Thermoplastic starch modified with microfibrillated cellulose and natural rubber latex: A broadband dielectric spectroscopy study

• Published in: Carbohydrate polymers Vol. 157; pp. 711 - 718
• Main Authors: Drakopoulos, S.X., Karger-Kocsis, J., Kmetty, Á., Lendvai, L., Psarras, G.C.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 10.02.2017
• Subjects: Broadband dielectric spectroscopy; Microfibrillar cellulose; Natural rubber latex; Thermoplastic starch; Water effect; Broadband dielectric spectroscopy; Water effect; Thermoplastic starch; Microfibrillar cellulose; Natural rubber latex
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2016.10.036

•Thermoplastic starch biocomposites were studied via dielectric spectroscopy.•Hydrophilic/hydrophobic nature of modifiers controls biocomposites' polarization.•A matrix-water-reinforcement interfacial polarization was observed.•Energy density values rise up to 4.5 times after water evaporation.•After environmental exposure water is partially retrieved into the specimens. Thermoplastic starch (TPS) biocomposites modified with cellulose microfibers and/or natural rubber were prepared via extrusion compounding. Glycerol and water served as plasticizers for starch. The dielectric properties of the TPS composites were examined via broadband dielectric spectroscopy in the temperature and frequency ranges of 30°C–65°C and 0.1Hz–10MHz, respectively. Each specimen was tested twice in order to study the effect of absorbed water. The hydrophobic/hydrophilic character of the modifiers governed the dielectric performance of the corresponding TPS biocomposites. Conducted analysis revealed two relaxation processes attributed to matrix-water-reinforcement interfacial polarization and glass to rubber transition of the TPS. Evaporation of water significantly affected the first process and only slightly the second one. Energy density, prior and after water evaporation, was also determined at constant field. By employing dielectric reinforcing function the contributions of water-assisted and constituents’ originated interfacial phenomena could be separated.