Constructing robust and antioxidant polyurethane–lignin coatings with biodegradable properties for grass press paper films

The practical applications of grass plastic mulch films are limited because their residues turn into microplastics and enter the food chain. This study solves this problem by preparing a degradable cellulose-lignin-waterborne polyurethane composite grass paper film. First, waterborne polyurethane prepared using a mild method was composited with lignin via an addition reaction and the formation of hydrogen bonding between the -OH groups of lignin and the -NCO and -OH groups of polyurethane. Finally, the as-prepared polyurethane-lignin composite was applied as a coating on the surface of a paper-based material to prepare a grass paper mulch film. The relationship between lignin content and the molecular weight, thermal stability, mechanical properties, polymer network crosslinking density, antioxidant capability, and light transmittance of the coating was studied, revealing that higher lignin contents considerably improved the barrier and mechanical properties of the coating and grass paper mulching film. In particular, a lignin content of 20 % resulted in a grass paper mulching film with outstanding grass pressing performance and degradability. Therefore, the multifunctional, ecofriendly grass paper mulch film prepared from cellulose-lignin-waterborne polyurethane composite materials provides an innovative approach to solve the pollution problem of traditional grass plastic paper mulch.