Abstract
Thermoplastic starch properties depends of plastification process. The aim of this study was to analyze the effect of concentration of glycerol and water on plastification, glass transition temperature (Tg) and tensile properties of thermoplastic waxy starch (TPWS). Formulations were extruded in the following concentrations of starch/glycerol/water: 70/30/0 (TPWS 0%); 70/25/5 (TPWS 5%); 70/20/10 (TPWS 10%) weight percentage. Crystalline peaks in WAXS diagrams and native grains present in SEM micrographs showed that the TPWS 0% and 5% were not sufficient to promote total plastification of the waxy starch, and TPWS 10% showed the higher starch plastification. Tg measurements by DMTA were 30 oC to TPWS 0%, 23 oC to TPWS 5% and 40 oC to TPWS 10%. These results showed that glycerol and water had effect plasticizer in TPWS 5% and antiplasticizer in TPWS 10%. Mechanical tensile results showed that higher tensile strength was observed in the systems with more effective starch plastification.
Highlights
Starch is a carbohydrate present in abundance on the environment, which has advantages over others biodegradable polymers such as low cost and biologically absorbable[1]
We proposed to investigate the effect of glycerol and water concentration on plastification, glass transition temperature (Tg) and tensile properties of thermoplastic waxy starch (TPWS) films processed by extrusion and pressing
scanning electron microscope (SEM) micrographs showed that TPWS 0% composition exhibits some native or partly melted starch granules spread over the film indicated by white arrows (Figure 2b)
Summary
Starch is a carbohydrate present in abundance on the environment, which has advantages over others biodegradable polymers such as low cost and biologically absorbable[1]. Starch consists of two major components, the linear amylose and the highly branched amylopectin[2,3]. There are three types of starch wherein the amylose concentration ranges: native starch (15-30 wt% amylose); waxy starch (0-5 wt% amylose); and high amylose starch (35-70 wt% amylose)[2,3]. Native starch is not processible and this drawback can be resolved by plastification process[4,5,6]. When starch is mixed with plasticizers under shear rate and temperature between 90-180 oC their amylose/amylopectin chains are interspersed, and the amylopectin structure original is destroyed. This material is called starch thermoplastic (TPS)[7,8]
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