Intrafibrillar bridging structures in strained isotactic polypropylene

The films made of isotactic polypropylene were strained up to 0.8 of their ultimate strain and subjected to isometric stress relaxation during 5 days. The strain–stress curves were measured at various stages of the sample treatment and the tangent moduli (Et) of unstrained, as-strained and relaxed films were determined. The changes of values of Et were put in comparison with the structural evolution of strained samples observed using the infrared and low-frequency Raman spectroscopic techniques. It was concluded that the three-dimensional intercrystallite bridges composed of straight-chain segments of lengths Lc<L<2Lc (Lc is the average thickness of crystallites) destruct as a result of chain-breaking process, but due to the chain-straightening events in isometrically relaxing samples, the intercrystallite space transforms to the rigid amorphous phase composed of ‘individual’ one-dimensional molecular stems.