6533b856fe1ef96bd12b2518

RESEARCH PRODUCT

Influence of the arrangement of the crystals and the structure of the noncrystalline regions on the mechanical properties of polyethylene terephthalate

subject

description

Amorphous samples of polyethylene terephthalate were stretched with different rates and stretching ratios at different temperatures. Afterwards they were crystallized. The arrangement of the crystals and the conformations of the chains in the noncrystalline regions were investigated by means of X-ray wide-angle scattering, X-ray small-angle scattering, birefringence measurements and nuclear magnetic resonance measurements. The influence of the morphological structure on the mechanical strength was determined. The stretching ratio itself generally does not characterize the orientation state. The structure obtained after crystallization depends mainly on the birefringence of the sample after stretching before crystallization. With increasing birefringence one obtains all intermediate structures starting from the well known spherulites composed of twisted lamellae in the unoriented material up to a paracrystalline lattice of lamellae split up into mosaic blocks in the highly oriented state. Also the conformations of the chains in the noncrystalline regions are influenced by the stretching. With increasing orientation the amount of tie molecules with comparatively large end-to-end distances becomes larger. The improvement of the mechanical properties with stretching is caused not only by the increasing orientation of the molecules but also by the increasing amount of taut tie molecules.