THE EFFECT OF BLEND COMPOSITION AND DRAW RATIO ON THE THERMAL, OPTICAL, AND MECHANICAL PROPERTIES IN PET/PEI FILMS

摘要

Thermal, optical, and mechanical properties of uniaxially stretched blends of PET/PEI films as a function of draw ratio were investigated. PET/PEI blends of compositions 0-30% PEI were prepared in a twin screw extruder, and cast into transparent amorphous films on a chilled roll fed by a single screw extruder. The DSC data showed a rapid rise in crystallinity followed by a much slower increase directly after the films reached the stress hardening point. The addition of PEI was found to hinder the formation of the crystalline lattice of PET and once formed, the crystallites were highly distorted. Also, PEI caused the onset of stress hardening to move to lower draw ratios. However, this influence on the stress-strain curves was not as a result of increased strain crystallizability but perhaps formation of a network that accelerated stress hardening in the presence of stiff and bulky molecules. This result clearly suggests that one can produce "self leveled" films at lower draw ratios by the addition of a small amount of PEI.