Abstract
Xylene solutions of rubber of the smoked plantation crepe type were placed in an atmosphere of nitrogen and maintained at a nearly constant temperature of 95° C. Solutions of five different concentrations were employed, namely, 5.12, 3.94, 2.88, 1.98, and 0.99 per cent, and measurements of the viscosity were made as before by the flow through a tube with an inside diameter of about 1 mm. In curves of the relative viscosity as a function of the time, the hyperbolic law already described (Comptes rendus 192, 946 (1931); Rubber Chemistry & Technology, 4, 505 (1931)) was again found to be true, but only for concentrations of 1.98 and 0.99%. With more concentrated solutions the curve presents a characteristic point, and can be separated into two distinct periods: (a) A period of disaggregation of the rubber swollen to the state of jelly in suspension in the xylene. The greater the concentration the more prolonged is this period (e. g., 320 hours for the 5.12 per cent solution and 110 hours for the 2.88 per cent solution). (b) A period of molecular degradation following that just described, during which the viscosity approaches more and more that of the solvent, while following the hyperbolic law observed previously.