Pseudoplastic liquid mulch film incorporating waste lignin and starch to improve its sprayability and available soil nitrogen

Because traditional slow-release fertilizers cannot effectively retain soil heat and moisture, their ability to increase crop yields is limited. To solve this problem, novel sprayable liquid mulch films (lignin-starch-acrylate, LSA) were prepared with a slow-release urea function, created by emulsion polymerization between lignin (extracted from papermaking waste liquor), starch, and acrylate monomers. The introduction of lignin transformed the LSA emulsion into a pseudoplastic fluid with enhanced sprayability. The presence of lignin in LSA film increased the elongation at break and lowered the Young's modulus, resulting in a film that is more easily pierced by crop seedlings and preserves the heat and moisture of the soil after seedling piercing. Experimental results showed that at a mass ratio of lignin to acrylate monomers of 3/7, the LSA mulch film had good sprayability and film-forming properties, suitable mechanical properties, and the lowest urea release rate. This optimized LSA film exhibited better soil insulation and water retention performance than other slow-release fertilizers. The contents of available soil nitrogen, including NH4+-N and NO3−-N, in soil covered with LSA film were 44.82 and 45.49% higher than those in soil covered with urea, respectively, and the corresponding cabbage yields increased by 33.73%. The results of this study provide a new method for preparing agricultural materials with urea slow-release as well as soil moisture and heat preservation functions.