CRYSTALLIZATION OF POLYETHYLENETEREPHTHALATE UNDER MOLECULAR ORIENTATION

Abstract

Crystallization of polyethyleneterephthalate (PET) was carried out in a steady state flow using a cone-plate type viscometer. The resultant texture was examined by means of (micro) differential thermal analysis (DTA) and of electron microscopy mainly as a function of shear rate (i.e., rotation speed of the cone). In order to avoid the rearrangement occuring during the DTA measurements, the crystallized films were treated with 70% aqueous solution of monoethyl amine and the extracted crystals were also examined by DTA and electron microscopy. The DTA thermograms revealed that two types of crystals with different melting temperatures were formed during the isothermal crystllization. The relative amount of the crystals with the higher melting temperature increased with the increasing rate of shear. The crystals with the lower melting temperature were susceptible to the amine treatment and apt to rearrange on heating, suggesting their instability. The electron microscopy revealed that in the case of the low shear, lamellae grown mormal to the direction of the shear were piled up along the shear direction just as in the case of polyethylene but in the case of higher shear, the two kinds of lamellae, big and very small, coexisted, the fomer having aligned along the direction of shear. It is postulated that the big lamellae might be grown from the bundle-like nuclei formed by intermolecular crystallization, which would be facilitated by molecular orientation and would show a higher melting temperature than that of the irregular lamellae resulted from the usual chain folding.