On the hairdressing of shish-kebabs

Summary

Factors determining the platelet-fibre morphology of polyethylene shish-kebabs were examined by varying systematically the initial temperature of formation, that of subsequent storage and the conditions of final cooling following the work ofPennings et al. (8). The morphologies observed could be classed as 1) smooth fibres, II) fibres with small, closely spaced platelet overgrowth, III) fibres with large, widely spaced overgrowth, where the platelet spacing was variable depending on storage temperature. It is shown how a shish-kebab bearing any of these three morphologies can transform intoany other. An explanation is offered in terms of the recrystallization of cilia which are attached to the shish-kebab core but are solvated at the original formation temperature.

The above model incorporates the findings and conclusions ofPennings et al. (8) with the important extension that it also includes the smooth fibres which accordingly do not in general represent perfect extended chain crystals, but are themselves in a general sense shish-kebabs with the central fibre enveloped in a sheath of parallel hairs.

Tensile moduli were also measured as a function of growth and storage temperature. It is shown, in accord with earlier findings, that this is determined essentially by the temperature at which the fibrous crystal has been grown initially and is unaffected by the external morphology where the lauer merely reflects the ‘hairdressing’ treatment of the basic load bearing central fibre.