Flame Retardant Silicone Rubber Research Articles

Recent Advances in Fire-Retardant Silicone Rubber Composites.

Silicone rubber (SR), as one kind of highly valuable rubber material, has been widely used in many fields, e.g., construction, transportation, the electronics industry, automobiles, aviation, and biology, owing to its attractive properties, including high- and low-temperature resistance, weathering resistance, chemical stability, and electrical isolation, as well as transparency. Unfortunately, the inherent flammability of SR largely restricts its practical application in many fields that have high standard requirements for flame retardancy. Throughout the last decade, a series of flame-retardant strategies have been adopted which enhance the flame retardancy of SR and even enhance its other key properties, such as mechanical properties and thermal stability. This comprehensive review systematically reviewed the recent research advances in flame-retarded SR materials and summarized and introduced the up-to-date design of different types of flame retardants and their effects on flame-retardant properties and other performances of SR. In addition, the related flame-retardant mechanisms of the as-prepared flame-retardant SR materials are analyzed and presented. Moreover, key challenges associated with these various types of FRs are discussed, and future development directions are also proposed.

Lightweight and flame retardant silicone rubber foam prepared by supercritical nitrogen: The influence of flame retardants combined with ceramicizable fillers

Silicone rubber foam has wide application potential because of the lightweight and good mechanical flexibility. Herein, silicone rubber foam with ceramicizable flame retardant coating was prepared by talc, ammonium polyphosphate (APP) and carbon black (CB). The composite foam density was 0.12 g/cm3. Talc had significant melting and flame retardant effects on the ceramicization. The molten crystal structure condensed APP and CB together in turn, and finally formed ceramics with higher bending strength, which improved the flame retardant and ceramic properties. When 30 % talc, 10 % APP and 20 % CB in the coating, the peak heat release rate was 98.7 kW/m2, which was reduced by 300 % compared with the pure silicone rubber coating. After ablation, the compression strength was 900 % higher than that of pure silicone rubber coating because of the formation of ceramicizable coating. This work provides a promising strategy for the preparation of highly efficient flame retardant silicone rubber foam.

Flame Retardancy and Excellent Electrical Insulation Performance of RTV Silicone Rubber.

Room temperature vulcanized (RTV) silicone rubber filled with aluminum trihydrate (ATH) is substantially engaged in electrical outdoor insulation applications. The pristine silicone rubber is highly combustible. ATH filled silicone rubber offers excellent electrical insulation but lacks in providing adequate flame retardancy. This short communication reports the novel results on improved flame retardancy of pristine and ATH filled silicone rubber whilst retaining the electrical insulation properties to a great extent. Results suggest that the presence of only one percent of graphene nanoplatelets with ATH sharply reduces the heat release rate and rate of smoke release. A minor reduction in dielectric breakdown strength and volume resistivity is noticed. Furthermore, permittivity and dielectric loss at power frequency suggest that a marginal 1% concentration of nanoplatelet with ATH is an excellent approach to fabricate flame retardant silicone rubber with an acceptable electrical insulation level.

Study on char reinforcing of different inorganic fillers for expandable fire resistance silicone rubber

AbstractSodium silicate monohydrate (NSH), glass frits (GF) and aluminum hydroxide (ATH) were incorporated into room temperature vulcanized (RTV) silicone rubber (SR) as char reinforcing materials to improve the fire resistance of intumescent flame retardant silicone rubber. SR composites containing only intumescent flame retardant such as phosphorus nitrogen composite flame retardant (NH2‐C) and expandable graphite (EG) were used as comparison samples. Limiting oxygen index (LOI) test, vertical burning test (UL‐94), flame resistance test, scanning electron microscopy (SEM) and X‐ray diffraction spectroscopy tests, as well as volume variation and compression strength of char residues were used to discuss the effects of the above‐mentioned fillers on the fire resistance, char residue strength and char integrity of SR composites. The results showed that SR composite filled with only intumescent flame retardants EG and NH2‐C had excellent flame retardancy. After adding ATH, the char residue was relatively dense and had good compressive strength, but its thermal insulation performance was reduced. GF or NSH reduced the flame retardancy of SR composites, but it obviously played a role in binding combustion residues, forming new crystals and improving the stability of char residues.

Thermal aging properties of flame retardant silicone rubber based on melamine cyanurate

AbstractIn this work, an efficient preparation method for flame retardant silicon rubbers (FRSR) was established with using melamine cyanurate (MCA) as flame retardants. In order to analyze the thermal aging mechanisms and flame retardancy of FRSR, cone calorimetric test (CCT), Fourier transform infrared (FTIR) spectra, scanning electronic microscopy (SEM), and energy dispersive X‐ray spectra were performed. Results indicated that the aging time significantly decreases the tensile strength and the elongation at break. SEM images revealed that the porous surface of the aged FRSR provide diffusion path for heat and oxygen, which resulted in a continuously increase in Shore A hardness due to the increase of cross‐linking density during the aging process. FTIR spectra further proved that the MCA is well‐embedded into samples and cross‐linking reaction between free radicals of silicone rubber (SR) and oxygen was occurring during the aging process. Besides, CCT results showed that all FRSR samples before and after thermal aging exhibit excellent flame retardancy with compact and stable char residue layers, effectively hindering the heat transfer and oxygen diffusion. It was expected that our findings could provide important information to fabricate SR with flame retardancy and outstanding long‐term thermal‐aging resistance.

Preparation and properties of ceramifiable flame-retarded silicone rubber composites

Ceramifiable flame-retardant silicone rubber composites were prepared by silicone rubber (SR) as the base polymer, and ammonium polyphosphate, calcium carbonate, sericite mica, and glass frits were utilized as additives. The flammability and thermal stability properties of ceramifying silicone rubber composites were studied by the limiting oxygen index (LOI), microscale combustion calorimetry (MCC), and thermogravimetric analysis (TG). The ceramic residues formed at various temperatures were studied by mechanical testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results indicated that the ceramifying silicone rubber achieved a LOI value of 31.2% and the flexural strength of ceramic residues formed at 1000 °C was 19.7 MPa. Moreover, the MCC results demonstrated that the heat release rate and total release rate of the composites were reduced significantly compared to the corresponding value of neat SR. The TG showed that the residue of composites was approximately 61.5% at 700 °C, as significantly higher than that the residue of neat SR. The XRD results demonstrated that fluoroapatite and Ca2SiO4 crystals were produced in the ceramic residue at high temperatures. The SEM analysis depicted that the number of holes was reduced and a dense structure was formed as the sintering temperature increased, leading to the excellent mechanical properties of formed ceramics at high temperatures.

Synthesis and properties of an intrinsic flame retardant silicone rubber containing phosphaphenanthrene structure

An intrinsic flame retardant silicone rubber was successfully prepared which possessed excellent self-extinguishing properties, high transparency and better mechanical properties.

Organic Nano-Montmorillonite for Simultaneously Improving the Flame Retardancy, Thermal Stability, and Mechanical Properties of Intumescent Flame-Retardant Silicone Rubber Composites

The flammability of room temperature vulcanized silicone rubber (RTVSR) composites filled with melamine phosphate (MP) as intumescent flame-retardant additives was characterized by limiting oxygen index (LOI), UL-94 test, and cone calorimeter. In addition, the thermal degradation of the composites was studied using thermogravimetric analysis (TGA). Furthermore, in order to relate to actual application requirements, the comprehensive performance of the RTVSR/MP composites was optimized by adding organic nano-montmorillonite (OMMT) as a partial substitute for the MP. The as-prepared intumescent flame-retardant RTVSR/MP/OMMT nanocomposites were characterized by LOI, UL-94 test, TGA, cone calorimetry, scanning electron microscopy (SEM), and mechanical tests. The residue morphology formed after the burning of the nanocomposites was analyzed by its SEM and digital photographs. The results showed that the flame-retardant nanocomposites filled with 10 phr OMMT and 35 phr MP displayed the best comprehensive performance in terms of the flame retardancy, mechanical properties, and heat stability at low cost. It is expected that the intumescent flame-retardant silicone rubber composites with simultaneously improved flame retardancy, thermal stability, and mechanical properties will meet more requirements of the increasingly complex applications.

Influence of Fe2O3 on smoke suppression and thermal degradation properties in intumescent flame-retardant silicone rubber

This article examines the feasibility of intumescent flame retardant (based on phosphorus acid, melamine, and pentaerythritol) as a flame retardant and Fe2O3 as a smoke suppression agent in silicone rubber (SR) composites. Smoke suppression of Fe2O3 on intumescent flame-retardant SR composites was investigated using smoke density test and cone calorimeter test (CCT). And, the flammability of SR composites was characterized using CCT at an incident heat flux of 50 kW m−2. The test results further revealed that Fe2O3 could increase smoke suppression efficiency and thermal degradation temperature. Fe2O3 can promote early cross-linking of polymer during decomposition to increase char formation. The silica ash layer integrity governs the efficiency of diffusion barrier that restricts the diffusion of fuels into combustion zone and access of oxygen to the unburned fuels.

Study on Preparation and Properties of APP Filled Flame Retardant Silicone Rubber Composites

A flame-retardant room-temperature vulcanizated silicone rubber (RTV) was prepared with the addition of APP. The effect of different amount of APP on flame retardance, tensile properties, and thermal stability of RTV were studied.Results showed that RTV/APP composites possessed better flame-retardant behaviour, better initial thermal stability, but worse tensile properties.

Influence of ferric hydroxide on smoke suppression properties and combustion behavior of intumescent flame retardant silicone rubber composites

New silicone rubbers(SR)-based hybrid material containing intumescent flame retardant (IFR) and ferric hydroxide (FeOOH) has been developed in order to improve flame retardancy of SR. The synergistic effects of FeOOH with IFR in halogen-free flame retardant SR/IFR blends have been studied by cone calorimeter test (CCT) and thermogravimetric analysis (TG). The data obtained from the CCT indicate that the SR/IFR/FeOOH sample with 4.0 mass% FeOOH has the lowest HRR, SPR, TSR, THR, and SF among all samples. The digital photo graphs give positive evidence that there is a synergistic effect between IFR with FeOOH. The TG results reveal that FeOOH can enhance the thermal stability of SR/IFR/FeOOH at high temperature. Besides the traditional investigations on cone calorimeter tests, an intensive study on the thermo-degradation kinetics was carried out to reveal the mechanism of the outstanding flame retarding performance of the SR/IFR/FeOOH. FeOOH can improve the flame retardancy, increase the thermal stability during the whole process of degradation, and strengthen the ability to form a thermally stable and condensed barrier for heat and mass transfer. These attractive features of SR/IFR/FeOOH suggest that the method proposed herein is a good approach to prepare very effective flame retardants and corresponding super flame retarding SR.

Synergistic effects of zinc oxide in intumescent flame retardant silicone rubber composites

The synergistic effects of zinc oxide (ZnO) with intumescent flame retardant (IFR; based on phosphorus acid, melamine and pentaerythritol) in silicone rubber (SR) composites have been studied using limiting oxygen index, UL-94, cone calorimeter test and digital photographs. The results showed that 2·0 wt-% loading ZnO in the flame retardant SR composites could greatly reduce the peak values of heat release rate and smoke production rate, and form a compact char layer on the surface of the sample. Thus, a suitable amount of ZnO plays a synergistic effect with IFR in flame retardant SR composites system.

Synergistic effects between red phosphorus and alumina trihydrate in flame retardant silicone rubber composites

The synergistic flame retardant effects between red phosphorus (RP) and alumina trihydrate (ATH) in silicone rubber (SR) composites were evaluated using limiting oxygen index, UL 94 rating, cone calorimeter, thermogravimetric analysis and digital photographs. It has been found that the SR composite containing only ATH does not show good flame retardancy at 39·0 wt-% loading. The cone calorimeter results showed that the heat release rate, mass loss rate, mass and total heat release of SR/ATH/RP composites decrease greatly in comparison with the SR/ATH composites. The digital photographs demonstrated that 1·0 wt-%RP could promote the formation of the homogenous and compact char layer. Thus, a suitable amount of RP has a synergistic effect with ATH in the flame retardant SR composite system.

Synergistic effects between red phosphorus and alumina trihydrate in flame retardant silicone rubber composites

Synergistic effects between red phosphorus and alumina trihydrate in flame retardant silicone rubber composites

Mechanical properties, fire performance and thermal stability of magnesium hydroxide sulfate hydrate whiskers flame retardant silicone rubber

Halogen-free flame retardant silicone rubber (SR) composites, using magnesium hydroxide sulfate hydrate (MHSH) whiskers as flame retardant have been prepared by a two-roll mill. Moreover, microencapsulated red phosphorus (MRP) was used as a synergist. Mechanical tests were performed to determine the tensile strength, elongation at break, and shore hardness of the composites. The morphology of fracture surface was observed by environmental scanning electron microscopy (ESEM). The results showed MHSH slightly reduced the tensile strength of the composites, but had obvious influence on the elongation at break. Meanwhile, Shore A hardness presented uptrend with increasing MHSH content. The addition of vinyl silicone fluid (VSF) could improve the compatibility of the MHSH whiskers in SR matrix, and therefore improved the mechanical properties of composites. The flammability properties of composites were investigated by limited oxygen index (LOI), UL-94 tests, and cone calorimetry experiments. It is found that MHSH whiskers can effectively improve the flame retardancy of SR composites due to the endothermic degradation of MHSH whiskers accompanied with the release of water vapor, and the formation of fibrous magnesia acting as a barrier layer. The incorporation of MRP in SR/MHSH whiskers system had a synergic fire retardant effect in the condensed and gas phase. In addition, thermogravimetric analysis (TGA) indicated the presence of MRP enhanced thermal stability of the SR/MHSH composites at higher temperature range, and remarkably promoted char residue yield.

Flame retardant mechanism of polydimethylsiloxane material containing platinum compound studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography

The flame retardant mechanism for silicone rubber induced by adding ppm order of a platinum compound, platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex was studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography. The thermal degradation measurement of the flame retardant silicone rubber sample (FR-SR) indicated that a considerable amount of methane was evolved from the FR-SR sample at around 400–800 °C while formations of cyclic siloxanes were fairly suppressed in comparison with that from the control SR sample. On the other hand, on the gas chromatogram of the hydrolysis products from the FR-SR residue samples thermally treated over 400 °C, significant amounts of characteristic products reflecting the cross-linking structures generating from methylene-bridge and trifunctional siloxane structures in the polymer chains were observed. These results suggest that the thermal decomposition of the FR-SR material is strongly suppressed by the formation of the cross-linking structures induced by the platinum compound during combustion, which leads to its flame retardancy.