{"id":1615,"date":"2026-09-15T14:42:29","date_gmt":"2026-09-15T06:42:29","guid":{"rendered":"https:\/\/dghtj.com\/?p=1615"},"modified":"2026-09-15T14:42:29","modified_gmt":"2026-09-15T06:42:29","slug":"2609151-2","status":"publish","type":"post","link":"https:\/\/dghtj.com\/en\/2609151-2\/","title":{"rendered":"How does silicone rubber achieve UL94 V-0 flame retardant rating? Analysis of formulation technical challenges"},"content":{"rendered":"

Silicone rubber has excellent high and low temperature resistance, weather resistance, and electrical insulation properties, and is widely used in electronic and electrical appliances, new energy vehicles, aerospace, power equipment, and other fields. However, ordinary silicone rubber itself has a limiting oxygen index of only about 21%, and its fire performance can hardly meet the industry's stringent safety standards.
\nUnmodified silicone rubber can mostly only reach HB level in the UL94 vertical burning test. After being ignited, it continues to burn and also produces flammable drips, posing a great safety hazard. To make silicone rubber reach UL94 V-0 level, there is a core difficulty: after the siloxane main chain of silicone rubber is heated, it mainly generates silica, and it is difficult to achieve flame retardancy by relying on the matrix itself to form char like ordinary plastics. Therefore, silicone flame retardancy cannot directly copy the mature flame retardant solutions of engineering plastics; it is necessary to match the material characteristics of silicone rubber and design a dedicated halogen-free flame retardant system.
\nI. Three Mainstream Technical Routes for Silicone Rubber to Achieve V-0 Flame Retardancy
\nAt present, in the industry, silicone rubber achieving V-0 flame retardancy is mainly divided into three routes: high inorganic filling, phosphorus-nitrogen intumescent flame retardancy, and platinum-based synergistic flame retardancy, and different routes have their own advantages and disadvantages.
\n1. High-Loading Inorganic Filler Route (ATH \/ Magnesium Hydroxide MH)
\nThis solution uses aluminum hydroxide ATH or magnesium hydroxide MH as the main flame retardant. ATH thermally decomposes above 200\u00b0C, releasing water of crystallization to carry away heat and achieve cooling, and decomposes to form aluminum oxide to create a physical heat insulation layer, blocking heat transfer.
\nThe disadvantages are very obvious: relying solely on an ATH system, the loading needs to reach more than 80 parts to achieve FV-0 flame retardancy. Excessive filler loading will directly destroy the elasticity of silicone rubber itself, causing a significant decline in mechanical properties such as tensile strength and tear strength, making the silicone rubber hard and lose its soft characteristics.
\n2. Phosphorus-Nitrogen Intumescent Flame Retardant Route (MPP, MCA, Aluminum Hypophosphite)
\nWith melamine polyphosphate MPP, melamine cyanurate MCA, and aluminum hypophosphite as core components. Relevant test data show that adding more than 30 parts of MPP to dealcoholized RTV silicone rubber can achieve UL94 V-0 flame retardant effect. The phosphorus-nitrogen flame retardant system decomposes upon heating, generating phosphoric acid derivatives, promoting char formation on the material surface, and releasing inert gases to dilute combustible smoke, achieving flame retardancy through dual condensed-phase and gas-phase effects.
\nNote: Many phosphorus-nitrogen products contain amino groups, which will interfere with the platinum curing system of addition-cure liquid silicone rubber, so selection requires extra attention.
\n3. Platinum-Based Synergistic Flame Retardant Route (Flame Retardant Technology Unique to Silicone Rubber)
\nPlatinum-based synergists are a flame retardant technology unique to silicone rubber. Adding a trace amount of platinum compounds (generally less than 1 phr) can catalyze rapid crosslinking of silicone rubber during combustion, generating a denser and more stable SiO\u2082-C composite char layer, greatly improving flame retardant efficiency. Platinum-based synergists have limited flame retardant effect when used alone and are almost never used alone as the main flame retardant; the conventional industry practice is to use them in compound synergy with ATH and phosphorus-nitrogen flame retardant systems.
\nII. Core of Efficient V-0 Flame Retardancy: Compound Synergistic System
\nTo balance flame-retardant rating and silicone mechanical properties, synergistic compounding is the key to formulation.
\nATH combined with platinum-based synergists is a classic compounding solution in the field of silicone rubber flame retardancy. ATH provides the basic functions of endothermic cooling and physical heat insulation; the platinum catalyst catalyzes rapid crosslinking and char formation of the matrix in the early stage of combustion. Through their synergy, the ATH loading can be reduced from over 80 parts to a total compounded amount of 35\u201340 parts, achieving UL94 V-0 while maximally preserving the original properties of silicone rubber such as flexibility and tear strength. The flame-retardant mechanism of platinum-based synergists is to inhibit transition complexes that promote molecular depolymerization during silicone rubber pyrolysis; with the aid of ATH fillers or metal oxide intermediates, they immobilize the condensed products of thermal cracking and build a stable insulating barrier layer.
\nFor thin-wall silicone products of 1 mm and below, formulation design becomes even more difficult. The addition amount of platinum-based synergists, ATH particle size distribution, and filler surface treatment process each directly determine whether the final product can pass the V-0 test. Thin-wall parts have higher requirements for flame-retardant system efficiency; simply applying formulations for thick products can easily lead to test failure.
\nIII. Key Considerations for Flame-Retardant Formulation Design of Silicone Rubber
\n1. The curing system determines flame retardant selection.
\nSilicone rubbers with different curing types differ greatly in flame retardant selection. Addition-cure liquid silicone rubber (LSR) itself relies on platinum to complete curing; if phosphorus-nitrogen flame retardants containing amino groups, such as APP and MCA, are directly introduced, the amino groups will undergo a coordination reaction with the platinum catalyst in the system, causing serious defects such as delayed curing and incomplete curing. For addition-cure LSR, preferentially use an ATH + platinum-synergist amino-free flame-retardant system; if phosphorus-nitrogen flame retardants must be used, grades with complete surface coating modification must be selected to isolate amino groups and avoid curing interference.
\n2. Filler surface treatment cannot be ignored.
\nAluminum hydroxide ATH, after surface modification with a silane coupling agent, shows significantly improved compatibility with the silicone rubber matrix. At the same loading level, modified fillers can achieve better flame-retardant performance while improving the tensile properties and resilience of the silicone rubber. Powder without surface treatment is prone to agglomeration, causing problems such as white spots on the product surface and deteriorated mechanical properties.
\n3. Product thickness directly affects flame-retardant test results.
\nUL94 V-0 test results are highly dependent on specimen thickness. With the same formulation, a 3 mm specimen can easily pass V-0, but when reduced to a 1 mm thin wall, it often fails to meet the standard. When developing thin-wall silicone sealing rings, silicone gaskets, and ultra-thin silicone sheets, the synergistic flame-retardant formulation must be adjusted according to thickness.
\nIV. Industrialized Flame-Retardant Silicone Rubber Solutions
\nIn the practical production implementation of V-0 flame-retardant silicone, Dongguan Hongtaiji Flame Retardant Materials Co., Ltd. has developed a dedicated series of high-performance halogen-free flame retardants for ordinary silicone rubber and foamed silicone. The product powders have good compatibility with the silicone rubber matrix and excellent anti-migration and anti-exudation performance; while achieving UL94 V-0 flame retardancy, they can preserve the silicone's original high resilience, tear strength, and product surface smoothness.
\nProduct references:
\nFR-3035: Nitrogen-containing halogen-free environmentally friendly fine powder, suitable for silicone products of general thickness;
\nFR-562A: Special flame retardant for thin-wall silicone, capable of achieving V-0 flame retardant rating on 0.8 mm specimens.
\nBoth products can serve as core components of ATH-platinum synergistic systems and phosphorus-nitrogen compound flame retardant solutions, helping formulation engineers achieve a balance among flame retardant performance, processing performance, and production cost. For product details, please visit the official website pagewww.dghtj.com<\/a>: Silicone flame retardant
\nSummary
\nFor silicone rubber to achieve UL94 V\u20110 flame retardancy, the core logic is: rely on ATH to provide the foundation of endothermic heat absorption and cooling; platinum-based synergists catalyze the formation of a dense char layer; the phosphorus-nitrogen flame retardant system supplements gas-phase flame retardancy and char promotion. Through multi-component compounding and synergy, the overall filler loading is reduced while ensuring the flame retardant reliability of thin-walled products.
\nDuring actual development, priority should be given to flame retardant powders that have undergone surface modification and are compatible with silicone rubber; targeted formulation adjustment based on the silicone vulcanization system and product thickness is the feasible path to stably achieve V\u20110 rating.<\/p>","protected":false},"excerpt":{"rendered":"

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