Synthesis and Physical–Chemical Characterization of a Biopolymer Derived from Cassava Starch, Cashew Nutshell Liquid, and Diammonium Phosphate

A biopolymer was synthesized using starch, cashew nutshell liquid (CNSL), and the commercial fertilizer diammonium phosphate (DAP). The biopolymer and its constituents were characterized using SEM, infrared spectroscopy, X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), and thermal analysis by TGA and DSC. The results showed that fertilizer particles could be encapsulated by the starch and CNSL matrix. Functional groups and ions in the biopolymer showed characteristic bands associated with starch, CNSL, and DAP fertilizer. Moreover, the biopolymer diffraction peaks contained XRD peaks of starch and DAP. The crystallinity of the biopolymer decreased. Starch, CNSL, and DAP electronic transitions appeared in the biopolymer, with possible signal overlapping. The bandgap of starch and biopolymer did not differ significantly (6.19 and 6.16 eV, respectively). Both materials acted as insulators. Differential scanning calorimetry/thermogravimetric evidenced the materials' thermal behavior, where water elimination, degradation, oxidation, and gas formation were registered.