Flame-retardant modified PVC plastic sheet and preparation method thereof

Abstract

The invention provides a flame-retardant modified PVC (polyvinyl chloride) plastic sheet which is formed by co-extruding a surface layer molten master batch and an inner layer molten master batch through a composite die head, the prepared flame-retardant modified PVC plastic sheet can realize self-triggering flame retardance and has self-repairing capability, and the repairing efficiency is 60-70%. Performance gradient is achieved through layered design, the high flame retardance and weather resistance of the outer layer material are combined with the toughness of the PVC matrix reserved in the inner layer, and the overall mechanical property of the material is improved; meanwhile, carboxylated CNTs and Fe < 3 + > form a Ph response dynamic cross-linked network, so that an acid source is catalyzed to decompose and cross-link while the flame retardant is rapidly released, the flame retardance of the material is improved, and the purpose of self-triggering flame retardance is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of PVC materials, and specifically to a flame-retardant modified PVC plastic sheet and a preparation method thereof. Background Art

[0002] PVC is a widely used thermoplastic. Due to its excellent chemical resistance, low cost, and good mechanical properties, it is widely used in fields such as construction, chemical industry, medical treatment, and food packaging. With the update and iteration of material technology, the inherent flame-retardant property of PVC has enabled it to be widely used in fields such as building materials, cables, and electronic equipment. However, since PVC contains a large amount of chloride ions, a large amount of acidic gases are generated when the PVC material burns, polluting the environment and endangering human health. At the same time, in some special places such as subways, high-speed rails, and cinemas, there are more stringent requirements for the flame retardancy of PVC. However, due to the poor compatibility between PVC and the flame retardant, the flame retardant is extremely easy to precipitate, resulting in material failure. Therefore, high-flame-retardant and stable PVC has become the key research direction of PVC development.

[0003] The invention CN202510268005.0 discloses a modified PVC material. By dispersing magnesium aluminum hydrotalcite powder on the surface of polyvinyl chloride, the agglomeration degree during mixing is reduced. At the same time, the magnesium aluminum hydrotalcite powder absorbs proton hydrogen to improve the flame retardant performance. However, the magnesium aluminum hydrotalcite itself has a relatively large particle size. As a filler, the magnesium aluminum hydrotalcite is a weak point of the material under stress, which will significantly reduce the mechanical properties of the material. At the same time, an excessive amount of proton hydrogen is generated during combustion, and the magnesium aluminum hydrotalcite cannot quickly absorb the proton hydrogen, resulting in a certain lag in flame retardancy. Therefore, it is urgent to solve the problem of how to improve the flame retardant response rate and flame retardancy on the basis of ensuring the strength of the PVC composite material. Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] Aiming at the deficiencies of the prior art, the present invention provides a flame-retardant modified PVC plastic sheet and a preparation method thereof to solve the problems raised in the above background art.

[0006] (II) Technical Solutions

[0007] To achieve the above object, the present invention is realized through the following technical solutions: A flame-retardant modified PVC plastic sheet is formed by co-extrusion of a surface layer and an inner layer molten masterbatch through a composite die head. The surface layer masterbatch includes the following components: 100 phr of PVC resin, 2 phr of carboxylated CNTs, 1 - 2 phr of heat stabilizer, 0.5 - 3 phr of hydrophilic nano-silica, 10 - 20 phr of nitrogen-phosphorus intumescent flame retardant, 0.5 - 1 phr of cross-linking agent, 1.5 - 2.5 phr of FeCl3; The inner layer masterbatch includes the following components: 100 phr of PVC resin, 1 phr of carboxylated CNTs, 1 - 2 phr of heat stabilizer, 0.5 - 3 phr of hydrophilic nano-silica, 10 - 20 phr of nitrogen-phosphorus intumescent flame retardant, 0.2 - 0.5 phr of cross-linking agent, 0.5 - 1 phr of FeCl3;

[0008] Among them, the flame-retardant modified PVC plastic sheet can be self-triggered to flame retardancy and has self-healing ability, and the healing efficiency is 60% - 70%.

[0009] As a further preference, the diameter of the hydrophilic nano-silica is 20 - 50 nm.

[0010] A method for manufacturing a flame-retardant modified PVC plastic sheet, which is used to manufacture a flame-retardant modified PVC plastic sheet, includes the following steps:

[0011] ① Place the carbon nanotubes in the reaction chamber of the ozone generator, control the ozone concentration at 30 - 50 ppm, and treat at room temperature for 3 - 5 min to obtain carboxylated CNTs. Take another portion of carbon nanotubes and place them in the reaction chamber of the ozone generator, control the ozone concentration at 60 - 80 ppm, and treat at room temperature for 10 - 15 min to obtain highly carboxylated CNTs;

[0012] ② Put 100 phr of PVC resin, 2 phr of highly carboxylated CNTs, and 1 - 2 phr of heat stabilizer into the internal mixer in proportion, mix at 150 - 155 °C and 60 rpm for 3 min, cool down to 120 °C, add 10 - 20 phr of nitrogen-phosphorus intumescent flame retardant and 0.5 - 1 phr of cross-linking agent, mix at 30 rpm for 2 min, control the temperature in the kettle at 110 °C, add an ethanol solution containing 1.5 - 2.5 phr of FeCl3 and 0.5 - 3 phr of hydrophilic nano-silica (Fe 3+ concentration 20%), mix at 40 rpm for 5 min to obtain the surface layer molten masterbatch;

[0013] ③ Put 100 phr of PVC resin, 1 phr of carboxylated CNTs, and 1 - 2 phr of heat stabilizer into an internal mixer in proportion. Mix at 155 - 160 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 10 - 20 phr of nitrogen - phosphorus intumescent flame retardant and 0.2 - 0.5 phr of cross - linker, mix at 30 rpm for 2 min, control the temperature in the kettle at 115 °C, and add an ethanol solution containing 0.5 - 1 phr of FeCl3 and 0.5 - 3 phr of hydrophilic nano - silica (Fe 3+ concentration 20%), mix at 40 rpm for 5 min to obtain the inner - layer molten masterbatch;

[0014] ④ Extrude the surface - layer molten masterbatch and the inner - layer molten masterbatch through a composite die head, roll them, and cool to obtain the flame - retardant modified PVC plastic sheet.

[0015] As a further preference, the heat stabilizer is one or more of calcium stearate, zinc stearate, hydrotalcite - based calcium - zinc, lanthanum stearate, and cerium stearate.

[0016] As a further preference, the heat stabilizer is preferably at least two of lanthanum stearate, calcium stearate, and zinc stearate, and more preferably a compound of lanthanum stearate, calcium stearate, and zinc stearate with a mass ratio of 1:1:1.

[0017] As a further preference, the nitrogen - phosphorus intumescent flame retardant consists of three parts: an acid source, a carbon source, and a gas source, and the mass ratio of the acid source, the carbon source, and the gas source is 2 - 3:1:0.5 - 0.7.

[0018] As a further preference, the acid source includes one or more of ammonium polyphosphate, ammonium phosphate, and phytic acid, the carbon source includes one or more of pentaerythritol and dipentaerythritol, and the gas source includes melamine, melamine cyanurate, and melamine polyphosphate.

[0019] As a further preference, the acid source is preferably ammonium polyphosphate or ammonium phosphate, the carbon source preferably includes pentaerythritol, the gas source is preferably melamine, and the mass ratio of the acid source, the carbon source, and the gas source is preferably 2.5 - 2.8:1:0.5.

[0020] As a further preference, the extrusion temperature of the composite die head is 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1 - 3.

[0021] (III) Beneficial effects

[0022] The present invention provides a flame - retardant modified PVC plastic sheet and its preparation method, having the following beneficial effects:

[0023] The present invention realizes performance gradient through hierarchical design. The rich carboxylated CNTs provide more active sites, form hydrogen bonds with the nitrogen - phosphorus flame retardant, improve the dispersion of the flame retardant, and at the same time, the carboxyl group reacts with Fe 3+The formed network and the high crosslinking agent jointly limit the flame retardant, reduce the precipitation of the flame retardant, improve the flame retardancy and weather resistance of the outer layer material. The inner layer material uses carboxylated CNTs to retain the strength characteristics of CNTs, cooperate with a low content of crosslinking agent, provide basic flame retardant performance while retaining the toughness of the PVC matrix, and improve the overall mechanical properties of the material;

[0024] At the same time, carboxylated CNTs and Fe 3+ form a Ph-responsive dynamic crosslinking network. In the initial stage of a fire, the smoke is alkaline, the carboxyl groups are deprotonated, and Fe 3+ forms coordination bonds with the deprotonated carboxyl groups, increasing the crosslinking density, forming a denser CNTs network, reducing the deformation of the material before combustion, and prolonging the ignition time of the material. When the material burns itself, the generated proton hydrogen causes the pH of the material itself to rapidly decrease, the hydrogen ions protonate the carboxyl groups, and the coordination bonds break. Fe 3+ is free, rapidly releases the flame retardant while catalyzing the decomposition and crosslinking of the acid source, improving the flame retardancy of the material and achieving the purpose of self-triggered flame retardancy;

[0025] Moreover, the constructed carboxylated CNTs and Fe 3+ dynamic crosslinking network, after being treated with alkaline steam, enables Fe 3+ to recombine with -COO - and can self-repair the scratches on the material. Brief Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the preparation process of the flame retardant modified PVC plastic sheet of the present invention. Detailed Embodiments

[0027] In the present invention, unless otherwise clearly specified and defined, the first feature being "above" or "below" the second feature may include the direct contact of the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "under" and "beneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0028] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0029] On the one hand, the present invention provides a flame-retardant modified PVC plastic sheet, which is formed by multi-layer co-extrusion of a surface layer and an inner layer molten masterbatch. The surface layer masterbatch includes the following components: 100 phr of PVC resin, 2 phr of carboxyl-rich CNTs, 1-2 phr of heat stabilizer, 0.5-3 phr of hydrophilic nano-silica, 10-20 phr of nitrogen-phosphorus intumescent flame retardant, 0.5-1 phr of cross-linking agent, and 1.5-2.5 phr of FeCl3; the inner layer masterbatch includes the following components: 100 phr of PVC resin, 1 phr of carboxylated CNTs, 1-2 phr of heat stabilizer, 0.5-3 phr of hydrophilic nano-silica, 10-20 phr of nitrogen-phosphorus intumescent flame retardant, 0.2-0.5 phr of cross-linking agent, and 0.5-1 phr of FeCl3.

[0030] Among them, the PVC resin is of SG-5 or SG-7 type, and the particle size is 100-120 um.

[0031] Specifically, through the cross-linking of surface layer hydroxyl-rich CNTs with Fe 3+ and high-concentration cross-linking agent to form a high-density cross-linking network, and the cross-linking of ordinary carboxylated CNTs with Fe 3+ in the inner layer and low-concentration cross-linking agent to form a low-density cross-linking network, which cooperate with each other to take into account the high flame retardancy of the PVC surface and the mechanical properties requirements of the overall material. At the same time, the cross-linking network limits the flame retardant and reduces the migration rate of the flame retardant.

[0032] Furthermore, the diameter of the hydrophilic nano-silica is 20-50 nm.

[0033] On the other hand, this embodiment also provides a method for manufacturing a flame-retardant modified PVC plastic sheet, which is used to manufacture the above-mentioned PVC plastic sheet, and includes the following steps:

[0034] ① Place the carbon nanotubes in the reaction chamber of the ozone generator, control the ozone concentration at 30 - 50 ppm, and treat them at room temperature for 3 - 5 min to obtain carboxylated CNTs. Take another portion of carbon nanotubes and place them in the reaction chamber of the ozone generator, control the ozone concentration at 60 - 80 ppm, and treat them at room temperature for 10 - 15 min to obtain highly carboxylated CNTs;

[0035] It should be noted that the carbon nanotubes are multi-walled CNTs with a diameter of 10 - 30 nm, a length of 1 - 10 μm, and an aspect ratio of 200 - 500. If the diameter of the carbon nanotubes is too small (such as single-walled CNTs), they are prone to agglomeration due to high surface energy, which affects their dispersion in PVC. If the diameter is too large, it will reduce the carboxylation efficiency and the specific surface area is insufficient, weakening the flame retardant synergistic effect. Similarly, if the length of the carbon nanotubes is too short (<1 μm), it is difficult to form an effective reinforcement network, and the improvement of mechanical properties is limited. If the length is too long (20 μm), they are prone to break due to shear force during the mixing process, and it will also cause a sudden increase in melt viscosity, affecting the co-extrusion process.

[0036] It can be understood that after carboxylation treatment, the compatibility of the carbon nanotubes with the PVC resin is improved, reducing agglomeration. At the same time, hydrogen bonds are formed between the carboxyl groups and the PVC molecular chains, enhancing the interfacial bonding force between the two.

[0037] ② Put 100 phr of PVC resin, 2 phr of highly carboxylated CNTs, and 1 - 2 phr of heat stabilizer into the mixer according to the ratio, mix at 150 - 155 °C and 60 rpm for 3 min, cool down to 120 °C, add 10 - 20 phr of nitrogen-phosphorus intumescent flame retardant and 0.5 - 1 phr of crosslinking agent, mix at 30 rpm for 2 min, control the temperature in the kettle at 110 °C, add an ethanol solution containing 1.5 - 2.5 phr of FeCl3 and 0.5 - 3 phr of hydrophilic nano-silica (Fe 3+ concentration 20%), mix at 40 rpm for 5 min to obtain the surface molten masterbatch;

[0038] Among them, the heat stabilizer is one or more of calcium stearate, zinc stearate, hydrotalcite-based calcium zinc, lanthanum stearate, and cerium stearate. Preferably, it is a compound of lanthanum stearate and calcium / zinc stearate with a mass ratio of 1:1:1.

[0039] It can be understood that the heat stabilizer replaces the unstable chlorine in the PVC material through a nucleophilic reaction, reducing the PVC degradation chain reaction and the generation of acidic gases during the processing.

[0040] Furthermore, carboxyl groups and Fe 3+ form a pH-responsive dynamic crosslinking network. In the initial stage of a fire, the smoke is alkaline, the carboxyl groups are deprotonated, and Fe 3+Form a coordination bond with the deprotonated carboxyl group, increasing the crosslinking density to form a denser CNTs network, reducing the deformation of the material before combustion, prolonging the ignition time of the material. When the material starts to burn by itself, the decomposed HCl reduces the pH of the material rapidly. The hydrogen ions protonate the carboxyl group, breaking the coordination bond, and Fe 3+ is released. While releasing the flame retardant rapidly, the free Fe 3+ catalyzes the decomposition and crosslinking of the acid source, improving the flame retardancy of the material and achieving the purpose of self-triggered flame retardancy.

[0041] Furthermore, hydrophilic nano-silica is connected to carboxyl CNTs through hydrogen bonds to form a "CNTs-SiO2-Fe 3 + " three-dimensional network, and hydrophilic channels are formed between hydrophilic nano-silicas, improving the penetration rate of Fe 3+ in the matrix material, thereby increasing the pH response rate of the enhanced dynamic crosslinking network. At the same time, the silanol groups on the surface of SiO2 can adsorb the acidic gases generated by combustion, delaying the 3+ over-protonation of Fe, prolonging the catalytic activity window, and reducing the generation of smoke gases.

[0042] ③ Put 100 phr of PVC resin, 1 phr of carboxylated CNTs, and 1 - 2 phr of heat stabilizer into an internal mixer in proportion, mix at 155 - 160 °C and 60 rpm for 3 min, cool down to 120 °C, add 10 - 20 phr of nitrogen-phosphorus intumescent flame retardant and 0.2 - 0.5 phr of crosslinking agent, mix at 30 rpm for 2 min, control the temperature in the kettle at 115 °C, add an ethanol solution containing 0.5 - 1 phr of FeCl3 and 0.5 - 3 phr of hydrophilic nano-silica (Fe 3+ concentration 20%), mix at 40 rpm for 5 min to obtain the inner layer molten masterbatch;

[0043] Among them, the nitrogen-phosphorus intumescent flame retardant consists of three parts: an acid source, a carbon source, and a gas source, and the mass ratio of the acid source, carbon source, and gas source is 2 - 3:1:0.5 - 0.7.

[0044] Specifically, the acid source includes one or more of ammonium polyphosphate, ammonium phosphate, and phytic acid, the carbon source includes one or more of pentaerythritol and dipentaerythritol, and the gas source includes melamine, melamine cyanurate, and melamine polyphosphate.

[0045] It can be understood that during combustion, hydrogen ions promote the thermal decomposition of the acid source, catalyze dehydration to form carbon, and the free Fe 3+ provides active sites to accelerate esterification crosslinking, enhancing the thermal stability of the carbon layer. The carbon source provides active groups such as hydroxyl groups to react with the acid source to form a porous carbon skeleton. At the same time, carbon nanotubes are embedded in the carbon layer as a skeleton to enhance the anti-collapse ability of the carbon layer. The gas source thermally decomposes to release non-combustible gases, promoting the expansion of the carbon layer and improving the flame retardancy of the material.

[0046] Furthermore, nano-silica is filled in the gaps of the carboxylated CNTs / Fe 3+ network to form a "riveting effect" in the expanded carbon layer, inhibiting crack propagation.

[0047] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head, roll and cool to obtain a flame-retardant modified PVC plastic sheet.

[0048] Among them, the extrusion temperature of the composite die head is 160°C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1 - 3.

[0049] It can be understood that using a composite die head and having the temperature of the inner layer masterbatch slightly higher than that of the outer layer masterbatch can reduce the interface delamination between the inner and outer layers.

[0050] To further understand the present invention, the CMP slurry composition provided by the present invention will be described below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0051] Example 1

[0052] ① Place multi-walled CNTs in the reaction chamber of an ozone generator, control the ozone concentration at 30 - 50 ppm, and treat at room temperature for 3 - 5 min. After washing and drying, carboxylated CNTs are obtained. Another multi-walled CNT tube is placed in the reaction chamber of the ozone generator, control the ozone concentration at 60 - 80 ppm, and treat at room temperature for 10 - 15 min. After washing and drying, highly carboxylated CNTs are obtained;

[0053] ② Put 100 g of PVC resin, 2 g of highly carboxylated CNTs, and 1.5 g of heat stabilizer (where 0.5 g of lanthanum stearate is compounded with 0.5 g each of calcium / zinc stearate) into a kneader in proportion, mix at 150°C and 60 rpm for 3 min, cool down to 120°C, add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.5 g of cross-linking agent, mix at 30 rpm for 2 min, control the temperature in the kettle at 110°C, add an ethanol solution containing 2 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the surface molten masterbatch;

[0054] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer according to the proportion. Mix at 155 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.2 g of cross-linking agent. Mix at 30 rpm for 2 min, control the temperature in the kettle at 115 °C, and add an ethanol solution containing 0.5 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the inner-layer molten masterbatch;

[0055] ④ Extrude the surface-layer molten masterbatch and the inner-layer molten masterbatch through a composite die head. The temperature of the composite die head is stabilized at 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1. After rolling and cooling, a flame-retardant modified PVC plastic sheet is obtained.

[0056] Example 2

[0057] ① Place multi-walled CNTs in the reaction chamber of an ozone generator. Control the ozone concentration at 30 - 50 ppm and treat at room temperature for 3 - 5 min. After washing and drying, carboxylated CNTs are obtained. Take another multi-walled CNT tube and place it in the reaction chamber of the ozone generator. Control the ozone concentration at 60 - 80 ppm and treat at room temperature for 10 - 15 min. After washing and drying, highly carboxylated CNTs are obtained;

[0058] ② Take 100 g of PVC resin, 2 g of highly carboxylated CNTs, and 1 g of calcium stearate and put them into a mixer according to the proportion. Mix at 155 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 6.25 g of ammonium polyphosphate, 2.5 g of dipentaerythritol, 1.75 g of melamine cyanurate, and 0.8 g of cross-linking agent. Mix at 30 rpm for 2 min, control the temperature in the kettle at 110 °C, and add an ethanol solution containing 1.5 g of FeCl3 and 2 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the surface-layer molten masterbatch;

[0059] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 1 g of heat stabilizer calcium stearate into a mixer according to the proportion. Mix at 160 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 6.25 g of ammonium polyphosphate, 2.5 g of dipentaerythritol, 1.75 g of melamine cyanurate, and 0.5 g of cross-linking agent. Mix at 30 rpm for 2 min, control the temperature in the kettle at 115 °C, and add an ethanol solution containing 0.8 g of FeCl3 and 3 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the inner-layer molten masterbatch;

[0060] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head. The temperature of the composite die head is stabilized at 160°C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:2. After rolling and cooling, a flame-retardant modified PVC plastic sheet is obtained.

[0061] Example 3

[0062] ① Place multi-walled CNTs in the reaction chamber of an ozone generator. Control the ozone concentration at 30 - 50 ppm and treat at room temperature for 3 - 5 minutes. After washing and drying, carboxylated CNTs are obtained. Take another multi-walled CNT tube and place it in the reaction chamber of the ozone generator. Control the ozone concentration at 60 - 80 ppm and treat at room temperature for 10 - 15 minutes. After washing and drying, highly carboxylated CNTs are obtained;

[0063] ② Put 100 g of PVC resin, 2 g of highly carboxylated CNTs, and 2 g of heat stabilizers (1 g each of calcium stearate and hydrotalcite-based calcium zinc) into a mixer according to the ratio. Mix at 153°C and 60 rpm for 3 minutes, then cool to 120°C. Add 13.03 g of phytic acid, 4.65 g (mass ratio of pentaerythritol to dipentaerythritol is 1:1), 2.32 g of melamine, and 1 g of cross-linking agent. Mix at 30 rpm for 2 minutes. Control the temperature in the kettle at 110°C and add an ethanol solution containing 2.5 g of FeCl3 and 3 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 minutes to obtain the surface molten masterbatch;

[0064] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 2 g of heat stabilizers (1 g each of calcium stearate and hydrotalcite-based calcium zinc) into a mixer according to the ratio. Mix at 158°C and 60 rpm for 3 minutes, then cool to 120°C. Add 13.03 g of phytic acid, 4.65 g (mass ratio of pentaerythritol to dipentaerythritol is 1:1), 2.32 g of melamine, and 0.5 g of cross-linking agent. Mix at 30 rpm for 2 minutes. Control the temperature in the kettle at 115°C and add an ethanol solution containing 1 g of FeCl3 and 3 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 minutes to obtain the inner layer molten masterbatch;

[0065] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head. The temperature of the composite die head is stabilized at 160°C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:3. After rolling and cooling, a flame-retardant modified PVC plastic sheet is obtained.

[0066] Comparative Example 1

[0067] ① Place multi-walled CNTs in the reaction chamber of an ozone generator. Control the ozone concentration at 30 - 50 ppm and treat at room temperature for 3 - 5 min. After washing and drying, carboxylated CNTs are obtained. Take another multi-walled CNT tube and place it in the reaction chamber of the ozone generator. Control the ozone concentration at 60 - 80 ppm and treat at room temperature for 10 - 15 min. After washing and drying, highly carboxylated CNTs are obtained;

[0068] ② Put 100 g of PVC resin, 2 g of highly carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer in proportion. Mix at 150 °C and 60 rpm for 3 min. Cool down to 120 °C, add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.5 g of crosslinking agent. Mix at 30 rpm for 2 min. Control the temperature in the kettle at 110 °C and add an ethanol solution containing 2 g of FeCl3 (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the surface molten masterbatch;

[0069] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer in proportion. Mix at 155 °C and 60 rpm for 3 min. Cool down to 120 °C, add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.2 g of crosslinking agent. Mix at 30 rpm for 2 min. Control the temperature in the kettle at 115 °C and add an ethanol solution containing 0.5 g of FeCl3 (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the inner layer molten masterbatch;

[0070] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head. The composite die head is stabilized at 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1. After rolling and cooling, a PVC plastic sheet is obtained.

[0071] Comparative Example 2

[0072] ① Put 100 g of PVC resin, 2 g of CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer in proportion. Mix at 150 °C and 60 rpm for 3 min. Cool down to 120 °C, add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.5 g of crosslinking agent. Mix at 30 rpm for 2 min. Control the temperature in the kettle at 110 °C and add an ethanol solution containing 2 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%). Mix at 40 rpm for 5 min to obtain the surface molten masterbatch;

[0073] ② Put 100 g of PVC resin, 1 g of CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a Banbury mixer in proportion. Mix at 155 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.2 g of crosslinking agent, and mix at 30 rpm for 2 min. Control the temperature in the kettle at 115 °C, add an ethanol solution containing 0.5 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the inner-layer molten masterbatch;

[0074] ③ Extrude the surface-layer molten masterbatch and the inner-layer molten masterbatch through a composite die head. The composite die head is stabilized at 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1. After rolling and cooling, a PVC plastic sheet is obtained.

[0075] Comparative Example 3

[0076] ① Place multi-walled CNTs in the reaction chamber of an ozone generator, control the ozone concentration at 60 - 80 ppm, and treat at room temperature for 10 - 15 min. After washing and drying, carboxylated CNTs are obtained;

[0077] ② Take 100 g of PVC resin, 2 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) and put them into a Banbury mixer in proportion. Mix at 150 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.5 g of crosslinking agent, and mix at 30 rpm for 2 min. Control the temperature in the kettle at 110 °C, add an ethanol solution containing 2 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the surface-layer molten masterbatch;

[0078] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a Banbury mixer in proportion. Mix at 155 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.2 g of crosslinking agent, and mix at 30 rpm for 2 min. Control the temperature in the kettle at 115 °C, add an ethanol solution containing 0.5 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the inner-layer molten masterbatch;

[0079] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head. The composite die head is stabilized at 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1. After rolling and cooling, a PVC plastic sheet is obtained.

[0080] Comparative Example 4

[0081] ① Place multi-walled CNTs in the reaction chamber of an ozone generator, control the ozone concentration at 30 - 50 ppm, and treat at room temperature for 3 - 5 min. After washing and drying, carboxylated CNTs are obtained.

[0082] ② Put 100 g of PVC resin, 2 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer according to the ratio. Mix at 150 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.5 g of cross-linking agent. Mix at 30 rpm for 2 min, control the temperature in the kettle at 110 °C, add an ethanol solution containing 2 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the surface molten masterbatch.

[0083] ③ Put 100 g of PVC resin, 1 g of carboxylated CNTs, and 1.5 g of heat stabilizer (a compound of 0.5 g of lanthanum stearate and 0.5 g each of calcium / zinc stearate) into a mixer according to the ratio. Mix at 155 °C and 60 rpm for 3 min, then cool down to 120 °C. Add 9.375 g of ammonium polyphosphate, 3.75 g of pentaerythritol, 1.875 g of melamine, and 0.2 g of cross-linking agent. Mix at 30 rpm for 2 min, control the temperature in the kettle at 115 °C, add an ethanol solution containing 0.5 g of FeCl3 and 0.5 g of hydrophilic nano-silica (Fe 3+ concentration 20%), and mix at 40 rpm for 5 min to obtain the inner layer molten masterbatch.

[0084] ④ Extrude the surface molten masterbatch and the inner layer molten masterbatch through a composite die head. The composite die head is stabilized at 160 °C, and the extrusion thickness ratio of the surface layer to the inner layer is 1:1. After rolling and cooling, a PVC plastic sheet is obtained.

[0085] Test Example:

[0086] Determine the limiting oxygen index (LOI) of the flame-retardant modified PVC plastic sheets obtained in Experimental Examples 1 - 3 and the PVC plastic sheet samples obtained in Comparative Examples 1 - 4 according to the ASTM D2863 / GB / T 2406 test standard.

[0087] The vertical burning (UL-94) test was carried out on the flame-retardant modified PVC plastic sheets obtained in Experimental Examples 1-3 and the PVC plastic sheet samples obtained in Comparative Examples 1-4 according to the UL 94 / GB / T 2408 test standard.

[0088] The cone calorimeter test was carried out on the flame-retardant modified PVC plastic sheets obtained in Experimental Examples 1-3 and the PVC plastic sheet samples obtained in Comparative Examples 1-4 according to the GB / T 16172 standard.

[0089] Table 1 is a statistical table of the flame retardancy test results of each example and comparative example

[0090] LOI(%) Flame retardant grade Peak heat release rate (kW / m²) Total heat release (MJ / m²) Peak smoke production rate (m² / s) Ignition time (S) Example 1 >45 V0 120 52 0.12 75 Example 2 >45 V0 132 48 0.15 73 Example 3 >45 V0 128 51 0.14 77 Comparative Example 1 >40 V0 141 60 0.23 67 Comparative Example 2 >28 V1 189 75 0.21 45 Comparative Example 3 >40 V0 166 54 0.17 70 Comparative Example 4 >28 V1 174 62 0.18 36

[0091] The flame-retardant modified PVC plastic sheets obtained in Experimental Examples 1-3 and the PVC plastic sheet samples obtained in Comparative Examples 1-4 were subjected to ultraviolet aging test. The materials were injection molded into 100×50 mm samples, and the surface was ensured to be clean and pollution-free. The lamp tube type UVB~313, irradiance 1~1.55 W / m², and cycle mode (4 hours UV (60°C) + 4 hours condensation (50°C)) were selected to observe the surface cracks of the materials.

[0092] Among them, the cracks were evaluated according to the ISO 4628-4:2016 standard by combining visual inspection (comparing with the standard grade chart) and optical microscope (measuring the width and density of microcracks).

[0093] The material cracks were placed in alkaline steam and treated for 15-25 min, and the crack repair rate was observed by optical microscope.

[0094] Table 2 is a statistical table of the weather resistance test results of each example and comparative example

[0095] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Crack grade 0 0 0 1 3 2 1 Repair rate 65%～70% 65%～70% 65%～70% <10% 0 <60% <30%

[0096] Using a universal material testing machine, according to the GB / T 1040.1-2018 test standard, the tensile strength of the flame-retardant modified PVC plastic sheets obtained in Experimental Examples 1-3 and the PVC plastic sheet samples obtained in Comparative Examples 1-4 was detected, and the falling weight impact test was carried out according to the GB / T 11548 test standard.

[0097] Table 3 is a statistical table of the mechanical property test results of each example and comparative example

[0098] Tensile strength MPa Maximum load N Failure mode Example 1 47 3125±150 Circular crack Example 2 51 3079±150 Circular crack Example 3 50 3137±150 Circular crack Comparative Example 1 40 2915±150 Star-shaped crack Comparative Example 2 30 2500±200 Central perforation Comparative Example 3 38 2100±180 Circular crack + partial penetration Comparative Example 4 37 2500±180 Circular crack

[0099] The physical recycling times test was carried out on the flame-retardant modified PVC plastic sheet samples obtained in Experimental Examples 1-3 and commercially available conventional flame-retardant PVC respectively. The samples were chopped, melt extruded and formed, and the tensile strength and limiting oxygen index of the new samples were tested after 3 recycling cycles.

[0100] Table 4 Performance Test Table of Recycled Samples

[0101] Tensile strength retention rate Limiting oxygen index decline rate Example 1 87% 5% Example 2 85% 4% Example 3 89% 7% Commercially available 60% >15%

[0102] In summary, the hierarchical design realizes performance gradient, and the carboxylated CNTs provide more active sites, form hydrogen bonds with nitrogen and phosphorus flame retardants, improve the dispersion of the flame retardant. At the same time, the carboxyl groups form a network with Fe 3+ to limit the flame retardant with a high crosslinking agent, reduce the precipitation of the flame retardant, improve the flame retardancy grade and weather resistance of the outer layer material, reduce the generation of a large amount of HCl gas during the combustion of PVC, and effectively extend the ignition time of the material. Secondly, the carboxylated CNTs are used in the inner layer material to retain the strength characteristics of CNTs, cooperate with a low content of crosslinking agent, and retain the toughness of the PVC matrix. The combination of the inner and outer layers significantly improves the tensile strength and impact strength; furthermore, the carboxylated CNTs and Fe 3+ form a pH-responsive dynamic crosslinking network. In the initial stage of a fire, the smoke is alkaline, the carboxyl groups are deprotonated, and Fe 3 + forms a coordination bond with the deprotonated carboxyl groups, increasing the crosslinking density and forming a denser CNTs network, reducing the deformation of the material before combustion. When the material itself burns, the generated HCl rapidly reduces the pH of the material itself, the carboxyl groups are protonated, the coordination bond breaks, and Fe 3+ is free, rapidly releasing the flame retardant and catalyzing the decomposition and crosslinking of the acid source at the same time, improving the flame retardancy of the material and achieving the purpose of self-triggered flame retardancy. Moreover, the constructed carboxylated CNTs and Fe 3+ dynamic crosslinking network, after being treated with alkaline steam, enables Fe 3+ to coordinate and recombine with -COO - to self-repair the scratches on the material; finally, the carboxylated CNTs and Fe 3+ crosslinking network inhibits the breakage of the PVC chain, limits the flame retardant at the same time, reduces the migration rate of the flame retardant, and reduces the recycling cost of the PVC material.

[0103] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flame retardant modified PVC plastic sheet, characterized in that: The surface layer and the inner layer molten masterbatch are co-extruded through a composite die, wherein the surface layer masterbatch includes the following components: 100phr of PVC resin, 2phr of carboxyl-rich CNTs, 1-2phr of heat stabilizer, 0.5-3phr of hydrophilic nano-silicon dioxide, 10-20phr of nitrogen-phosphorus intumescent flame retardant, 0.5-1phr of cross-linking agent, and 1.5-2.5phr of FeCl3; the inner layer masterbatch includes the following components: 100phr of PVC resin, 1phr of carboxyl-rich CNTs, 1-2phr of heat stabilizer, 0.5-3phr of hydrophilic nano-silicon dioxide, 10-20phr of nitrogen-phosphorus intumescent flame retardant, 0.2-0.5phr of cross-linking agent, and 0.5-1phr of FeCl3; The flame-retardant modified PVC plastic sheet can be self-triggering and flame-retardant, and has self-repairing ability, with a repair efficiency of 60% to 70%.

2. The flame retardant modified PVC plastic sheet according to claim 1, characterized in that: The diameter of the hydrophilic nano-silicon dioxide is 20-50 nm.

3. A method for manufacturing a flame retardant modified PVC plastic sheet, used to manufacture a flame retardant modified PVC plastic sheet according to any one of claims 1 to 2, characterized in that: The following steps are involved: ① Place carbon nanotubes in the reaction chamber of an ozone generator, control the ozone concentration to 30-50ppm, treat at room temperature for 3-5min to obtain carboxylated CNTs, and place another carbon nanotube in the reaction chamber of an ozone generator, control the ozone concentration to 60-80ppm, treat at room temperature for 10-15min to obtain carboxyl-rich CNTs; ②Put 100phr PVC resin, 2phr carboxyl-rich CNTs, and 1-2phr heat stabilizer into an internal mixer in proportion, mix at 150-155℃, 60rpm for 3min, cool to 120℃, add 10-20phr nitrogen-phosphorus intumescent flame retardant and 0.5-1phr crosslinking agent, mix at 30rpm for 2min, control the temperature in the kettle at 110℃, add 1.5-2.5phr FeCl3 and 0.5-3phr hydrophilic nano-silica ethanol solution (Fe 3+ Concentration 20%), 40rpm mixing for 5min to obtain a surface molten masterbatch; ③Put 100phr PVC resin, 1phr carboxylated CNTs, and 1-2phr heat stabilizer into an internal mixer in proportion, mix at 155-160℃, 60rpm for 3min, cool to 120℃, add 10-20phr nitrogen-phosphorus intumescent flame retardant and 0.2-0.5phr crosslinking agent, mix at 30rpm for 2min, control the temperature in the kettle at 115℃, add 0.5-1phr FeCl3 and 0.5-3phr hydrophilic nano-silica ethanol solution (Fe 3+ Concentration 20%), 40rpm mixing for 5min to obtain the inner layer molten masterbatch; ④ Extruding the surface layer molten masterbatch and the inner layer molten masterbatch through a composite die, rolling, and cooling to obtain a flame retardant modified PVC plastic sheet.

4. The method for manufacturing a flame retardant modified PVC plastic sheet according to claim 3, characterized in that: The heat stabilizer is one or more of calcium stearate, zinc stearate, hydrotalcite-based calcium zinc, lanthanum stearate, and cerium stearate.

5. The method for manufacturing a flame retardant modified PVC plastic sheet according to claim 4, characterized in that: The heat stabilizer is preferably at least two of lanthanum stearate, calcium stearate and zinc stearate, and more preferably lanthanum stearate and calcium stearate / zinc stearate are compounded in a mass ratio of 1:1:

1.

6. The method for manufacturing a flame retardant modified PVC plastic sheet according to claim 3, characterized in that: The nitrogen-phosphorus intumescent flame retardant consists of three parts: an acid source, a carbon source and a gas source, and the mass ratio of the acid source, the carbon source and the gas source is 2-3:1:0.5-0.

7.

7. The method for producing a flame retardant modified PVC plastic sheet according to claim 6, characterized in that: The acid source includes one or more of ammonium polyphosphate, ammonium phosphate, and phytic acid; the carbon source includes one or more of pentaerythritol and dipentaerythritol; and the gas source includes melamine, melamine cyanurate, and melamine polyphosphate.

8. The method for manufacturing a flame retardant modified PVC plastic sheet according to claim 7, characterized in that: The acid source is preferably ammonium polyphosphate or ammonium phosphate, the carbon source preferably includes pentaerythritol, the gas source is preferably melamine, and the mass ratio of the acid source, the carbon source and the gas source is preferably 2.5-2.8:1:0.

5.

9. The method for manufacturing a flame retardant modified PVC plastic sheet according to claim 4, characterized in that: The extrusion temperature of the composite die head is 160° C., and the extrusion thickness ratio of the surface layer to the inner layer is 1:1-3.

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