Achieving proper fibre impregnation with thermoplastic matrices is a critical challenge for developing high-performance thermoplastic composites. To address this, a new strategy has been employed in this research to improve impregnation of Kevlar fibres by using a polypropylene (PP) matrix with superior melt flow behaviour. Hybrid yarns were produced in a comingling machine using Kevar yarn and two types of PP multifilament yarns with different mel flow index (MFI). Unidirectional (UD) Kevlar/PP composites were produced using these hybrid yarns and thoroughly characterized for different mechanical properties. As expected, the higher MFI PP yarns exhibited lower tensile properties, lower flexural rigidity, lower crystallinity and lower heat of melting as compared to the low MFI PP yarns. Nevertheless, the Kevlar/PP composites developed using high MFI PP yarns exhibited superior fibre impregnation and adhesion with the PP matrix, resulting in a very low void content (<2%), 35% higher tensile strength, 22% higher tensile strain, 17% higher flexural strength, 36% higher impact strength and 21% higher ILSS as compared to the composites developed using low MFI PP yarns. Moreover, the developed high MFI PP-based composites showed the lowest void content and significantly higher tensile strength as compared to the previously reported Kevlar fibre-reinforced thermoplastic composites.
Gupta et al. (2026) studied this question.