Effect of processing parameters on degree of crystallinity and mechanical performance of CF/PEKK aerospace composites

In this study, CF/PEKK composites were manufactured using hot press under different processing conditions above melting and cold crystallization temperatures of the polymer. The effect of different processing conditions on degree of crystallinity, as well as the viscoelastic and interfacial properties of the composite were examined. Differential Scanning Calorimetry (DSC) technique was used to study the crystallinity within CF/PEKK composites as a function of thermal history. The viscoelastic properties of a quasi-isotropic composite beam were determined using Dynamic Mechanical Analysis (DMA) temperature sweep tests, and Short Beam Shear (SBS) tests were conducted at different temperatures to measure the interlaminar shear strength (ILSS). DSC results indicated that increasing the temperature above melting temperatures of PEKK i.e. from 350°C to 400°C had an insignificant effect on degree of crystallinity, whereas increasing hold-time at these temperatures resulted in a reduction in degree of crystallinity of up to 21%. The DMA test results indicated that increasing the temperature above melting temperature resulted in an increase in storage modulus of up to 34%. Similarly, SBS test data showed that, increasing the hold time at 350°C increased the ILSS by 65%; however, increasing the temperature to 400°C did not enhance interlaminar properties.