Preparation Of Ceramized Refractory Silicone Rubber And The Study On Flame-Retardant Mechanism

As an environmentally friendly polymer,Silicone rubber?SR?has widely applications in many fields such as medicine,materials and coatings.Silicone rubber will be completely burnt into SiO₂ and CO₂ without any toxic pollution to the environment.In particular,a ceramized SR can be achieved by combining SR with other inorganic fillers and fluxes due to its high thermal stability.As a novel composite fire resistant material,ceramized SR has broad application prospects in the field of fireproof cables.The ceramization mechanism of silicone rubber can be mainly explained that the Si-O bond would transforms into continuous and thermal isolated SiO₂ network.Simultaneously,fluxes can melt to form a fluid liquid which fills between the ceramic filler and SiO₂ network to serve as a"bridge"at high temperature.After cooling,the formed ceramic structure can effectively protect the metal substrate.How to reduce the ceramization temperature of silicone rubber and increase the ceramization conversion rate as well as the ceramization strength are becoming a big challenge in recent years.In this paper,polyphosphazene microspheres?PZS?with excellent thermal stability and flame retardancy were synthesized and then were used as carriers to support platinum on the surface.The ceramized fireproof SR composites were prepared by combing the obtained Pt/PZS with other inorganic fillers.The flame retardancy and ceramization mechanism,as well as the catalytic carbonization effect of Pt-PZS to SR were investigated.That aim of the research in this paper is to improve the fire resistance and ceramization properties of SR.In this paper,poly?cyclotriphosphazene-co-4,4-sulfonyldiphenol?microspheres?PZS?with highly cross-linking structure were synthesized and which is insoluble or meltable under high temperature.Then,the PZS microspheres were used as supports for Pt nanoparticles.The chemical structure was characterized by FTIR and crystal structure of Pt nanoparticles was studied through X-ray diffractometer?XRD?.The morphology of PZS and Pt/PZS microspheres was characterized by scanning electron microscope?SEM?and transmission electron microscope?TEM?.The thermal stability of PZS microspheres was studied through Thermogravimetric analysis?TGA?.The results indicated that Pt nanoparticles were successfully loaded on the surface of PZS microspheres with good dispersion and the average diameter of Pt particles was about 6 nm.TGA results showed that Pt/PZS microspheres have outstanding thermal stability and charring ability,the initial decomposition temperature were421.7? and the char yield were 56.0%at 800?.Pt/PZS microspheres and other inorganic ceramic fillers were incorporated into the silicone rubber to prepare the fireproof SR composites.The thermal stability of SR composites were characterized by TG and the flammability was studied through cone calorimeter?CONE?tests.The ablation performance of SR composites was studied in the temperature range of 400-1000?.The morphology of the ablated composites was surveyed by SEM and the crystal structure change during ablation was studied through XRD.The fire resistance of SR composite cables under a true fire was studied by burning using a blowtorch.TG data suggested that flame retardant SR composites?Pt/F-SR?with 0.01 wt%of Pt/PZS addition greatly enhanced the char yield?54.89 wt%?,which increased by 10.5%comparing with the normal SR composite without Pt/PZS composites?F-SR?.It indicated that the addition of an ultra-low loading of Pt/PZS microspheres?0.01 part?can obviously improve the thermal stability of the SR composites.Compared with F-SR,Cone results revealed that the incorporation of Pt/PZS microspheres brings about a 23.4%reduction in heat release rate,9.9%decrease in total smoke production and the mean effective heat combustion was reduced by 5.9%.The samples shape of Pt/F-SR could be well maintained at different ablation temperatures?400-1000??,and the toughness was also significantly enhanced after400? of ablation.The flexural strength was improved to 5.62 MPa from 0.11 MPa,about 50times higher than the pure SR.From the results of SEM observation,a continuous network-like ceramic phase appeared along with the ablation temperature,indicating that the addition of Pt/PZS microspheres significantly promotes the ceramification of the SR composites.XRD analysis also suggested that the presence of Pt/PZS promoted the formation of new crystalline phase:CaSi₂O₅ and Quartz.The shape of the SR cables with 0.01 wt%Pt/PZS addition could be well maintained with less surface cracks.The metal core inside the cable had no oxidative blackening after the ablation.It indicated that the incorporation of Pt/PZS microspheres obviously improved the fire resistant and ability of thermal insulation.The water resistance tests showed that the formed ceramic cable structure was still remained without breaking and the metal core was not wetted by water even after violently shaking up and down in water.In conclusion,an ultra-low loading of Pt/PZS microspheres can enhance the fire and water resistance as well as the ceramization properties for SR.This paper will provide theoretical supports and research ideas for ceramic-based silicone rubber flame retardant system and the corresponding industrialization process.