Densely crosslinked protein bioplastics with superior stretchability and desirable wet stability via quality protein restoration

Abstract

We have demonstrated that dithiol-based crosslinkers are most suitable for protein materials with high contents of cysteine. Crosslinking is always the effective approach to improvement in properties of protein materials. However, most crosslinking technologies damage structures of protein materials due to harsh crosslinking conditions, or form uncontrollable and unstable crosslinkages. In this work, we selected dithiols with different chain lengths and flexibility to form disulfide crosslinkages via reduction and oxidation at room temperature. Sustainable dithiols were screened by computational simulation for bioplastic uses. Since the reactions were performed at room temperature, keratin backbone structures were intact. Our developed model indicates that number of sigma bonds in crosslinkages and retention of crosslinking, dominated by sigma bonds in crosslinkages, quantitatively controlled mechanical properties of regenerated keratin films. Wet-stable keratin films with excellent stretchability were developed without any plasticizers and secondary polymers. Some properties of our bioplastics via quality restoration were similar to some petroleum-based products. For example, feather-derived bioplastics had dry stress, wet stress, dry breaking elongation, and wet elongation of 35 MPa, 10.2 MPa, 70%, and 105%, respectively. After seven days in water, the stress retention of films was as high as 85%. This work promoted the application of keratin bioplastics in food, pharmaceutical and cosmetic industries.