Polypropylene polystyrene composite board and preparation method thereof

Abstract

The invention relates to the technical field of composite boards, in particular to a polypropylene polystyrene composite board and a preparation method thereof, and the polypropylene polystyrene composite board comprises the following raw materials: polypropylene, polystyrene, borate-silane copolymer, wollastonite, calcium stearate modified hydrotalcite, chlorinated polyethylene and tetrakis [beta-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester. According to the borate-silane copolymer, through physical entanglement of a borate group and a PP chain and diffusion compatibility of a silane group and PS, the interface bonding force is remarkably improved, and microcracks caused by phase separation are effectively inhibited. Long-chain alkyl of the calcium stearate covers the surface of the hydrotalcite, so that the hydrophilicity of the hydrotalcite is reduced, the compatibility of the hydrotalcite and non-polar PP / PS is improved, and agglomeration is reduced; the modified hydrotalcite is uniformly dispersed in a matrix, the lamellar structure of the hydrotalcite is used as a physical blocking agent to inhibit PP / PS phase separation micro-area expansion, and the bonding strength is improved through interface mechanical interlocking.

Description

Technical Field

[0001] This invention relates to the field of composite board technology, and more specifically, to a polypropylene-polystyrene composite board and its preparation method. Background Technology

[0002] Polypropylene (PP) has advantages such as light weight, high mechanical strength, good heat resistance, and good chemical stability. It has a low density and is lightweight for the same volume, making it easy to transport and install. In terms of mechanical properties, it has high tensile strength and flexural strength, and can withstand certain external forces without easily deforming. Polystyrene (PS) is known for its good transparency, electrical insulation and easy processing and molding, and is widely used, especially in electronic and electrical products.

[0003] Since both PP and PS are non-polar materials with significant differences in molecular structure, direct blending can easily lead to phase separation, reducing interfacial bonding and mechanical properties. Composite boards are prone to delamination and cracking. Therefore, we propose a polypropylene-polystyrene composite board and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a polypropylene-polystyrene composite board and its preparation method, in order to solve the problems mentioned in the background art, which are that since PP and PS are both non-polar materials with large differences in molecular structure, direct blending can easily lead to phase separation, reduce interfacial bonding and mechanical properties, and cause delamination and cracking of the composite board.

[0005] To achieve the above objectives, the present invention provides a polypropylene-polystyrene composite board comprising the following raw materials: polypropylene, polystyrene, borate-silane copolymer, wollastonite, calcium stearate modified hydrotalcite, chlorinated polyethylene, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Boronate-silane copolymers are prepared by copolymerization of tris(trimethylsilyl) borate and vinyltrimethoxysilane. Calcium stearate modified hydrotalcite is prepared by surface adsorption modification of hydrotalcite with calcium stearate.

[0006] Preferably, the composition comprises 55-75 parts by weight of polypropylene, 25-40 parts by weight of polystyrene, 3-8 parts by weight of borate ester-silane copolymer, 10-25 parts by weight of wollastonite, 5-12 parts by weight of calcium stearate modified hydrotalcite, 2-7 parts by weight of chlorinated polyethylene, and 0.3-1 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0007] Preferably, the borate ester-silane copolymer is prepared by the following method: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane in a molar ratio and dissolved in toluene to obtain a mixture. Under nitrogen protection, p-toluenesulfonic acid was added to the mixture, the temperature was raised to 70-90℃, and the mixture was stirred at 400-500 rpm for 4-8 hours to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 40-50℃ and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed 3-4 times with acetone and dried under vacuum at 60℃ to constant weight to obtain the borate ester-silane copolymer.

[0008] During melt blending, the copolymer backbone migrates to the two-phase interface and forms a physical cross-linked network through the physical entanglement of borate ester groups with PP chains and the diffusion compatibility of silane groups with PS chains, thereby enhancing the interfacial bonding force.

[0009] Preferably, the molar ratio of the dehydrated tri(trimethylsilyl) borate to the purified vinyltrimethoxysilane is 1:1-3.

[0010] Preferably, the amount of p-toluenesulfonic acid added is 0.5-1.5% of the mass of the mixture.

[0011] Preferably, the preparation method of the calcium stearate modified hydrotalcite is as follows: Activated hydrotalcite was added to a calcium stearate solution and mechanically stirred at 300-400 rpm for 1.5-2 hours in a water bath at 70-80℃. The pH of the system was maintained at 8-9 with 1-2 mol / L ammonia. After the reaction was completed, the mixture was washed 2-3 times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 hours to obtain calcium stearate modified hydrotalcite.

[0012] The long-chain alkyl groups of calcium stearate cover the surface of hydrotalcite, reducing its hydrophilicity and improving its compatibility with non-polar PP / PS, thus reducing agglomeration. After modification, hydrotalcite is uniformly dispersed in the matrix, and its layered structure acts as a physical barrier, inhibiting the expansion of PP / PS phase separation micro-regions and improving the bonding strength through interfacial mechanical interlocking.

[0013] Preferably, the calcium stearate solution has a mass concentration of 5-10%. The mass ratio of activated hydrotalcite to calcium stearate solution is 1:0.1-0.3.

[0014] On the other hand, the present invention provides a method for preparing a polypropylene-polystyrene composite board, for use in any one of the polypropylene-polystyrene composite boards described above, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 55-75 parts polypropylene, 25-40 parts polystyrene, 3-8 parts borate ester-silane copolymer, 10-25 parts wollastonite, 5-12 parts calcium stearate modified hydrotalcite, 2-7 parts chlorinated polyethylene and 0.3-1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600-800 rpm for 5-10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 90-110℃ and continue mixing for 10-15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 200-300 rpm, with temperature control in stages; the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a pellet length of 3-5 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 160-180℃ for 5-10 minutes, and perform staged pressurization; under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0015] Preferably, in S1.3, the specific zone temperatures for segmented temperature control are: Zone 1 160℃, Zone 2 180℃, Zone 3 200℃, and Zone 4 190℃.

[0016] Preferably, in step S1.4, the staged pressurization involves initial pressurization at 5 MPa for 2 minutes, followed by final pressurization at 15 MPa for 8 minutes.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this invention, the borate ester-silane copolymer significantly improves the interfacial bonding force and effectively suppresses microcracks caused by phase separation through the physical entanglement of borate ester groups with PP chains and the diffusion compatibility of silane groups with PS.

[0018] 2. In this invention, the long-chain alkyl group of calcium stearate covers the surface of hydrotalcite, reducing its hydrophilicity, improving its compatibility with non-polar PP / PS, and reducing agglomeration; after modification, hydrotalcite is uniformly dispersed in the matrix, and its lamellar structure acts as a physical barrier to inhibit the expansion of PP / PS phase separation micro-regions, and improves the bonding strength through interfacial mechanical interlocking. Detailed Implementation

[0019] 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.

[0020] This invention provides a polypropylene-polystyrene composite board, comprising the following raw materials: polypropylene, polystyrene, borate-silane copolymer, wollastonite, calcium stearate modified hydrotalcite, chlorinated polyethylene, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Boronate-silane copolymers are prepared by copolymerization of tris(trimethylsilyl) borate and vinyltrimethoxysilane. Calcium stearate modified hydrotalcite is prepared by surface adsorption modification of hydrotalcite with calcium stearate.

[0021] Dehydrated tri(trimethylsilyl) borate: Crude tri(trimethylsilyl) borate is placed in a nitrogen-protected reactor, zeolite adsorbent is added, and dehydrated to a moisture content of ≤3000ppm to avoid hydrolysis side reactions.

[0022] Purified vinyltrimethoxysilane: Polymer inhibitors (such as hydroquinone) and low-boiling-point impurities in vinyltrimethoxysilane are removed by vacuum distillation (60-80℃ / 10kPa), and the collected fraction has a purity of ≥99%.

[0023] Activated hydrotalcite: The hydrotalcite was placed in a muffle furnace and heated to 480°C at a rate of 5°C / min, and calcined for 5 hours; after grinding, it was passed through a 200-mesh sieve to obtain activated hydrotalcite.

[0024] Dry polypropylene and polystyrene: Dry polypropylene and polystyrene separately in an oven at 80℃ for 4 hours, and the moisture content must be ≤0.05%.

[0025] Polypropylene CAS: 9003-07-0; Vinyltrimethoxysilane CAS: 2768-02-7; both are from Hubei Shishun Biotechnology Co., Ltd. Polystyrene CAS: 9003-53-6; sourced from Shanghai Jiachen Chemical Co., Ltd.; Chlorinated polyethylene CAS: 63231-66-3; purchased from Zhengzhou Alpha Chemical Co., Ltd. Tris(trimethylsilyl)borate CAS: 4325-85-3; sourced from Suzhou Junye Biomedical Technology Co., Ltd. Calcium stearate CAS: 1592-23-0; Hydrotalcite CAS: 11097-59-9; both are from Shanghai Yuanye Biotechnology Co., Ltd.

[0026] Example 1: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 55 parts polypropylene, 25 parts polystyrene, 3 parts borate ester-silane copolymer, 10 parts wollastonite, 5 parts calcium stearate modified hydrotalcite, 2 parts chlorinated polyethylene and 0.3 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0027] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane in a molar ratio of 1:1 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0028] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.1), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a 60℃ vacuum oven for 12 h to obtain calcium stearate modified hydrotalcite.

[0029] Example 2: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 60 parts by weight of polypropylene, 32 parts by weight of polystyrene, 6 parts by weight of borate ester-silane copolymer, 17 parts by weight of wollastonite, 8 parts by weight of calcium stearate modified hydrotalcite, 5 parts by weight of chlorinated polyethylene and 0.6 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0030] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:2 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0031] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.2), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0032] Example 3: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 75 parts polypropylene, 40 parts polystyrene, 8 parts borate ester-silane copolymer, 25 parts wollastonite, 12 parts calcium stearate modified hydrotalcite, 7 parts chlorinated polyethylene and 1 part pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0033] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:3 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0034] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.3), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0035] Example 4: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 60 parts by weight of polypropylene, 32 parts by weight of polystyrene, 11 parts by weight of borate ester-silane copolymer, 17 parts by weight of wollastonite, 8 parts by weight of calcium stearate modified hydrotalcite, 5 parts by weight of chlorinated polyethylene and 0.6 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0036] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:2 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0037] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.2), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0038] Example 5: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 60 parts by weight of polypropylene, 32 parts by weight of polystyrene, 10 parts by weight of borate ester-silane copolymer, 17 parts by weight of wollastonite, 8 parts by weight of calcium stearate modified hydrotalcite, 5 parts by weight of chlorinated polyethylene and 0.6 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0039] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:2 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0040] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.2), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0041] Example 6: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 60 parts by weight of polypropylene, 32 parts by weight of polystyrene, 6 parts by weight of borate ester-silane copolymer, 17 parts by weight of wollastonite, 15 parts by weight of calcium stearate modified hydrotalcite, 5 parts by weight of chlorinated polyethylene and 0.6 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0042] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:2 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0043] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.2), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0044] Example 7: A method for preparing a polypropylene-polystyrene composite board, comprising the following steps: S1.1 Weigh the following raw materials in parts by weight: 60 parts by weight of polypropylene, 32 parts by weight of polystyrene, 6 parts by weight of borate ester-silane copolymer, 17 parts by weight of wollastonite, 14 parts by weight of calcium stearate modified hydrotalcite, 5 parts by weight of chlorinated polyethylene and 0.6 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600 rpm for 10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 100℃ and continue mixing for 15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 300 rpm, with temperature control in stages (zone 1 160℃, zone 2 180℃, zone 3 200℃ and zone 4 190℃); the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a granule length of 4 mm; S1.4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 170℃ for 5 minutes, and perform staged pressurization (initial press at 5MPa pressure, hold for 2 minutes; final press at 15MPa pressure, hold for 8 minutes); under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

[0045] Furthermore, the preparation method of the borate ester-silane copolymer is as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane at a molar ratio of 1:2 and dissolved in toluene to obtain a mixture. Under nitrogen protection, 1.0% by mass of p-toluenesulfonic acid was added to the mixture, the temperature was raised to 80°C, and the mixture was stirred at 400 rpm for 6 h to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 45°C and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed four times with acetone and dried under vacuum at 60°C to constant weight to obtain the borate ester-silane copolymer.

[0046] The preparation method of calcium stearate modified hydrotalcite is as follows: The activated hydrotalcite was added to a 5% calcium stearate solution (mass ratio 1:0.2), and mechanically stirred at 300 rpm for 2 h in a 70℃ water bath. The pH of the system was maintained at 8 with 1 mol / L ammonia. After the reaction was completed, the hydrotalcite was washed three times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 h to obtain calcium stearate modified hydrotalcite.

[0047] Comparative Example 1: The method of Example 2 was used in the preparation of polypropylene polystyrene composite board without the addition of borate ester-silane copolymer.

[0048] Comparative Example 2: Using the method of Example 2, in the preparation method of polypropylene polystyrene composite board, calcium stearate-modified hydrotalcite was not used, and hydrotalcite was used directly.

[0049] Comparative Example 3: The method of Example 2 was used in the preparation of polypropylene polystyrene composite board without the addition of wollastonite.

[0050] This invention involves adding borate ester-silane copolymer and calcium stearate-modified hydrotalcite during the preparation of polypropylene-polystyrene composite boards. The performance indicators and testing standards for the prepared polypropylene-polystyrene composite boards are as follows: The surface of the polypropylene-polystyrene composite board is polished and solvent-cleaned to remove oil and oxide layers; a universal testing machine (range ≤30kN) is used with a loading rate of 1-2mm / min; tensile clamps are installed to ensure that the specimen axis is aligned with the loading direction to avoid off-center loading errors; the specimen is symmetrically clamped and the equipment is started to load it at a uniform speed until the specimen breaks; the load-displacement curve is recorded in real time, and the tensile shear strength of the specimen is calculated according to the tensile shear strength formula.

[0051] Using a universal testing machine with a three-point bending fixture, the loading head radius is 5mm and the support roller radius is 2mm. The specimen is placed in the center on the support roller, and the loading head is applied vertically until the specimen breaks or the deflection reaches 1.5 times the specimen thickness. The load-deflection curve is recorded, the maximum load is read, and the bending strength is calculated.

[0052] The polypropylene-polystyrene composite boards prepared in Examples 1-7 and Comparative Examples 1-3 were tested according to the above standards, and the data obtained are shown in Table 1: Table 1 Performance data of polypropylene-polystyrene composite boards in Examples 1-7 and Comparative Examples 1-3 As can be seen from Examples 1-3, changes in the raw material composition of polypropylene / polystyrene (PP / PS) composite boards enhance the tensile shear strength and flexural strength of the composite material. The introduction of borate ester-silane copolymers forms a denser physical cross-linking network at the PP / PS interface: borate ester groups form dynamic hydrogen bonds with tertiary hydrocarbons in the PP molecular chain, enhancing the anchoring effect; while silane groups entwine with the PS chain through hydrophobic interactions, thereby improving the compatibility between the two phases; calcium stearate-modified hydrotalcite, with its hydrophobic long chain coating, uniformly disperses the lamellar structure, forming a microskeleton that penetrates both the PP and PS phases, and hinders the slippage of molecular chains through mechanical interlocking effects, while suppressing crystallization shrinkage stress and reducing the generation of internal defects; wollastonite needle-like crystals penetrate the reinforcing phase interface, forming a complementary structure with the compatibilizer network, further enhancing the interfacial bonding force of the material; chlorinated polyethylene buffers local stress through toughening, protecting the integrity of the rigid skeleton; and antioxidants maintain the stability of the molecular structure under high-temperature processing conditions, preventing thermal degradation.

[0053] A comparison of Examples 2 and 4-5 shows that: when other components of the polypropylene-polystyrene composite board remain unchanged, and the weight percentage of the borate-silane copolymer continuously increases, the tensile shear strength and flexural strength of the polypropylene-polystyrene composite board continuously decrease; uniform dispersion of the compatibilizer can effectively reduce the phase separation size of PP / PS, thereby improving the interfacial shear strength; an appropriate amount of compatibilizer can also promote the formation of finer β-crystalline spherulites in PP, reducing microcracks caused by crystallization shrinkage, and thus improving flexural strength; however, excessive compatibilizer self-polymerizes at the interface to form micelles, becoming stress concentration points and inducing microcrack propagation; in addition, the condensation of silane hydrolysis products to form hard siloxane particles leads to local brittle fracture, causing a sharp drop in tensile shear strength; high compatibilizer content significantly increases melt viscosity, hindering the dispersion of inorganic fillers (such as wollastonite), and causing uneven stress distribution.

[0054] Furthermore, as can be seen from Examples 2 and 6-7: when other components of the polypropylene-polystyrene composite board remain unchanged, and the weight of calcium stearate-modified hydrotalcite continuously increases, the tensile shear strength and flexural strength of the polypropylene-polystyrene composite board continuously decrease; the stearic acid groups on the surface of calcium stearate-modified hydrotalcite form physical adsorption with the PP / PS molecular chains, effectively improving the interfacial bonding force between the inorganic filler and the resin matrix, thereby reducing stress concentration; the layered structure of hydrotalcite forms a microskeleton in the matrix, hindering molecular chain slippage and improving the rigidity of the material; however, when the hydrotalcite content is too high, due to insufficient surface stearic acid coating, agglomeration easily occurs, forming micron-sized agglomerates, which become stress concentration points.

[0055] Based on the above test experiments, Example 3 is considered the optimal example. A comparison of Example 2 and Comparative Example 1 shows that: without the addition of borate ester-silane copolymer, the tensile shear strength and flexural strength of polypropylene-polystyrene composite board are significantly reduced; PP and PS are thermodynamically incompatible systems, and without the addition of borate ester-silane copolymer, the interfacial bonding force between the two phases is weak, making phase separation easy and forming micropores or cracks; under stress, the interface preferentially fractures rather than being uniformly dispersed into the whole material; if the compatibilizer is missing, the interface relies only on physical entanglement or weak van der Waals forces, and is prone to debonding under shear load.

[0056] A comparison of Example 2 and Comparative Example 2 shows that: without calcium stearate modification, the tensile shear strength and flexural strength of the polypropylene / polystyrene composite board are significantly reduced when hydrotalcite is used directly; the surface of unmodified hydrotalcite is rich in polar hydroxyl groups, resulting in poor compatibility with the non-polar PP / PS matrix and weak interfacial bonding; by introducing calcium stearate for modification, its hydrophobic long chains can cover the surface of hydrotalcite, reducing polarity and thus improving compatibility with the polymer; unmodified hydrotalcite is prone to agglomeration due to its high surface energy, forming micron-sized particle aggregates, which become stress concentration points; after modification, its dispersibility is significantly improved, reducing defects; in addition, unmodified hydrotalcite hinders the movement of PP molecular chains, delays the crystallization process, and leads to a wider grain size distribution and a decrease in crystallinity, thereby weakening the rigidity of the matrix.

[0057] A comparison of Example 2 and Comparative Example 3 shows that: without the addition of wollastonite, the tensile shear strength of the polypropylene-polystyrene composite board is significantly reduced; due to its unique needle-like structure, wollastonite can penetrate the interface between the PP and PS phases, forming physical anchoring points, thereby enhancing stress transfer efficiency; without the addition, there is weak compatibility (thermodynamic incompatibility) between PP and PS, leading to easy interface peeling and exacerbating stress concentration; as a rigid inorganic filler, wollastonite can effectively share external loads, and without it, the composite material mainly relies on the resin matrix, resulting in a significant decrease in its resistance to deformation.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polypropylene-polystyrene composite board, characterized in that, The raw materials include: polypropylene, polystyrene, borate ester-silane copolymer, wollastonite, calcium stearate modified hydrotalcite, chlorinated polyethylene, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; Boronate-silane copolymers are prepared by copolymerization of tris(trimethylsilyl) borate and vinyltrimethoxysilane. Calcium stearate modified hydrotalcite is prepared by surface adsorption modification of hydrotalcite with calcium stearate.

2. The polypropylene-polystyrene composite board according to claim 1, characterized in that, The composition includes 55-75 parts by weight of polypropylene, 25-40 parts by weight of polystyrene, 3-8 parts by weight of borate ester-silane copolymer, 10-25 parts by weight of wollastonite, 5-12 parts by weight of calcium stearate modified hydrotalcite, 2-7 parts by weight of chlorinated polyethylene, and 0.3-1 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

3. The polypropylene-polystyrene composite board according to claim 2, characterized in that, The borate ester-silane copolymer is prepared as follows: Dehydrated tri(trimethylsilyl) borate was mixed with purified vinyltrimethoxysilane in a molar ratio and dissolved in toluene to obtain a mixture. Under nitrogen protection, p-toluenesulfonic acid was added to the mixture, the temperature was raised to 70-90℃, and the mixture was stirred at 400-500 rpm for 4-8 hours to obtain a reaction mixture. Subsequently, 0.1% by mass of triethylamine was added to the reaction mixture, and the mixture was distilled under reduced pressure at 40-50℃ and 5 kPa to remove unreacted monomers and solvents. The copolymer was precipitated with methanol. The precipitate was washed 3-4 times with acetone and dried under vacuum at 60℃ to constant weight to obtain the borate ester-silane copolymer.

4. The polypropylene-polystyrene composite board according to claim 3, characterized in that, The molar ratio of the dehydrated tri(trimethylsilyl) borate to the purified vinyltrimethoxysilane is 1:1-3.

5. The polypropylene-polystyrene composite board according to claim 3, characterized in that, The amount of p-toluenesulfonic acid added is 0.5-1.5% of the mass of the mixture.

6. The polypropylene-polystyrene composite board according to claim 2, characterized in that, The preparation method of the calcium stearate modified hydrotalcite is as follows: Activated hydrotalcite was added to a calcium stearate solution and mechanically stirred at 300-400 rpm for 1.5-2 hours in a water bath at 70-80℃. The pH of the system was maintained at 8-9 with 1-2 mol / L ammonia. After the reaction was completed, the mixture was washed 2-3 times with anhydrous ethanol and dried in a vacuum oven at 60℃ for 12 hours to obtain calcium stearate modified hydrotalcite.

7. The polypropylene-polystyrene composite board according to claim 6, characterized in that, The mass concentration of the calcium stearate solution is 5-10%; The mass ratio of activated hydrotalcite to calcium stearate solution is 1:0.1-0.

3.

8. A method for preparing a polypropylene-polystyrene composite board, used to prepare the polypropylene-polystyrene composite board as described in any one of claims 1-7, characterized in that, The preparation method of the polypropylene-polystyrene composite board is as follows: S1.1 Weigh the following raw materials in parts by weight: 55-75 parts polypropylene, 25-40 parts polystyrene, 3-8 parts borate ester-silane copolymer, 10-25 parts wollastonite, 5-12 parts calcium stearate modified hydrotalcite, 2-7 parts chlorinated polyethylene and 0.3-1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; S1.2 Add dried polypropylene, polystyrene, and chlorinated polyethylene to a high-speed mixer, and simultaneously add pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and mix at 600-800 rpm for 5-10 min; then add borate ester-silane copolymer, wollastonite, and calcium stearate modified hydrotalcite, heat to 90-110℃ and continue mixing for 10-15 min to obtain the mixture. S1.3 Transfer the mixture to a twin-screw extruder and extrude it at a speed of 200-300 rpm, with temperature control in stages; the extruded strips are cooled in a 25℃ water cooling tank, granulated and dried, with a pellet length of 3-5 mm; S1.

4. Spread the granules evenly into the mold, place it in a flat hot press, preheat at 160-180℃ for 5-10 minutes, and perform staged pressurization; under pressure, pass 20℃ cooling water to below 60℃ to demold, and obtain polypropylene polystyrene composite board.

9. The method for preparing polypropylene-polystyrene composite board according to claim 8, characterized in that, In S1.3, the specific zone temperatures for segmented temperature control are: Zone 1 160℃, Zone 2 180℃, Zone 3 200℃ and Zone 4 190℃.

10. The method for preparing the polypropylene-polystyrene composite board according to claim 8, characterized in that, In S1.4, the staged pressurization involves initial pressurization at 5 MPa and holding for 2 minutes; and final pressurization at 15 MPa and holding for 8 minutes.

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