MECHANISMS OF DRYING OF SKIN-FORMING MATERIALS .2. DROPLETS OF HEAT-SENSITIVE MATERIALS

Drying studies were carried out on single droplets of gelatin solution , typifying a skin forming, heat-sensitive material. Each droplet was suspended from a novel rotating glass nozzle which enabled direct meas urement of its weight and temperature during drying. Observations usin g this apparatus successfully detected the decrease in core temperatur e and increase in drying rate resulting from granule dissolution at 30 -degrees-C. The study covered air temperatures in the range 19-degrees -C-175-degrees-C. Scanning Electron Microscopy was used to examine the dried crusts. The resistance of the skin to vapour diffusion was sign ificantly increased with an increase in the air temperature. At air te mperature > 60-degrees-C the dried particle lost the structure and pro perties of the original powder. The optimum drying conditions to avoid this were predicted for this type of skin forming-material.