Research On Properties Reinforcement&Modification Of High Temperature Vulcanized Silicone Rubber By Novel Inorganic Fillers

Silicone rubber is a kind of elastomer which is fabricated by crosslinking reaction of linear polysiloxanes with Si-O-Si as backbone and organic groups(i.e.methyl and phenyl)by the curing agents.Due to the special chemical structure of polysiloxanes,the interactions between molecular chains are fairly weak.This is the reason why silicone rubber obtained from crosslinked pure polysiloxanes has rather low mechanical properties and almost has no application.For the purpose of practical use,therefore,reinforcement of silicone rubber is necessary.The most common means to reinforce silicone rubber is blending inorganic fillers with silicone rubber.The methods of blending include traditional mechanical mixing and sol-gel in-situ reinforcement.Compared to the former method,the later achieves better dispersion of fillers in silicone rubber,stronger interactions between fillers and rubber.Moreover,filler size and morphology can be controlled by reaction conditions.In this article,we mixed silica,zirconia and boron nitride(BN)with high temperature vulcanized silicone rubber(HTV-SR)in different ways.Based on previous researches,novel routings are designed and developed for the sake of reinforcing HTV-SR.Contraposing the properties of HTV-SR,utilizing TMOS,TEOS and Zirconium n-propoxide,we successfully prepared prehydrolyzed Sol-gel systems(PH-SGSs)by Sol-gel reactions.Then,HTV-SR and PH-SGSs were mixed together evenly.PH-SGSs would continue hydrolysis and condensation after mixing and in-situ reinforcing fillers are formed.We analysed the reinforcement effect of various PH-SGSs which were synthesized with various sol-gel reaction catalysts-HCl,ammonia and dibutyltin dilaurate(DBTDL).We monitored and controlled PH-SGSs by pH,temperature,liquidity and reaction time.The degrees of reinforcement were determined by mechanical properties,SEM images,curing behaviors,crosslinking densities,thermal stability,etc.The conclusions and predictions indicated from experiment results are as follows.The silicas obtained from PH-SGSs which catalyzed by HC1 and DBTDL have fine particle size and uniform dispersion in the HTV-SR matrix.Mechanical properties and crosslinking densities of corresponding HTV-SR were improved significantly.The time needed for completely vulcanization was reduced.Thermal stability of these HTV-SR had no obvious change.In contrast,ammonia-generated silica in HTV-SR appears with larger size,uncertain shape and nonuniform dispersion.Almost no reinforcement was achieved for the related HTV-SR.Furthermore,the enhancing effect of silane coupling agent is limited,more attempts are needed.The in-situ zirconia generated for Sol-gel reaction had a unique morphology.Tear strength of certain samples was more than doubled.HTV-SR blended in-situ formed zirconia have better thermal stability compared to those without in-situ formed zirconia,especially in the range of 500 ? to 600 ?.Mechanical blended boron nitride with HTV-SR,by contrast,weak interactions were confirmed.And agglomerations were formed among boron nitride particles.Only thermal conductivity was enhanced after the blending.Other properties were unchanged,or even reduced.Attempts were made for surface modification of boron nitride.However,little progress has been achieved.In conclusion,the outcome of experiments met our expectation basically.Further work is needed for the study.