Abstract
AbstractThe microstructural changes in isotactic polypropylene (PP), subsequent to quench from the melt to around Tg were studied using dynamic mechanical loss, volume dilatometry, small and wide angle X‐ray scattering, infrared and NMR spectroscopy. The β‐transition loss tangent and the specific volume decreased linearly with logarithm of aging time. Dynamic mechanical loss and NMR spectroscopy results established that amorphous chain mobility reduced during aging. X‐ray and IR techniques showed that the crystallinity, the crystalline density, and the average chain conformation do not change during aging. Tensile tests indicated that diffusion of air or moisture into the polymer is not a competitive mechanism for the aging phenomenon. A simple free‐volume model is quantitatively consistent with these observations. The fraction of the material which cannot age increased as the quench temperature decreased. Further, at lower temperatures a portion of the nonageable fraction is shown to reside in the amorphous fraction.
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