Behavior of Highly-Filled Rubber Vulcanizates

Abstract

Abstract Examination of the stress-strain curves of vuloanizates containing up to 60 per cent by volume of mineral filler of particle size greater than 1 µ has led to the discovery of a plateau at which the elongation increases several hundred-fold at constant stress. This has been demonstrated for a number of fillers with several rubbers, natural and synthetic. The effect of filler content, particle size, and degree of cure on the stress at which the plateau occurs, and its length, have been investigated. An explanation is suggested and the significance of the observations for the experimental verification of equations relating modulus to filler content is pointed out. The volume changes accompanying the elongation of these vulcanizates have also been investigated at varying filler contents, particle sizes, and degrees of cure, and shown to correlate with the stress-strain curves. The possible bearing of these results on the nature of the rubber-filler bonds, and hence on the reinforcing action of fillers, is briefly discussed.