SPECIAL LOW SURFACE SILICA AS FILLER IN FLUOROELASTOMERS

While precipitated silica is the well-established reinforcing filler for the so-called “Green Tire” and polar polymers, and fumed silica is used as the major filler for silicones; fluoropolymers are, in most cases, filled with low-surface carbon black, such as N 990 or non-reinforcing white fillers. Silica cannot be used due to the strong interaction with the polymer, caused by the high polarity of both the silica and the rubber. The development of a silica with a BET surface area of only 20 m²/g (trade name SIDISTAR^® R) and a low silanole group density, now allows silica to be used as reinforcing filler in fluoroelastomers for coloured products. A significant improvement of the physical properties compared to other non-black fillers and even to N 990, can be achieved. The processing of these compounds is excellent due to the spherical shape of the primary particles of this silica type, even at loadings higher than normally possible with other fillers. Of great interest to the end-user are the improvements in thermal stability and chemical resistance, achievable by replacing N 990 with this specialty silica.