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Background: Lignin played an important role in the establishment of coated fertilizers coating material as a substitute for petrochemical raw materials. However, so far, the lignin-based coated fertilizers was limited in only the poor slow-release performance. To achieve good slow-release performance of lignin-based coated fertilizers, hydrophilic of lignin need to be resolved to establish an green and better controllable lignin-based coated fertilizers. Results: In the study, a novel green double layer coating with lignin-based polyurethane (LPU) as the inner coating and epoxy resin (EP) as the outer coating was effectively constructed for coated urea. Fourier transform infrared spectra confirmed that lignin and polycaprolactone diol successfully reacted with Hexamethylene diisocyanate. The loss weight and water contact angle (WCA, 75.6–63.6°) of the LPUs decreased with the increased lignin content. The average particle hardness of the lignin-based double-layer coated urea (LDCU) first increased from 58.1 N (lignin of 30%) to 67.0 N (lignin of 60%), but then decreased to 62.3 N (lignin of 70%). The release longevity of the coated urea was closely related to the preparation parameters of the coating material. The optimal cumulative nutrient release rate (79.4%) of LDCU was obtained (lignin of 50%, –CNO/–OH molar ratios of 1.15, EP of 35%, and coating ratio of 5%). The aggregates of hydrone on the LDCU caused the dissolution and swelling of nutrients, and then the diffusion of nutrients through the concentration gradient. Conclusions: A though the nutrient release of the LDCUs was affected by many factors, the successful development of the LDCUs will help improve the rapid development of the coated fertilizer industry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An advanced hydrophobic lignin-based polyurethane coated urea (HLPCU) was successfully developed by synergy of carbon black (CB) and polysiloxane. In this work, CB and polysiloxane were employed to modify the liquefied lignin-based polyurethane (LLPU) and improve it's the hydrophobicity. The effects of polysiloxane contents and coating rates on the nutrient release of HLPCU were thoroughly investigated. The lignin was degraded into polyol with a low molecular weight. FT-IR, XPS and EDX results confirmed that polysiloxane was grafted to the LLPU. The water contact angle (WCA) of the HLPUs (89.39°–98.68°) gradually increased as the polysiloxane content rose (5 %–15 %). However, when the polysiloxane content further increased to 20 %, the WCA of the HLPUs rapidly declined (90.82°). A proper amount of polysiloxane molecules could increase thermo-physical properties of LLPU. The almost no pores were observed on the section micrograph of the HLPCU obtained by synergy of CB and polysiloxane. Synergy between CB and polysiloxane could significantly improve hydrophobicity and then enhance N release longevity of HLPCU (polysiloxane content of 15 %, coating rates of 7 %) up to 44 days. Compared to traditional urea, HLPCU could improve total N use efficiency the cabbage. The HLPCU and HLPCU85 treatments (15 % weight loss with fertilization) reduced the greenhouse effect of N 2 O, CO 2 and CH 4 and finally reduced GWP, especially for HLPCU85 treatment. This work will supply an advanced approach and process technology for progress of HLPCU and sustainable agriculture. • An advanced hydrophobic lignin-based polyurethane coated urea (HLPCU) was prepared. • Synergy between carbon black and polysiloxane improved nutrient release of HLPCU. • The coating material appeared excellent biodegradability in the soil. • The HLPCU improved the N use efficiency and reduced greenhouse gas emissions. [ABSTRACT FROM AUTHOR]