Method for improving pyrolysis carbon formation rate of liquid silicone rubber and application of method

Abstract

The invention relates to the technical field of production and processing of rubber products, and discloses a method for improving the pyrolysis carbon formation rate of liquid silicone rubber and application of the method, and the method comprises the steps of screening of a carrier material and hybrid deposition of a nano carbon formation catalyst on the carrier material. Meanwhile, the invention provides an application method of the silicon rubber in a liquid silicon rubber foaming material, a coating material and a cable material. According to the method, the nano charring catalyst is uniformly dispersed in a material system by utilizing an electrostatic adsorption principle, and the liquid silicone rubber is converted into residues through in-situ catalysis, so that the effect of improving the pyrolysis charring of a liquid silicone rubber product is achieved, and the important application of the nano charring catalyst in the aspects of flame retardance, ablation resistance, heat insulation and the like of the material is obviously shown.

Description

Technical Field

[0001] The present invention belongs to the technical field of rubber product production and processing, and specifically relates to a method for improving the carbonization rate of liquid silicone rubber by pyrolysis and its application. Background Art

[0002] After carbon-based polymers are thermally decomposed, they are released in the forms of CO, CO2, unsaturated hydrocarbons, etc., and the residue is almost zero. Therefore, most carbon-based polymers are highly flammable polymers. Due to the presence of carbon chain organic groups such as methyl, phenyl, and vinyl on the side chains of silicon-based polymers, they have the same flammability as carbon-based polymers. However, due to the presence of some inorganic silicon oxides remaining after the pyrolysis of silicon-based polymers, this plays a certain solid-phase flame retardant role. Therefore, their flame retardant performance and high temperature resistance already have certain advantages. The pyrolysis of silicon-based polymers is a typical "unzipping" pyrolysis or "back-biting" pyrolysis, which is the key to affecting their flame retardancy and high temperature resistance and is also a difficult problem faced by the scientific community at present. Therefore, increasing the residual carbon after the pyrolysis of polymers is of great significance for improving the flame retardant performance and thermal performance of polymers.

[0003] To solve the above problems, researchers on carbon-based polymers usually use technical approaches such as macromolecular flame retardant structure design, surface modification, and ultrafine structure design to prepare highly efficient charring catalysts in order to increase the pyrolysis char residue rate of carbon-based polymers, enhance the barrier effect of the condensed phase layer, and improve the flame retardancy of polymers. For example, Professor Qian Lijun et al. in "Macromolecules. 2018(Vol.51), No.23:9992-10002" designed and synthesized a series of phosphorus phenanthrene / phenyl silicone double-group macromolecules, and the pyrolysis char amount was increased after adding them to epoxy resin. Professor Hao Jianwei et al. in "Chem. J. Chin. Univ. 2013(Vol.34), No.11:2674-2680" effectively increased the char residue amount of rigid polyurethane materials by loading boric acid on the surface of graphite using the surface grafting silane coupling agent method. Professor Hu Yuan et al. in "Composites. Part A - Appl. Sci. 2018(Vol.111):94-105" prepared SnO2 metal oxide nanoparticles using dopamine, which effectively improved the pyrolysis charring property of epoxy composites. Professor Wang Qi et al. in J. Mater. Chem. A. 2020(Vol.5), No.8:2529-2538 introduced iron-loaded polydopamine nanospheres as a green flame retardant into epoxy resin, which promoted the carbonization process in the condensed phase. In these innovative studies above, the char layer structure formed after the high-temperature pyrolysis of the prepared polymer composites increased. The mechanism is that the charring catalyst promotes the cross-linking and carbonization of alkyl small molecules. In recent years, this research on preparing high-performance charring catalysts by introducing trace transition metals has become one of the hotspots in the field of flame retardancy of carbon-based polymer materials.

[0004] Due to the relatively low content of organic groups in the side chains of silicone-based polymers, they inherently possess certain flame retardancy and high-temperature resistance. Therefore, in previous research, researchers did not focus on optimizing the flame retardancy and heat resistance of silicone-based polymers. In recent years, due to the development of the aerospace industry and the development needs of the new energy vehicle industry, the research and development of lightweight, flame-retardant, heat-insulating, and ablative-resistant silicone-based polymer composites have become a strategic requirement of the country and the industry. In particular, the improvement of the flame retardancy and ablative resistance of silicone-based polymer composites is needed. As mentioned above, some inorganic silicon oxides are formed after the pyrolysis of silicone-based polymers. Therefore, increasing the yield of inorganic silicon oxide residues after the pyrolysis of silicone-based polymers will be very beneficial for improving their flame retardancy and high-temperature resistance. The pyrolysis products of silicone-based polymer materials mainly form inorganic silicon-oxygen cross-links through free radical reactions. However, during the pyrolysis process, silicon and oxygen elements often escape in the form of small molecule siloxanes, resulting in a low yield of pyrolysis residues. According to the investigation, there are few reports on the related research of catalyzing the pyrolysis of silicone-based polymers into "carbon (C-C, Si-O, Si-C)". If the pyrolysis of silicone-based polymers into carbon can be achieved through the above-mentioned carbon-based polymer carbonization catalysis technology, it will be very beneficial for realizing the above hypothesis. In fact, due to the relatively low content of carbon chains in the side chains of silicone-based polymers, the cross-linking of their alkyl groups into carbon cannot be effectively achieved. In other words, the carbonization catalyst for carbon-based polymers is not applicable to silicone-based polymers. During the pyrolysis of silicone-based polymers, a part of the small molecule siloxanes undergo free radical cross-linking under high temperature to form cyclic siloxanes, and finally, the small molecules in the side chains are removed to form Si-O and Si-C residues. Inspired by the above-mentioned carbon-based polymer carbonization catalysis mechanism, theoretically, if a substance that can enhance the free radical activity of small molecule siloxanes is introduced to improve the cross-linking efficiency of small molecule siloxane free radicals, it is expected to improve the carbonization of silicone-based polymers during pyrolysis, and further improve the flame retardancy, ablative resistance, and even heat insulation performance of silicone-based polymers. This will also transfer the "unbuttoning" pyrolysis problem of silicone-based polymers from another aspect.

[0005] In terms of applications, for example, in the thermal protection system of power batteries for new energy vehicles, the silicone-based polymer fireproof sealing material is an indispensable key material. To meet the requirements of its fireproof performance, domestic materials often require relatively thick silicone foam or fiber cloth composite silicone coating materials, which is contrary to the development requirements of lightweight new energy vehicles. However, the thickness and density of imported product materials are far lower than those of domestic materials to achieve effective fire prevention. It is found that there are few volatile substances released during the ablation pyrolysis process of imported products, while domestic products often release a large amount of combustible or non-combustible substances, which leads to poor compactness of their residues and even obvious cracks, resulting in poor thermal protection effect. Therefore, if the carbonization efficiency of silicone-based polymers during pyrolysis can be improved, it is expected to further improve the thermal protection efficiency of domestic silicone-based polymer products and achieve the lightweight goal of domestic silicone-based polymer product materials. Similarly, in the field of aerospace, if the carbonization efficiency of silicone-based polymers during pyrolysis can be improved, it is expected to further achieve the lightweight goal on the basis of meeting the ablation resistance performance of aerospace silicone-based polymer materials. For the field of special cables, especially communication cables, improving the charring rate of silicone-based polymer cables during pyrolysis will be beneficial to improving their heat insulation performance, providing material conditions for ensuring the normal power supply of cables during a fire, and also bringing great convenience to the fire rescue work. In summary, it is particularly important to invent a method that can effectively improve the charring rate of liquid silicone rubber products in the applications of enhancing the flame retardancy, ablation resistance, heat insulation, etc. of silicone-based polymers.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] Aiming at the deficiencies existing in the above-mentioned prior art, the purpose of the present invention is to improve the charring rate of liquid silicone rubber products while solving the problems of the large addition of inorganic fillers, preparation processes, and the difficulty in balancing the comprehensive properties of materials during the production process of the chemical industry. To this end, the present invention proposes a method for improving the charring rate of liquid silicone rubber products, which achieves the effect of increasing carbon by enhancing the activity of small molecule siloxane free radicals after pyrolysis, and significantly improves the charring rate of liquid silicone rubber products. The basic concept of the technical solution adopted by the present invention is:

[0008] A method for improving the carbonization rate of liquid silicone rubber includes the following steps:

[0009] Step (1): First, place the inorganic nano-carbonization catalyst carrier material with a layered structure in a container resistant to acid and alkali solutions, add deionized water with a volume four times that of it, adjust the pH of the system to 5 - 7, perform ultrasonic-assisted peeling on it, and at the same time, carry out stirring treatment at a rotation speed of 600 r / min for 1 h;

[0010] Step (2): Remove the ultrasonic treatment equipment, add a transition metal compound containing boron or phosphorus to the system in step (1), adjust the pH of the system to 1.5 - 1.7, and simultaneously carry out stirring treatment at a speed of 600 r / min for 2 h;

[0011] Step (3): Slowly drop 0.5 mol / L NaOH solution into the mixed system in step (2) above, adjust the pH of the system to 8 - 9, and simultaneously carry out stirring treatment at a speed of 1000 r / min. After the system reaches the predetermined pH condition, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases. If it decreases, continue to drop 0.5 mol / L NaOH solution to the target value, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases, and repeat the above operations until the pH value of the system remains constant under the target value;

[0012] Step (4): Filter and wash the mixed system in step (3) above, place it in an oven and dry it to constant weight to obtain a boron or phosphorus-doped transition metal hybrid layered inorganic filler carbonization catalytic system.

[0013] As a preferred embodiment of the present invention, the surface of the nano-carbonization catalyst support material described in step (1) is electronegative under the condition that the pH is greater than 2.

[0014] As a preferred embodiment of the present invention, the carbonization catalyst support material described in step (1) is an inorganic filler with a high specific surface area and a layered structure.

[0015] As a preferred embodiment of the present invention, the layered inorganic filler described in step (1) is one or a combination of montmorillonite, sericite, diatomite, bentonite.

[0016] As a preferred embodiment of the present invention, the transition metal compound containing boron or phosphorus described in step (2) is one of zinc borate, zinc phytate, zinc phosphate, zinc phosphite, zinc metaphosphate.

[0017] As a preferred embodiment of the present invention, the reagent for adjusting the pH of the system in steps (1) and (2) is 3 mol / L hydrochloric acid.

[0018] As a preferred embodiment of the present invention, the mass ratio of the carbonization catalyst support material to the transition metal compound containing boron or phosphorus in steps (1) and (2) is 7 - 5.

[0019] The charring catalyst system material prepared by the method for improving the pyrolysis char yield of liquid silicone rubber products of the present invention can be applied in flame-retardant liquid silicone rubber coatings, lightweight and ablative-resistant liquid silicone rubber foams, ablative-resistant and heat-insulating ceramicizable liquid silicone rubber composite glass fiber fire belts, and fire-resistant liquid silicone rubber cables, or other related fields that require improving the flame retardancy, ablative resistance, and heat insulation performance of liquid silicone rubber products.

[0020] Furthermore, for the above applications of the present invention, under actual formulation conditions, it can directly replace the same inorganic filler without hybridization treatment with the same fraction, or a filler with a non-layered structure that meets other characteristics of the above carrier material can also be used as the charring catalyst carrier material to improve the pyrolysis char yield of its liquid silicone rubber products.

[0021] The present invention has the following beneficial effects compared with the prior art:

[0022] ① For the -Si-O- molecular chain, the cross-linking reaction that occurs is the cross-linking reaction of Si· and O· free radicals. When there are transition metal ions and boron or phosphorus elements with strong electronegativity in the system, they will respectively affect the local charge distribution of Si and O in the -Si-O- molecular chain, thereby enhancing the activity of Si· and O·. Under the above action, small molecule siloxanes after the pyrolysis of liquid silicone rubber can undergo efficient in-situ cross-linking, increasing the molecular weight to form non-volatile substances, thus increasing its pyrolysis carbonization rate.

[0023] ② The doping introduction of boron or phosphorus elements further enhances the activity of Si· and O· in the -Si-O- molecular chain, avoiding the limitations of the platinum metal catalyst system (Note: For silicone rubber products of the platinum catalyst system, under the catalytic action of platinum metal, they have certain carbonization advantages, and their flame retardancy and fire prevention effects are better than those of silicone rubber products of non-platinum catalyst systems, but the cost of platinum catalysts is relatively high). The doping introduction of boron or phosphorus elements makes up for the catalytic carbonization effect when platinum metal is absent, and can reduce the material cost without losing or reducing the carbonization performance of the material, or can further optimize the carbonization performance of the material in the platinum metal catalyst system, thereby improving the flame retardancy and fire prevention performance of the material.

[0024] ③ Using a layered inorganic filler with a high specific surface area as the carrier (while increasing the layer spacing of the inorganic filler through ultrasonic treatment) effectively increases the contact between the boron and phosphorus doped transition metal compounds and liquid silicone rubber. On the one hand, it avoids the influence on the forming process when the charring catalyst is added in the form of nanoparticles, and on the other hand, it solves the problem of high filling and low efficiency of nano-catalyst materials.

[0025] ④Compared with the technical means of improving the thermal performance, especially the char-forming performance, of liquid silicone rubber through molecular structure design, the method for improving the pyrolytic char yield of liquid silicone rubber products proposed by the present invention has a simple process, strong feasibility for batch operation, and is applicable to almost all liquid silicone rubbers, with a wide application range and broad prospects for industrial promotion.

[0026] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Description of the Drawings

[0027] In the drawings:

[0028] Figure 1 It is a statistical chart of the microscopic morphology and element content before and after phosphorus-doped zinc hybrid montmorillonite of the present invention;

[0029] Figure 2 It is a schematic diagram of the apparent morphology and main element composition of sericite before and after unmodified and hybrid modification of the present invention;

[0030] Figure 3 It is a schematic diagram of the test result of the char yield performance of the liquid silicone rubber coating under the technical scheme of Example 1 of the present invention;

[0031] Figure 4 It is a schematic diagram of the test result of the char yield performance of the liquid silicone rubber foam material under the technical scheme of Example 2 of the present invention;

[0032] Figure 5 It is a schematic diagram of the ablation resistance effect before and after the application of the carbon catalytic material system prepared under the technical scheme of Example 1 of the present invention in the liquid silicone rubber coating composite fiberglass cloth;

[0033] Figure 6 It is a schematic diagram of the ablation resistance effect before and after the application of the carbon catalytic material system prepared under the technical scheme of Example 2 of the present invention in the liquid silicone rubber foam material. Specific Embodiments

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments in conjunction with the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention.

[0035] Comparative Example 1

[0036] 10 parts of glass powder (softening point 550°C, provided by Foshan Jinggu New Materials Co., Ltd.) and 30 parts of montmorillonite were added to a commercial liquid silicone organic coating (the system includes phenyl vinyl silicone oil, hydrogen-containing silicone oil, and platinum catalyst) with platinum as the catalyst, and used as a refractory coating. The refractory coating was applied to the surface of a high-silica glass fiber cloth to characterize its refractory effect in actual applications, and the coating thickness was controlled at 1 ± 0.05 mm.

[0037] The performance test results are shown in Tables 1, 2, 3, 4 and 5.

[0038] Comparative Example 2

[0039] 12 parts of glass powder (softening point 700 °C, provided by Shanggao Mingzheng New Materials Co., Ltd.) and 28 parts of sericite were added to a commercial liquid silicone foam with organotin as the catalyst (the system includes hydroxyl-terminated silicone oil with a viscosity of 20,000, hydroxyl-terminated silicone oil with a viscosity of 5,000, hydroxyl-terminated silicone oil with a viscosity of 2,300, hydrogen-containing silicone oil, low-viscosity hydroxyl-terminated silicone oil, and organotin catalyst) to prepare a fireproof liquid silicone foam material with a thickness of 3 ± 0.05 mm.

[0040] The performance test results are shown in Tables 1, 2, 3, 4 and 5.

[0041] Example 1

[0042] A method for improving the pyrolysis carbonization rate of liquid silicone rubber, as Figure 1 , Figure 3 and Figure 5 shown, includes the following working steps:

[0043] Step 1): First, place an inorganic nano-carbonization catalyst support material with a layered structure (70 g of montmorillonite) in a container lined with polytetrafluoroethylene, add four times its volume of deionized water, adjust the pH of the system to 5 using 3 mol / L hydrochloric acid, perform ultrasonic-assisted exfoliation on it, and at the same time stir it at a speed of 600 r / min for 1 h;

[0044] Step 2): Remove the ultrasonic treatment equipment, add a transition metal compound containing boron or phosphorus (10 g of zinc phytate) to the system in step (1), adjust the pH of the system to 1.5, and at the same time stir it at a speed of 600 r / min for 2 h;

[0045] Step 3): Slowly drop 0.5 mol / L NaOH solution into the mixed system in the above step (2), adjust the pH of the system to 8, and at the same time stir it at a speed of 1000 r / min. After the system reaches the predetermined pH condition, continue to stir it at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases. If it decreases, continue to drop 0.5 mol / L NaOH solution to the target value, continue to stir it at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases, and repeat the above operations until the pH value of the system remains constant at 8;

[0046] Step 4): Filter and wash the mixed system in the above step (3), place it in an oven and dry it to constant weight to obtain a phosphorus-doped transition metal zinc hybrid montmorillonite carbonization catalytic system.

[0047] All the unmodified montmorillonite in Comparative Example 1 above was replaced with the phosphorus-doped transition metal zinc hybrid layered montmorillonite prepared in this example to prepare the refractory coating of this example, and it was used as a refractory coating to coat the surface of high silica glass fiber cloth to characterize its refractory effect in actual applications, and the coating thickness was controlled to be 1 ± 0.05 mm.

[0048] The performance test results are shown in Tables 1, 2, 3, 4 and 5.

[0049] As Figure 1 shown, Figure 1 On the left is the apparent morphology and main element composition of the unmodified montmorillonite used in Example 1. Figure 1 On the right is the apparent morphology and main element composition of the montmorillonite after hybrid modification in Example 1.

[0050] It can be Figure 1 seen that the surface of the unmodified montmorillonite is relatively smooth, and its elemental analysis test shows that it does not contain C, P, and Zn elements. While obvious other substances are deposited on the surface of the modified montmorillonite, that is, phosphorus-doped transition metal zinc compounds, and its elemental analysis can also prove this. This shows the reliability of the technical solution of the present invention.

[0051] It can be Figure 3 seen from Figure 3 what is shown that it is the test result of the char yield performance of the liquid silicone rubber coating under the technical solution of Example 1; it can be Figure 3 seen that when the modified montmorillonite with the same mass fraction is used to replace the unmodified montmorillonite, the pyrolysis char yield of the liquid silicone coating is increased from 59.3% to 68.7%. And it should be noted that the stability of montmorillonite is actually better than that of the deposited substances, and the weight loss within 0 - 800 °C is less than 4%. It can be seen from this that the increased residual carbon comes from the liquid silicone rubber.

[0052] It can be Figure 5 seen from Figure 5 what is shown that it is the ablation resistance effect before and after the application of the carbon catalytic material system prepared under the technical solution of Example 1 in the liquid silicone rubber coating composite glass fiber cloth; it can be Figure 5 seen that for the unmodified montmorillonite coating system, cracking occurred under high-temperature ablation, so it can be speculated that under continuous flame ablation, the flame and heat will be transmitted along the cracks and cannot play a fire prevention effect. While for the modified montmorillonite coating system, no ablation cracking occurred under the same high-temperature ablation for the same time, so it can play a good fire prevention effect. This is mainly attributed to the fact that the increase in char yield fills the cracks in the material caused by material shrinkage and the consumption and volatilization of combustibles and incombustibles. This application material is also a key thermal protection material for the upper and lower cover plates of the thermal protection system of new energy vehicle power batteries.

[0053] Example 2

[0054] A method for improving the carbonization rate of liquid silicone rubber during pyrolysis is as follows Figure 2 , Figure 4 and Figure 6 shown, and it includes the following working steps:

[0055] Step 1): First, place the inorganic nano-carbonization catalyst carrier material with a layered structure (60 g of sericite) in a container lined with polytetrafluoroethylene, add deionized water with a volume four times that of it, adjust the pH of the system to 6 using 3 mol / L hydrochloric acid, perform ultrasonic-assisted exfoliation on it, and at the same time perform stirring treatment at a speed of 600 r / min for 1 h;

[0056] Step 2): Remove the ultrasonic treatment equipment, add a transition metal compound containing boron or phosphorus (10 g of zinc borate) to the system in step (1), adjust the pH of the system to 1.6, and at the same time perform stirring treatment at a speed of 600 r / min for 2 h;

[0057] Step 3): Slowly drip 0.5 mol / L NaOH solution into the mixed system in the above step (2), adjust the pH of the system to 8, and at the same time perform stirring treatment at a speed of 1000 r / min. After the system reaches the predetermined pH condition, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases. If it decreases, continue to drip 0.5 mol / L NaOH solution to the target value, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases, and repeat the above operations until the pH value of the system remains constant at 8.5;

[0058] Step 4): Filter and wash the mixed system in the above step (3), place it in an oven and dry it to a constant weight to obtain a boron-doped transition metal zinc hybrid sericite carbonization catalyst system.

[0059] Replace all the unmodified sericite in Comparative Example 2 above with the boron-doped transition metal zinc hybrid sericite prepared in this example to prepare the liquid silicone rubber fireproof foam of this example, with a thickness of 3 ± 0.05 mm.

[0060] The performance test results are shown in Table 1, Table 2, Table 3, Table 4 and Table 5.

[0061] As Figure 2 shown, Figure 2 On the left is the apparent morphology and main element composition of the unmodified sericite used in Example 2, Figure 2 and on the right is the apparent morphology and main element composition of the sericite after hybrid modification in Example 2.

[0062] From Figure 2It can be seen that the surface of unmodified sericite is relatively smooth, and its elemental analysis shows that it does not contain B and Zn elements. However, other substances are obviously deposited on the surface of the modified sericite, that is, boron-doped transition metal zinc compounds, which can also be proved by its elemental analysis. This shows the reliability of the technical solution of the present invention.

[0063] As Figure 4 shown, Figure 4 Figure 7 is the test result of the char yield performance of the liquid silicone rubber foam material under the technical solution of Example 2; as Figure 4 can be seen, when the modified sericite with the same mass fraction is used to replace the unmodified sericite, the pyrolysis char yield of the liquid silicone coating is increased from 60.6% to 73.4%. It should be noted that the stability of sericite is actually better than that of the deposited substances, and the weight loss within 0-800°C is within 3%. Thus, it can be known that the increased residual carbon comes from the liquid silicone rubber.

[0064] As Figure 6 shown, Figure 6 Figure 16 is the ablation resistance effect of the carbon catalytic material system prepared under the technical solution of Example 2 before and after being applied in the liquid silicone rubber foam material; as Figure 6 can be seen, obvious cracks appeared in the liquid silicone foam material prepared with unmodified sericite during the ablation process, and the ablation surface was relatively wide, almost completely ablated, so the thermal protection effect was poor. However, the liquid silicone foam material prepared with sericite hybridized by boron-doped transition metal zinc did not show obvious cracks under the same ablation conditions, and the ablation area was very small and almost no combustion spread phenomenon occurred. This is mainly due to the fact that the sericite after hybridization treatment improves the pyrolysis char formation performance of the liquid silicone rubber, thereby increasing the contact between the combustibles and oxygen under its cell structure, reducing the flame retardancy of the material. At the same time, the increased carbon residue remains in the cell wall structure to avoid the destruction of the pore structure and the appearance of cracks. This application material is also a key thermal protection material for shock absorption and buffering between battery cells in the thermal protection system of new energy vehicle power batteries.

[0065] Example 3

[0066] A method for increasing the pyrolysis carbon yield of liquid silicone rubber, comprising the following working steps:

[0067] Step 1): First, place the inorganic nano char-forming catalyst carrier material with a layered structure (50 g of sericite) in a container coated with a polytetrafluoroethylene liner, add four times its volume of deionized water, adjust the pH of the system to 7 with 3 mol / L hydrochloric acid, perform ultrasonic-assisted exfoliation on it, and at the same time stir it at a speed of 600 r / min for 1 h;

[0068] Step 2): Remove the ultrasonic treatment device, add a transition metal compound containing boron or phosphorus (10 g of zinc borate) to the system in step (1), adjust the pH of the system to 1.7, and simultaneously perform stirring treatment at a speed of 600 r / min for 2 h;

[0069] Step 3): Slowly drop 0.5 mol / L NaOH solution into the mixed system in the above step (2), adjust the pH of the system to 8, and simultaneously perform stirring treatment at a speed of 1000 r / min. After the system reaches the predetermined pH condition, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases. If it decreases, continue to drop 0.5 mol / L NaOH solution to the target value, continue to stir at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases, and repeat the above operations until the pH value of the system remains constant at 9;

[0070] Step 4): Filter and wash the mixed system in the above step (3), place it in an oven and dry it to constant weight to obtain a boron-doped transition metal zinc hybrid layered sericite charring catalytic system.

[0071] Replace all the unmodified sericite in the above Comparative Example 2 with the boron-doped transition metal zinc hybrid sericite prepared in this Example to prepare the liquid silicone rubber fireproof foam of this Example, with a thickness of 3 ± 0.05 mm.

[0072] The performance test results are shown in Tables 1, 2, 3, 4 and 5.

[0073] Table 1 shows the charring performance test results of the materials in the Example and the Comparative Example

[0074] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Carbonization rate (%) 68.7 73.4 66.5 59.3 60.6

[0075] Table 2 shows the limiting oxygen index test results of the materials in the Example and the Comparative Example

[0076]

[0077] Table 3 shows the smoke release performance test results of the materials in the Example and the Comparative Example

[0078]

[0079] Table 4 shows the ablation resistance test results of the materials in the Example and the Comparative Example

[0080]

[0081] Table 5 shows the heat insulation performance test results of the materials in the Example and the Comparative Example

[0082]

[0083] ① The test conditions for the pyrolysis of the samples in Table 1 into char are as follows. Analyzed by a thermogravimetric analyzer, in an air atmosphere, the heating rate is 10 °C / min, and the heating range is from room temperature to 800 °C;

[0084] ② The limiting oxygen index of the samples in Table 2 was measured according to ISO4589-1981;

[0085] ③ Table 3 shows the smoke release of the samples after cone calorimeter tests under the ISO 5660 standard;

[0086] ④ The ablation resistance of the samples in Table 4 was tested by a propane / butane spray gun flame ablation, with the flame temperature controlled at about 1200 °C and the ablation time of 30 min;

[0087] ⑤ The test method for the heat insulation performance of the samples in Table 5 is to connect a temperature sensor to the back of the samples described in ④.

[0088] The charring catalyst system material prepared by the method for improving the charring rate of liquid silicone rubber products according to the present invention can be applied in flame-retardant liquid silicone rubber coatings, lightweight and ablation-resistant liquid silicone rubber foams, ablation-resistant and heat-insulating ceramicizable liquid silicone rubber composite fiberglass fire belts, and fire-resistant liquid silicone rubber cables, or other related fields that require improving the flame retardancy, ablation resistance, and heat insulation performance of liquid silicone rubber products. (Note: The present invention only defines silicone rubber as liquid silicone rubber. For solid silicone rubber, the inventor has verified through experiments that the charring rate cannot be effectively improved by the method provided by the present invention, and the reason is not yet clear.)

[0089] For the above applications of the present invention, under actual formulation conditions, it can directly replace the same inorganic filler without hybridization treatment in the same fraction, or a non-layered structure filler that meets other characteristics of the above carrier material can also be used as the charring catalyst carrier material to improve the charring rate of its liquid silicone rubber products.

[0090] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for improving the carbonization rate of liquid silicone rubber during pyrolysis, characterized in that, It includes the following steps: Step (1): First, place the inorganic nano charring catalyst support material with a layered structure in a container resistant to acid and alkali solutions, add deionized water with a volume four times that of the material, adjust the pH of the system to 5 - 7, perform ultrasonic-assisted exfoliation on it, and simultaneously stir the system at a speed of 600 r / min for 1 h; Step (2): Remove the ultrasonic treatment equipment, add a transition metal compound containing boron or phosphorus to the system in step (1), adjust the pH of the system to 1.5 - 1.7, and simultaneously stir the system at a speed of 600 r / min for 2 h; Step (3): Slowly drop 0.5 mol / L NaOH solution into the mixed system in step (2) above, adjust the pH of the system to 8 - 9, and simultaneously stir the system at a speed of 1000 r / min. After the system reaches the predetermined pH condition, continue to stir the system at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases. If it decreases, continue to drop 0.5 mol / L NaOH solution to the target value, continue to stir the system at a speed of 1000 r / min for 0.5 h, check whether the pH of the system decreases, and repeat the above operations until the pH value of the system remains constant under the target value; Step (4): Filter and wash the mixed system in step (3) above, place it in an oven and dry it to a constant weight to obtain a boron or phosphorus-doped transition metal hybrid layered inorganic filler charring catalyst system.

2. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 1, characterized in that, Under the condition that the pH of the nano charring catalyst support material described in step (1) is greater than 2, its surface is electronegative.

3. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 1, characterized in that, The charring catalyst support material described in step (1) is an inorganic filler with a layered structure and a high specific surface area.

4. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 3, wherein The layered inorganic filler described in step (1) is one or a combination of montmorillonite, sericite, diatomite, and bentonite.

5. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 1, wherein The transition metal compound containing boron or phosphorus described in step (2) is one of zinc borate, zinc phytate, zinc phosphate, zinc phosphite, and zinc phosphite.

6. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 1, characterized in that, The reagent for adjusting the pH of the system in steps (1) and (2) is 3 mol / L hydrochloric acid.

7. The method for increasing the carbonization rate of liquid silicone rubber by pyrolysis according to claim 1, characterized in that, The mass ratio of the charring catalyst support material to the transition metal compound containing boron or phosphorus in steps (1) and (2) is 7 - 5.

8. The charring catalyst system material prepared by the method for improving the pyrolysis charring rate of liquid silicone rubber products according to any one of claims 1 - 8 can be applied in flame-retardant liquid silicone rubber coatings, lightweight and ablative-resistant liquid silicone rubber foams, ablative-resistant and heat-insulating ceramicizable liquid silicone rubber composite fiberglass fireproof tapes, and fireproof liquid silicone rubber cables, or other related fields that require improving the flame retardancy, ablative resistance, and heat insulation performance of liquid silicone rubber products.

9. Use of the char-forming catalytic system material according to claim 8, characterized in that, Under actual formulation conditions, it can directly replace the same inorganic filler without hybridization treatment with the same fraction, or a non-layered structure filler that meets other characteristics of the carrier material can also be used as the charring catalyst support material to improve the pyrolysis charring rate of its liquid silicone rubber products.

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