AbstractDynamic mechanical properties as determined by a torsion pendulum were used to study the effect on the crystalline structure of polypropylene of annealing at a temperature very near to its melting point. Crystallinity values as determined by both x‐ray techniques and density measurements were reported for the specimens used in this study. Differential thermal analysis was used to show the differences in melting behavior of annealed and unannealed polypropylene. It was found that, although crystallinity may increase slightly, the major effect of annealing polypropylene is an increase in the size and/or perfection of the resulting crystallites. A damping peak not normally found for polypropylene was present at −50°C. in the damping curves for those specimens annealed in silicone oil without protective wrappings. This peak was found to be due to the freezing of the absorbed silicone oil, present in the specimen as small drop
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