Thermal treatments strongly influence physical properties of isotropic polymers. This influence is very dramatic in crystalline polymers were the process deeply modifies the morphology. In amorphous polymers, annealing has the effect of changing the free volume modifying particularly long term physical properties; phenomenon which has been given the name of physical aging. Moreover if the polymer is oriented, the recovery will follow a different mechanism depending on whether the polymer is crystalline or not and whether the annealing is made on samples with free or fixed ends. For an amorphous oriented polymer a small degree of recovery takes place when the samples are exposed at temperatures below the equilibrium glass transition temperature, Tg, and the process reaches asymptotic values which are function of the annealing temperaturel. At temperatures above Tg the recovery phenomenon is much faster and the equilibrium recovery is not a function of temperature. As a matter of fact the process can be interpreted as a relaxation phenomenon which takes place in the sample and the behavior can be predicted by using W.L.F. equation2.
KeywordsMaster Curve Crystalline Polymer Relaxation Phenomenon Cold Drawing Recovery Behavior
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