The effect of cooling rate on toughness and crystallinity in poly(ether ketone ketone) (PEKK)/G30-500 composites
Six poly(ether ketone ketone)/carbon composite panels were manufactured from powder coated towpreg. All six panels were initially processed using a hot press equipped with controlled cooling. Four of the panels were used to investigate the effect of cooling rate on crystallinity. A fifth panel was used to investigate the effect of annealing the composite after completion of the standard fabrication process. The sixth panel was used to investigate changes in toughness due to manufacturing towpreg with polymer that had been reclaimed from the towpreg fabrication system’s air cleaner.
Cooling rates of 2°C/min, 4°C/min, 6°C/min, and 8°C/min resulted in composites with crystallinities of 33%, 27%, 24%, and 23%, respectively. The principal investigation of the effect of cooling rate on crystallinity and mode I and mode II strain energy release rates, GIc and GIIc, respectively, showed that GIc and GIIc values increase with increasing cooling rate. Comparison of the toughness values as a function of crystallinity showed that the dependence of toughness on crystallinity is approximately equivalent to the dependence of toughness on cooling rate.
Comparison of the data from the annealed panel to that from the analogous principal panel showed that annealing increased the crystallinity and decreased the mode I strain energy release rate. There was no effect, however, on the mode II strain energy release rate. Comparison of the data from the panel made with reclaimed polymer to that from its analogous principal panel showed that the reclaimed polymer panel had equivalent crystallinity and GIc values. On the other hand, the GIIc values in this panel were lower than in the analogous principal panel.