PhD ceremony Mr. M.B.K. Niazi: Production of plasticized thermoplastic starch by spray drying

PhD ceremony: Mr. M.B.K. Niazi, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Production of plasticized thermoplastic starch by spray drying

Promotor(s): prof. A.A. Broekhuis

Faculty: Mathematics and Natural Sciences

The aims of this thesis are to study the product, property, processing relationship of thermoplastic starch (TPS) films produced via compression molding of spray dried powder, and to obtain amorphous starches with the potential to be used as biodegradable bio-plastics.

Different plasticizers were used to study the properties of TPS blends. Special attention was given to retrogradation behavior of films at different humidity conditions. The solution spray drying of starch plasticizer blends produced amorphous powder with low moisture contents and these were applied to produce thin films. The results clearly show that the effective mixing followed by drying and film production resulted in film performance different from films produced by classical extrusion technology or solvent casting. Urea was found to be a more effective plasticizer than glycerol, i.e. a lower Tg, a lower degree of retrogradation, a lower tensile strength and a higher elongation. These results can be understood by the smaller molecular dimensions of urea and a more intimate interaction between urea and the amylopectin fractions in the system.

Similarly, malic acid strongly inhibit retrogradation, but showed yet unpredictable water absorption phenomena without reaching equilibrium. It is concluded that carboxylic acids act different than the common plasticizers like glycerol or urea. Carboxylic acids clearly show more intensive interaction and malic acid in particular, reduces retrogradation significantly. However, lack of retrogradation also is correlated with high moisture absorption and other pathways have to be developed to reduce the effect of moisture in order to achieve better mechanical properties.