Flame-retardant PVC sheet and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a flame-retardant PVC (polyvinyl chloride) sheet and a preparation method thereof.Carboxymethyl chitosan is adsorbed on the surface and in pores of sepiolite through the adsorption effect of sepiolite powder, the carboxymethyl chitosan contains a large number of hydroxyl groups and amino groups, and the hydroxyl groups and the amino groups can chelate zinc ions, so that the flame-retardant PVC sheet is prepared. Then calcining is performed in a nitrogen atmosphere, carboxymethyl chitosan is converted into a relatively compact carbon layer, zinc salt is converted into zinc oxide, and the flame retardant property of sepiolite is improved through the generated carbon layer and zinc oxide composite layer; then through addition reaction between double bonds, 1, 4-butylene glycol and diethyl vinylphosphonate are grafted on the surface of the sepiolite composite material, so that the mechanical property and flame retardant property of the PVC sheet material are further improved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a flame-retardant PVC sheet and a preparation method thereof. Background Art

[0002] PVC (polyvinyl chloride) sheet is a thermoplastic material widely used in the fields of construction, decoration, packaging, etc. It has the advantages of low cost, corrosion resistance, and easy processing. It can be made into sheets of different thicknesses and properties through extrusion, calendering and other processes to meet diverse market needs. However, traditional PVC sheets have certain limitations in flame retardancy and mechanical properties, which restricts its application in some high-end or special environments.

[0003] At present, the flame retardancy of ordinary PVC sheets usually relies on the addition of halogen flame retardants, but this may cause environmental pollution and toxicity problems; and halogen-free flame retardant solutions often lead to a decrease in mechanical properties, such as reduced impact strength and tensile strength. In addition, the brittleness and insufficient heat resistance of PVC itself also affect the long-term stability of the material.

[0004] Chinese patent document CN202310240849.5 discloses a high-strength PVC composite material, a preparation method and application thereof. By using maleic anhydride to graft PE to modify the PVC resin, the interfacial compatibility and adhesion between the PVC resin and the modified calcium carbonate whiskers and polyester are increased, thereby improving the mechanical strength, toughness and impact resistance of the composite material. At the same time, the modified PVC resin and the polyester form intermolecular crosslinks through the action of a peroxide initiator, further enhancing the mechanical properties of the composite material; however, the flame retardant properties of the prepared PVC composite material still need to be further improved.

[0005] Therefore, developing PVC sheets with both excellent flame retardancy and mechanical properties has become a technical problem that the industry urgently needs to solve. Summary of the invention

[0006] In view of the deficiencies in the prior art, an object of the present invention is to provide a flame retardant PVC sheet and a preparation method thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A flame-retardant PVC sheet material comprises the following raw materials, measured by weight: 80-100 parts of PVC resin, 10-15 parts of composite modified sepiolite, 5-10 parts of ethylene vinyl acetate grafted maleic anhydride, 2-5 parts of epoxy soybean oil, 3-5 parts of calcium zinc heat stabilizer, 2-4 parts of lubricant and 1-3 parts of antioxidant.

[0008] In the technical solution disclosed by the present invention, the PVC resin can be selected from 80 parts, 82 parts, 84 parts, 85 parts, 88 parts, 90 parts, 92 parts, 95 parts, 98 parts, 100 parts, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0009] In the technical solution disclosed by the present invention, the compound modified sepiolite can be selected from 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0010] Specifically, the present invention also discloses a preparation method of the compound modified sepiolite, and the specific steps are as follows: S1. Disperse sepiolite powder in deionized water, then add carboxymethyl chitosan thereto, stir evenly, then add soluble zinc salt, continue to stir evenly, filter, dry, calcine in a nitrogen atmosphere, and grind after cooling to obtain a sepiolite composite material; S2. Disperse the sepiolite composite material in an ethanol aqueous solution, then add vinyltriethoxysilane thereto, stir, filter, wash, and dry to obtain a double bond grafted sepiolite composite material; S3. Disperse the double bond grafted sepiolite composite material in an organic solvent, then add 1,4-butanediol and diethyl vinylphosphonate thereto, stir evenly, introduce nitrogen to exhaust air, add benzoyl peroxide, heat and stir for reaction, after the reaction is completed, filter, wash, and dry to obtain the compound modified sepiolite.

[0011] In the technical solution disclosed by the present invention, in step S1, the mass ratio of sepiolite powder, carboxymethyl chitosan and soluble zinc salt is 5-10:4-8:2-4.

[0012] Specifically, the soluble zinc salt is selected from zinc chloride, zinc nitrate or zinc sulfate.

[0013] In the technical solution disclosed by the present invention, in step S1, the calcination temperature is 400-600 °C, for example, it can be selected from 400 °C, 420 °C, 450 °C, 480 °C, 500 °C, 520 °C, 550 °C, 580 °C, 600 °C; the calcination time is 1-2 h, for example, it can be selected from 1 h, 1.5 h, 2 h; but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0014] In step S1, through the adsorption of sepiolite powder, carboxymethyl chitosan is adsorbed on the surface and pores of sepiolite. Carboxymethyl chitosan contains a large number of hydroxyl and amino groups, and the hydroxyl and amino groups can chelate zinc ions. Then, it is calcined in a nitrogen atmosphere. Carboxymethyl chitosan is converted into a relatively dense carbon layer, and zinc salt is converted into zinc oxide. The formed carbon layer and zinc oxide composite layer improve the flame retardancy of sepiolite.

[0015] In the technical solution disclosed by the present invention, in step S2, the mass ratio of the sepiolite composite material to vinyltriethoxysilane is 8 - 12:1 - 3. For example, 8:1, 8:2, 8:3, 10:1, 10:2, 10:3, 12:1, 12:2, 12:3 can be selected, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0016] In step S2, by using vinyltriethoxysilane to treat the sepiolite composite material, carbon - carbon double bonds are introduced on the surface of the sepiolite composite material, which is beneficial to the subsequent reaction.

[0017] In the technical solution disclosed by the present invention, in step S3, the mass ratio of the double - bond grafted sepiolite composite material, 1,4 - butanediol, diethyl vinylphosphonate, and benzoyl peroxide is 8 - 12:3 - 6:3 - 6:0.5 - 1.

[0018] In the technical solution disclosed by the present invention, in step S3, the temperature of the heating and stirring reaction is 60 - 80 °C. For example, 60 °C, 62 °C, 65 °C, 68 °C, 70 °C, 72 °C, 75 °C, 78 °C, 80 °C can be selected; the time of the heating and stirring reaction is 2 - 4 h. For example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h can be selected; but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0019] In step S3, through the addition reaction between double bonds, 1,4 - butanediol and diethyl vinylphosphonate are grafted on the surface of the sepiolite composite material. Diethyl vinylphosphonate is rich in phosphorus elements, and its phosphate ester group can decompose to generate polyphosphoric acid at high temperature, which promotes the formation of a carbon layer through catalytic dehydration, forming a dense heat - insulating barrier. Acting together with the carbon layer formed by carboxymethyl chitosan and the zinc oxide composite layer, it further improves the flame retardancy of sepiolite; meanwhile, 1,4 - butanediol, as a flexible - chain cross - linker, introduces a long - chain structure on the surface of the sepiolite composite material through copolymerization reaction, increasing the compatibility with the polymer matrix. The alcohol hydroxyl group in 1,4 - butanediol undergoes chemical cross - linking with the epoxy group in epoxidized soybean oil, enhancing the interfacial bonding force and making the stress more evenly dispersed, thereby improving the mechanical properties of the PVC sheet, especially the low - temperature impact resistance.

[0020] In the technical solution disclosed by the present invention, the ethylene vinyl acetate grafted maleic anhydride can be selected as 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0021] In the technical solution disclosed by the present invention, the epoxy soybean oil can be selected as 2 parts, 3 parts, 4 parts, 5 parts, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0022] In the technical solution disclosed by the present invention, the calcium zinc heat stabilizer can be selected as 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0023] In the technical solution disclosed by the present invention, the lubricant can be selected as 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0024] Specifically, the lubricant is selected from at least one of calcium stearate, zinc stearate, barium stearate, polyethylene wax, and butyl stearate.

[0025] In the technical solution disclosed by the present invention, the antioxidant can be selected as 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0026] Specifically, the antioxidant is selected from antioxidant 168, antioxidant 1010, or antioxidant 1076.

[0027] The present invention also provides a method for preparing the above flame-retardant PVC sheet, which includes the following steps: adding PVC resin, composite modified sepiolite, ethylene vinyl acetate grafted maleic anhydride, epoxy soybean oil, calcium zinc heat stabilizer, lubricant, and antioxidant into a mixer according to parts by weight and mixing evenly to obtain a mixture, and extruding and cooling the mixture through a conical twin-screw extruder to obtain the flame-retardant PVC sheet.

[0028] In the technical solution disclosed by the present invention, the temperatures of each section of the screw of the conical twin-screw extruder are as follows: the conveying section is 180 - 220 °C, the melting section is 185 - 210 °C, the homogenizing section is 175 - 205 °C, and the head is 180 - 210 °C.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1)The flame-retardant PVC sheet provided by the present invention uses PVC resin as the base material, and compoundedly adds functional fillers such as ethylene vinyl acetate grafted maleic anhydride, epoxy soybean oil, calcium zinc heat stabilizer, lubricant, antioxidant, etc., and introduces sepiolite powder that has been subjected to multi-step modification treatment. The prepared material has excellent flame-retardant properties and good mechanical properties.

[0030] (2)Through the adsorption of sepiolite powder, the present invention adsorbs carboxymethyl chitosan on the surface and pores of sepiolite. Carboxymethyl chitosan contains a large number of hydroxyl and amino groups, and the hydroxyl and amino groups can chelate zinc ions. Then, it is calcined under a nitrogen atmosphere. Carboxymethyl chitosan is converted into a relatively dense carbon layer, and zinc salt is converted into zinc oxide. The formed carbon layer and zinc oxide composite layer improve the flame-retardant properties of sepiolite.

[0031] (3)Through the addition reaction between double bonds, 1,4-butanediol and diethyl vinylphosphonate are grafted on the surface of the sepiolite composite material. Diethyl vinylphosphonate is rich in phosphorus elements, and its phosphate ester group can decompose to generate polyphosphoric acid at high temperatures, promoting the formation of a carbon layer through catalytic dehydration, forming a dense heat insulation barrier, which acts together with the carbon layer formed by carboxymethyl chitosan and the zinc oxide composite layer to further improve the flame-retardant properties of sepiolite; at the same time, 1,4-butanediol, as a flexible chain crosslinking agent, introduces a long-chain structure on the surface of the sepiolite composite material through copolymerization reaction, increasing the compatibility with the polymer matrix. The alcohol hydroxyl group in 1,4-butanediol undergoes chemical crosslinking with the epoxy group in epoxy soybean oil, enhancing the interfacial bonding force and making the stress more evenly dispersed, thereby improving the mechanical properties of the PVC sheet, especially the low-temperature impact resistance. Specific Embodiments

[0032] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0033] It should be noted that unless otherwise specified, the chemical reagents involved in the present invention are all purchased through commercial channels.

[0034] The CAS number of the PVC resin used in the embodiments of the present invention is: 9002-86-2, and the grade is SG-5; The mesh number of sepiolite powder is 400 mesh; The grade of ethylene vinyl acetate grafted maleic anhydride is: Bynel 3810; The CAS number of epoxy soybean oil is: 8013-07-8; The calcium zinc heat stabilizer is purchased from Jinan Junteng Chemical Co., Ltd.

[0035] Example 1 A preparation method of a flame-retardant PVC sheet includes the following steps: Add 100 parts of PVC resin, 15 parts of composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 5 parts of epoxidized soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of calcium stearate and 3 parts of antioxidant 1010 into a blender and mix evenly at 110°C, and maintain for 10 minutes within this temperature range to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190°C, melting section 200°C, homogenizing section 180°C, head 190°C, and cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 4 g of carboxymethyl chitosan thereto, stir evenly, then add 2 g of zinc nitrate, continue to stir evenly, filter, dry, and calcine in a nitrogen atmosphere. The calcination temperature is 400°C and the calcination time is 2 h. After cooling, grind through a 200-mesh sieve to obtain the sepiolite composite material; S2. Disperse 8 g of the sepiolite composite material in 100 mL of 75 wt% ethanol aqueous solution, then add 1 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash, and dry to obtain the double-bond grafted sepiolite composite material; S3. Disperse 8 g of the double-bond grafted sepiolite composite material in 150 mL of the organic solvent DMF, then add 3 g of 1,4-butanediol and 3 g of diethyl vinylphosphonate thereto, stir evenly, pass nitrogen to exhaust air, add 0.5 g of benzoyl peroxide, and heat and stir at 60°C for 4 h. After the reaction is completed, filter, wash, dry, and grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0036] Example 2 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 80 parts of PVC resin, 10 parts of composite modified sepiolite, 5 parts of ethylene vinyl acetate grafted maleic anhydride, 2 parts of epoxidized soybean oil, 3 parts of calcium zinc heat stabilizer, 1 part of zinc stearate, 2 parts of polyethylene wax and 1 part of antioxidant 168 into a blender and mix evenly at 110°C, and maintain for 10 minutes within this temperature range to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190°C, melting section 200°C, homogenizing section 180°C, head 190°C, and cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 10 g of sepiolite powder in 150 mL of deionized water, then add 8 g of carboxymethyl chitosan thereto, stir evenly, subsequently add 4 g of zinc nitrate, continue to stir evenly, filter and dry, and conduct calcination under a nitrogen atmosphere. The calcination temperature is 600 °C, the calcination time is 1 h, cool and grind through a 200-mesh sieve to obtain a sepiolite composite material; S2. Disperse 12 g of the sepiolite composite material in 100 mL of a 75 wt% ethanol aqueous solution, then add 3 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash and dry to obtain a double-bond grafted sepiolite composite material; S3. Disperse 12 g of the double-bond grafted sepiolite composite material in 150 mL of an organic solvent DMF, then add 6 g of 1,4-butanediol and 6 g of diethyl vinylphosphonate thereto, stir evenly, pass nitrogen to expel air, add 1 g of benzoyl peroxide, heat and stir at 80 °C for 2 h. After the reaction is completed, filter, wash and dry, and grind through a 200-mesh sieve to obtain a composite modified sepiolite.

[0037] Example 3 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 85 parts of PVC resin, 12 parts of the composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 3 parts of epoxidized soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of polyethylene wax and 2 parts of antioxidant 168 to a mixer, mix evenly at 110 °C, and maintain at this temperature range for 10 min to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, die head 190 °C, cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 8 g of sepiolite powder in 150 mL of deionized water, then add 6 g of carboxymethyl chitosan thereto, stir evenly, subsequently add 3 g of zinc nitrate, continue to stir evenly, filter and dry, and conduct calcination under a nitrogen atmosphere. The calcination temperature is 600 °C, the calcination time is 1 h, cool and grind through a 200-mesh sieve to obtain a sepiolite composite material; S2. Disperse 10 g of the sepiolite composite material in 100 mL of a 75 wt% ethanol aqueous solution, then add 2 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash and dry to obtain a double-bond grafted sepiolite composite material; S3. Disperse 10 g of the double-bond grafted sepiolite composite in 150 mL of the organic solvent DMF, then add 4 g of 1,4-butanediol and 5 g of diethyl vinylphosphonate thereto, stir evenly, introduce nitrogen to expel air, add 0.8 g of benzoyl peroxide, and heat and stir the reaction at 70 °C for 3 h. After the reaction is completed, filter, wash, dry, grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0038] Example 4 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 90 parts of PVC resin, 14 parts of the composite modified sepiolite, 6 parts of ethylene vinyl acetate grafted maleic anhydride, 4 parts of epoxidized soybean oil, 5 parts of calcium-zinc heat stabilizer, 4 parts of zinc stearate and 2 parts of antioxidant 168 to a blender and mix evenly at 110 °C, and maintain at this temperature range for 10 min to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, die head 190 °C, and cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 8 g of carboxymethyl chitosan thereto, stir evenly, then add 4 g of zinc nitrate, continue to stir evenly, filter, dry, and calcine in a nitrogen atmosphere. The calcination temperature is 600 °C, the calcination time is 1 h, cool and grind through a 200-mesh sieve to obtain the sepiolite composite; S2. Disperse 8 g of the sepiolite composite in 100 mL of 75 wt% ethanol aqueous solution, then add 2 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash, dry to obtain the double-bond grafted sepiolite composite; S3. Disperse 8 g of the double-bond grafted sepiolite composite in 150 mL of the organic solvent DMF, then add 6 g of 1,4-butanediol and 6 g of diethyl vinylphosphonate thereto, stir evenly, introduce nitrogen to expel air, add 1 g of benzoyl peroxide, and heat and stir the reaction at 70 °C for 3 h. After the reaction is completed, filter, wash, dry, grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0039] Comparative Example 1 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 100 parts of PVC resin, 15 parts of composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 5 parts of epoxidized soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of calcium stearate and 3 parts of antioxidant 1010 into a blender, mix evenly at 110 °C, and maintain for 10 min within this temperature range to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, die head 190 °C, and then cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 2 g of zinc nitrate, continue to stir evenly, filter and dry, and calcine under a nitrogen atmosphere. The calcination temperature is 400 °C, the calcination time is 2 h, cool and grind through a 200-mesh sieve to obtain the sepiolite composite material; S2. Disperse 8 g of the sepiolite composite material in 100 mL of 75 wt% ethanol aqueous solution, then add 1 g of vinyltriethoxysilane to it, stir at room temperature for 2 h, filter, wash and dry to obtain the double-bond grafted sepiolite composite material; S3. Disperse 8 g of the double-bond grafted sepiolite composite material in 150 mL of the organic solvent DMF, then add 3 g of 1,4-butanediol and 3 g of diethyl vinylphosphonate to it, stir evenly, pass nitrogen to exhaust air, add 0.5 g of benzoyl peroxide, heat and stir at 60 °C for 4 h. After the reaction is completed, filter, wash and dry, and grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0040] Compared with Example 1, in Step S1 of Comparative Example 1, carboxymethyl chitosan was not added.

[0041] Comparative Example 2 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 100 parts of PVC resin, 15 parts of composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 5 parts of epoxidized soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of calcium stearate and 3 parts of antioxidant 1010 into a blender, mix evenly at 110 °C, and maintain for 10 min within this temperature range to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, die head 190 °C, and then cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 4 g of carboxymethyl chitosan thereto, stir evenly, then add 2 g of zinc nitrate, continue to stir evenly, filter and dry, and calcine in a nitrogen atmosphere at a calcination temperature of 400 °C for 2 h. After cooling, grind through a 200-mesh sieve to obtain composite modified sepiolite.

[0042] Compared with Example 1, in Comparative Example 2, steps S2 and S3 are omitted.

[0043] Comparative Example 3 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 100 parts of PVC resin, 15 parts of composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 5 parts of epoxy soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of calcium stearate and 3 parts of antioxidant 1010 into a blender and mix evenly at 110 °C, and maintain for 10 min within this temperature range to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, and head 190 °C. Cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 4 g of carboxymethyl chitosan thereto, stir evenly, then add 2 g of zinc nitrate, continue to stir evenly, filter and dry, and calcine in a nitrogen atmosphere at a calcination temperature of 400 °C for 2 h. After cooling, grind through a 200-mesh sieve to obtain a sepiolite composite material; S2. Disperse 8 g of the sepiolite composite material in 100 mL of 75 wt% ethanol aqueous solution, then add 1 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash and dry to obtain a double-bond grafted sepiolite composite material; S3. Disperse 8 g of the double-bond grafted sepiolite composite material in 150 mL of organic solvent DMF, then add 3 g of 1,4-butanediol thereto, stir evenly, pass nitrogen to discharge air, add 0.5 g of benzoyl peroxide, heat and stir at 60 °C for 4 h. After the reaction is completed, filter, wash and dry, and grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0044] Compared with Example 1, in Comparative Example 3, in step S3, diethyl vinylphosphonate is not added.

[0045] Comparative Example 4 A preparation method of a flame-retardant PVC sheet, comprising the following steps: Add 100 parts of PVC resin, 15 parts of composite modified sepiolite, 8 parts of ethylene vinyl acetate grafted maleic anhydride, 5 parts of epoxidized soybean oil, 4 parts of calcium zinc heat stabilizer, 2 parts of zinc stearate, 2 parts of calcium stearate and 3 parts of antioxidant 1010 into a blender, mix evenly at 110 °C, and keep it within this temperature range for 10 min to obtain a mixture. Extrude the mixture through a conical twin-screw extruder. The temperatures of each section of the screw of the conical twin-screw extruder are: conveying section 190 °C, melting section 200 °C, homogenizing section 180 °C, head 190 °C, and then cool and shape to obtain the flame-retardant PVC sheet; Among them, the preparation method of the composite modified sepiolite is as follows: S1. Disperse 5 g of sepiolite powder in 150 mL of deionized water, then add 4 g of carboxymethyl chitosan thereto, stir evenly, then add 2 g of zinc nitrate, continue to stir evenly, filter, dry, and calcine in a nitrogen atmosphere. The calcination temperature is 400 °C, the calcination time is 2 h, cool and then grind through a 200-mesh sieve to obtain the sepiolite composite material; S2. Disperse 8 g of the sepiolite composite material in 100 mL of 75 wt% ethanol aqueous solution, then add 1 g of vinyltriethoxysilane thereto, stir at room temperature for 2 h, filter, wash, and dry to obtain the double-bond grafted sepiolite composite material; S3. Disperse 8 g of the double-bond grafted sepiolite composite material in 150 mL of the organic solvent DMF, then add 3 g of diethyl vinylphosphonate thereto, stir evenly, pass nitrogen to discharge air, add 0.5 g of benzoyl peroxide, heat and stir at 60 °C for 4 h. After the reaction is completed, filter, wash, dry, and grind through a 200-mesh sieve to obtain the composite modified sepiolite.

[0046] Compared with Example 1 in Comparative Example 4, in step S3, 1,4-butanediol was not added.

[0047] Perform performance tests on the PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4 as follows: Limiting oxygen index test: Test according to the GB / T 2406.2-2009 standard; Tensile strength test: Refer to the GB / T 1040.2-2006 standard, perform tensile tests on dumbbell-shaped 50×10×4 mm standard specimens, and stretch the specimens at a rate of 50 mm / min under room temperature conditions; Impact strength test: Refer to the GB / T1843-2008 standard, perform impact tests on 80×10×4 mm standard specimens at low temperature (-25 °C); The test results are shown in Table 1.

[0048] Table 1 Performance test results of different groups of samples As can be seen from Table 1, the PVC sheets prepared in the embodiments of the present invention have excellent flame retardant properties and good mechanical properties.

[0049] Finally, it should be noted that the above embodiments do not limit the present invention in any form. For those skilled in the art, based on the present invention, some modifications and improvements can be made. Therefore, any modification or improvement made without departing from the spirit of the present invention falls within the scope of protection required by the present invention.

Claims

1. A flame-retardant PVC sheet, characterized in that, Raw materials comprising the following components by weight parts: 80 - 100 parts of PVC resin, 10 - 15 parts of composite modified sepiolite, 5 - 10 parts of ethylene vinyl acetate grafted maleic anhydride, 2 - 5 parts of epoxidized soybean oil, 3 - 5 parts of calcium zinc heat stabilizer, 2 - 4 parts of lubricant, 1 - 3 parts of antioxidant.

2. The flame-retardant PVC sheet according to claim 1, wherein The preparation method of the composite modified sepiolite is as follows: S1. Disperse sepiolite powder in deionized water, then add carboxymethyl chitosan thereto, stir evenly, then add soluble zinc salt, continue to stir evenly, filter, dry, calcine under nitrogen atmosphere, and grind after cooling to obtain sepiolite composite material; S2. Disperse the sepiolite composite material in an ethanol aqueous solution, then add vinyltriethoxysilane thereto, stir, filter, wash, and dry to obtain a double bond grafted sepiolite composite material; S3. Disperse the double bond grafted sepiolite composite material in an organic solvent, then add 1,4 - butanediol and diethyl vinylphosphonate thereto, stir evenly, pass nitrogen to discharge air, add benzoyl peroxide, heat and stir to react, after the reaction is completed, filter, wash, and dry to obtain the composite modified sepiolite.

3. The flame-retardant PVC sheet according to claim 2, wherein, In step S1, the mass ratio of sepiolite powder, carboxymethyl chitosan and soluble zinc salt is 5 - 10:4 - 8:2 - 4, and the soluble zinc salt is selected from zinc chloride, zinc nitrate or zinc sulfate.

4. The flame-retardant PVC sheet according to claim 2, wherein, In step S1, the calcination temperature is 400 - 600 °C, and the calcination time is 1 - 2 h.

5. The flame-retardant PVC sheet according to claim 2, wherein, In step S2, the mass ratio of the sepiolite composite material and vinyltriethoxysilane is 8 - 12:1 - 3.

6. The flame-retardant PVC sheet according to claim 2, wherein In step S3, the mass ratio of the double bond grafted sepiolite composite material, 1,4 - butanediol, diethyl vinylphosphonate and benzoyl peroxide is 8 - 12:3 - 6:3 - 6:0.5 - 1.

7. The flame-retardant PVC sheet according to claim 2, wherein In step S3, the temperature of the heat - stirring reaction is 60 - 80 °C, and the time of the heat - stirring reaction is 2 - 4 h.

8. The flame-retardant PVC sheet according to claim 1, wherein, The lubricant is selected from at least one of calcium stearate, zinc stearate, barium stearate, polyethylene wax, butyl stearate; the antioxidant is selected from antioxidant 168, antioxidant 1010 or antioxidant 1076.

9. The preparation method of the flame-retardant PVC sheet according to any one of claims 1-8, characterized in that, It includes the following steps: Add PVC resin, composite modified sepiolite, ethylene vinyl acetate grafted maleic anhydride, epoxidized soybean oil, calcium zinc heat stabilizer, lubricant and antioxidant by weight parts into a mixer and mix evenly to obtain a mixture, and extrude and cool the mixture through a conical twin - screw extruder to obtain a flame - retardant PVC sheet.

10. The preparation method according to claim 9, characterized in that: The temperature of each section of the screw of the conical twin - screw extruder is: the feeding section is 180 - 220 °C, the melting section is 185 - 210 °C, the homogenizing section is 175 - 205 °C, and the die head is 180 - 210 °C.

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