Green Bio-composite Coating Film from Lignin/Pre-vulcanized Natural Rubber Latex for Controlled-release Urea Fertilizer

Economically feasible and biodegradable lignin/pre-vulcanized natural rubber latex (pVLA) bio-composite coating films for controlled-release fertilizer (CRF) were prepared by blending pVLA with different lignin ratios and used as a part of coating material to regulate the nitrogen release characteristics of urea fertilizer. The morphological, mechanical, thermal, chemical as well as biodegradable properties of the coating films were investigated and discussed. The results revealed that the hardness of bio-composite films increased with increasing lignin contents. Moreover, FTIR showed a new peak at 1656 cm(-1), which indicated the characteristic interaction between (C = C) of pVLA and (-OH) of lignin. The multi-layer coated urea granules were coated in rotary coating drum with ethyl cellulose as a pre-coating, lignin/pVLA, and wax, respectively. The presence of lignin in pVLA not only reinforced the film property but also reduced the agglomeration of the pVLA-CRF during the coating process. The lignin/pVLA layer enhanced the mechanical resistance from the osmotic pressure building up within the granule core and the wax was used as outer coating shell to further improve the release characteristic of the coated urea. The urea granules coated with lignin/pVLA and wax layer (w-Lignin/pVLA) exhibited exceptional release behavior up to 224 days in soil compared to uncoated urea (7 days). Therefore, findings from this work not only demonstrated the preparation and application of bio-based materials for coated urea but also showed a potential nitrogen slow-release fertilizer which could be widely used in agriculture to minimize adverse environmental and economic impacts.