Shrinkage and deformation during convective drying of calcium alginate

The effect of air temperature (40-70 °C) and gelation time (10-60 min) on drying kinetics and structure of calcium alginate (3 g/100 mL) particles dried in a convective packed bed drier were investigated. All drying conditions showed constant (initially) and decreasing drying rate periods during most of drying time. The drying time was reduced by a factor of 1.8 when increasing air temperature from 40 to 70 °C. Particle diameter decreased by 54-60% and was not affected by air temperature. However, the increase of drying rate due to a temperature beyond 40 °C resulted in formation of internal voids and higher shape deformation, i. e, it increased elongation and decreased roundness of the alginate particles. The formation of internal voids started in the transition between the constant and decreasing drying rate period. Besides, packed bed drying resulted in heterogeneous particles size distribution during intermediate drying times and more homogeneous size distribution in the end of the drying, when particles shrinkage is reduced. Finally, particles crosslinked during shorter gelation times presented less homogeneous structure, with irregular surface and collapsed center after drying, in comparison to longer gelation times.