Preparation And Properties Of Cross-linked Ceramizable-silicone-rubber Composites By Electron-beam Irradiation

When a fire occurs in large places such as supermarkets,hospitals,and high-rise buildings,fire-resistant and flame-retardant materials can ensure the smoothness of the circuit,ensure the normal operation of fire-fighting equipment,and provide firefighters with more time to rescue trapped people and reduce property damage.Ceramizable-silicone-rubber composites are prepared by adding refractory fillers and fluxes,as well as some other inorganic fillers,to the silicone rubber matrix.As a recently developed refractory material,ceramizable-silicone-rubber has attracted much attention due to their combination of workability at room temperature and ease of porcelain formation at high temperatures.However,the poor flame retardant effect of ceramizable-silicone-rubber and the incomplete formation of ceramicized layers have seriously limited their application.In this paper,new functional fillers are designed to improve the flame retardancy and porcelain forming properties of ceramizable-silicone-rubber.Meanwhile,electron-beam（EB）irradiation cross-linked technique was used to irradiate the ceramizable-silicone-rubber and obtain the electron-beam irradiation cross-linked ceramizable-silicone-rubber composites,and their microstructure,thermal properties,mechanical properties and flame retardant properties were investigated.Firstly,we synthesized allyl-functionalized cyclotriphosphazene（CP-Allyl）by nucleophilic substitution reaction.A series of ceramizable-silicone-rubber composites（CP-Allyl/CSR）containing allyl-functionalized cyclotriphosphazene at different irradiation doses were prepared by electron-beam irradiation technique for the study of new refractory insulating materials.The results showed that the addition of CP-Allyl would have a great influence on the comprehensive performance of the composites.The CP-Allyl/CSR-3 samples had the best comprehensive performance,in which the gel content of CP-Allyl/CSR-3 reached 98.8%at an irradiation dose of 120 k Gy.The tensile strength reached 5.2 MPa,and the ultimate oxygen index was as high as 32.4%.In addition,CP-Allyl/CSR-3 was observed to retain their shape well after 700-1000℃ ablation,and a hard,continuous and complete ceramicized layer was formed for the CP-Allyl/CSR samples.To further investigate the ceramizable-silicone-rubber,we prepared a poly（phosphonitrile）-loaded silica nanospheres（SiO₂@PZS）with a core-shell structure by precipitation polymerization.A series of ceramizable-silicone-rubber composites（SiO₂@PZS/CSR）based on polyphosphazene nitrile-loaded nano-silica microspheres were prepared by adding different mass fractions of SiO₂@PZS and some other inorganic fillers to the methyl vinyl silicone rubber matrix.The EB irradiation cross-linked SiO₂@PZS/CSR composites were obtained by irradiated the composites with electron-beam,which could substantially improve their mechanical properties.Among them,the prepared SiO₂@PZS/CSR-3 samples reached 97.7%gel content,4.1 MPa tensile strength and 32.8%ultimate oxygen index under 120 k Gy irradiation.In addition,SEM and EDS characterization of the ablated composites observed that the shape of the samples could be well maintained.SiO₂@PZS can also participate in the construction of the ceramicized layer,which makes the formed ceramicized layer more dense and harder.This results in effective protection of wires and cables.