Natural polymers are an attractive alternative for fertilizer-release because allow providing specific nutrients for plant nutrition in a prolonged time while also reducing their impact on the environment. Chitosan is attractive because of its amino groups that can be positively charged under an acidic environment, allowing it to form electrostatic interaction with anionic fertilizers. On the other hand, the abundant surface hydroxyls in cellulose allow to functionalize its chemical surface toward greater interactions. Esterification with sulfuric acid introduces anionic sulfate groups on the cellulose chain, providing electrostatic interaction with cationic nature fertilizers as well as polymers positively charged (i.e., chitosan). Therefore, combining sulfated cellulose with charged chitosan could be exploited for fertilizer-release. In this study, cellulose was submitted to sulfuric acid hydrolysis (65 wt.%, 40 mL g-1 cellulose, 50 °C, 2 h) and then mechanically homogenized via turrax to yield cellulose nanofibrils. Chitosan (1 wt.%) was solubilized in water acidified by 0.5 w/v% CH3COOH for 24 h. Then, 0.1 w/v% sulfated cellulose was added into 100 mL chitosan solution, and 2.7 g NPK fertilizer was added and mixed. It was dried by spray dryer B-290-BUCH using a two-fluid nozzle (180 °C, 100% aspirator, 7 ml min-1 flow rate) and resultant particles were compacted to produce tablets. Hydrolysis followed by homogenization yielded cellulose nanofibrils with uniform dimension and sulfate groups incorporated on its surface. Upon spray drying, solids were composed of rounded-shape and crushed particles, and non-encapsulated fertilizers were not observed. Charged chitosan reduced the release rate of HPO4- compared to NH4+ and K+ due to the electrostatic interactions generated from its protonated amino groups with hydrogen phosphate ions while reaching a plateau region within 2 h. Sulfated cellulose incorporation prolonged the release rate of all nutrients near 5 h, suggesting a barrier performer against fertilizers release, which increased their diffusion path through the chitosan.

Chitosan-sulfated cellulose nanofibrils based spray-dried microparticles exhibiting prolonged release of nitrogen, potassium, and phosphorous

ACS Spring Meeting 2021

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