Flame-retardant polyvinyl chloride plastic particles and preparation method thereof

Abstract

The invention belongs to the technical field of plastic particles, and discloses flame-retardant polyvinyl chloride plastic particles and a preparation method thereof. The flame-retardant polyvinyl chloride plastic particle is prepared from the following raw materials in parts by mass: 100 to 120 parts of chlorinated polyvinyl chloride resin, 3.5 to 4.5 parts of methyltin, 0.6 to 0.8 part of calcium stearate, 1 to 1.5 parts of oxidized polyethlene wax, 8 to 12 parts of modified nano cellulose whisker, 2 to 3 parts of melamine cyanurate, 10 to 15 parts of flexibilizer, 0.3 to 0.6 part of ultraviolet light absorber, 2 to 3 parts of processing aid and 0.2 to 0.4 part of antioxidant 1076. And 0.2 to 0.4 part of an antioxidant 168. The introduction of the modified nano cellulose whisker and the flexibilizer ensures that the polyvinyl chloride plastic particles have excellent flame retardant ability, and also effectively improves the low temperature resistance and weather resistance of the polyvinyl chloride plastic particles. Therefore, the method has a wider application prospect.

Description

Technical Field

[0001] This invention belongs to the field of plastic granule technology, specifically relating to a flame-retardant polyvinyl chloride plastic granule and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) is a thermoplastic synthesized from vinyl chloride monomer through free radical polymerization. Due to its unique combination of properties and cost advantages, PVC is widely used in construction, medical, and industrial fields. Chlorinated PVC, a chlorinated product of PVC, has a higher chlorine content, resulting in superior heat distortion temperature, mechanical strength, chemical corrosion resistance, flame retardancy, and smoke suppression properties compared to PVC. Therefore, it has also gained widespread application.

[0003] While chlorinated polyvinyl chloride (PVC) exhibits excellent flame-retardant properties in practical applications, it still suffers from issues such as a high embrittlement temperature, a sharp decline in mechanical strength at low temperatures, and insufficient weather resistance. Prolonged outdoor exposure leads to yellowing of the product surface and a decrease in mechanical strength. Therefore, the low-temperature resistance and weather resistance of existing flame-retardant PVC materials still need improvement. Summary of the Invention

[0004] To address the shortcomings mentioned in the background section, the present invention aims to provide flame-retardant polyvinyl chloride (PVC) plastic granules and a method for preparing the same, thereby solving the following technical problems: Existing flame-retardant chlorinated polyvinyl chloride materials still suffer from poor low-temperature resistance and weather resistance.

[0005] The objective of this invention can be achieved through the following technical solutions: A flame-retardant polyvinyl chloride (PVC) plastic granule comprises the following raw materials in parts by weight: 100-120 parts of chlorinated polyvinyl chloride resin, 3.5-4.5 parts of methyltin, 0.6-0.8 parts of calcium stearate, 1-1.5 parts of oxidized polyethylene wax, 8-12 parts of modified nanocellulose whiskers, 2-3 parts of melamine cyanurate, 10-15 parts of toughening agent, 0.3-0.6 parts of ultraviolet absorber UV-531, 2-3 parts of processing aid ACR-401, 0.2-0.4 parts of antioxidant 1076, and 0.2-0.4 parts of antioxidant 168; The modified nanocellulose whiskers were prepared by reacting nanocellulose whiskers treated with silane coupling agent KH-550 with hexachlorocyclotriphosphazene, 4,4'-dihydroxydiphenyl sulfone, and triethylamine. The toughening agent is obtained by emulsion polymerization of octamethylcyclotetrasiloxane, vinyltriethoxysilane, methyl methacrylate, and butyl acrylate under potassium persulfate initiation.

[0006] Preferably, the modified nanocellulose whiskers are prepared as follows: A1: Mix anhydrous ethanol and deionized water, then add silane coupling agent KH-550 and stir for 20-30 min. Adjust the pH to 4.5-5.5 with acetic acid, then add nanocellulose whiskers and stir at 68-72℃ for 4-5 h. After filtration, wash the precipitate with anhydrous ethanol 3-5 times, dry it under vacuum at 75-80℃, and pass it through a 300-mesh sieve to obtain pretreated nanocellulose whiskers. A2: Under a nitrogen atmosphere, hexachlorocyclotriphosphazene was dissolved in N,N-dimethylacetamide, followed by the addition of 4,4'-dihydroxydiphenyl sulfone and triethylamine. The mixture was reacted at 0-5℃ for 2-2.5 h, then at 23-27℃ for 3-4 h. Pretreated nanocellulose whiskers were then added and ultrasonically treated at 38-40℃ for 1-1.5 h, followed by stirring for 7-7.5 h. The mixture was then poured into methanol and allowed to stand for 12-15 h. After filtration, the mixture was extracted with methanol using a Soxhlet extractor for 48-50 h. Finally, the mixture was vacuum dried at 55-60℃ and passed through a 200-300 mesh sieve to obtain modified nanocellulose whiskers.

[0007] Preferably, the mass ratio of anhydrous ethanol, deionized water, silane coupling agent KH-550, and nanocellulose whiskers in A1 is 142-190:8-10:3-4:25-30.

[0008] Preferably, the mass ratio of hexachlorocyclotriphosphazene, N,N-dimethylacetamide, 4,4'-dihydroxydiphenyl sulfone, triethylamine, pretreated nanocellulose whiskers, and methanol in A2 is 15-18:150-180:8-9.6:7-8.4:25-30:800-1000.

[0009] Preferably, the toughening agent is prepared by the following method: B1: Add octamethylcyclotetrasiloxane, vinyltriethoxysilane, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether, and tetramethylammonium hydroxide aqueous solution to deionized water and emulsify at 43-45℃ and 8000-10000r / min for 30-40min to form an organosilicon pre-emulsion. B2: Dissolve potassium persulfate in deionized water at 38-40℃ to obtain an initiator solution; B3: Add methyl methacrylate, butyl acrylate, and sodium dodecyl sulfate to deionized water and emulsify at 8000-9000 r / min for 20-30 min. Then add silane coupling agent KH-560 and emulsify at 8000-9000 r / min for 5-7 min to obtain acrylate phase pre-emulsion. B4: Add deionized water, sodium dodecyl sulfate, and sodium bicarbonate to the reaction vessel and purge with nitrogen. Then add organosilicon pre-emulsion and initiator solution at 74-76℃ and react for 1-1.5 hours to obtain seed emulsion. B5: While stirring at 77-79℃, add organosilicon pre-emulsion at a rate of 0.4-0.5 g / min to the seed emulsion, and simultaneously add initiator solution 1 at a rate of 0.12-0.13 g / min. Stir at 150 r / min for 30-40 min at 77-79℃. Then, add acrylate pre-emulsion at a rate of 1.2-1.3 g / min, and simultaneously add initiator solution 2 at a rate of 0.13-0.14 g / min. Stir at 100 r / min for 2-2.5 h at 77-79℃. After cooling to room temperature, filter through a 150-mesh sieve. Finally, spray dry at an inlet temperature of 140-150℃, an outlet temperature of 70-80℃, an atomizer speed of 18000 r / min, and a feed rate of 500 mL / h to obtain the toughening agent.

[0010] Preferably, the mass ratio of the deionized water, octamethylcyclotetrasiloxane, vinyltriethoxysilane, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether, and tetramethylammonium hydroxide aqueous solution in B1 is 50-60:20-25:3-5:0.8-1:0.7:0.1-0.2; The mass fraction of the tetramethylammonium hydroxide aqueous solution described in B1 is 25%.

[0011] Preferably, the mass ratio of potassium persulfate to deionized water in B2 is 0.8:30-40; The mass ratio of deionized water, methyl methacrylate, butyl acrylate, sodium dodecyl sulfate, and silane coupling agent KH-560 in B3 is 30-35:28:18:0.3:0.2.

[0012] Preferably, the mass ratio of deionized water, sodium dodecyl sulfate, sodium bicarbonate, organosilicon preemulsion, and initiator solution in B4 is 120:0.3:0.4:24-26:7-10.

[0013] Preferably, the mass ratio of the seed emulsion, organosilicon pre-emulsion, initiator solution 1, acrylate pre-emulsion, and initiator solution 2 in B5 is 151-156:48-54:15-20:76-81:8-10.

[0014] A method for preparing flame-retardant polyvinyl chloride plastic granules includes the following steps: Methyltin, calcium stearate, oxidized polyethylene wax, modified nanocellulose whiskers, melamine cyanurate, toughening agent, UV absorber UV-531, processing aid ACR-401, antioxidant 1076, and antioxidant 168 are added to chlorinated polyvinyl chloride resin and mixed at 200-300 r / min to 90-100℃. Then, the mixture is mixed at 800-1000 r / min for 5-10 min. After heating to 120-122℃, the mixture is discharged. Then, it is mixed and stirred at 98-100℃ for 5-7 min, followed by cold mixing at 35-40℃ for 6-8 min. Finally, the mixture is melt-extruded using a twin-screw extruder, water-cooled, granulated, centrifuged at 800-1000 r / min for 3-5 min, and then fluidized bed dried at 70-80℃ for 20-30 min to obtain flame-retardant polyvinyl chloride plastic granules.

[0015] The beneficial effects of this invention are: This invention provides flame-retardant polyvinyl chloride (PVC) plastic granules and their preparation method. The invention effectively improves the low-temperature resistance and weather resistance of flame-retardant PVC plastic granules through the following method.

[0016] (1) In this invention, the modified nanocellulose whiskers can be uniformly dispersed in the matrix after the introduction of siloxane groups on the surface. Their high aspect ratio can also form a fiber-reinforced network in the resin, effectively transferring stress, inhibiting crack propagation, and reducing local stress concentration under stress. After the modified whiskers are dispersed, their nanoscale physical barrier can buffer the internal stress generated by the shrinkage of the resin at low temperature, and the interface bonding between the whiskers and chlorinated polyvinyl chloride can reduce the initiation of low-temperature cracks. At the same time, the whiskers themselves still maintain a certain degree of flexibility at low temperature, which can further improve the mechanical strength at low temperature. The siloxane groups on the surface of the modified whiskers are resistant to ultraviolet rays and oxidation, and can form a protective layer on the resin surface, reducing the damage of photo-oxidative aging to the molecular chains of chlorinated polyvinyl chloride. At the same time, the network structure of the whiskers can inhibit the propagation of aging cracks and improve the tensile strength retention rate after aging. The modified whiskers can adsorb some ultraviolet rays, reduce the consumption of ultraviolet absorbers by ultraviolet rays, and delay the generation of resin chromophores. At the same time, the tight bonding between the whiskers and the resin can hinder the penetration of oxygen and moisture, further inhibiting oxidative yellowing. The high specific surface area of ​​whiskers can adsorb melamine cyanurate particles, preventing melamine cyanurate from agglomerating and forming flame-retardant blind zones, and ensuring uniform decomposition of melamine cyanurate when in contact with flame. During combustion, whiskers can serve as a char layer skeleton, supporting the expanded char layer formed by the degradation of melamine cyanurate and chlorinated polyvinyl chloride, making it denser and less prone to falling off, effectively blocking heat and oxygen transfer. The interfacial bonding between whiskers and chlorinated polyvinyl chloride can enhance the molten viscosity of the matrix, suppressing the dripping of molten droplets during combustion, and further improving the flame retardant ability of the material.

[0017] (2) The butyl acrylate in the toughening agent of this invention has an extremely low glass transition temperature and can still maintain flexibility at low temperatures, which can alleviate the stress concentration of chlorinated polyvinyl chloride at low temperatures; at the same time, the organosilicon segments have excellent low-temperature resistance, which can further weaken the interaction forces between chlorinated polyvinyl chloride molecular chains and reduce the restriction of chain segment movement at low temperatures. The organosilicon segments in the toughening agent are resistant to ultraviolet light and oxidation, and can form a barrier layer on the material surface to reduce the degradation of chlorinated polyvinyl chloride molecular chains by photo-oxidation; at the same time, it works synergistically with antioxidants and ultraviolet absorbers to inhibit the generation and diffusion of free radicals during aging and improve the tensile strength retention rate after aging; the organosilicon-acrylate copolymer itself has better yellowing resistance than chlorinated polyvinyl chloride, and KH-560 can reduce the migration of small molecule additives in the toughening agent and avoid the yellowing caused by oxidation of the migrated products. The good compatibility of the toughening agent can promote the uniform dispersion of modified nanocellulose whiskers and melamine cyanurate in chlorinated polyvinyl chloride matrix, avoiding local flame retardant failure caused by flame retardant agglomeration; during combustion, organosilicon segments may synergistically form a denser char layer with the degradation products of chlorinated polyvinyl chloride, blocking heat and oxygen transfer, reducing the release of combustible gases, and improving flame retardancy.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. 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] In the description of this invention, it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inner", "around", etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0021] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: Chlorinated polyvinyl chloride resin was purchased from Shanghai Yuanye Biotechnology Co., Ltd., item number: S51649-250g; processing aid ACR-401 was purchased from Kunshan Maijisen Composite Materials Co., Ltd.

[0022] Example 1: A method for preparing flame-retardant polyvinyl chloride plastic granules is as follows: S1: Mix 142g of anhydrous ethanol and 8g of deionized water evenly, then add 3g of silane coupling agent KH-550 and stir for 20min. Adjust the pH to 4.5 with acetic acid, then add 25g of nanocellulose whiskers and stir at 68℃ for 4h. After filtration, wash the precipitate three times with anhydrous ethanol, dry it under vacuum at 75℃, and pass it through a 300-mesh sieve to obtain pretreated nanocellulose whiskers. S2: Under a nitrogen atmosphere, 15g of hexachlorocyclotriphosphazene was dissolved in 150g of N,N-dimethylacetamide, followed by the addition of 8g of 4,4'-dihydroxydiphenyl sulfone and 7g of triethylamine. The mixture was reacted at 0℃ for 2h, then at 23℃ for 3h. Next, 25g of pretreated nanocellulose whiskers were added and ultrasonically treated at 38℃ for 1h, followed by stirring for 7h. The mixture was then poured into 800g of methanol and allowed to stand for 12h. After filtration, the mixture was extracted with methanol using a Soxhlet extractor for 48h. Finally, the mixture was vacuum dried at 55℃ and passed through a 200-mesh sieve to obtain modified nanocellulose whiskers. S3: Add 20g of octamethylcyclotetrasiloxane, 3g of vinyltriethoxysilane, 0.8g of sodium dodecyl sulfate, 0.7g of nonylphenol polyoxyethylene ether, and 0.1g of a 25% tetramethylammonium hydroxide aqueous solution to 50mL of deionized water and emulsify at 8000r / min for 30min at 43℃ to obtain an organosilicon pre-emulsion. S4: Dissolve 0.8g of potassium persulfate in 30mL of deionized water at 38℃ to obtain an initiator solution; S5: Add 28g methyl methacrylate, 18g butyl acrylate, and 0.3g sodium dodecyl sulfate to 30mL of deionized water and emulsify at 8000r / min for 20min. Then add 0.2g silane coupling agent KH-560 and emulsify at 8000r / min for 5min to obtain acrylate phase pre-emulsion. S6: Add 120 mL of deionized water, 0.3 g of sodium dodecyl sulfate, and 0.4 g of sodium bicarbonate to the reaction vessel and purge with nitrogen. Then add 24 g of organosilicon pre-emulsion and 7 g of initiator solution at 74 °C and react for 1 h to obtain seed emulsion. S7: While stirring at 77℃, 48g of organosilicon pre-emulsion was added dropwise at 0.4g / min to 151g of seed emulsion, and 15g of initiator solution was added dropwise at 0.12g / min. The mixture was stirred at 77℃ and 150r / min for 30min. Then, 76g of acrylate pre-emulsion was added dropwise at 1.2g / min, and 8g of initiator solution was added dropwise at 0.13g / min. The mixture was stirred at 77℃ and 100r / min for 2h. After cooling to room temperature, the mixture was filtered through a 150-mesh sieve. Finally, it was spray-dried at an inlet temperature of 140℃, an outlet temperature of 70℃, an atomizer speed of 18000r / min, and a feed rate of 500mL / h to obtain the toughening agent. S8: Add 3.5g methyltin, 0.6g calcium stearate, 1g oxidized polyethylene wax, 8g modified nanocellulose whiskers, 2g melamine cyanurate, 10g toughening agent, 0.3g UV absorber UV-531, 2g processing aid ACR-401, 0.2g antioxidant 1076, and 0.2g antioxidant 168 to 100g chlorinated polyvinyl chloride resin and mix at 200r / min to 90℃. Then mix at 800r / min for 5min. After heating to 120℃, discharge the material. Then mix and stir at 98℃ for 5min, then cold mix at 35℃ for 6min. Finally, melt extrude the mixture using a twin-screw extruder, water cool, granulate, centrifuge at 800r / min for 3min, and fluidize in a 70℃ bed for 20min to obtain flame-retardant polyvinyl chloride plastic granules.

[0023] Example 2: A method for preparing flame-retardant polyvinyl chloride plastic granules is as follows: S1: Mix 166g of anhydrous ethanol and 9g of deionized water evenly, then add 3.5g of silane coupling agent KH-550 and stir for 25min. Adjust the pH to 5 with acetic acid, then add 27.5g of nanocellulose whiskers and stir at 70℃ for 4.5h. After filtration, wash the precipitate 4 times with anhydrous ethanol, dry it under vacuum at 78℃, and pass it through a 300-mesh sieve to obtain pretreated nanocellulose whiskers. S2: Under a nitrogen atmosphere, 16.5 g of hexachlorocyclotriphosphazene was dissolved in 165 g of N,N-dimethylacetamide, followed by the addition of 8.8 g of 4,4'-dihydroxydiphenyl sulfone and 7.7 g of triethylamine. The mixture was reacted at 3 °C for 2.2 h, then at 25 °C for 3.5 h. Next, 27.5 g of pretreated nanocellulose whiskers were added and the mixture was sonicated at 39 °C for 1.2 h, followed by stirring for 7.2 h. The mixture was then poured into 900 g of methanol and allowed to stand for 14 h. After filtration, the mixture was extracted with methanol using a Soxhlet extractor for 49 h. Finally, the mixture was vacuum dried at 58 °C and passed through a 250-mesh sieve to obtain modified nanocellulose whiskers. S3: Add 22.5g octamethylcyclotetrasiloxane, 4g vinyltriethoxysilane, 0.9g sodium dodecyl sulfate, 0.7g nonylphenol polyoxyethylene ether, and 0.15g tetramethylammonium hydroxide aqueous solution with a mass fraction of 25% to 55mL of deionized water and emulsify at 9000r / min for 35min at 44℃ to form an organosilicon pre-emulsion. S4: Dissolve 0.8g of potassium persulfate in 35mL of deionized water at 39℃ to obtain an initiator solution; S5: Add 28g methyl methacrylate, 18g butyl acrylate, and 0.3g sodium dodecyl sulfate to 33mL of deionized water and emulsify at 8500r / min for 25min. Then add 0.2g silane coupling agent KH-560 and emulsify at 8500r / min for 6min to obtain acrylate phase pre-emulsion. S6: Add 120 mL of deionized water, 0.3 g of sodium dodecyl sulfate, and 0.4 g of sodium bicarbonate to the reaction vessel and purge with nitrogen. Then add 25 g of organosilicon pre-emulsion and 8.5 g of initiator solution at 75 °C and react for 1.3 h to obtain seed emulsion. S7: While stirring at 78℃, 51g of organosilicon pre-emulsion was added dropwise at 0.4g / min to 154g of seed emulsion, and 17.5g of initiator solution was added dropwise at 0.12g / min. The mixture was stirred at 78℃ and 150r / min for 35min. Then, 79g of acrylate pre-emulsion was added dropwise at 1.2g / min, and 9g of initiator solution was added dropwise at 0.13g / min. The mixture was stirred at 78℃ and 100r / min for 2.2h. After cooling to room temperature, the mixture was filtered through a 150-mesh sieve. Finally, it was spray-dried at an inlet temperature of 145℃, an outlet temperature of 75℃, an atomizer speed of 18000r / min, and a feed rate of 500mL / h to obtain the toughening agent. S8: Add 4g methyltin, 0.7g calcium stearate, 1.3g oxidized polyethylene wax, 10g modified nanocellulose whiskers, 2.5g melamine cyanurate, 13.5g toughening agent, 0.5g UV absorber UV-531, 2.5g processing aid ACR-401, 0.3g antioxidant 1076, and 0.3g antioxidant 168 to 110g chlorinated polyvinyl chloride resin and mix at 250r / min to 95℃. Then mix at 900r / min for 8min. After heating to 121℃, discharge the material. Then mix and stir at 99℃ for 6min, then cold mix at 38℃ for 7min. Finally, melt extrude the mixture using a twin-screw extruder, water cool, granulate, centrifuge at 900r / min for 4min, and fluidize at 75℃ for 25min to obtain flame-retardant polyvinyl chloride plastic granules.

[0024] Example 3: A method for preparing flame-retardant polyvinyl chloride plastic granules is as follows: S1: Mix 190g of anhydrous ethanol and 10g of deionized water evenly, then add 4g of silane coupling agent KH-550 and stir for 30min. Adjust the pH to 5.5 with acetic acid, then add 30g of nanocellulose whiskers and stir at 72℃ for 5h. After filtration, wash the precipitate 5 times with anhydrous ethanol, dry it under vacuum at 80℃, and pass it through a 300-mesh sieve to obtain pretreated nanocellulose whiskers. S2: Under a nitrogen atmosphere, 18g of hexachlorocyclotriphosphazene was dissolved in 180g of N,N-dimethylacetamide, followed by the addition of 9.6g of 4,4'-dihydroxydiphenyl sulfone and 8.4g of triethylamine. The mixture was reacted at 5°C for 2.5h, then at 27°C for 4h. 30g of pretreated nanocellulose whiskers were then added and ultrasonically treated at 40°C for 1.5h, followed by stirring for 7.5h. The mixture was then poured into 1000g of methanol and allowed to stand for 15h. After filtration, the mixture was extracted with methanol using a Soxhlet extractor for 50h. Finally, the mixture was vacuum dried at 60°C and passed through a 300-mesh sieve to obtain modified nanocellulose whiskers. S3: Add 25g of octamethylcyclotetrasiloxane, 5g of vinyltriethoxysilane, 1g of sodium dodecyl sulfate, 0.7g of nonylphenol polyoxyethylene ether, and 0.2g of 25% tetramethylammonium hydroxide aqueous solution to 60mL of deionized water and emulsify at 10000r / min for 40min at 45℃ to form an organosilicon pre-emulsion. S4: Dissolve 0.8g of potassium persulfate in 40mL of deionized water at 40℃ to obtain an initiator solution; S5: Add 28g methyl methacrylate, 18g butyl acrylate, and 0.3g sodium dodecyl sulfate to 35mL of deionized water and emulsify at 9000r / min for 30min. Then add 0.2g silane coupling agent KH-560 and emulsify at 9000r / min for 7min to obtain acrylate phase pre-emulsion. S6: Add 120 mL of deionized water, 0.3 g of sodium dodecyl sulfate, and 0.4 g of sodium bicarbonate to the reaction vessel and purge with nitrogen. Then add 26 g of organosilicon pre-emulsion and 10 g of initiator solution at 76 °C and react for 1.5 h to obtain seed emulsion. S7: While stirring at 79℃, 54g of organosilicon pre-emulsion was added dropwise at 0.5g / min to 156g of seed emulsion, and 20g of initiator solution was added dropwise at 0.13g / min. The mixture was stirred at 79℃ and 150r / min for 40min. Then, 81g of acrylate pre-emulsion was added dropwise at 1.3g / min, and 10g of initiator solution was added dropwise at 0.14g / min. The mixture was stirred at 79℃ and 100r / min for 2.5h. After cooling to room temperature, the mixture was filtered through a 150-mesh sieve. Finally, it was spray-dried at an inlet temperature of 150℃, an outlet temperature of 80℃, an atomizer speed of 18000r / min, and a feed rate of 500mL / h to obtain the toughening agent. S8: Add 4.5g methyltin, 0.8g calcium stearate, 1.5g oxidized polyethylene wax, 12g modified nanocellulose whiskers, 3g melamine cyanurate, 15g toughening agent, 0.6g ultraviolet absorber UV-531, 3g processing aid ACR-401, 0.4g antioxidant 1076, and 0.4g antioxidant 168 to 120g chlorinated polyvinyl chloride resin and mix at 300r / min to 100℃. Then mix at 1000r / min for 10min. After heating to 122℃, discharge the material. Then mix and stir at 100℃ for 7min, then cold mix at 40℃ for 8min. Finally, melt extrude the mixture using a twin-screw extruder, water cool, granulate, centrifuge at 1000r / min for 5min, and dry in a fluidized bed at 80℃ for 30min to obtain flame-retardant polyvinyl chloride plastic granules.

[0025] Comparative Example 1: Compared with Example 1, this comparative example only replaces the "modified nanocellulose whiskers" added in the preparation process of S8 with "pretreated nanocellulose whiskers". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, flame-retardant polyvinyl chloride plastic particles are obtained.

[0026] Comparative Example 2: Compared with Example 1, this comparative example only did not add "modified nanocellulose whiskers" in the preparation process of S8. All other steps and parameters were the same, and will not be repeated here. The final result was flame-retardant polyvinyl chloride plastic particles.

[0027] Comparative Example 3: Compared with Example 1, this comparative example only did not add a "toughening agent" in the preparation process of S8. All other steps and parameters were the same, and will not be repeated here. The final result was flame-retardant polyvinyl chloride plastic particles.

[0028] Performance testing: Determination of tensile strength: Referring to GB / T 1040.3-2006 standard, the tensile strength (MPa) of the flame-retardant polyvinyl chloride plastic particles prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention was determined at a tensile rate of 50 mm / min. The particles were made into specimens with a size of 170 mm × 10 mm × 4 mm at 23 °C. The test results are shown in Table 1.

[0029] Determination of low-temperature resistance: Referring to GB / T 1040.3-2006 standard, the flame-retardant polyvinyl chloride plastic particles prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were measured at a tensile rate of 50 mm / min. After being made into samples with a size of 170 mm × 10 mm × 4 mm, the tensile strength retention rate (%) at -30 °C for 2 h was measured relative to the tensile strength at 23 °C. The results are shown in Table 1.

[0030] Weather resistance testing: Determination of tensile strength retention rate after aging treatment: Referring to GB / T 16422.2-2014 and GB / T 1040.3-2006 standards, the flame-retardant polyvinyl chloride plastic particles prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were tested at a tensile rate of 50 mm / min. The particles were prepared into samples with dimensions of 170 mm × 10 mm × 4 mm and then subjected to irradiation at 340 nm at a rate of 0.55 W / m². 2 The tensile strength retention rate (%) after 1000 h (a cycle of 102 min light exposure + 18 min water spraying) at a blackboard temperature of 65℃ and a relative humidity of 50% is shown in Table 1. Determination of the yellowing index (ΔE) of aged materials: Referring to GB / T 16422.2-2014 standard, the yellowing index of flame-retardant polyvinyl chloride plastic particles prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was measured. The particles were prepared into samples with dimensions of 150mm × 70mm × 4mm and then subjected to irradiation at 340nm at 0.55W / m². 2 The yellowing index ΔE after 1000 h of treatment with a blackboard temperature of 65℃ and a relative humidity of 50% (a cycle of 102 min of light exposure + 18 min of water spraying) is shown in Table 1.

[0031] Determination of flame retardancy: Referring to GB / T 2408-2021 standard, the vertical burning flame retardancy rating of the flame-retardant polyvinyl chloride plastic particles prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was determined after being made into specimens with a size of 125mm×13mm×4mm. The test results are shown in Table 1.

[0032] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-3 Data Analysis: As can be seen from Table 1, the flame-retardant polyvinyl chloride plastic particles prepared in the embodiments of the present invention have excellent tensile strength, low temperature resistance, weather resistance and flame retardancy.

[0033] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0034] 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 illustrative of the principles of 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 claimed invention.

Claims

1. A flame-retardant polyvinyl chloride plastic granule, characterized in that, The raw materials include the following parts by weight: 100-120 parts of chlorinated polyvinyl chloride resin, 3.5-4.5 parts of methyltin, 0.6-0.8 parts of calcium stearate, 1-1.5 parts of oxidized polyethylene wax, 8-12 parts of modified nanocellulose whiskers, 2-3 parts of melamine cyanurate, 10-15 parts of toughening agent, 0.3-0.6 parts of UV absorber UV-531, 2-3 parts of processing aid ACR-401, 0.2-0.4 parts of antioxidant 1076, and 0.2-0.4 parts of antioxidant 168; The modified nanocellulose whiskers were prepared by reacting nanocellulose whiskers treated with silane coupling agent KH-550 with hexachlorocyclotriphosphazene, 4,4'-dihydroxydiphenyl sulfone, and triethylamine. The toughening agent is obtained by emulsion polymerization of octamethylcyclotetrasiloxane, vinyltriethoxysilane, methyl methacrylate, and butyl acrylate under potassium persulfate initiation.

2. The flame-retardant polyvinyl chloride plastic granules according to claim 1, characterized in that, The modified cellulose nanofibers are prepared as follows: A1: Mix anhydrous ethanol and deionized water, then add silane coupling agent KH-550 and stir for 20-30 min. Adjust the pH to 4.5-5.5, then add nanocellulose whiskers and stir at 68-72℃ for 4-5 h. After filtration, wash the precipitate, vacuum dry, and sieve to obtain pretreated nanocellulose whiskers. A2: Under a nitrogen atmosphere, hexachlorocyclotriphosphazene was dissolved in N,N-dimethylacetamide, followed by the addition of 4,4'-dihydroxydiphenyl sulfone and triethylamine. The mixture was reacted at 0-5°C for 2-2.5 h, then at 23-27°C for 3-4 h. Pretreated nanocellulose whiskers were then added and sonicated for 1-1.5 h, followed by stirring for 7-7.5 h. The mixture was then poured into methanol and allowed to stand. After filtration, the mixture was extracted with methanol, vacuum dried, and sieved to obtain modified nanocellulose whiskers.

3. The flame-retardant polyvinyl chloride plastic granules according to claim 2, characterized in that, The mass ratio of anhydrous ethanol, deionized water, silane coupling agent KH-550, and nanocellulose whiskers in A1 is 142-190:8-10:3-4:25-30.

4. The flame-retardant polyvinyl chloride plastic granules according to claim 2, characterized in that, The mass ratio of hexachlorocyclotriphosphazene, N,N-dimethylacetamide, 4,4'-dihydroxydiphenyl sulfone, triethylamine, pretreated nanocellulose whiskers, and methanol in A2 is 15-18:150-180:8-9.6:7-8.4:25-30:800-1000.

5. The flame-retardant polyvinyl chloride plastic granules according to claim 1, characterized in that, The toughening agent is prepared as follows: B1: Add octamethylcyclotetrasiloxane, vinyltriethoxysilane, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether, and tetramethylammonium hydroxide aqueous solution to deionized water and emulsify at 43-45℃ for 30-40 min to form an organosilicon pre-emulsion. B2: Dissolve potassium persulfate in deionized water to obtain an initiator solution; B3: Add methyl methacrylate, butyl acrylate, and sodium dodecyl sulfate to deionized water and emulsify for 20-30 min. Then add silane coupling agent KH-560 and emulsify for 5-7 min to obtain acrylate phase pre-emulsion. B4: Add deionized water, sodium dodecyl sulfate, and sodium bicarbonate to the reaction vessel and purge with nitrogen. Then add organosilicon pre-emulsion and initiator solution at 74-76℃ and react for 1-1.5 hours to obtain seed emulsion. B5: While stirring at 77-79℃, simultaneously add organosilicon pre-emulsion and initiator solution 1 to the seed emulsion and stir for 30-40 minutes. Then, simultaneously add acrylate pre-emulsion and initiator solution 2 and stir for 2-2.5 hours. After cooling, filter and finally spray dry to obtain the toughening agent.

6. The flame-retardant polyvinyl chloride plastic granules according to claim 5, characterized in that, The mass ratio of the deionized water, octamethylcyclotetrasiloxane, vinyltriethoxysilane, sodium dodecyl sulfate, nonylphenol polyoxyethylene ether, and tetramethylammonium hydroxide aqueous solution described in B1 is 50-60:20-25:3-5:0.8-1:0.7:0.1-0.2; The mass fraction of the tetramethylammonium hydroxide aqueous solution described in B1 is 25%.

7. The flame-retardant polyvinyl chloride plastic granules according to claim 5, characterized in that, The mass ratio of potassium persulfate to deionized water mentioned in B2 is 0.8:30-40; The mass ratio of deionized water, methyl methacrylate, butyl acrylate, sodium dodecyl sulfate, and silane coupling agent KH-560 in B3 is 30-35:28:18:0.3:0.

2.

8. The flame-retardant polyvinyl chloride plastic granules according to claim 5, characterized in that, The mass ratio of deionized water, sodium dodecyl sulfate, sodium bicarbonate, organosilicon preemulsion, and initiator solution in B4 is 120:0.3:0.4:24-26:7-10.

9. The flame-retardant polyvinyl chloride plastic granules according to claim 5, characterized in that, The mass ratio of the seed emulsion, organosilicon pre-emulsion, initiator solution 1, acrylate pre-emulsion, and initiator solution 2 described in B5 is 151-156:48-54:15-20:76-81:8-10.

10. A method for preparing flame-retardant polyvinyl chloride plastic granules according to any one of claims 1-9, characterized in that, Includes the following steps: Methyltin, calcium stearate, oxidized polyethylene wax, modified nanocellulose whiskers, melamine cyanurate, toughening agent, UV absorber UV-531, processing aid ACR-401, antioxidant 1076, and antioxidant 168 are added to chlorinated polyvinyl chloride resin and mixed to 90-100℃. Then, the mixture is stirred at 800-1000 r / min for 5-10 min. After heating to 120-122℃, the material is discharged. Then, it is stirred at 98-100℃ for 5-7 min, followed by cold mixing at 35-40℃ for 6-8 min. Finally, it is melt-extruded using a twin-screw extruder, water-cooled, granulated, centrifuged dewatered, and fluidized bed dried to obtain flame-retardant polyvinyl chloride plastic granules.

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