Refined determination of dsc-measured crystallinity for thermoplastic composite materials

Abstract

Differential scanning calorimetry (DSC) is a widely used method for determining the degree of crystallinity of semi-crystalline thermoplastic matrix materials, which is often used as an indicator of part performance. However, the calculation of crystallinity using this method is vulnerable to errors at several stages in the process, including assumptions and oversights when receiving reference values from material manufacturers. In this study, the sensitivity of the calculated degree of crystallinity to the assumed fiber volume fraction is investigated, with manufacturer-provided data compared with in-house measurements. Results show that for the reference CF/LM-PAEK material, the nominal fiber volume fraction of 60% (as reported in the material datasheet) can in fact range from 42.79% to 59.74%, as determined through digital microscopy. Using the fixed nominal value for all measured samples resulted in a relatively high (overestimated) degree of crystallinity (30.01% ± 4.24), while using measured values for the fiber volume fraction yielded a substantially lower value; 24.76% ± 3.50. A significant improvement in the standard deviation was also observed when the fiber volume fraction is measured rather than assumed, a strong indicator that this approach yields a net improvement for more accurate reporting of the degree of crystallinity.