On the deformation mechanisms of β-polypropylene: 1. Effect of necking on β-phase PP crystals

Abstract

PP samples containing β-phase crystals were prepared by doping with a β-nucleating agent. The β-PP specimens were tensile stretched at room temperature under various crosshead rates and the yielding behaviour was analyzed on the basis of Eyring's theory. After tensile testing, the β-phase was examined with WAXS and D.S.C. over the necking region and the deformation mechanisms were discussed. The β-phase was found to be mechanically stable at room temperature up to yielding point. However, once the samples were stretched to necking, the β-phase began to transform to the α-phase; this phase transformation continued over the necking region. The phase transformation implied that local melting and crystallization occurred during cold drawing and gave powerful support to Flory's model of the deformation mechanism of crystalline plastics.