Hydrophobic-densified high-elastic waste-carton-derived biopolymer-coated fertilizers: Enhanced performance and controlled-release mechanism

Reasonably utilize the recyclable waste cardboard (175 million tons every year) had attracted the increasing environmental concern. However, the poor hydrophobicity and the loose porous structure of the cardboard-derived coating materials caused the rapid release of nutrients, thereby limiting the development and application of the bio-derived synthetic polymer coated controlled-release fertilizers (BPCFs). In this work, the hydrophobic-densified double-modified waste-carton-derived controlled-release fertilizers (HDCFs) were developed with nontoxic modifying agent and the simple production technology. The controlled release abilities of HDCFs were significantly enhanced (< 2 h to 120.45 days) and the nutrient release prediction models were established. The enhanced performance was attributed to the improved hydrophobicity and the obviously compact coating structure characterized by the three-dimensional computerized tomography (5.76–1.08 %). Furthermore, the enhanced elasticity (5025.52–1325.68 MPa) of the HDCFs coatings also contributed to improve the controlled-release abilities. The controlled-release mechanism was also clarified: the atmosphere "stopper" in the "smaller and less" micropores in HDCFs coating only allows water vapor molecules (instead of liquid) slowly permeate into the internal urea core and significantly enhance the controlled-release longevities. The dramatically increased oilseed rape yield (71.75 %) showed the efficient application effect of the HDCFs. All the results indicate that HDCF with 90:10 of the proportion of the castor oil and liquefaction polyhydric alcohols from cardboard (LPAC) and 5 % of the siloxane of the total polyols exhibits the best performance effect. This work provides the efficient strategy to foster the end-user confidence in the low-cost and eco-friendly biowaste-derived controlled-release fertilizers.