Mastication of rubber. VII. Mechanical degradation of polymers during mastication

The degradation on mastication of polymers brought into a rubbery state by incorporation of liquids or rise in temperature is accounted for by the mechanicochemical mechanism previously advanced to explain the degradation of rubbers. The dependence of the reaction on shear rate has been shown indirectly, as with rubbers, by the negative temperature coefficient of reaction, and also directly by variation of masticator rotor speed and design. A further new feature is the influence of the nature as well as concentration of plasticizer on the rate of degradation and a correlation with the softening of the polymer. A limiting molecular weight is reached on prolonged mastication from whatever initial molecular weight.