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Issue 22, 2018
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Orientation direction dependency of cavitation in pre-oriented isotactic polypropylene at large strains

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Abstract

Orientation direction dependency of whitening activated at large strains was studied using four pre-oriented isotactic polypropylene (iPP) samples with different molecular weights stretched along different directions with respect to the pre-orientation (0°, 45°, and 90°) by means of in situ wide-, small-, and ultra-small-angle X-ray scattering techniques. A macroscopic fracture of iPP materials was also observed following the stress whitening at large strains. These two associated processes in pre-oriented iPP samples at elevated temperatures were found to be governed by not only the molecular weight of iPP but also the pre-orientation direction. For a certain pre-orientation direction of iPP, both the critical stress of cavitation induced-whitening and failure stress increased with increasing molecular weight. For one given molecular weight, the pre-oriented iPP showed the smallest critical stress for whitening and failure stress along the pre-orientation direction (0°) while the samples displayed larger values for the same behaviors when stretched at 45° or 90° with respect to the pre-orientation direction. Such behavior suggested that oriented amorphous networks, with different mechanical strengths, can be generated during the second deformation processes in these pre-oriented iPP samples. The evolution of inter-fibrillar tie chains in highly oriented amorphous networks was considered as the main factor controlling the response of the inner network to the external stress since the cavitation-induced whitening activated at large strains was caused by the failure of load bearing inter-fibrillar tie chains in the oriented amorphous network.

Graphical abstract: Orientation direction dependency of cavitation in pre-oriented isotactic polypropylene at large strains

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Publication details

The article was received on 13 Dec 2017, accepted on 20 Mar 2018 and first published on 20 Mar 2018


Article type: Paper
DOI: 10.1039/C7SM02446K
Citation: Soft Matter, 2018,14, 4432-4444
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    Orientation direction dependency of cavitation in pre-oriented isotactic polypropylene at large strains

    Y. Lu, G. Thompson, D. Lyu, P. Caton-Rose, P. Coates and Y. Men, Soft Matter, 2018, 14, 4432
    DOI: 10.1039/C7SM02446K

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