Anomalous strengthening behavior of nanocrystal-reinforced polyurethane fibers

Although the strength of conventional polyurethane fibers can be modulated using strain-induced crystallization strategies, current fabrication processes cannot achieve sufficient strength and toughness. Here, we report a novel strategy involving precise adjustment of hydrogen-bond donor unit positions and directed arrangement of the polyurethane backbone to enhance the strength and toughness of a new fiber type (i-PUF). New nanocrystals could be formed continuously in the amorphous phases of the i-PUFs due to strong interchain interactions in response to the increasing strain, causing anomalous strengthening behavior. The tensile strength of the i-PUFs was 1.3 GPa, 3.1 times that of the strongest polyurethane fibers. Moreover, the toughness value of the i-PUFs was 244.8 MJ/m3, 1.4 times higher than that of spider dragline silk. Additionally, the i-PUFs exhibited excellent self-healing properties since the slip effect of the hydrogen bonds in the nanocrystals were enhanced by external thermal stimulation. The proposed approach can be applied to various commercial polymers to fabricate durable polymer fibers with enhanced strength and toughness.