Thermal Plasticization of Rubber. I. Structural Changes in Thermally Plasticized Rubber

Abstract

Abstract 1. The results of the experiments give a more or less complete picture of the relative changes in rubber brought about by mechanical and thermal plasticization, and show that there is an analogy between the two effects. 2. The fundamental factor in thermal plasticization is oxygen (for a given set of thermal conditions), whereby a definite numerical relation exists between the plasticization effect and the oxygen concentration. In the experiments described, the quantity of oxygen absorbed by rubber did not exceed 0.55 per cent at the maximum temperature and time of treatment (170° C. for 120 minutes). Thermal plasticization in a medium devoid of oxygen (in carbon dioxide, nitrogen, and ammonia) proceeds very feebly. 3. In treatment at reduced pressure (in vacuo), and consequently with a diminished oxygen content, the higher the vacuum, i. e., the lower the concentration of oxygen, the less was the plasticization obtained. 4. The effect of temperature in thermal plasticization was evident in the acceleration of the reaction between rubber and oxygen. The most effective temperature was in the interval of 150° and 170° C. 5. For an equal plasticity, the internal structure of rubber was preserved to a greater degree after thermal treatment than after mechanical plasticization, judged by the structural viscosity, n, and the magnitude, Q. 6. It was observed that rubber treated at high temperature (170° C.) in carbon dioxide, nitrogen, and ammonia lost to a considerable degree its ability to dissolve in common rubber solvents.