Solid-state drawing of β-nucleated poly(propylene): Effect of additives on drawability and mechanical properties
Isotactic polypropylene (i-PP) can crystallize in different crystal modifications. In this article, the effect of sepiolite (one-dimensional) and carbon black (three-dimensional) fillers on the solid-state drawability of i-PP is discussed. The crosshatched structure of thermodynamically most stable a-crystal phase in i-PP does not allow for perfect chain alignment during solid-state drawing. The b-phase i-PP, obtained by addition of specific nucleating agents, crystallizes in a non-cross-hatched spherulitic structure and allows more easy drawing. Depending on the filler type, b–a transformation takes place at different draw ratios, as was observed by in situ wide-angle X-ray diffraction measurements. It was observed that b-nucleated i-PP has a lower yield stress and can be drawn further than i-PP crystallized in the a-crystal phase. If added in the right amount, both carbon black and sepiolite have a reinforcing effect on PP tapes.