Conductive drying kinetics of pregelatinized starch thin films

Thin film drying of pregelatinized starch over a hot surface in the absence of forced airflow was investigated by analyzing simultaneous loss-in-weight, heat flow and temperature data records. This kind of drying is chiefly related to drum drying applications. Experiments were performed by varying the film thickness, preparation conditions (pasting temperature and pasting duration) and drying temperature. For the examined range of values, film thickness played the most decisive role in determining the kinetic characteristics of drying. An analysis was conducted testing several heterogeneous reaction kinetic models as well as a semi-empirical model from literature in an effort to identify a suitable rate expression and investigate probable mechanisms of the process. Results indicate that removal of moisture from these thin films follows both a boiling-type and a conductive type of drying. It appears that boiling prevails in the thinner films whereas both mechanisms can exist in the thicker ones.