Approach to Elastic Equilibrium in Lightly Cross-Linked Systems

Approach to Elastic Equilibrium in Lightly Cross-Linked Systems 

While the equilibrium Young s modulus cannot be obtained directly from such measurements, it can be estimated from an empirical equation which is found to fit many such data extremely well, including relaxation measurements of other lightly cross-linked polymers  

Creep data in shear, in small deformations, are shown for four of the above five samples in Fig. 14-9, after reduction to 30 from various temperatures of measurement. When J t) is converted to (/) by equation 47 of Chapter 4, and the latter is multiplied by 3 to give (t), Poisson s ratio being of course negligibly different from i, these data are in excellent agreement with the stress relaxation results extrapolated by equation 8. The very large ordinate scale and high precision of the data should be noted. 

Other creep data on the same samples have been extrapolated to infinite time to obtain Jg by the analog of equation 3  

Though the time-dependent processes are very slow, they are affected by temperature in the same manner as the friction coefficient which controls short-range molecular motions many decades removed in the time scale, since temperature reduction can be made with the same WLF coefficients as in the transition zone. Moreover, they are affected in the same manner by the introduction of diluent, which reduces the friction coefficient in a manner attributable to an increase in fractional free volume (Chapter 17). 

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