Uniform Micronano Network Affords All-Chitin Films with Water Resistance, Biodegradability, and High Strength

Xuan paper can be moistened without breaking, thus possessing good water resistance. These remarkable properties come from its uniform three-dimensional network structure constructed by micro- and nanofibers. Inspired by the multiscale structural design of Xuan paper, herein, we report a facile method to develop high-performance all-chitin films from crab shell wastes by introducing chitin nanofibers (ChNFs) into chitin microfiber (ChMF) networks. The resultant chitin micronanofiber (ChMNF) films integrated a high tensile strength (∼227.0 MPa), a low thermal expansion coefficient (∼10.3 ppm/K), high light transmittance (∼89.1%), and biodegradability. Moreover, this micronano structure endowed the chitin films with good water resistance and a high wet strength of ∼48.7 MPa which surpassed that of commercial paper (∼1.2 MPa) and some petroleum-based plastics (e.g., polyethylene, ∼24.8 MPa). One interesting finding was that after recycling treatments, the obtained recycled chitin films still showed a high strength of ∼126.2 MPa, similar to the chitin films with nanofiber structures (∼128.4 MPa). Moreover, the developed all-chitin films could be biodegraded in a natural environment in 3 months. Due to the combination of degradability, high strength, water resistance, transparency, and thermal stability, the flexible ChMNF films could be employed as environmentally friendly film materials applied in smart packaging and flexible electronics.