Fine structure and dynamic mechanical properties of cold-drawn and annealed polypropylene. II

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Abstract
The dynamic tensile modulii E' of cold-drawn and subsequently annealed polypropylene film samples were measured as a function of annealing temperature. The modulus E' at 23°C along the draw direction was found to decrease with an increase in the annealing temperature, but the degree of crystallinity of the samples became greater with increasing annealing temperature. This conflicting behavior can be explained on the basis of the volume fraction of tie molecules. Tie molecules must sustain a large portion of the applied stress, and their volume fraction decreases with an increase in the annealing temperature, in spite of the increase in the degree of crystallinity. The decrease in volume fraction of tie molecules results in the formation of folded chain lamellar crystals, leaving only a small portion of the original tie molecules in the amorphous region.

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