Spray-dried materials components ratio evaluation by TGA

Controlled release fertilizers based on chitosan (Ch), TPP, KNO3, and MMt have been prepared by Spray Dryer with different atomizer nozzles (2FN and 3FN)[1]. However, one of the disadvantages of spray drying technique is the loss of material adhered on glass wall of drying chamber affecting the initial ratio formulation. TGA was suggested to determine the real content of Ch, nutrient and clay. TG curves of pure components were separately analyzed and interpreted to obtain the values of the KNO3 in each sample. After, they were compared to the results from spectroscopic techniques. DSC, FTIR and DRX were performed to evaluate the interactions among all components. These analyses supported the formation of (i) NaNO3 from the exchange cations into the MMt layers (DRX:2θ = 29.46º and 41.01º); (ii) chitosan salts from interactions between amine groups and free nitrates from KNO3 (DRX:2θ = 27°, DSC exothermic peak around 300°C). KNO3 content in the samples obtained by 2FN was close to those of theoretical, but it was larger for 3FN materials. Also, the TGA confirm that the samples sprayed by 3FN have higher Ch and lower KNO3 content than those prepared by 2FN, due to the extra layer of Ch (shell). All results were corroborated by the values obtained from Flame Photometry measurements (not shown). TGA was very useful to determine the real content of the spray-dried materials since the ratio composition was altered during the process.