High-temperature-resistant CPVC plate and preparation method thereof

Abstract

The invention provides a high-temperature-resistant CPVC plate and a preparation method thereof, and belongs to the technical field of high-temperature-resistant CPVC plates, and the preparation method comprises the following steps: step S1, preparing modified graphite particles; step S2, preparing a microcapsule; s3, adding the N-COF powder, absolute ethyl alcohol and deionized water into a beaker, performing ultrasonic dispersion to obtain an N-COF suspension, performing heating and stirring, sequentially dropwise adding a calcium chloride solution, a zinc chloride solution and a sodium stearate solution, adjusting the pH value, and performing a reaction to prepare core-shell particles; s4, CPVC, the core-shell particles and paraffin are taken and put into a double-screw extruder to be premixed, then modified graphite particles, nano SiO2, octavinyl POSS, microcapsules and surface modified magnesium hydroxide are put into the double-screw extruder, extrusion is conducted, and the high-temperature-resistant CPVC board is prepared. The heat deformation temperature of the high-temperature-resistant CPVC plate can be increased, and the heat stability of the high-temperature-resistant CPVC plate can be improved.

Description

Technical Field

[0001] This invention relates to the field of CPVC sheet technology, specifically to a high-temperature resistant CPVC sheet and its preparation method. Background Technology

[0002] Compared to PVC, CPVC has a higher chlorine content and glass transition temperature, theoretically allowing for a higher upper limit of operating temperature. However, CPVC is prone to chain thermal degradation caused by dehydrochlorination during high-temperature processing and long-term service, leading to decreased mechanical properties and stability. Simultaneously, CPVC sheets are susceptible to limitations in Vicat softening temperature and load deformation temperature under heat and load conditions, restricting their application in high-temperature and high-durability environments. Existing improvement methods typically employ stabilizer systems and inorganic filler reinforcement to enhance the heat resistance and strength of CPVC sheets. However, these methods generally suffer from filler agglomeration, insufficient interfacial compatibility leading to stress concentration and performance fluctuations, and the potential migration / volatilization and time-dependent decay of stabilizers during processing or use. These challenges make it difficult to achieve a synergistic improvement in heat resistance and stability while maintaining mechanical toughness.

[0003] Patent application CN111925663A discloses a CPVC sheet comprising the following key components: 40-50 parts sheet powder, 20-30 parts chlorinated polyvinyl chloride (CPVC) powder, 3-6 parts plasticizer, 2-4 parts preservative, 1-3 parts bactericide, 3-6 parts antioxidant, 2-4 parts modified ABS resin, 5-8 parts lubricant, 2-6 parts defoamer, 6-10 parts thickener, 3-6 parts fire retardant, 1-3 parts heat insulation film, 1 part sound insulation board, 2-5 parts insect repellent, and 10-15 parts water. The CPVC sheet prepared using this method exhibits deficiencies in thermal stability during processing and in mechanical properties and stability during actual use.

[0004] Therefore, there is a need to provide a high-temperature resistant CPVC sheet and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0005] In view of this, the present invention provides a high-temperature resistant CPVC sheet and its preparation method, which can achieve the purpose of improving the heat distortion temperature and thermal stability of the high-temperature resistant CPVC sheet.

[0006] To achieve the above objectives, the present invention provides a method for preparing high-temperature resistant CPVC sheets, comprising the following steps: Step S1: Mix modified nano-graphite powder, CPVC, grafting agent and additives evenly, place in an extruder and extrude to obtain modified graphite particles; Step S2: Add deionized water and polyvinyl alcohol to a stirred tank, heat and stir until completely dissolved, add tris(2,4-di-tert-butylphenyl) phosphite dropwise, shear and stir to obtain an emulsion; mix urea and formaldehyde solution, then add it to the emulsion, adjust the pH, heat and stir the reaction, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules. Step S3: Add N-COF powder, anhydrous ethanol and deionized water to a beaker, disperse by ultrasonication to obtain N-COF suspension, heat and stir, add calcium chloride solution, zinc chloride solution and sodium stearate solution dropwise in sequence, adjust pH, react, cool, stand, centrifuge, wash, vacuum dry, grind, and sieve to obtain core-shell microparticles; Step S4: Take CPVC, core-shell microparticles and paraffin wax and put them into a twin-screw extruder for premixing. Then add modified graphite particles, nano SiO2, octavinyl POSS, microcapsules and surface-modified magnesium hydroxide, and extrude. After sheeting, cool, calender, anneal, and cool to room temperature to obtain high-temperature resistant CPVC sheets.

[0007] Modified nano-graphite has a high thermal conductivity. By extruding and preforming it into modified graphite particles, it can form a thermally conductive network with a certain degree of connectivity inside the CPVC sheet. This facilitates the rapid conduction of heat during processing and use along the in-plane direction of the sheet, reducing local overheating inside the material and at the interface layer. This weakens the local decomposition and stress concentration of CPVC, and helps improve the thermal and dimensional stability of the sheet near its glass transition temperature.

[0008] Tris(2,4-di-tert-butylphenyl) phosphite, as a phosphite-based heat stabilizer and antioxidant, can react with peroxides and free radicals generated during the thermal decomposition of CPVC, reducing them to stable compounds, thus lowering the rate of thermo-oxidative degradation of CPVC and delaying molecular chain breakage. Simultaneously, it reacts with HCl and metal chlorides generated in the system, acting as an acid trap and inhibiting autocatalytic degradation. In-situ polycondensation coating of tris(2,4-di-tert-butylphenyl) phosphite with urea-formaldehyde resin yields core-shell microcapsules. Through microencapsulation, the volatilization loss and migration of tris(2,4-di-tert-butylphenyl) phosphite during processing are significantly reduced. Furthermore, under thermal stress, the UF shell gradually develops microcracks, achieving the slow release of the internal tris(2,4-di-tert-butylphenyl) phosphite, thereby providing relatively long-lasting thermal stability protection during CPVC sheet processing and long-term use.

[0009] The nitrogen coordination sites on the N-COF framework can coordinate with metal ions such as calcium and zinc ions, providing anchoring points for the subsequent directional deposition of Ca / Zn stearate on its surface to form a shell, resulting in core-shell microparticles with an N-COF core and a Ca-Zn stearate shell. Compared with traditional small-molecule Ca / Zn stabilizers, this core-shell structure uniformly fixes Ca / Zn stearate on the COF surface. On the one hand, the porous framework structure of the COF enables the spatially oriented distribution of the stabilizer in the CPVC sheet, avoiding local enrichment; on the other hand, the coordination of calcium and zinc ions with the nitrogen atoms of the COF framework reduces the activity of free zinc ions, weakening their excessive catalysis of CPVC deHCl removal. Therefore, the core-shell microparticles achieve a balance between improved thermal stability and suppression of side reactions, significantly improving the processing thermal stability and long-term service stability of the sheet.

[0010] Preferably, in step S1, the preparation of modified nano-graphite powder includes the following steps: Nano-graphite powder was added to anhydrous ethanol, stirred at room temperature, and then sonicated to obtain a suspension. Tetraethyl silicate was dissolved in ethanol and added dropwise to the suspension. The mixture was heated and stirred, and deionized water was added to adjust the pH to 8-9. After the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain modified nano-graphite powder.

[0011] Tetraethyl silicate was used to sol-gel modify nano-graphite under alkaline conditions, generating an in-situ SiO2 shell on the graphite surface. The polar groups such as hydroxyl groups on the surface of the shell can interact with the matrix material and filler material to form a stable interface layer. Under external force, this facilitates the transfer of stress from the matrix to the graphite reinforcement phase, thereby improving the flexural modulus and heat distortion temperature of CPVC sheets.

[0012] Preferably, the stirring speed at room temperature is 200-300 rpm and the time is 5-10 min; the stirring temperature during heating is 30-40℃ and the speed is 600-800 rpm.

[0013] Preferably, the grafting agent in step S1 is PE-g-MAH; the additives include at least one of chlorinated polyethylene and MBS resin.

[0014] The main chain of PE-g-MAH is a non-polar polyethylene chain segment, which is compatible with CPVC resin. The maleic anhydride polar groups on the side chain can form carboxyl or ester groups, which can form hydrogen bonds or coordination with other fillers. This allows it to act as an interfacial bridge and compatibilizer between the CPVC matrix and various functional fillers, significantly improving the dispersion of fillers in the matrix, reducing agglomeration and interfacial debonding, and thus reducing stress concentration.

[0015] Preferably, in step S2, the heating and stirring temperature is 50-60℃ and the speed is 500-700 rpm; the shearing and stirring speed is 2000-3500 rpm and the time is 2-4 min; the heating and stirring reaction temperature is 55-65℃, the speed is 500-700 rpm, and the time is 1.5-2.5 h.

[0016] Preferably, the preparation of the N-COF powder includes the following steps: Add pyromellitic aldehyde and melamine to the reaction vessel, then add 1,4-dioxane and anhydrous ethanol. Stir at 400-600 rpm for 10-15 min at room temperature, add glacial acetic acid, continue stirring for 10-15 min, introduce nitrogen gas, raise the temperature to 110-120℃, and react in an oil bath for 18-24 h. After the reaction is completed, allow it to cool naturally to room temperature, filter, wash, and vacuum dry to obtain N-COF powder.

[0017] N-COF powder, obtained by polycondensation of pyromellitic methyl ether and melamine, has a covalent organic framework structure, is rich in C=N bonds and triazine nitrogen atoms, and has a high thermal decomposition temperature and a rigid framework. As an organic nanofiller in CPVC materials, N-COF can create spatial constraints on CPVC chain segments, thereby improving the heat distortion temperature and high-temperature mechanical retention of CPVC sheets.

[0018] Preferably, in step S3, the heating and stirring temperature is 50-60℃, the speed is 600-800 rpm, the pH is adjusted to 8-9, and the reaction time is 1.5-3h.

[0019] Preferably, in step S4, the preparation of surface-modified magnesium hydroxide includes the following steps: Magnesium hydroxide powder was dispersed in toluene, stearic acid was added, and the mixture was stirred at 500-700 rpm while reacting in an oil bath at 60-80℃ for 1-2 hours. The mixture was then filtered, washed, and dried to obtain surface-modified magnesium hydroxide.

[0020] Surface modification of magnesium hydroxide with stearic acid transforms its surface from highly polar to relatively hydrophobic, improving its compatibility with the CPVC matrix and organic phases in the formulation. This helps inhibit magnesium hydroxide agglomeration and promotes dispersion. Magnesium hydroxide decomposes at high temperatures to generate MgO and water vapor. This decomposition process absorbs a large amount of heat, slowing down the material's temperature rise. Simultaneously, the released water vapor dilutes combustible gases and oxygen in the air. The MgO residue forms a heat-insulating and oxygen-barrier inorganic protective layer, thereby improving the flame-retardant and smoke-suppressing properties of the board. Furthermore, magnesium hydroxide can neutralize the acidic gases produced by the thermal decomposition of CPVC, playing a supporting stabilizing role in inhibiting the thermal degradation of CPVC.

[0021] Preferably, in step S4, the extrusion temperature is 175-185℃ and the rotation speed is 220-280rpm; the annealing temperature is 120-130℃ and the annealing time is 2-3h.

[0022] Annealing helps release the stress generated during the forming process of the sheet material and can also promote the optimization of the internal structure of the sheet material, so that the sheet material has a higher heat distortion temperature and less tendency to warp, shrink and crack during subsequent use, and significantly improves the high-temperature dimensional stability.

[0023] To achieve the above objectives, the present invention also provides a high-temperature resistant CPVC sheet prepared by the above-described method for preparing high-temperature resistant CPVC sheets, comprising the following components in parts by weight: 100-120 parts CPVC, 3-3.6 parts core-shell microparticles, 0.5-0.6 parts paraffin, 8-9.6 parts modified graphite particles, 6-7.2 parts nano SiO2, 4-4.8 parts octavinyl POSS, 1-1.2 parts microcapsules, and 4-4.8 parts surface-modified magnesium hydroxide.

[0024] The high-temperature resistant CPVC sheets prepared using the above-mentioned components in parts by weight can achieve improved thermal stability, mechanical properties, and extended service life.

[0025] The above-described technical solution of the present invention has at least the following beneficial effects: 1. Modified nano-graphite has a high thermal conductivity. By extruding and pre-forming modified graphite particles, it can form a thermally conductive network with a certain degree of connectivity inside the CPVC sheet, thereby reducing local overheating inside the material and at the interface layer, thus weakening the local decomposition and stress concentration of CPVC, which is beneficial to improving the thermal stability and dimensional stability of the sheet near the glass transition temperature.

[0026] 2. In-situ polycondensation coating of tris(2,4-di-tert-butylphenyl) phosphite with urea-formaldehyde resin was used to obtain core-shell microcapsules. Microencapsulation reduces the volatilization loss and migration of phosphite during processing, and the UF shell gradually ruptures or forms microcracks at high temperatures, achieving slow release of the heat stabilizer. This provides more durable thermal stability protection during the processing and long-term use of CPVC sheets.

[0027] 3. Compared with traditional small molecule Ca / Zn stabilizers, the core-shell structure prepared by this invention uniformly fixes Ca / Zn stearate on the COF surface, which can avoid the local enrichment of calcium and zinc ions and reduce the activity of free zinc ions, weakening their excessive catalysis of CPVC deHCl removal, thereby improving the processing thermal stability and long-term use stability of the board. Detailed Implementation

[0028] 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 some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0029] Example 1 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 250rpm for 8min at room temperature, and then sonicate for 15min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 35℃ and stir continuously at 700rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 3h, centrifuge, wash, and vacuum dry at 65℃ for 5h to obtain modified nano-graphite powder. Mix 25g of modified nano-graphite powder, 72g of CPVC, 2g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1g of chlorinated polyethylene evenly, and extrude in an extruder to obtain modified graphite granules.

[0030] Add 350 mL of deionized water and 2 g of polyvinyl alcohol to a stirred tank, heat to 55 °C, and stir at 600 rpm until completely dissolved. Add 10 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 3000 rpm for 3 min to obtain an emulsion. Mix 3.5 g of urea and 4.2 g of 37 wt% formaldehyde solution, and add the mixture to the emulsion. Adjust the pH to 2.8-3.5, heat to 55 °C, and stir at 500 rpm for 2.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0031] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 0.9g of stearic acid, stir at 600rpm, and react for 1.5h in an oil bath at 80℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0032] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 500 rpm for 12 min at room temperature. Then, 3 mL of glacial acetic acid was added, and the mixture was stirred for another 15 min. Nitrogen gas was introduced, and the temperature was raised to 110 °C. The mixture was reacted in an oil bath for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0033] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 65℃ until completely dissolved to obtain a sodium stearate solution.

[0034] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 20min to obtain an N-COF suspension. Heat to 55℃ and stir continuously at 700rpm. Add calcium chloride solution dropwise over 15min, then add zinc chloride solution dropwise over 15min, and finally add sodium stearate solution dropwise over 30min. Adjust the pH to 8-9 and react for 2.5h. Cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0035] 120g of CPVC, 3.6g of core-shell microparticles and 0.6g of paraffin wax were premixed in a twin-screw extruder. Then, 9.6g of modified graphite granules, 7.2g of nano-SiO2, 4.8g of octavinyl POSS, 1.2g of microcapsules and 4.8g of surface-modified magnesium hydroxide were added. The mixture was extruded at 180℃ and 250rpm. After sheeting, the mixture was cooled, calendered, annealed at 130℃ for 2 hours, and cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0036] Example 2 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 200rpm for 10min at room temperature, and then sonicate for 20min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 40℃ and stir continuously at 800rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 2.5h, centrifuge, wash, and vacuum dry at 60℃ for 6h to obtain modified nano-graphite powder. Mix 30g of modified nano-graphite powder, 86.4g of CPVC, 2.4g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1.2g of chlorinated polyethylene and MBS resin evenly, and extrude in an extruder to obtain modified graphite particles.

[0037] Add 350 mL of deionized water and 3 g of polyvinyl alcohol to a stirred tank, heat to 60 °C, and stir at 700 rpm until completely dissolved. Add 15 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 2000 rpm for 4 min to obtain an emulsion. Mix 5.25 g of urea and 6.3 g of 37 wt% formaldehyde solution, and add the mixture to the emulsion. Adjust the pH to 2.8-3.5, heat to 65 °C, and stir at 700 rpm for 1.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0038] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 1.2g of stearic acid, stir at 500rpm, and react for 1h in an oil bath at 80℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0039] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 400 rpm for 15 min at room temperature. 2 mL of glacial acetic acid was added, and stirring was continued for 10 min. Nitrogen gas was introduced, and the temperature was raised to 120 °C. The mixture was reacted in an oil bath for 18 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0040] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 65℃ until completely dissolved to obtain a sodium stearate solution.

[0041] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 20min to obtain an N-COF suspension. Heat to 50℃ and stir continuously at 800rpm. Add calcium chloride solution dropwise over 10min, then add zinc chloride solution dropwise over 10min, and finally add sodium stearate solution dropwise over 40min. Adjust the pH to 8-9 and react for 1.5h. Cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0042] 100g of CPVC, 3g of core-shell microparticles and 0.5g of paraffin wax were premixed in a twin-screw extruder, followed by 8g of modified graphite granules, 6g of nano-SiO2, 4g of octavinyl POSS, 1g of microcapsules and 4g of surface-modified magnesium hydroxide. The mixture was extruded at 175℃ and 220rpm. After sheeting, the mixture was cooled, calendered, annealed at 120℃ for 3 hours, and then cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0043] Example 3 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 300rpm for 5min at room temperature, and then sonicate for 20min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 30℃ and stir continuously at 600rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 3.5h, centrifuge, wash, and vacuum dry at 70℃ for 4h to obtain modified nano-graphite powder. Mix 30g of modified nano-graphite powder, 86.4g of CPVC, 2.4g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1.2g of chlorinated polyethylene and MBS resin evenly, and extrude in an extruder to obtain modified graphite granules.

[0044] Add 350 mL of deionized water and 2 g of polyvinyl alcohol to a stirred tank, heat to 50 °C, and stir at 500 rpm until completely dissolved. Add 10 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 3500 rpm for 2 min to obtain an emulsion. Mix 3.5 g of urea and 4.2 g of 37 wt% formaldehyde solution, and then add it to the emulsion. Adjust the pH to 2.8-3.5, heat to 55 °C, and stir at 500 rpm for 2.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0045] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 0.6g of stearic acid, stir at 700rpm, and react for 2h in an oil bath at 60℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0046] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 600 rpm for 10 min at room temperature. Then, 3 mL of glacial acetic acid was added, and the mixture was stirred for another 15 min. Nitrogen gas was introduced, and the temperature was raised to 110 °C. The mixture was reacted in an oil bath for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0047] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 65℃ until completely dissolved to obtain a sodium stearate solution.

[0048] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 15min to obtain an N-COF suspension. Heat to 60℃ and stir continuously at 600rpm. Add calcium chloride solution dropwise over 12min, then add zinc chloride solution dropwise over 12min, and finally add sodium stearate solution dropwise over 35min. Adjust the pH to 8-9, react for 2h, cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0049] 120g of CPVC, 3.6g of core-shell microparticles and 0.6g of paraffin were premixed in a twin-screw extruder. Then, 9.6g of modified graphite granules, 7.2g of nano-SiO2, 4.8g of octavinyl POSS, 1.2g of microcapsules and 4.8g of surface-modified magnesium hydroxide were added. The mixture was extruded at 185℃ and 280rpm. After sheeting, the mixture was cooled, calendered, annealed at 130℃ for 2 hours, and cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0050] Example 4 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 250rpm for 8min at room temperature, and then sonicate for 15min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 35℃ and stir continuously at 700rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 3h, centrifuge, wash, and vacuum dry at 65℃ for 5h to obtain modified nano-graphite powder. Mix 25g of modified nano-graphite powder, 72g of CPVC, 2g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1g of chlorinated polyethylene evenly, and extrude in an extruder to obtain modified graphite granules.

[0051] Add 350 mL of deionized water and 3 g of polyvinyl alcohol to a stirred tank, heat to 60 °C, and stir at 700 rpm until completely dissolved. Add 15 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 2000 rpm for 4 min to obtain an emulsion. Mix 5.25 g of urea and 6.3 g of 37 wt% formaldehyde solution, and add the mixture to the emulsion. Adjust the pH to 2.8-3.5, heat to 65 °C, and stir at 700 rpm for 1.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0052] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 0.9g of stearic acid, stir at 550rpm, and react for 1.5h in an oil bath at 75℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0053] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 450 rpm for 15 min at room temperature. Then, 2.5 mL of glacial acetic acid was added, and stirring was continued for 12 min. Nitrogen gas was introduced, and the temperature was raised to 115 °C. The mixture was reacted in an oil bath for 21 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0054] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 60℃ until completely dissolved to obtain a sodium stearate solution.

[0055] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 15min to obtain an N-COF suspension. Heat to 55℃ and stir continuously at 750rpm. Add calcium chloride solution dropwise over 15min, then add zinc chloride solution dropwise over 15min, and finally add sodium stearate solution dropwise over 30min. Adjust the pH to 8-9, react for 2h, cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0056] 100g of CPVC, 3.6g of core-shell microparticles, and 0.5g of paraffin wax were premixed in a twin-screw extruder. Then, 8g of modified graphite granules, 7.2g of nano-SiO2, 4.8g of octavinyl POSS, 1.2g of microcapsules, and 4.8g of surface-modified magnesium hydroxide were added. The mixture was extruded at 180℃ and 250rpm. After sheeting, the mixture was cooled, calendered, annealed at 125℃ for 2.5h, and cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0057] Example 5 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 200rpm for 10min at room temperature, and then sonicate for 20min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 40℃ and stir continuously at 800rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 2.5h, centrifuge, wash, and vacuum dry at 60℃ for 6h to obtain modified nano-graphite powder. Mix 30g of modified nano-graphite powder, 86.4g of CPVC, 2.4g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1.2g of chlorinated polyethylene and MBS resin evenly, and extrude in an extruder to obtain modified graphite particles.

[0058] Add 350 mL of deionized water and 2 g of polyvinyl alcohol to a stirred tank, heat to 55 °C, and stir at 600 rpm until completely dissolved. Add 10 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 3000 rpm for 3 min to obtain an emulsion. Mix 3.5 g of urea and 4.2 g of 37 wt% formaldehyde solution, and add the mixture to the emulsion. Adjust the pH to 2.8-3.5, heat to 55 °C, and stir at 500 rpm for 2.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0059] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 1.2g of stearic acid, stir at 500rpm, and react for 1h in an oil bath at 80℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0060] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 600 rpm for 10 min at room temperature. Then, 3 mL of glacial acetic acid was added, and the mixture was stirred for another 15 min. Nitrogen gas was introduced, and the temperature was raised to 110 °C. The mixture was reacted in an oil bath for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0061] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 70℃ until completely dissolved to obtain a sodium stearate solution.

[0062] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 20min to obtain an N-COF suspension. Heat to 55℃ and stir continuously at 700rpm. Add calcium chloride solution dropwise over 15min, then add zinc chloride solution dropwise over 15min, and finally add sodium stearate solution dropwise over 30min. Adjust the pH to 8-9 and react for 2.5h. Cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0063] 120g of CPVC, 3g of core-shell microparticles and 0.6g of paraffin wax were premixed in a twin-screw extruder, followed by 9.6g of modified graphite granules, 6g of nano-SiO2, 4g of octavinyl POSS, 1.2g of microcapsules and 4g of surface-modified magnesium hydroxide. The mixture was extruded at 175℃ and 250rpm. After sheeting, the mixture was cooled, calendered, annealed at 120℃ for 3 hours, and then cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0064] Example 6 Add 40g of nano-graphite powder to 700mL of anhydrous ethanol, stir at 300rpm for 5min at room temperature, and then sonicate for 20min to obtain a suspension. Dissolve 4g of tetraethyl orthosilicate in 50mL of ethanol and add it dropwise to the suspension. Heat to 30℃ and stir continuously at 600rpm. Add 2mL of deionized water to adjust the pH to 8-9, react for 3.5h, centrifuge, wash, and vacuum dry at 70℃ for 4h to obtain modified nano-graphite powder. Mix 30g of modified nano-graphite powder, 86.4g of CPVC, 2.4g of PE-g-MAH (maleic anhydride grafted polyethylene), and 1.2g of chlorinated polyethylene and MBS resin evenly, and extrude in an extruder to obtain modified graphite granules.

[0065] Add 350 mL of deionized water and 3 g of polyvinyl alcohol to a stirred tank, heat to 60 °C, and stir at 700 rpm until completely dissolved. Add 15 g of tris(2,4-di-tert-butylphenyl) phosphite dropwise, and stir at 2000 rpm for 4 min to obtain an emulsion. Mix 5.25 g of urea and 6.3 g of 37 wt% formaldehyde solution, and add the mixture to the emulsion. Adjust the pH to 2.8-3.5, heat to 65 °C, and stir at 700 rpm for 1.5 h. After the reaction is complete, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules.

[0066] Take 40g of magnesium hydroxide powder, disperse it in 300mL of toluene, add 0.9g of stearic acid, stir at 550rpm, and react for 1.5h in an oil bath at 75℃. Filter, wash, and dry to obtain surface-modified magnesium hydroxide.

[0067] 1.5 g of trimesin and 1.26 g of melamine were added to the reaction vessel, followed by 60 mL of 1,4-dioxane and 40 mL of anhydrous ethanol. The mixture was stirred at 400 rpm for 15 min at room temperature. 2 mL of glacial acetic acid was added, and stirring was continued for 10 min. Nitrogen gas was introduced, and the temperature was raised to 120 °C. The mixture was reacted in an oil bath for 18 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed, and vacuum dried to obtain N-COF powder.

[0068] Dissolve 3g of calcium chloride dihydrate in 50mL of deionized water to obtain a calcium chloride solution; dissolve 2.7g of zinc chloride in 50mL of deionized water to obtain a zinc chloride solution; dissolve 23g of sodium stearate in 150mL of deionized water and stir at 60℃ until completely dissolved to obtain a sodium stearate solution.

[0069] Add 10g of N-COF powder, 125mL of anhydrous ethanol, and 125mL of deionized water to a beaker, and sonicate for 15min to obtain an N-COF suspension. Heat to 60℃ and stir continuously at 600rpm. Add calcium chloride solution dropwise over 12min, then add zinc chloride solution dropwise over 12min, and finally add sodium stearate solution dropwise over 35min. Adjust the pH to 8-9, react for 2h, cool to room temperature, let stand for 30min, centrifuge to separate the solid, wash, vacuum dry, grind, and pass through a 200-mesh sieve to obtain core-shell microparticles.

[0070] 110g of CPVC, 3.6g of core-shell microparticles, and 0.5g of paraffin wax were premixed in a twin-screw extruder. Then, 8g of modified graphite particles, 6g of nano-SiO2, 4.8g of octavinyl POSS, 1.2g of microcapsules, and 4.8g of surface-modified magnesium hydroxide were added. The mixture was extruded at 180℃ and 280rpm. After sheeting, the mixture was cooled, calendered, annealed at 130℃ for 2.5h, and cooled to room temperature to obtain high-temperature resistant CPVC sheets.

[0071] The present invention also includes comparative examples and related experiments.

[0072] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no modified graphite particles were prepared in Comparative Example 1. The other components and preparation methods are the same as in Example 1, and high-temperature resistant CPVC sheets are prepared.

[0073] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no microcapsules were prepared. The other components and preparation methods were the same as in Example 1, and a high-temperature resistant CPVC board was prepared.

[0074] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that core-shell microparticles were not prepared; instead, a calcium-zinc stabilizer was used instead. The other components and preparation methods were the same as in Example 1, and a high-temperature resistant CPVC sheet was prepared.

[0075] Performance testing The high-temperature resistant CPVC sheets prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests, wherein the tensile strength was tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molding and extruded plastics"; The thermal aging test was conducted according to GB / T 7141-2008 "Plastics Thermal Aging Test Method". The test conditions were 160℃×168h. After the test, the tensile strength test was conducted and compared with the original tensile strength. The tensile strength retention rate after thermal aging was used as the result of the thermal stability test. According to GB / T 9341-2008 "Determination of Flexural Properties of Plastics", the high-temperature resistant CPVC sheets prepared in Examples 1-6 and Comparative Examples 1-3 were tested for flexural properties, and the flexural strength was used as the test result. According to GB / T 1633-2000 "Determination of Vicat softening temperature of thermoplastic plastics", the high-temperature resistant CPVC sheets prepared in Examples 1-6 and Comparative Examples 1-3 were tested for Vicat softening temperature. The heating rate was 50℃ / h and the pressure was 10N. According to GB / T 1634-2019 "Determination of Load Deformation Temperature of Plastics", the high-temperature resistant CPVC sheets prepared in Examples 1-6 and Comparative Examples 1-3 were tested for load deformation temperature. The applied bending stress was 1.80 MPa, the heating rate was 120℃ / h, and the temperature at which the deflection reached 0.34 mm was taken as the result. The test results are summarized in Table 1.

[0076] Table 1

[0077] As shown in Table 1 above, the high-temperature resistant CPVC sheet prepared in Comparative Example 1 shows a significant decrease in tensile and flexural strength compared to the high-temperature resistant CPVC sheet prepared in Example 1. This indicates that skipping the preparation of modified graphite particles directly leads to easier graphite agglomeration, resulting in stress concentration points and micro-defects in the sheet, ultimately causing a decrease in tensile / flexural strength. Simultaneously, its Vicat softening temperature and load deformation temperature also decrease significantly, indicating that graphite agglomeration leads to reduced interfacial heat transfer efficiency, making thermal deformation more likely. Compared to Example 1, the high-temperature resistant CPVC sheet prepared in Comparative Example 2 shows a significant decrease in tensile and flexural strength. The significant decrease in the retention rate of aging tensile strength indicates that the microcapsules can be released slowly during thermal aging, continuously capturing peroxides / free radicals, delaying the CPVC degradation chain reaction, and thus maintaining the thermal stability of the board. Compared with Example 1, the various properties of the high-temperature resistant CPVC board prepared in Comparative Example 3 are all reduced to a certain extent, indicating that the core-shell microparticles uniformly fix Ca / Zn stearate on the COF surface, which can not only avoid the local enrichment of calcium and zinc ions, but also reduce the activity of free zinc ions, weaken their excessive catalysis of CPVC deHCl removal, and improve the thermal stability and long-term service stability of the board.

[0078] The above are preferred embodiments of the present invention. Those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant CPVC sheet, characterized in that, Includes the following steps: Step S1: Mix modified nano-graphite powder, CPVC, grafting agent and additives evenly, place in an extruder and extrude to obtain modified graphite particles; Step S2: Add deionized water and polyvinyl alcohol to a stirred tank, heat and stir until completely dissolved, add tris(2,4-di-tert-butylphenyl) phosphite dropwise, shear and stir to obtain an emulsion; mix urea and formaldehyde solution, then add it to the emulsion, adjust the pH, heat and stir the reaction, adjust the pH to neutral, cool, filter, wash, and vacuum dry to obtain microcapsules. Step S3: Add N-COF powder, anhydrous ethanol and deionized water to a beaker, disperse by ultrasonication to obtain N-COF suspension, heat and stir, add calcium chloride solution, zinc chloride solution and sodium stearate solution dropwise in sequence, adjust pH, react, cool, stand, centrifuge, wash, vacuum dry, grind, and sieve to obtain core-shell microparticles; Step S4: Take CPVC, core-shell microparticles and paraffin wax and put them into a twin-screw extruder for premixing. Then add modified graphite particles, nano SiO2, octavinyl POSS, microcapsules and surface-modified magnesium hydroxide, and extrude. After sheeting, cool, calender, anneal, and cool to room temperature to obtain high-temperature resistant CPVC sheets.

2. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S1, the preparation of modified nano-graphite powder includes the following steps: Nano-graphite powder was added to anhydrous ethanol, stirred at room temperature, and then sonicated to obtain a suspension. Tetraethyl silicate was dissolved in ethanol and added dropwise to the suspension. The mixture was heated and stirred, and deionized water was added to adjust the pH to 8-9. After the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain modified nano-graphite powder.

3. The method for preparing a high-temperature resistant CPVC sheet according to claim 2, characterized in that, The stirring speed at room temperature is 200-300 rpm for 5-10 min; the stirring temperature during heating is 30-40℃ and the stirring speed is 600-800 rpm.

4. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S1, the grafting agent is PE-g-MAH; the additives include at least one of chlorinated polyethylene and MBS resin.

5. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S2, the heating and stirring temperature is 50-60℃ and the speed is 500-700 rpm; the shearing and stirring speed is 2000-3500 rpm and the time is 2-4 min; the heating and stirring reaction temperature is 55-65℃, the speed is 500-700 rpm, and the time is 1.5-2.5 h.

6. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, The preparation of the N-COF powder includes the following steps: Add pyromellitic aldehyde and melamine to the reaction vessel, then add 1,4-dioxane and anhydrous ethanol. Stir at 400-600 rpm for 10-15 min at room temperature, add glacial acetic acid, continue stirring for 10-15 min, introduce nitrogen gas, raise the temperature to 110-120℃, and react in an oil bath for 18-24 h. After the reaction is completed, allow it to cool naturally to room temperature, filter, wash, and vacuum dry to obtain N-COF powder.

7. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S3, the heating and stirring temperature is 50-60℃, the speed is 600-800 rpm, the pH is adjusted to 8-9, and the reaction time is 1.5-3 hours.

8. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S4, the preparation of surface-modified magnesium hydroxide includes the following steps: Magnesium hydroxide powder was dispersed in toluene, stearic acid was added, and the mixture was stirred at 500-700 rpm while reacting in an oil bath at 60-80℃ for 1-2 hours. The mixture was then filtered, washed, and dried to obtain surface-modified magnesium hydroxide.

9. The method for preparing a high-temperature resistant CPVC sheet according to claim 1, characterized in that, In step S4, the extrusion temperature is 175-185℃ and the rotation speed is 220-280rpm; the annealing temperature is 120-130℃ and the time is 2-3h.

10. A high-temperature resistant CPVC sheet, characterized in that, The high-temperature resistant CPVC sheet is prepared by the method described in any one of claims 1-9, comprising the following components in parts by weight: 100-120 parts CPVC, 3-3.6 parts core-shell microparticles, 0.5-0.6 parts paraffin, 8-9.6 parts modified graphite particles, 6-7.2 parts nano SiO2, 4-4.8 parts octavinyl POSS, 1-1.2 parts microcapsules, and 4-4.8 parts surface-modified magnesium hydroxide.

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