[Effect of fillers on the strength of silicone systems]

The present paper examines the strength behaviour of addition silicone systems composed of Lukopren A 6200 and three inorganic fillers (Skron SF 600, Cab-O-Sil LM 150, sodium chloride) in different concentrations and particle sizes. The tensile strength sigma (MPa) and the relative lengthening of samples on rupture epsilon (%) were measured. With increasing concentration of the filler in the system relative lengthening of matrices is decreased. This trend corresponds with the theoretical hypotheses and it is understandable also with regard to the fact that the filler, in comparison with silicone rubber, possesses very low ductility. An addition of Sikron increases tensile strength of samples. Dependence of tensile strength on the amount of Sikron in the system is linear. This behaviour is typical of fibrous composites and the composites with high adhesion between the filler and matrix. Concentrations of Cab-O-Sil up to 5% did not exert an effect on tensile strength. An important increase in strength was shown only by the systems containing 10% of Cab-O-Sil. Experimental dependence of tensile strength on the amount of Cab-O-Sil in the system can be described by the equation for composites with Hookean behaviour till destruction. The effect of sodium chloride on tensile strength is more complicated. In the systems with NaCl particles of 20 microns, strength is not practically changed up to a content of 40% of NaCl in the system. In larger size fractions, tensile strength is decreased, and with a change in particle size, shape is probably changed as well.