Relating microhardness of poly(ethylene terephthalate) to microstructure

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Abstract
The microhardness (H) of poly(ethylene terephthalate) (PET) containing catalysts, as well as of PET without catalysts has been investigated. Two types of morphologies have been examined: (a) structures where spherulitic growth is incomplete, resulting from a primary crystallization from the glassy state and (b) samples in which spherulitic crystallization is completed. It is shown that for the former materials,His an increasing linear function of the volume of the spherulites and depends on annealing time and catalyst content. For the latter materials,His nearly constant with increasing annealing temperature (TA). Results are discussed in the light of three principal structural factors which determine the microhardness behavior: (1) the volume content of spherulites within the material; (2) the value of crystallinity within the stacks of the lamella, which turns out to be a constant; (3) the average thickness of the crystals, which increases slightly withTAafter crystallization is completed. An expression which takes into account the above parameters and offers a description of theHof polyethylene terephthalate is proposed.