Synthesis of lignin-based polyurethane (LPU) and fabrication of degradable mulch film through LPU coating on cellulose paper

The use of non-degradable plastic mulch film causes significant environmental pollution and poses a threat to human and ecological safety. To address this issue, a viable solution is to develop bio-based and biodegradable paper mulch films to replace non-biodegradable ones in agricultural soils. In this study, a green and straightforward process was used to synthesize lignin-based polyurethane (LPU), which was then coated on cellulose paper (CP) of low basis weight of 30 g/m2 to fabricate a composite LPU/CP mulch film. An ultra-thin and lightweight LPU/CP mulch film was successfully fabricated with basis weight, thickness, and specific density of 40 g/m2, 80 µm, and 0.5 g/cm3, respectively. It was observed that surface coating was very effective in improving the physical strength of composite film as indicated by the improvement of tensile index from 19.3 N·m/g of CP to 65.0 N·m/g of LPU/CP mulch film. Moreover, LPU/CP mulch film presented excellent water resistance properties as suggested by the water contact angle of 107° and the water vapor transmission rate of 639.3 g/m2·day. LPU/CP mulch film also shows a balance between degradability and durability that it starts to break down into fractions after being buried for 28 days as a result of microbiological degradation. This work provides a feasible technology for fabricating eco-friendly, cost-effective, and biodegradable paper mulch film.