Effect of the Degree of Crystallinity on Friction and Wear of Poly(ethylene terephthalate)

Measurements of friction and wear were made on poly (ethylene-terephthalate) (PET) sliding against a smooth steel disk. The friction was little dependent upon crystallinity, while the wear rate increased with increase in crystallinity, especially remarkable in the range above about 40%. It was found that the reciprocal of wear rate was closely related to the Vickers hardness in PET of different crystallinity. The wear of PET with a low crystallinity as small as 8% was mainly due to transfer. On the other hand, wear of high crystallinity PET is different from that of the low crystallinity PET and seemed to be mainly due to a surface fatigue during sliding. The differnce between the mechanisms in PET of low and high crystallinity was essentially due to the differnce in morphological structures.