Cellulose Nanofibers/Engineered Biochar Hybrid Materials as Biodegradable Coating for Slow-Release Phosphate Fertilizers

Even if substantial efforts have been made to produce coated fertilizers with more efficient nutrients release, the development of simple processes using greener materials is still challenging to date. Herein, designed biobased formulations, prepared using biochar materials and oxidized cellulose nanofibers filled into methyl hydroxyethyl cellulose, were developed and then used as coating agents of phosphate fertilizer (triple superphosphate). Biochars were elaborated via direct pyrolysis of lignocellulosic biomass. In the case of the so-called engineered biochar (i.e., montmorillonite modified), a co-pyrolysis process of montmorillonite (MT) and biomass was performed. Nanocomposite films were then prepared from the as-prepared coating formulations prior to examine their surface wetting, swelling capacity, and biodegradability in the soil medium. Collected results show that biochar materials significantly reduce the hydrophilicity of cellulosic materials. Furthermore, the addition of MT during the biomass pyrolysis impacts reaction yield (by 54.54%) and also tunes the porous structure of biochar. Moreover, this MT addition induces a decrease of the swelling capacity and degradation rate of cellulose/biochar films by a factor of 45.74 and 44.48%, respectively. Interestingly, the developed cellulose/engineered biochar coating material induces an increase of the crushing strength of fertilizer granules by 30.29% in comparison with the uncoated fertilizer. Furthermore, the soil water holding capacity was also considerably improved by 7.78% with a water retention capacity of 3.00% after 25 days when cellulose/engineered biochar-coated fertilizer was added into the soil. In fact, this fertilizer impacts considerably on the release of phosphorus (P) in the soil with a reduction of 43.90% of P leaching within 80 days of soil incubation. These findings indicate that the biobased developed nanocomposite formulations of cellulosic biochars are suitable to produce slow-release phosphate fertilizers with reduced P leaching and water-saving properties.