Characterization of flax/epoxy prepregs before and after cure

Abstract

This paper aims to better understand the nature of flax/epoxy hot melt prepreg systems as well as the mechanical properties of their cured composites. Two uncured systems were subjected to thermal gravimetric analysis and compaction experiments. Composites were then produced in an autoclave at pressures of 1, 3 and 5 bars. Void analysis was carried out on the cured laminates by optical microscopy and void contents ranging from below 1% to over 20% were obtained by image analysis. The primary source of voids was shown to be resin starvation based on the results of the compaction tests. Tensile properties were shown to be strongly degraded by fabric crimp. Short beam tests revealed a 16% decrease in interlaminar shear strength with a 3.5% increase in void content. Similarly, water absorption tests showed a significant increase in rate of absorption likely due to the presence of voids. The results suggest that in order for flax/epoxy prepregs to reach their full potential, the level of crimp and the evacuation of moisture during cure should be of primary concern.