Structural investigations of polyurethane and silk‐polyurethane composite fiber studied by 13 C solid‐state NMR spectroscopy

Bombyx mori silk fibroin (SF) fibers possess excellent mechanical properties together with biocompatibility and have attracted great attention in applications including biomaterials. The SF‐polyurethane (PU) composite materials are expected to improve the mechanical properties and expand the application of SF. In this article, PU consisting of isophorone diisocyanate (IPDI) and poly (butylene adipate) is synthesized and characterized using 13 C solid‐state NMR spectroscopy. Then, the regenerated SF‐PU (95: 5 wt%) fiber is prepared, which results in a 11.7% increase in tensile strength and 81% increase in elongation‐at‐break compared with those of SF fiber. The reason for the increase is due to the increase of random coil conformation in SF observed by 13 C solid‐state NMR and the presence of IPDI in the PU. Thus, it can be emphasized that this PU is very effective in changing the conformation of SF fiber by increasing random coil fraction and improve the mechanical properties.