Influence of the Initial Morphology on the Elasticity of Oriented Syndiotactic Polypropylene

Abstract

The influence of the initial phase composition and crystallite size on the mechanical properties and the elastic behavior of oriented syndiotactic polypropylene (sPP) was investigated. Two samples (A25 and B100) were crystallized from the melt respectively at 25 and 100 °C, obtaining the same crystalline forms but different morphologies, in terms of crystallinity, crystal dimensions, and phase composition. X-ray diffraction was used to determine the crystallinity and the crystal dimensions, whereas the vapor transport properties allowed to evidence and quantify the presence of an intermediate phase. Sample A25 shows smaller crystals, lower crystallinity, and a lower amorphous fraction but a larger mesomorphic component as compared to B100. The two samples were then stretched to a draw ratio of 7. They showed very different stress−strain curves, which appear to correlate with the initial structure. On releasing the tension both fibers undergo a large shrinkage, reaching λ = 4. The presence of the trans-pla...