True self-reinforced composites enabled by tuning of molecular structure for lightweight structural materials in future mobility

The development of vehicle bodies based on lightweight structural composites is urgently required to upgrade electric cars and to commercialize urban air mobility. Self-reinforced composites (SRCs) are attracting attention due to their advantages in terms of price, lightness, disposal and recycling compared to carbon fiber-reinforced polymers (CFRPs). In this study, a new concept for 100% polypropylene (PP) SRC was proposed to simultaneously improve the adhesive, tensile and impact properties of SRCs without undermining the advantages of SRCs. For this implementation, a facile engineering strategy using quad screw extrusion (QSE) capable of generating high shear stress was employed to modify the melting temperature and impregnation properties of the PP matrix via controlling polymer chain structure. As the screw rotation speed of QSE increased, low molecular weight polymer chains with uniform chain lengths were prepared, which led to a decrease in the melting temperature of the PP matrix and an increase in the flowability and impregnation property of the matrix. Using this strategy, the adhesive strength, tensile strength and impact resistance of the optimized SRC improved by 333%, 228%, and 2700%, respectively. Racing drone flight experiments with the SRC and CFRP frames illustrated the advantages of the SRC frame such as the increase of the flight time due to low density of the SRC, the excellent impact resistant characteristics (which improves user safety), and the superior electrical insulation properties suitable for frequency transmission and reception. Therefore, the proposed SRC can be an ideal choice as a lightweight structural material for future mobility.