The effect of pea fiber and potato pulp on thermal property, surface tension, and hydrophilicity of extruded starch thermoplastics

The objective of this study was to investigate the effect of the addition of pea fiber and potato pulp on the thermal property, surface tension and hydrophilic character of extruded potato starch films plasticized with glycerol and triethyl citrate. Film samples were prepared from a film device attached with twin screw extruder. The surface tension and hydrophilicity of samples conditioned at 50% relative humidity (RH) were determined through Zisman method and water contact angle measurement, respectively. Addition of fiber or pulp resulted in higher surface energy and hydrophilicity. The thermal property analysis did not indicate that the fiber and pulp had any effect on glass transition temperature (Tg), which was in the range of 20–25 °C. Incorporation of fiber and pulp did not show any effect on the monolayer moisture content and specific surface area of the films. The moisture sorption behaviour of the thermoplastic starch films was also investigated, indicating GAB, Flory-Huggins, and Smith models worked well. Overall analysis exhibited that addition of fiber or pulp increased the hydrophilic character, water wettability, and moisture content of the TPS film. These effects could be related to the addition of hydroxyl groups in the cellulose molecules.