Journal of Applied Polymer Science, Vol.82, No.9, 2326-2341, 2001
Replacement of virgin rubbers by waste ground vulcanizates in blends of silicone rubber and fluororubber based on tetrafluoroethylene/propylene/vinylidene fluoride terpolymer
This study reports the results of investigations on blends of silicone rubber and fluororubber based on tetrafluoroethylene/propylene/vinylidene fluoride terpolymer and the effects of replacement of silicone rubber and/or fluororubber in their 50/50 blend by the respective vulcanizate powders of known compositions. To simulate the aging condition of factory wastes, the silicone rubber or fluororubber vulcanizates were aged for 72 h at 200 degreesC and then converted into powder by mechanical grinding. The fluororubber vulcanizate powder (FVP), mostly spherical in shape with average diameter varying between 2 and 10 mum, exists in a highly aggregated state displaying chainlike structures that, however, break down during blending with virgin rubbers. The silicone rubber vulcanizate powder (SVP) is irregular in shape, with larger particles in the range of 30-100 mum, and the smaller particles exist in highly aggregated chainlike structures, as in the case of FVP, which break down during milling to mostly spherical particles of 2-10 mum in diameter. Measurements of physical properties reveal that the blends of silicone rubber and fluororubber are technologically compatible. SEM photomicrographs of THF-etched samples show the biphasic structure of the blends, in which the fluororubber forms the dispersed phase in a continuous silicone rubber matrix of lower viscosity. Replacement of silicone rubber in the 50/50 silicone rubber/fluororubber blend by its vulcanizate powder (SV-P) increases the Mooney viscosity, but replacement of fluororubber in the blend by its vulcanizate powder (FV-P) has little effect on the Mooney viscosity. Monsanto rheometric studies reveal that replacement of silicone rubber by SVP or fluororubber by FVP in the 50/50 silicone rubber/fluororubber blend increases the minimum rheometric torque but decreases the maximum torque, and the effect is more pronounced in the case of SVP. Furthermore, the replacement of silicone rubber in the blend by SVP causes a decline in the physical properties (25% replacement causing about 10% decline in properties, for example), whereas even 75% replacement of fluororubber by FVP has little effect on the physical properties. When both silicone rubber and fluororubber are partially replaced by SVP and FVP in the same blend, properties of the resulting blend composition are controlled more by SVP incorporation, whereas fluororubber replacement has only a marginal effect on blend properties. It is evident from dynamic mechanical spectra that the blends are immiscible in all compositions and addition of SVP or FVP does not affect the glass-rubber transitions of the constituent polymers.