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Natural Biopolymer Alloys with Superior Mechanical Properties

Natural biopolymer materials have enormous potential in important, rapidly growing applications ranging from green electronics, dye and heavy metal removal, oil/water separation, therapeutic agent delivery, tissue engineering scaffolds, biological devices, optics, and sensing. However, the application of advanced functional biopolymer materials suffers from their poor processability and weak mechanical properties. Regarding this, there are enormous challenges to break the strong intermolecular interactions (hydrogen bonding) in their native forms, while re-establishing predominant hydrogen bonding in the processed materials in a cost-effective way. Here, we report our breakthrough to prepare biopolymer alloy materials based on chitosan and silk peptide (SP) with outstanding mechanical properties via a facile, "dry", melt processing method. The 1:1 (wt./wt.) chitosan-SP film had a toughness of 19.9 J cm, Young's modulus of 1855 MPa, and tensile strength of 95.9 MPa, which are similar to, or even better than, most engineering polymers. We propose that our method could maximize the molecular interactions between chitosan and SP via a simple and effective thermomechanical mixing, which resulted in considerably enhanced mechanical properties. Moreover, dehydration/rehydration can reversibly adjust the mechanical properties of the new biopolymer alloys, which demonstrates the dominant effect of hydrogen bonding in enabling the mechanical properties of these interesting alloys. Our simple approach to engineering high-performance biopolymer materials without resorting to complex chemistries and 3D-structural construction can be envisioned to bring about a new direction in the design of advanced functional materials where cost effectiveness is the priority.