Impacts of thermoplastics content on mechanical properties of continuous fiber-reinforced thermoplastic composites

Continuous fiber reinforcements are widely used to enhance mechanical properties of composite materials, but the impregnation of continuous fiber reinforcements with thermoplastics is a challenge due to high melt viscosity of the thermoplastic matrix. One of promising routes to improve the impregnation is to prepare commingled yarns with continuous matrix filaments and reinforcement fibers. In this study, we investigate mechanical properties of commingled yarns comprising different ratios of continuous glass fibers and polypropylene filaments, and of the composite plates made up of fabrics woven by the commingled yarns with a different polypropylene content. We found that undistributed or bunched glass fibers occur at high PP contents (>50 wt%), inducing an inhomogeneous mixing of the continuous reinforcement fibers and polypropylene filaments, which resultantly leads to abrupt changes in mechanical properties of both commingled yarns and resulting composites. Notably, the inhomogeneous distribution of continuous glass fibers in the commingled yarn at high PP contents gives rise to unexpected viscoelastic characteristics of resulting composites although impregnation of continuous glass fibers with polypropylene matrix is enhanced as the absolute amount of the polymer matrix increases.