Effects of mechanical drawing on the structure and properties of peek

Publisher Website
Google Scholar
Abstract
This study examines the effects of crystallinity and temperature on the mechanical properties of PEEK. Crystallinity in PEEK Increases with annealing temperature up to a maximum of 28 percent with a melting point at 335°C. A minor melting peak also occurs about 10°C above the annealing temperature. In cold drawing the samples exhibited a yield stress and necking followed by homogeneous drawing. The yield stress increases with crystallinity, but there is no change in the modulus. The extension in the necking process also increases with crystallinity, however there is only a slight increase in extension‐to‐break since necking is compensated by the final amount of homogeneous drawing. The yield stress of PEEK when drawn at Tg (145°C) is significantly lower than at room temperature indicating a reduction in mechanical properties at temperatures approaching Tg. After mechanical drawing the minor melting peak disappears and on heating the material undergoes cold crystallization near the onset of Tg. There is evidence that this minor crystalline component might contribute to the yield stress changes with annealing history. Cold drawing induces crystallization of amorphous PEEK but decreases crystallinity and generates microscopic voids in crystalline PEEK, The various effects of crystallinity on mechanical properties could be important in determining the stress response of PEEK as the matrix in composites.