Design,Construction And Research Of High-Performance,Halogen-Free And Synergistic Flame-Retarding Silicone Rubber System

As one of the key members of the rubber family,silicone rubber has been widely used in the construction,electronics industry,moulding,automotive,shipping,aviation,medical,biological,transportation,food safety and hygiene fields due to its excellent weather resistance,non-toxicity,electrical insulation and chemical stability.Although the main chain structural unit of silicone rubber consists of inorganic silicone oxygen bonds,the large number of fatty alkyl structures in its side chains can still lead to severe combustion and melt drops when exposed to heat.In such cases,the application and development of silicone rubber materials is greatly limited.Halogenated flame retardant fillers,widely used in the market,have been progressively banned because they release large amounts of toxic and harmful gases when materials burn.However,although the use of traditional non-halogenated flame retardants,such as single phosphorus-nitrogen compounds or metal hydroxides,solves the problem of flame retardant toxicity,it is accompanied by low efficiency,high addition,non-renewable raw materials,easy moisture migration and poor compatibility,which greatly hinders the development of non-halogenated flame retarded silicone rubber in practical applications.Therefore,the development of a highly efficient synergistic flame retardant system has become a key issue to be solved for the application and development of silicone rubber composites.In this thesis,three different types of halogen-free synergistic flame retardant systems are designed and constructed to solve the three core problems of low flame retardant performance,high flame retardant addition and non-renewable flame retardant raw materials in turn,and to improve the water resistance and mechanical properties of silicone rubber materials to a certain extent.The main studies are as follows:Firstly,to solve the bottleneck problem of poor flame retardancy of silicone rubber,modified melamine polyphosphate（H-Ni@MPP）was successfully prepared by successive introduction of transition metal(Ni²⁺)and epoxy-modified silicone resin by a simple experimental method.At the same time,a physicochemical synergistic flame retardant system was constructed to improve the flame retardancy of silicone rubber by using it in combination with expandable graphite（EG）,and the effect of the H-Ni@MPP/EG ratio on the flame retardancy of silicone rubber composites was systematically investigated.The best flame retardant performance of the silicone rubber composites was achieved when the total amount of flame retardant added was 40 parts,with an ultimate oxygen index of 49.5%and a vertical burning class of UL-94 V-0.In addition,the flame retardant properties of the silicone rubber composites were largely retained after water erosion tests,with the ultimate oxygen index of the silicone rubber composites decreasing by only 2%at the optimum amount of flame retardant,indicating that the water resistance of the silicone rubber composites was improved.The thermal weight loss analysis shows that the synergistic flame retardant system can decompose before the thermal degradation of the silicone rubber matrix and form a protective layer to protect the silicone rubber in time,which improves the thermal stability of the silicone rubber.Based on the residue analysis,the effective flame retardant mechanism of the silicone rubber composites can be attributed to a gas phase and condensed phase physical/chemical synergistic flame retardant process under the effect of transition metal catalysed carbon formation.Then,to solve the bottleneck problem of high flame retardant addition to halogen-free flame retardant silicone rubber,a low additive halogen-free synergistic flame retardant system was constructed by preparing hydrophobic layered bimetallic hydroxides loaded with melamine polyphosphate（P-MPP@LDH）and co-constructed with expandable graphite（EG）.With a total addition of only 5 parts of flame retardant,the ultimate oxygen index of the silicone rubber composite can reach 36.4%,and the excellent performance of this new halogen-free synergistic flame retardant system is confirmed by a UL-94 V-0 rating for vertical combustion.The cone calorimetric test results show that the fire risk of the flame-retardant silicone rubber composites is significantly reduced compared to pure silicone rubber.Based on the thermal degradation process and combustion residue analysis of the silicone rubber composites,the efficient flame retardant mechanism can be attributed to the combined effect of catalytic carbon formation of heavy metals in LDH and the synergistic physical/chemical swelling barrier effect.Therefore,the highlight of the research in this chapter is to achieve a perfect balance of flame retardancy,water resistance and mechanical properties in silicone rubber systems,providing a new flame retardant strategy to achieve the goal of high performance flame retardant silicone rubber.Finally,in order to overcome the non-renewable and environment-friendly bottleneck of phosphorus-and nitrogen-based flame retardants,a hydrophobically modified gum arabic-loaded layered bimetallic hydroxide（H-GA@LDH）was designed and prepared around the natural product gum arabic（GA）,which was compounded with multi-walled carbon nanotubes（MWCNT）to obtain an environment-friendly phosphorus-free synergistic flame retardant system.When the total amount of flame retardant was 7 parts,the ultimate oxygen index value of the silicone rubber composite was 29.4%,and the composite could achieve a UL-94 V-0 class for vertical combustion.After water erosion tests,the ultimate oxygen index value of the silicone rubber composite decreased by only 4.5%,demonstrating the improved effect of hydrophobic modifications on the water resistance of the flame retardant silicone rubber material.Compared to pure silicone rubber,the peak heat release rate and total heat release rate of the silicone rubber composites were reduced by 22.14%and 12.43%respectively,indicating that the fire risk of the silicone rubber composites was reduced.In addition,the tensile strength and elongation at break of the flame-retardant silicone rubber composites were increased by 115.63%and 23.85%,respectively,compared to pure silicone rubber,which can be attributed to the good dispersion and compatibility of H-GA@LDH and MWCNT in the silicone rubber matrix.Under these conditions,the prepared eco-friendly phosphorus-free synergistic flame retardant system achieves a good balance between flame retardance,water resistance and mechanical properties.Thus,this chapter presents a green and effective bio-based material synergistic flame retardant system that achieves the goal of high performance flame retardant silicone rubber and breaks the limitations of flame retardant silicone rubber,which is highly dependent on traditional toxic halogen-based flame retardants and environmentally harmful phosphorus-based flame retardants.