Controlling the assembly modes of polymer chains and the interfacial interactions between the filler and polymer matrix is vital for improving the mechanical properties of the composites. Herein, we report an approach for significantly enhancing the toughness of unmodified silk fibroin (SF) powder from silk waste-incorporated polyurethane (PU) composite films via nonsolvent-induced phase separation (NIPS) using binary solvents. The incorporation of 50 wt % SF into the PU3 film (NIPS, binary solvents) resulted in a toughness value of 54.9 ± 0.4 MJ·m-3, exhibiting 1670.9 and 6000.0% increments compared to those of PU1-50% SF (NIPS, one solvent) and PU2-50% SF (solvent evaporation, one solvent), respectively. The toughness enhancement in the PU3-50% SF composite film benefits from the good interfacial interaction between SF and PU and the unique structure of the compacted "fishing net" with reinforced connections, which can transfer stress under loading effectively. Furthermore, the PU-SF composites with good mechanical properties may have potential applications in silklike fibers and biomimetic materials.
Keywords: fibroin powder; fracture mechanism; interface; polyurethane; silk waste.