Physical aging yield strength

Some of the most important early experimental observations were of transitions from the quasi-brittle crazing deformation mode to the ductile shear deformation mechanisms with changes in the experimental conditions, such as temperature and strain rate, as well as in polymer variables, such as polymer backbone architecture, blend composition, crosslinking and physical aging state of the polymer glass. One of the strengths of the model of craze growth outlined above is that it allows one to make sense out of some experimentally observed craze-to-shear transitions that had previously defied explanation . The idea behind this explanation is quite simple One writes an expression for the shear yield stress, viz ... 

The effect of E-beam irradiation on the physical properties of these resins is summarized in Tables 1-4. Unsterilized samples are used as a control. E-beam irradiation does not induce any significant changes in physical properties. There appears to be a small increase in the tensile yield strength of the PET homopolymer and the various copolyester resins. These increases in yield stress are consistent with the effects of physical aging (2). The PET and copolyesters have glass transition... 

A property of great importance in applications for various carbon blacks in plastics, impact strength will be illustrated with ABS. The physical properties of ABS compounds are extremely sensitive to both quality of dispersion and aging. In this case, as indicated by Figure 11.11, precolored compounds show unproved dispersion over salt and pepper blends mixed in the holding machine. Better dispersion yields better impact retention. 

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