Influence of resin curing cycle on the characterization of the tensile properties of flax fibers by impregnated fiber bundle test

This study sheds light on the effect of resin cure cycle on the tensile properties of unidirectional flax fibers, which are assessed by the impregnated fiber bundle test (IFBT). The experimental protocol combines hand-layup and isothermal compression molding processes to fabricate unidirectional flax composites according to four different curing cycles. Isothermal and modulated DSC results indicate that the cross-linking reaction and glass transition temperature of the epoxy are affected by the resin curing cycle. SEM analyses before and after the tensile tests show that the improvement of the tensile properties of composites can be correlated to an increase of the fiber-matrix interfacial bonding. The results of the back-calculated tensile properties of flax fibers indicate that the application of the IFBT to untreated flax fibers depends on the mechanical interlocking between the matrix and the cell wall of the fibers.