vacuum distillation at a vacuum degree of 0.092-0.095 MPa. The product is then placed in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B and stirred at 3000-4000 r / min for 20-30 min. The mixture is then transferred to a mold and polycondensed at 60-70℃ to form a modified phenolic resin prepolymer.

7. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 6, characterized in that, The ratio of formaldehyde solution, ammonium dihydrogen phosphate, phenol, spiky thermally expandable microspheres, deionized water A, sodium hydroxide solution, Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B is 700-900 mL: 120-122 g: 800-900 g: 15-20 g: 5000-6000 mL: 100-120 mL: 10-12 mL: 140-180 mL: 40-50 mL: 100-110 mL.

8. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 1, characterized in that, The specific preparation steps of the phenolic plastic based on PCB circuit board scrap are as follows: PCB circuit board scraps, starch, glycerol, modified phenolic resin prepolymer, and deionized water are added to a reactor and stirred for 35 minutes at 60-70℃ and 500-600 rpm. Then, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 are added and stirred until homogeneous. The mixture is stirred for 1-2 hours at 50-60℃ and 500-600 rpm, sealed, and stored at 20-25℃ for 24-26 hours. The mixture is then transferred to a mixer and heated and plasticized at 155-158℃. The plasticized material is extruded using a twin-screw extruder and then pelletized using a pelletizer to obtain phenolic plastic modified from PCB circuit board scraps.

9. The method for preparing phenolic plastic based on PCB circuit board scrap modification according to claim 8, characterized in that, The ratio of the following ingredients to be used is 20-30g: 35-40g: 2-4g: 70-80g: 200-220mL: 3-5g: 3-5g: 45-48g: 6-8g.

10. A phenolic plastic modified from PCB circuit board scraps, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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