Study On The Catalytic Action Of Aminothriethoxysilane On Deacidified RTV Silicone Rubber

The deacidified room temperature vulcanized silicone rubber(RTV silicone rubber)is a kind of silicone rubber material with outstanding high transparency,excellent heat resistance and cold resistance.The main components of RTV silicone rubber include basic polymer,crosslinking agent,catalyst,filler and other parts.Currently,the organotin is the most widely used catalyst in RTV silicone rubber system.With the enhancement of awareness of environmental protection,more restrictions will be imposed on its application.Therefore,finding and developing environmental friendly organotin-free catalysts is of great urgency.In this paper,three aminotriethoxysilanes 3-aminopropyltriethoxysilane(APTES),3-(2-aminoethylamino)propyltriethoxysilane(AATS)and diethylaminomethyltriethoxysilane(DMTS)have been used as catalysts in two systems.One system is composed of low viscocity hydroxylterminated polydimethylsiloxane(HTPDMS)and methyltriacetoxysilane.The other one system is reinforced with silica.The catalytic effect of catalysts and mechanical properties and thermal stability of silicong rubber after curing have been studied with promising tin-free catalysts.In the deacidified RTV silicone rubber system which consists of HTPDMS and methyltriacetoxysilane,it is found that all of these three aminotriethoxysilanes have certain curing effects.According to the change of loss coefficient(tan?)and complex viscosity within1 h of the process of the rubber curing process,the catalytic efficiency is related to the aminotriethoxysilanes'alkalinity directly.The alkalinity of DMTS is stronger than that of APTES,so its catalytic efficiency is higher than that of APTES.As the addition of aminotriethoxysilanes increases,both DMTS and APTES systems show a significant increase on the curing rate.When their addition exceeds 1.5 phr,the speed of curing rate slows down.Under 1.0 phr addition,the most alkaline AATS has a stronger catalytic effiency than DMTS.However,AATS will lead to a decline of catalysis efficiency with higher addition because of self-condensation.When the addition of DMTS,APTES and AATS is 1.5 phr,it needs 7 min,8min and 14 min for tan?to decrease to 1.And the tack free time is 18 min,21 min and 28 min respectively.The catalysis efficiency of aminotriethoxysilanes has a certain gap with dibutyltin dilaurate(DBTDL)'s.Furthermore,DMTS has a closer catalysis efficiency to DBTDL at higher addition.The results of cross-linking degree after curing 12 h reveal that the aminotriethoxysilanes mainly play a catalytic role instead of cross-linking effect in the rubber stocks.The catalytic effect of three aminotriethoxysilanes in the RTV silicone rubber system reinforced with silica has been studied.It is found that DMTS shows the best catalytic performance.With 1.5 phr addition,DMTS system has a good catalytic effect.Its tan?only needs 8 min to decrease to 0.1;the complex viscosity rises to 2×10~6 at 36 min and its tack free time is 8 min.Compared with DBTDL system,the chemical cross-linking density,structural stability,thermal stability,metal adhesion,intensity and elasticity of RTV silicone rubber increase with the addition of three aminotriethoxysilanes.Besides,DMTS has better performance than APTES and AATS.With less than 1.5 phr DMTS amount,the crosslinked structure is imperfect.And the mechanical properties become better when the DMTS amount increases.Under 1.5 phr DMTS amount,the chemical crosslinking density ratio of RTV silicone rubber is 83.7%.The shear strength,tensile strength and elongation at break of RTV silicone rubber reach the maximum,which are 7.66 MPa,0.85 MPa and 81.24%respectively.When the amount is more than 1.5 phr,the excess catalyst destroys the structure and the mechanical properties are degraded.