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.

Mechanical and impact characterisation of flax and basalt fibre vinylester composites and their hybrids

“…The only positive value is offered by tensile stiffness, in which case it might be suggested that the effect of the voids is possibly overwhelmed by the rigidity during tension offered by basalt layers. As a matter of fact, it is suggested that flax fibre composites produced with similar techniques than the one adopted may present a quite considerably large amount of voids, due to variability of crimp characteristics, which may result in resin starvation [28][29].…”

Developing plant fibre composites for structural applications by optimising composite parameters: a critical review

“…This is in agreement with typical literature values observed for PFRPs (Table 9). Various studies report that the vacuum-infused PFRPs have a low-void volume fraction of 0.5-4.0 % [71,135,152] and prepreg-based PFRPs have a typical void volume fraction of 0.0-4.0 % [158,159], although, it may be as high as 10 % if low-autoclave pressures (\3 bar) are used [158,159]. It is of interest to note that Madsen et al [75] shown that the porosity in hemp yarn reinforced thermoplastics increases linearly (R 2 = 0.98) with the logarithm of the matrix processing viscosity.…”

Evaluation of the damping of hybrid carbon–flax reinforced composites

“…Thus, due to their good specific properties, natural fibres could constitute, in particular applications, an interesting alternative to glass fibres [2,3]. Consequently, various natural fibres reinforced polymer composites were the subject of several studies [4][5][6][7][8][9][10][11][12][13][14]. In particular, the effect of natural fibres treatment on the mechanical properties of these composites, the degradation of their mechanical properties in a hygrothermal environment and their different damage modes during the failure process were studied [4,9,11,14].…”