Fabrication and evaluation of biodegradable multi-cross-linked mulch film based on waste gelatin

Microplastics from wasted traditional nondegradable plastic mulching films pose a great threat to both the ecological environment as well as human health. Currently, eco-friendly and cost-effective biodegradable films are considered the most promising substitutes for nondegradable plastic mulching films. In this study, we demonstrate a simple and eco-friendly strategy to utilize the gelatin extracted from scrap skin in leather processing and prepare novel biodegradable mulch films. The gelatin chains were covalently cross-linked with tetrakis(hydroxymethyl)phosphonium chloride to reduce the hygroscopicity of gelatin. Then, polyvinyl alcohol (PVOH) was introduced into the gelatin network. The hydrogen bonds between the gelatin and PVOH and several PVOH crystalline domains acted as sacrificial bonds for energy dissipation. Thus, the multi-cross-linked gelatin matrix (GP) films showed high fracture stress (12.03-31.99 MPa) and fracture strain (211.99%-379.73%). Such high mechanical performance is comparable to that of traditional low-density polyethylene mulch films and conforms to the GB/T 35,795 regulatory standards. In addition to their excellent mechanical properties, the mulch films exhibited good water resistance, excellent light transmittance, and good biodegradability in soil. All properties of the GP films are tunable, and their eco-friendliness, low cost, and excellent properties endow them with great application potential as eco-friendly mulch films for agriculture.