Structural and Thermal Characterization of Some Thermoplastic Starch Mixtures
Maria Daniela Stelescu, Ovidiu Oprea, Maria Sönmez, Anton Ficai, Ludmila Motelică, Denisa Ficai, Mihai Géorgescu, Dana Gurău
Abstract
The paper presents the production of thermoplastic starch (TPS) mixtures using potato starch and two types of plasticizers: glycerol and sorbitol. The effects of plasticizers, citric acid, organically modified montmorillonite clay nanofiller (OMMT) and an additive based on ultrahigh molecular weight siloxane polymer on the structure and physical–mechanical and thermal properties of TPS samples were analysed. Starch mixtures plasticized with glycerol were obtained, where the starch/glycerol mass ratio was 70:30, as well as starch mixtures plasticized with glycerol and sorbitol, with a starch/glycerol/sorbitol mass ratio of 60:20:20. The starch gelatinization process to obtain TPS was carried out in a Brabender Plasti-Corder internal mixer at 120 °C, with a mixing speed of 30–80 rpm, for 10 min. The obtained results indicate that by adding 2% (weight percentage) of citric acid to the TPS mixtures, there is an improvement in the physical–mechanical properties, as well as structural changes that can indicate both cross-linking reactions by esterification in stages and depolymerisation reactions. The sample of TPS plasticized with glycerol, which contains OMMT, shows an increase in tensile strength by 34.4%, compared to the control sample.