Abstract
Synthetic polymers-based controlled release urea (CRU) leaves non-biodegradable coating shells when applied in soil. Several alternative green materials are used to produce CRU, but most of these studies have issues pertaining to nitrogen release longevity, process viability, and the ease of application of the finished product. In this study, we utilized tapioca starch, modified by polyvinyl alcohol and citric acid, as coating material to produce controlled release coated urea granules in a rotary fluidized bed equipment. Response surface methodology is employed for studying the interactive effect of process parameters on urea release characteristics. Statistical analysis indicates that the fluidizing air temperature and spray rate are the most influential among all five process parameters studied. The optimum values of fluidizing air temperature (80 °C), spray rate (0.13 mL/s), atomizing pressure (3.98 bar), process time (110 min), and spray temperature (70 °C) were evaluated by multi-objective optimization while using genetic algorithms in MATLAB®. Urea coated by modified-starch was double coated by a geopolymer to enhance the controlled release characteristics that produced promising results with respect to the longevity of nitrogen release from the final product. This study provides leads for the design of a fluidized bed for the scaled-up production of CRU.
Highlights
Pristine urea is vulnerable to losses through ammonia volatilization, leaching, and surface runoff [1]
We have addressed almost all of the major issues pertaining to the production and efficacy evaluation of controlled release urea (CRU), such as longevity of nitrogen release, environment-friendliness, cost, viability of production for up-scaling, and ease of application of the final product
The viscosity of starch/polyvinyl alcohol/citric acid based spray solution (SPCSS) determines the droplet size during the spray process [25]
Summary
Pristine urea is vulnerable to losses through ammonia volatilization, leaching, and surface runoff [1]. Significant interest is triggered in this research niche for the development of CRU while using bio-based polymers as coating materials, such as starch [7], lignin [8], cellulose [9], and bio-based polyurethane [10]. These materials are not suitable for the production of CRU unless modified with some appropriate crosslinker, plasticizer, or stabilizer, due to their poor mechanical and thermophysical properties [11,12]. Different starches were modified by (i) borax/urea [13],
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