Environmentally friendly preparation of lignin/paraffin/epoxy resin composite-coated urea and evaluation for nitrogen efficiency in lettuce

Novel lignin/paraffin/epoxy resin composite coated urea (LPECCU) was successfully prepared. Paraffin and epoxy resin (ER) were used to improve the slow-release properties of the lignin-based polyurethane (LPU) coated urea. The relationships among the N release characteristics, liquid-solid rate, –CNO/–OH molar rate and film formation rate in the coating material of LPECCU were investigated. The results showed that the water contact angle (WCA) of the LPU-paraffin increased with the rate of liquid-solid rate (73.61–88.19°) and –CNO/–OH molar rate (65.17–82.24°) increased. The average particle hardness of LPECCU decreased with the increased of liquid-solid rate (57.10–66.80 N) and the reduced of –CNO/–OH molar rate (48.11–63.00 N). The LPECCU emerged compact micro-structure, low sustained release and high compressive resistance by adding paraffin and ER. The coating material of LPECCU appeared excellent biodegradability in the soil. The optimal N cumulative release rate (72.49 %) of LPECCU was obtained (liquid-solid rate of 1.43, –CNO/–OH molar rate of 2, and the film formation rate of 6.66 %). The lettuce growth study was conducted to further evaluate the pot application of the LPECCU. In comparison to conventional urea, LPECCU could improve the total dry matter accumulation and N use efficiency of the lettuce. •Novel lignin/paraffin/epoxy resin composite coated urea (LPECCU) was prepared.•The release longevity of LPECCU was related to preparation of coating material.•The coating material appeared excellent biodegradability in the soil.•The LPECCU could improve the N use efficiency and growth of lettuce.