| abstract |
A process of making a polydiorganosiloxane-silica mixture from a free-flowing, powdered, surface-modified, reinforcing silica-polydiorganosiloxane suitable, for example, for producing RTV silicone sealant compositions which are non-sag. These mixtures are made by combining, mixing and heating a reinforcing silica filler and a surface modifying agent at 90°C. to 180°C. using 0.1 to 0.5 parts by weight of the surface modifying agent per one part by weight of the silica. Polydiorganosiloxane is added gradually to the resulting fluidized filler over a time period of less than 10 minutes to yield the free flowing powdered reinforcing silica-polydiorganosiloxane. The final mixture is obtained by massing the concentrate and adding more polydiorganosiloxane to obtain a mixture which has from 8 to 20 weight percent silica filler. RTV silicone sealant compositions are obtained in 10 to 15 minutes from the initiation of our process. |