Melt-spinning of polyether-ether-ketone(PEEK) and the structure and properties of resulting fibers.

Abstract

Polyether-ether-ketone (PEEK) fibers were prepared at a range of take-up speed from 9.9 to 920m/min, and the effects of take-up speed, drawing (draw ratio=x1-x4) and heat treatment (200-325°C) on structure and properties were investigated. The molecular, crystalline and amorphous orientations, crystallinity and crystallite size were determined from the measurements of WAXS, SAXS, density and birefringence. In a range of take-up speed up to 110m/min, the molecular orientation of as-spun fibers increased with increasing take-up speed, and then showed a tendency to level-off. The birefringence of the amorphous region of as-spun fibers was more than ten times larger as the crystalline region. This suggests that the crystallization proceeds mainly in a highly oriented structural region in fibers on the spin line. The crystallite size of as-spun fibers was comparable to that of heat-treated fibers. The crystallite size was the largest in the direction of the normal of the (110) plane for all the fibers prepared, irrespectively of take-up speed, drawing and heat treatment. With the fibers heat-treated after drawing, the amorphous orientation showed a maximum at a heat-treatment temperature of about 250°C. On the other hand, with the fibers heat-treated at a fixed length it increased monotonically by heat treatments up to 325°C. For analysing the mechanical properties measured for PEEK fibers prepared under various conditions, the theoretical modulus of an extended PEEK molecule was calculated, and as the moduli of the crystalline and amorphous regions, values of 69 and 63 GPa were obtained, respectively. It has been found that the initial moduli of the PEEK fibers of various crystallinities can be related to the orientations of amorphous region. By applying a two-phase model combining the crystalline and amorphous regions in series, it has been obtained for various PEEK fibers that the initial compliance of the amorphous region can be represented as a linear function of the amorphous orientation.The glass-transition, cold crystallization and melting behaviors were also measured by DSC, and their relation to fiber preparation conditions were studied. The heat of fusion, which was calculated for the PEEK crystal from the DSC measurement, was about 130kJ/kg.