High-temperature-resistant PVC flame-retardant material and preparation method thereof

Abstract

The invention provides a high-temperature-resistant PVC flame-retardant material and a preparation method thereof, and belongs to the field of flame-retardant high polymer materials, and the preparation method comprises the following steps: mixing and stirring an ethanol solution, tetraethoxysilane and a ZrOCl2. 8H2O solution, heating, mixing with PVC resin powder, carrying out ultrasonic dispersion, introducing nitrogen, and heating to obtain modified PVC powder; the preparation method comprises the following steps: heating and stirring tannin, NaOH, water and epichlorohydrin, cooling, carrying out rotary evaporation, adding tetrahydrofuran, and drying to obtain tannin-based epoxy resin; the pretreated halloysite nanotubes, an ethanol water solution and phytic acid are subjected to vacuum stirring and centrifugation, CuCl2. 2H2O, ethanol and water are added for mixing and stirring, centrifugation and freeze drying are performed, and a composite flame retardant is prepared; pVC resin, modified PVC powder, tannin-based epoxy resin, a composite flame retardant and an auxiliary agent are mixed at a high speed, banburying and granulation are performed, and the high-temperature-resistant PVC flame-retardant material is obtained. The flame retardant property and the high temperature resistance of the PVC material can be improved, and meanwhile, the discharge of toxic smoke is reduced.

Description

Technical Field

[0001] The present invention relates to the field of flame - retardant polymer materials, and particularly to a high - temperature resistant PVC flame - retardant material and a preparation method thereof. Background Art

[0002] Polyvinyl chloride (PVC), a thermoplastic plastic formed through free - radical polymerization reaction, has been applied in numerous industries due to its high cost - effectiveness, easy availability of raw materials, and stable chemical properties. The application fields of PVC cover multiple industries such as aerospace, transportation, electronics and electrical appliances, construction engineering, etc., and even have applications in frontier technology fields such as bionic materials and supramolecular materials. As the second - largest engineering plastic globally, PVC occupies an important position in engineering materials. However, the flammability of PVC is one of its main drawbacks, which limits its application in some high - requirement environments. To overcome this problem, the common solution is to add flame retardants to PVC to improve its fire - prevention performance. This method is not only low - cost but also suitable for large - scale production, and can effectively improve the flammability problem of PVC, enabling it to be applied in more fields.

[0003] Research on PVC flame - retardant technology mainly focuses on the following directions: Traditional halogen - based flame retardants are one of the most commonly used types. These flame retardants can effectively inhibit flame spread at high temperatures. However, since they produce toxic gases during combustion, posing threats to the environment and human health and increasing the difficulty of fire rescue, they are gradually being phased out. Secondly, phosphorus - nitrogen - based organic flame retardants decompose to produce non - flammable gases and form a carbon layer under high - temperature conditions, showing relatively low toxicity. Nevertheless, the thermal stability of such flame retardants is poor, which in turn affects the thermal stability of the polymer, and the smoke volume during combustion is large. Another option is inorganic flame retardants such as aluminum hydroxide, magnesium hydroxide, and zinc borate, etc. These substances achieve the flame - retardant purpose by releasing water vapor through high - temperature decomposition and forming non - flammable metal oxides. They not only have low toxicity but also have good flame - retardant performance, and can also provide heat insulation and smoke suppression effects. However, the compatibility of such flame retardants with the polymer matrix is poor, which may weaken the mechanical strength of the material.

[0004] Therefore, it is necessary to provide a high - temperature resistant PVC flame - retardant material and a preparation method thereof to solve the problems existing in the above - mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a high - temperature resistant PVC flame - retardant material and a preparation method thereof, which can improve the flame - retardant performance and high - temperature resistance of PVC materials while reducing the emission of toxic smoke.

[0006] To achieve the above object, the present invention provides a preparation method of a high - temperature resistant PVC flame - retardant material, comprising the following steps: S1. Mix the ethanol solution and tetraethyl orthosilicate, add ZrOCl 2 ·8H 2 O solution and stir. After heating, mix it with PVC resin powder, disperse it by ultrasound, dry it under vacuum, keep it warm by introducing nitrogen, and rapidly raise the temperature to obtain modified PVC powder; S2. Add tannin and NaOH to water and stir mechanically. Slowly add epichlorohydrin, heat and stir, cool, perform rotary evaporation, add tetrahydrofuran, filter, and dry under vacuum to obtain tannin-based epoxy resin; S3. Disperse the pretreated halloysite nanotubes in an ethanol aqueous solution, add phytic acid, stir under vacuum, perform centrifugal separation, add CuCl 2 ·2H 2 O, ethanol and deionized water, mix, stir by ultrasound, centrifuge, wash, and freeze-dry to obtain the flame retardant; S4. Put PVC resin, modified PVC powder, AS resin, POE resin, tannin-based epoxy resin, composite flame retardant, and lubricant into a high-speed mixer, mix at high speed, knead, and granulate to obtain the high-temperature resistant PVC flame retardant material.

[0007] The sol system generated by the hydrolysis of tetraethyl orthosilicate in the present invention has high chemical activity and can introduce the complex of silicon and zirconium oxide into the PVC powder; zirconium oxide has high thermal stability and excellent high-temperature resistance performance, enabling the modified PVC to maintain good mechanical properties under high-temperature conditions. The hydrolysis reaction of silicon and zirconium oxide can form a uniformly dispersed inorganic network structure, effectively isolating oxygen and moisture at high temperatures, reducing the oxidation and degradation reactions of the PVC material at high temperatures, and playing a certain role in improving the overall high-temperature resistance performance and also having a flame retardant effect; in addition, the cross-linking effect of silicon / zirconium oxide improves the mechanical strength of PVC, making the material less likely to embrittle or rupture at high temperatures.

[0008] The present invention prepares tannin-based epoxy resin as a heat stabilizer. Due to the chemical structure of tannin, it reacts with epichlorohydrin in an alkaline medium to introduce epoxy groups into tannin and synthesize tannin-based epoxy resin; tannin-based epoxy resin contains a large number of hydroxyl groups and epoxy groups formed after epoxidation treatment. These functional groups can effectively capture the hydrogen chloride released during the PVC processing process, thus preventing the occurrence of dehydrochlorination reaction and further preventing PVC degradation; in addition, the polyphenol structure in the tannin molecule endows it with excellent antioxidant performance. Due to the cross-linking effect of the epoxy groups, the formation of tannin-based epoxy resin not only improves the thermal stability of the resin itself but also enhances the interaction between it and PVC molecules. This cross-linked network enhances the overall thermal stability of the material, enabling PVC to exhibit a longer service life and a lower degradation rate under high-temperature conditions.

[0009] In the present invention, the halloysite nanotube cavity encapsulates the phytic acid-copper complex, thereby enhancing the flame retardancy performance. When heated, the phytic acid-copper complex first decomposes to generate phosphoric acid, which promotes the dehydration of halloysite nanotubes, leading to their early degradation. The generated phosphoric acid further promotes the carbonization of the PVC matrix, forming a thermally insulating carbonaceous layer that restricts the exchange of heat and mass and improves the flame retardancy effect. And at higher temperatures, the dehydrated halloysite nanotubes generate stable SiO 2 , and move to the surface of the substrate to form a protective barrier. In addition, the cavity of halloysite nanotubes can adsorb and capture free radicals generated by the degradation of PVC, effectively inhibiting the spread of combustion. In the gas phase, Cu 2+ is loaded in the inner cavity of halloysite nanotubes, catalyzing the conversion of CO to CO 2 , and inhibiting the toxicity of the smoke.

[0010] Optionally, in step S1, after adding ZrOCl 2 ·8H 2 O solution and stirring, ammonia water is added to adjust the pH value to 4-9. After heating at 100 °C for 20 h, it is mixed with PVC resin powder, ultrasonically dispersed at 40 kHz for 1-2 h, then vacuum dried, purged with nitrogen for protection, held at 120 °C for 1 h, and rapidly heated to 300 °C and held for 2 h to obtain the modified PVC powder.

[0011] Optionally, in step S2, the temperature of mechanical stirring is 30 °C and the time is 60 min, the temperature of heating and stirring is 95 °C and the time is 5 h, the temperature of rotary evaporation is 60 °C, and the temperature of vacuum drying is 60-80 °C and the time is 16-24 h.

[0012] Optionally, the pretreated halloysite nanotubes in step S3 are prepared by mixing halloysite nanotubes with a sulfuric acid solution with a molar concentration of 2 mol / L, magnetically stirring at 50-80 °C for 2-5 h, washing with deionized water, and freeze-drying.

[0013] In the present invention, the cavity of halloysite nanotubes is expanded by sulfuric acid etching, improving its loading capacity to encapsulate more phytic acid-copper complexes, thereby enhancing the flame retardancy performance.

[0014] Optionally, in step S3, after freeze-drying, it is immersed in an acetic acid solution containing an amino-functionalized phosphazene component, ultrasonically treated, continuously stirred at 80 °C for 6 h, then ammonia water is added dropwise, and reflux stirring is continued for 16 h, followed by centrifugal washing and freeze-drying to finally obtain the composite flame retardant.

[0015] In the present invention, an amino-functionalized phosphazene component is grafted onto the outer surface of halloysite nanotubes to achieve the modification of the outer surface of halloysite nanotubes, forming a phosphazene polymer layer. This not only enhances the surface activity of halloysite but also helps reduce the agglomeration phenomenon among halloysite nanotubes and promotes their uniform distribution in the matrix, further improving the dispersibility of halloysite in the matrix. Moreover, the amino-functionalized phosphazene component and halloysite nanotubes construct a Si-P synergistic flame retardant system, and the phosphoric acid compounds generated by its decomposition have high dehydration properties, promoting the cyclization and crosslinking of the carbon layer and improving the flame retardancy of the PVC matrix.

[0016] Optionally, the amino-functionalized phosphazene component is prepared by adding 3-aminopropyltriethoxysilane and triethylamine into a three-necked flask containing toluene solution, dissolving hexachlorocyclotriphosphazene in toluene and dropping it into the three-necked flask, heating for reaction, filtering, and rotary evaporation; the volume concentration of the acetic acid solution is 1.7%.

[0017] The present invention utilizes the nucleophilic substitution reaction between the active P-Cl bond of hexachlorocyclotriphosphazene and -NH to generate an amino-functionalized phosphazene component.

[0018] Optionally, in the step S3, the vacuum stirring time is 1 - 2 h, the ultrasonic stirring temperature is 80 °C, the time is 1 - 3 h, and the washing is carried out successively with ethanol and deionized water.

[0019] The present invention washes successively with ethanol and deionized water to remove solvents and impurities and improve the product purity.

[0020] Optionally, in the step S4, PVC resin, modified PVC powder, AS resin, POE resin, tannin-based epoxy resin, composite flame retardant, and lubricant are put into a high-speed mixer, mixed at a high speed of 1200 rpm for 10 - 20 min, then the mixture is loaded into a torque rheometer, and at 170 - 200 °C, the rotation speed is 40 rpm, and it is kneaded until the torque is stable, discharged and pelletized to obtain a high-temperature resistant PVC flame retardant material.

[0021] Optionally, the high-temperature resistant PVC flame retardant material comprises the following raw materials in parts by weight: 60 - 100 parts of PVC resin, 30 - 50 parts of modified PVC powder, 10 - 15 parts of AS resin, 5 - 10 parts of POE resin, 10 - 30 parts of tannin-based epoxy resin, 22 - 30 parts of composite flame retardant, and 2 - 5 parts of lubricant.

[0022] The present invention adopts the above-mentioned mass fraction matching ratio, which can improve the overall performance of the high-temperature resistant PVC flame retardant material in multiple aspects, and its flame retardancy and high-temperature resistance are optimized.

[0023] The above technical solutions of the present invention at least include the following beneficial effects: 1. In the present invention, a sol system generated by the hydrolysis of tetraethyl orthosilicate introduces silicon and zirconia composites into PVC, significantly enhancing the high-temperature resistance and flame retardancy of PVC. The excellent thermal stability of zirconia effectively prevents the oxidation and degradation reactions of PVC at high temperatures. The cross-linked network of the silicon / zirconia composite enhances the mechanical strength of PVC, making it more durable in high-temperature environments, reducing the risk of embrittlement, and extending the service life of the material.

[0024] 2. Tannin-based epoxy resin introduces epoxy groups through reaction with epichlorohydrin, which can effectively capture hydrogen chloride during the processing of PVC and prevent PVC degradation. The polyphenolic structure of tannin provides antioxidant properties, while the cross-linking effect of the epoxy groups enhances the thermal stability of the material, improves the mechanical properties of PVC, and ensures that PVC maintains a low degradation rate and a longer service life at high temperatures.

[0025] 3. In the present invention, by encapsulating phytic acid-copper composites in the cavities of halloysite nanotubes, the flame retardancy of PVC is significantly improved. Phosphoric acid generated after heating the phytic acid-copper composites promotes the dehydration of halloysite nanotubes, forming a heat-insulating carbonaceous layer, which effectively inhibits heat propagation. At the same time, the SiO 2 layer on the surface of halloysite nanotubes protects the substrate, adsorbs degradation free radicals and catalyzes the conversion of CO to CO 2 , reduces smoke toxicity, and enhances the flame retardancy effect. Detailed implementation manners

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0027] Example 1 After pre-hydrolyzing 3.4 g of tetraethyl orthosilicate in 50 mL of an ethanol solution with a volume concentration of 30%, 4.08 mL of ZrOCl 2 ·8H 2 O solution was added and stirred at room temperature, and then ammonia water was added to adjust the pH value to 8; the mixture was transferred to a Teflon-lined stainless steel autoclave and sealed, and heated at 100 °C for 20 h to obtain a sol mixture; 100 g of PVC resin powder was mixed with 15 g of the sol mixture, ultrasonically dispersed at 40 kHz for 1.5 h, vacuum dried, placed in a tubular furnace, purged with nitrogen for protection, held at 120 °C for 1 h, and rapidly heated to 300 °C and held for 2 h to obtain the modified PVC powder.

[0028] Add 10 g of tannin and 4 g of NaOH to 100 ml of water, stir mechanically at 30 °C for 60 min, then slowly add 32 g of epichlorohydrin, heat and stir at 95 °C for 5 h, cool, spin evaporate at 60 °C, dissolve in 100 mL of tetrahydrofuran, filter the salt by-products in the reaction vessel, and dry in vacuo at 70 °C for 20 h to obtain tannin-based epoxy resin.

[0029] Add 1.0 g of halloysite nanotubes to 100 mL of sulfuric acid solution with a molar concentration of 2 mol / L, stir magnetically at 70 °C for 4 h, wash with deionized water, and freeze-dry to obtain pretreated halloysite nanotubes; disperse 1.0 g of pretreated halloysite nanotubes in 100 mL of ethanol aqueous solution with a volume concentration of 50%, then add 0.7 g of phytic acid, stir under vacuum for 1.5 h, after centrifugal separation, add 1.1 g of CuCl 2 ·2H 2 O, 50 mL of ethanol and 50 mL of deionized water are mixed, ultrasonically stirred at 80 °C for 2 h, centrifuged, washed successively with ethanol and deionized water, and freeze-dried to obtain the flame retardant.

[0030] Add 21.03 g of 3-aminopropyltriethoxysilane and 10.57 mL of triethylamine to a three-necked flask containing 50 mL of toluene solution, dissolve 5 g of hexachlorocyclotriphosphazene in 20 mL of toluene and add it dropwise to the three-necked flask, then react at 110 °C for 4 h, filter, and spin evaporate at 60 °C to obtain the amino-functionalized phosphazene component; under ultrasonic treatment, add 3 g of the amino-functionalized phosphazene component to a three-necked culture flask, add 60 mL of acetic acid solution with a volume concentration of 1.7%, then add 0.5 g of the flame retardant, continuously stir at 80 °C for 6 h, then add 4 mL of ammonia water, continue to reflux and stir for 16 h, and obtain the composite flame retardant after centrifugal washing and freeze-drying.

[0031] Add 60 g of PVC resin, 50 g of modified PVC powder, 13 g of AS resin, 8 g of POE resin, 30 g of tannin-based epoxy resin, 30 g of composite flame retardant, and 5 g of lubricant to a high-speed mixer, mix at 1200 rpm for 20 min at high speed, then put the mixture into a torque rheometer, rotate at 40 rpm at 200 °C, knead until the torque is stable, discharge and pelletize to obtain the high-temperature resistant PVC flame retardant material.

[0032] Example 2 After pre-hydrolyzing 3.4 g of tetraethyl orthosilicate in 50 mL of ethanol solution with a volume concentration of 30%, add 4.08 mL of ZrOCl 2 ·8H 2The O solution was stirred at room temperature, and then ammonia water was added to adjust the pH value to 4. The mixture was transferred to a Teflon-lined stainless steel autoclave and sealed, and then heated at 100 °C for 20 h to obtain a sol mixture. 100 g of PVC resin powder was mixed with 15 g of the sol mixture, ultrasonically dispersed at 40 kHz for 1 h, vacuum dried, placed in a tube furnace, purged with nitrogen, held at 120 °C for 1 h, rapidly heated to 300 °C, and held for 2 h to obtain the modified PVC powder.

[0033] 10 g of tannin and 4 g of NaOH were added to 100 ml of water, mechanically stirred at 30 °C for 60 min, then 32 g of epichlorohydrin was slowly added and heated with stirring at 95 °C for 5 h. After cooling, it was rotary evaporated at 60 °C, dissolved in 100 mL of tetrahydrofuran, the salt by-products in the reaction vessel were filtered, and vacuum dried at 60 °C for 16 h to obtain tannin-based epoxy resin.

[0034] 1.0 g of halloysite nanotubes was added to 100 mL of sulfuric acid solution with a molar concentration of 2 mol / L, magnetically stirred at 50 °C for 5 h, washed with deionized water, and freeze-dried to obtain pretreated halloysite nanotubes. 1.0 g of the pretreated halloysite nanotubes was dispersed in 100 mL of an ethanol-water solution with a volume concentration of 50%, then 0.7 g of phytic acid was added, stirred under vacuum for 1 h, after centrifugal separation, 1.1 g of CuCl 2 ·2H 2 O, 50 mL of ethanol and 50 mL of deionized water were mixed, ultrasonically stirred at 80 °C for 1 h, centrifuged, washed successively with ethanol and deionized water, and freeze-dried to obtain the flame retardant.

[0035] 21.03 g of 3-aminopropyltriethoxysilane and 10.57 mL of triethylamine were added to a three-necked flask containing 50 mL of toluene solution. 5 g of hexachlorocyclotriphosphazene was dissolved in 20 mL of toluene and added dropwise to the three-necked flask, and then reacted at 120 °C for 3 h. After filtration, it was rotary evaporated at 60 °C to obtain the amino-functionalized phosphazene component. Under ultrasonic treatment, 3 g of the amino-functionalized phosphazene component was added to a three-necked culture flask, 60 mL of acetic acid solution with a volume concentration of 1.7% was added, then 0.5 g of the flame retardant was added, continuously stirred at 70 °C for 6 h, then 4 mL of ammonia water was added dropwise, and refluxed and stirred for 16 h. After centrifugal washing and freeze-drying, the composite flame retardant was obtained.

[0036] 100 g of PVC resin, 30 g of modified PVC powder, 10 g of AS resin, 5 g of POE resin, 10 g of tannin-based epoxy resin, 22 g of composite flame retardant, and 4 g of lubricant were added to a high-speed mixer and mixed at 1200 rpm for 10 min. Then, the mixture was loaded into a torque rheometer, and the speed was 40 rpm at 1700 °C. The mixture was kneaded until the torque was stable, discharged, and pelletized to obtain a high-temperature resistant PVC flame retardant material.

[0037] Example 3 After pre-hydrolyzing 3.4 g of tetraethyl orthosilicate in 50 mL of ethanol solution with a volume concentration of 30%, 4.08 mL of ZrOCl 2 ·8H 2 O solution was stirred at room temperature, and then ammonia water was added to adjust the pH value to 9. The mixture was transferred to a Teflon-lined stainless steel autoclave, sealed, and heated at 100 °C for 20 h to obtain a sol mixture. 100 g of PVC resin powder was mixed with 15 g of the sol mixture, ultrasonically dispersed at 40 kHz for 2 h, vacuum dried, placed in a tubular furnace, purged with nitrogen for protection, kept at 120 °C for 1 h, and rapidly heated to 300 °C and kept for 2 h to obtain modified PVC powder.

[0038] 10 g of tannin and 4 g of NaOH were added to 100 ml of water, mechanically stirred at 30 °C for 60 min, then 32 g of epichlorohydrin was slowly added and heated and stirred at 95 °C for 5 h. After cooling, it was rotary evaporated at 60 °C and dissolved in 100 mL of tetrahydrofuran. The salt by-products in the reaction vessel were filtered, and vacuum dried at 80 °C for 24 h to obtain tannin-based epoxy resin.

[0039] 1.0 g of halloysite nanotubes was added to 100 mL of sulfuric acid solution with a molar concentration of 2 mol / L, magnetically stirred at 80 °C for 2 h, washed with deionized water, and freeze-dried to obtain pretreated halloysite nanotubes. 1.0 g of pretreated halloysite nanotubes was dispersed in 100 mL of ethanol aqueous solution with a volume concentration of 50%, then 0.7 g of phytic acid was added, stirred under vacuum for 2 h, centrifuged, and then 1.1 g of CuCl 2 ·2H 2 O, 50 mL of ethanol, and 50 mL of deionized water were mixed, ultrasonically stirred at 80 °C for 2 h, centrifuged, washed successively with ethanol and deionized water, and freeze-dried to obtain a composite flame retardant.

[0040] 80 g of PVC resin, 40 g of modified PVC powder, 12 g of AS resin, 10 g of POE resin, 20 g of tannin-based epoxy resin, 25 g of composite flame retardant, and 3 g of lubricant were added to a high-speed mixer and mixed at 1200 rpm for 15 min. Then, the mixture was loaded into a torque rheometer, and at 180 °C, the rotation speed was 40 rpm. After kneading until the torque was stable, the material was discharged and granulated to obtain a high-temperature resistant PVC flame retardant material.

[0041] Example 4 After pre-hydrolyzing 3.4 g of tetraethyl orthosilicate in 50 mL of ethanol solution with a volume concentration of 30%, 4.08 mL of ZrOCl 2 ·8H 2 O solution was stirred at room temperature, and then ammonia water was added to adjust the pH value to 6. The mixture was transferred to a Teflon-lined stainless steel autoclave and sealed, and heated at 100 °C for 20 h to obtain a sol mixture. 100 g of PVC resin powder was mixed with 15 g of the sol mixture, ultrasonically dispersed at 40 kHz for 1.5 h, vacuum dried, placed in a tubular furnace, purged with nitrogen for protection, held at 120 °C for 1 h, and rapidly heated to 300 °C and held for 2 h to obtain modified PVC powder.

[0042] 10 g of tannin and 4 g of NaOH were added to 100 ml of water, mechanically stirred at 30 °C for 60 min, then 32 g of epichlorohydrin was slowly added and heated and stirred at 95 °C for 5 h. After cooling, it was rotary evaporated at 60 °C and dissolved in 100 mL of tetrahydrofuran. The salt by-products in the reaction vessel were filtered, and vacuum dried at 70 °C for 18 h to obtain tannin-based epoxy resin.

[0043] 1.0 g of halloysite nanotubes was added to 100 mL of sulfuric acid solution with a molar concentration of 2 mol / L and magnetically stirred at 60 °C for 3 h, then washed with deionized water and freeze-dried to obtain pretreated halloysite nanotubes. 1.0 g of pretreated halloysite nanotubes was dispersed in 100 mL of ethanol aqueous solution with a volume concentration of 50%, then 0.7 g of phytic acid was added, and stirred under vacuum for 2 h. After centrifugal separation, 1.1 g of CuCl 2 ·2H 2 O, 50 mL of ethanol and 50 mL of deionized water were mixed, ultrasonically stirred at 80 °C for 2 h, centrifuged, washed successively with ethanol and deionized water, and freeze-dried to obtain the flame retardant.

[0044] 21.03 g of 3-aminopropyltriethoxysilane and 10.57 mL of triethylamine were added to a three-necked flask containing 50 mL of toluene solution. 5 g of hexachlorocyclotriphosphazene was dissolved in 20 mL of toluene and added dropwise to the three-necked flask. Then, the reaction was carried out at 110 °C for 3.5 h. After filtration, the amino-functionalized phosphazene component was obtained by rotary evaporation at 60 °C. Under ultrasonic treatment, 3 g of the amino-functionalized phosphazene component was added to a three-necked culture flask, and 60 mL of acetic acid solution with a volume concentration of 1.7% was added. Then, 0.5 g of a flame retardant was added. The mixture was continuously stirred at 80 °C for 6 h, and then 4 mL of ammonia water was added dropwise. The mixture was refluxed and stirred for 16 h, and the composite flame retardant was obtained by centrifugal washing and freeze-drying.

[0045] 90 g of PVC resin, 30 g of modified PVC powder, 10 g of AS resin, 5 g of POE resin, 25 g of tannin-based epoxy resin, 27 g of composite flame retardant, and 2 g of lubricant were added to a high-speed mixer and mixed at a high speed of 1200 rpm for 10 min. Then, the mixture was loaded into a torque rheometer, and the rotation speed was 40 rpm at 190 °C. The mixture was kneaded until the torque was stable, discharged, and granulated to obtain a high-temperature resistant PVC flame retardant material.

[0046] Example 5 After pre-hydrolyzing 3.4 g of tetraethyl orthosilicate in 50 mL of ethanol solution with a volume concentration of 30%, 4.08 mL of ZrOCl 2 ·8H 2 O solution was stirred at room temperature, and then ammonia water was added to adjust the pH value to 7. The mixture was transferred to a Teflon-lined stainless steel autoclave and sealed, and heated at 100 °C for 20 h to obtain a sol mixture. 100 g of PVC resin powder was mixed with 15 g of the sol mixture, ultrasonically dispersed at 40 kHz for 1 h, vacuum dried, placed in a tubular furnace, purged with nitrogen, held at 120 °C for 1 h, and rapidly heated to 300 °C and held for 2 h to obtain modified PVC powder.

[0047] 10 g of tannin and 4 g of NaOH were added to 100 ml of water, mechanically stirred at 30 °C for 60 min, and then 32 g of epichlorohydrin was slowly added and heated and stirred at 95 °C for 5 h. After cooling, it was rotary evaporated at 60 °C and then dissolved in 100 mL of tetrahydrofuran. The salt by-products in the reaction vessel were filtered, and vacuum dried at 60 °C for 16 h to obtain tannin-based epoxy resin.

[0048] 1.0 g of halloysite nanotubes was added to 100 mL of sulfuric acid solution with a molar concentration of 2 mol / L. After magnetic stirring at 50 °C for 2 h, it was washed with deionized water and freeze-dried to obtain pretreated halloysite nanotubes; 1.0 g of pretreated halloysite nanotubes was dispersed in 100 mL of ethanol aqueous solution with a volume concentration of 50%. Then 0.7 g of phytic acid was added and stirred under vacuum for 1 h. After centrifugal separation, 1.1 g of CuCl 2 ·2H 2 O, 50 mL of ethanol and 50 mL of deionized water were mixed, and ultrasonic stirring was carried out at 80 °C for 1 h, followed by centrifugation, washing with ethanol and deionized water in sequence, and freeze-drying to obtain the flame retardant.

[0049] 21.03 g of 3-aminopropyltriethoxysilane and 10.57 mL of triethylamine were added to a three-necked flask containing 50 mL of toluene solution. 5 g of hexachlorocyclotriphosphazene was dissolved in 20 mL of toluene and added dropwise to the three-necked flask. Then the reaction was carried out at 100 °C for 5 h, followed by filtration and rotary evaporation at 60 °C to obtain the amino-functionalized phosphazene component; under ultrasonic treatment, 3 g of the amino-functionalized phosphazene component was added to a three-necked culture flask, 60 mL of acetic acid solution with a volume concentration of 1.7% was added, then 0.5 g of the flame retardant was added, and continuous stirring was carried out at 80 °C for 6 h. Then 4 mL of ammonia water was added dropwise and reflux stirring was continued for 16 h. After centrifugal washing and freeze-drying, the composite flame retardant was obtained.

[0050] 70 g of PVC resin, 45 g of modified PVC powder, 15 g of AS resin, 10 g of POE resin, 10 g of tannin-based epoxy resin, 22 g of composite flame retardant, and 4 g of lubricant were added to a high-speed mixer and mixed at a high speed of 1200 rpm for 10 min. Then the mixture was loaded into a torque rheometer and kneaded at 170 °C with a rotation speed of 40 rpm until the torque was stable, and then discharged and pelletized to obtain the high-temperature resistant PVC flame retardant material.

[0051] The present invention also carried out comparative examples and related tests.

[0052] Comparative Example 1 Compared with Example 1, the difference was only that the modified PVC powder was not prepared, and other preparation steps and components remained unchanged. Finally, the high-temperature resistant PVC flame retardant material was obtained.

[0053] Comparative Example 2 Compared with Example 1, the difference was only that the tannin-based epoxy resin was not prepared, and epoxy resin was directly added. Other preparation steps and components remained unchanged. Finally, the high-temperature resistant PVC flame retardant material was obtained.

[0054] Comparative Example 3 Compared with Example 1, the difference is only that the composite flame retardant was not prepared, and phytic acid was directly added as the flame retardant, while other preparation steps and components remained unchanged, and finally a high-temperature resistant PVC flame retardant material was obtained.

[0055] Performance detection test The high-temperature resistant PVC flame retardant materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were respectively loaded into a flat vulcanizing machine, the temperature was controlled at 200 ± 5 °C, the pressure was 2.0 MPa, and the holding pressure hot pressing time was 7 min. The high-temperature resistant PVC flame retardant materials were pressed into sheet blanks. Samples were taken from the sheet blanks, and a tensile test was carried out with reference to the standard of GB / T1040.1-2018 Determination of Tensile Properties of Plastics, and the tensile rate was 35 mm / min; specimens with a thickness of 2 mm were prepared, and a combustion test was carried out using a UL94 combustion tester; the smoke density was tested with reference to the standard of GB / T8323.2-2008 Plastics - Smoke Generation - Part 2: Determination of Smoke Density by the Single Chamber Method; with reference to GB / T2951.32-2008 General Test Methods for Insulating and Sheathing Materials of Cables and Optical Fibre Cables - Part 32: Special Test Methods for Polyvinyl Chloride Compounds - Loss of Mass Test - Thermal Stability Test, a high-temperature test at 200 °C was carried out on the test samples, and the thermal stability time of the test samples was measured. The test samples were narrow strips with a length of 30 - 40 mm. The above specific basic performance test results are summarized in Table 1 as follows.

[0056] Table 1: Basic performance test results

[0057] As can be seen from Table 1, the tensile strength of the high-temperature resistant PVC flame retardant materials prepared in Examples 1 to 5 of the present invention reached 32.9 - 38.7 MPa, showing higher mechanical strength compared with Comparative Examples 1 to 3. The combustion grades all reached V-0 level, and the smoke density was lower than 80 mg / g, showing excellent flame retardant and low smoke performance.

[0058] Combined with the test data in Table 1, it can be seen that compared with Comparative Example 1, in Example 1, the silicon / zirconium composite sol hydrolyzed from tetraethyl orthosilicate and ZrOCl 2 formed a cross-linked structure in the PVC resin, which improved the interfacial bonding force while significantly increasing the tensile strength and thermal stability. The enhancement of the bonding force also further reduced the smoke density; in Comparative Example 2, the epoxy resin was not modified, resulting in a significant decrease in the tensile strength and thermal stability. This is because the hydroxyl groups in the tannin molecules cross-linked with the epoxy groups to form a network structure, effectively improving the overall tensile strength, and the polyphenol structure in the tannin-based epoxy resin delayed the thermal oxidative degradation of PVC, further improving the overall thermal stability; compared with Comparative Example 3, in Example 1, the preparation of the composite flame retardant achieved better flame retardant and low smoke effects; the performance of Example 3 was slightly lower because the surface modification was not carried out using the amino-functionalized phosphazene component, which affected the tensile strength and smoke suppression to a certain extent.

[0059] To further verify the high-temperature flame retardant properties of the high-temperature resistant PVC flame retardant materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3, the sheet blanks were placed in a nitrogen atmosphere furnace, heated to 100 ± 5 °C, kept warm and baked for 3 h, then cooled to room temperature with the furnace and left to stand for 2.5 h, and this cycle was repeated 30 times. After the high-temperature cycle, specimens were cut again for tensile and combustion tests. The specific test data results are shown in Table 2.

[0060] Table 2: Test results of tensile strength and flame retardant properties after high-temperature cycle

[0061] As can be seen from the data in Table 2, the mechanical property retention rate of the high-temperature resistant PVC flame retardant materials prepared in Examples 1 to 5 of the present invention is still > 90% after high-temperature cycle, the flame retardant property has no obvious change and still remains at V-0 level. The tensile strength of the comparative examples decreased significantly, and the flame retardant property is also much worse. This further proves that the high-temperature resistant PVC flame retardant material prepared by the present invention can resist the damage of thermal stress through the synergistic cross-linking structure of tannin-based epoxy resin and modified PVC material, and the rigid skeleton of halloysite nanotubes and the phosphazene polymer layer can still maintain good flame retardant properties during multiple thermal cycles.

[0062] The above are the preferred embodiments of the present invention. Without departing from the principle of the present invention, those of ordinary skill in the art can also make several improvements and refinements, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high temperature resistant PVC flame retardant material, characterized in that: The steps include: S1. Mix the ethanol solution and ethyl orthosilicate, add the ZrOCl2·8H2O solution and stir, mix with the PVC resin powder after heating, ultrasonically disperse, vacuum dry, pass nitrogen to keep warm, and quickly heat up to obtain modified PVC powder; S2, adding tannin and NaOH into water with mechanical stirring, slowly adding epichlorohydrin with heating and stirring, cooling, rotary evaporation, adding tetrahydrofuran, filtering, and vacuum drying to obtain tannin-based epoxy resin; S3, dispersing the pretreated halloysite nanotubes in an ethanol aqueous solution, adding phytic acid, vacuum stirring, centrifugal separation, adding CuCl2·2H2O, ethanol and deionized water to mix, ultrasonic stirring, centrifuging, washing, and freeze-drying to obtain a composite flame retardant; S4, putting PVC resin, modified PVC powder, AS resin, POE resin, tannin-based epoxy resin, composite flame retardant and lubricant into a high-speed mixer, mixing, kneading and granulating at high speed to obtain high temperature resistant PVC flame retardant material.

2. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: In the step S1, after adding ZrOCl2·8H2O solution and stirring, ammonia water is added to adjust the pH value to 4-9, and after heating at 100°C for 20 hours, the solution is mixed with PVC resin powder, ultrasonically dispersed at 40kHz for 1-2 hours, vacuum dried, nitrogen protection is introduced, the solution is kept at 120°C for 1 hour, and the temperature is rapidly raised to 300°C and kept for 2 hours to obtain modified PVC powder.

3. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: In step S2, the temperature of mechanical stirring is 30°C and the time is 60 minutes, the temperature of heating stirring is 95°C and the time is 5 hours, the temperature of rotary evaporation is 60°C, and the temperature of vacuum drying is 60-80°C and the time is 16-24 hours.

4. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: The pretreated halloysite nanotubes in step S3 are prepared by mixing the halloysite nanotubes with a sulfuric acid solution having a molar concentration of 2 mol / L, stirring the mixture by magnetic force at 50-80° C. for 2-5 hours, washing the mixture with deionized water, and freeze-drying the mixture.

5. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: In the step S3, after freeze drying, the mixture is immersed in an acetic acid solution containing an amino-functionalized phosphazene component, ultrasonically treated, and continuously stirred at 80° C. for 6 hours, then ammonia water is added dropwise, reflux stirring is continued for 16 hours, centrifuged and washed, and freeze dried to finally obtain a composite flame retardant.

6. The method for preparing a high temperature resistant PVC flame retardant material according to claim 5, characterized in that: The amino-functionalized phosphazene component is prepared by adding 3-aminopropyltriethoxysilane and triethylamine into a three-necked flask filled with a toluene solution, dissolving hexachlorocyclotriphosphazene in toluene and adding the mixture dropwise into the three-necked flask, heating for reaction, filtering, and rotary evaporation; the volume concentration of the acetic acid solution is 1.7%.

7. The method for preparing a high temperature resistant PVC flame retardant material according to claim 6, characterized in that: The heating reaction temperature is 100-120°C, the time is 3-5h, and the rotary evaporation temperature is 60°C.

8. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: In step S3, the vacuum stirring time is 1-2 hours, the ultrasonic stirring temperature is 80° C. and the time is 1-3 hours, and washing is carried out with ethanol and deionized water in sequence.

9. The method for preparing a high temperature resistant PVC flame retardant material according to claim 1, characterized in that: In the step S4, PVC resin, modified PVC powder, AS resin, POE resin, tannin-based epoxy resin, composite flame retardant and lubricant are put into a high-speed mixer, mixed at a high speed of 1200 rpm for 10-20 minutes, and then the mixture is put into a torque rheometer, and the rotation speed is 40 rpm at 170-200° C., and the mixture is mixed until the torque is stable, and the material is discharged and granulated to obtain a high temperature resistant PVC flame retardant material.

10. A high temperature resistant PVC flame retardant material, prepared by the method for preparing a high temperature resistant PVC flame retardant material according to any one of claims 1 to 9, characterized in that: The invention comprises the following raw materials in parts by weight: 60-100 parts of PVC resin, 30-50 parts of modified PVC powder, 10-15 parts of AS resin, 5-10 parts of POE resin, 10-30 parts of tannin-based epoxy resin, 22-30 parts of composite flame retardant and 2-5 parts of lubricant.

Images