Thermoelastic Phenomena in Natural Rubber Compounds during Cyclic Deformation

1. The initial stages of stretching of natural rubber gum compounds ((λ≦4.5)) and of filled compounds ((λ=1.8−4)) are characterized by liberation of heat equivalent to the work of deformation according to Equation (lb). Further deformation takes place with liberation of surplus heat caused by- crystallization of the rubber. The relation between the work of deformation and the heat effect is given by Equation (1a) 2. The beginning of crystallization and its degree at a given elongation depend on the degree of vulcanization and on the nature of the dispersed fillers. The rubbers with the highest modulus crystallize the poorest. Active fillers such as channel black promote crystallization to a greater degree than silica gel and chalk. 3. A rate of deformation of 100% per second assures adiabatic conditions without taking special measures. 4. It was determined that errors in the quantitative analysis of the process of adiabatic stretching of rubbers result from lack of knowledge of the true heat capacity of the compound and especially from inaccuracy of measurement of elongation during the relaxation cycle.