Investigation on resistance to attrition of coated particles by response surface methodology

The purpose of the present study is to obtain better understanding of the influence of the coating thickness, h, coating formulation, T_g, and fluid bed temperature, T_bed, variables on the resistance to attrition of the coated sodium benzoate reference particles. Three reference coating materials (T_g = 50 – 125 – 150 °C) have been sprayed by using top spray fluid bed coater. Per each coating formulation three different coating levels (h = 1% – 5% – 9% w/w) have been obtained. The coating processes were performed at three different fluid bed temperatures (T_bed = 40 – 55 – 70 °C). The experiments have been designed according to the response surface methodology (RSM). Both single effects and interactions between single effects on the resistance to attrition (response variable) calculated by means of repeated impact tester were evaluated. From statistical analysis, the coating quantity appears to have a predominant effect on the resistance to attrition of the coated particle in these studied ranges of variables. This relationship is linear and positive, which means that an increasing quantity leads to more resistance to attrition. The interaction coating thickness – coating formulation, the interaction between the fluid bed temperature and the coating formulation and the coating formulation as well as the interaction costing thickness – fluid bed temperature were found to be very significant. On the contrary, no direct effect of the fluid bed temperature on the resistance to attrition is detected.