REACTIVE EXTRUSION OF PHOSPHATE CROSSLINKED POTATO STARCH

Abstract

<p>Biobased engineering materials from natural polymers such as potato starch and sisal fiber have increasingly attracted more attention compared with their petroleum counterparts due to biodegradability, environmental protection, and sustainable development. A novel biobased composite was developed based on phosphate crosslinked thermoplastic potato starch and sisal cellulose fiber aimed at improving mechanical properties and hydrophobicity.</p> <p>First of all, potato starch has a much narrow processing window in extrusion machinery for manufacturing thermoplastic starch. Statistical analysis of differential scanning calorimetry data aided in extrusion processing design and optimization.</p> <p>Then, bulk crosslinking of potato starch with sodium trimetaphosphate in the presence of rheological controlling additives (xanthan gum and glycerol) was investigated. Batch kinetics for the reaction was studied using in-situ attenuated total reflectance infrared spectroscopy monitoring. The spectra data were processed by multivariate analysis to reveal vibrational bands related to crosslinking and to identify important variables for reaction optimization. A kinetics model was created to facilitate developing a reactive extrusion process for bulk starch phosphate crosslinking. The effects of hydrocolloidal xanthan gum and glycerol on starch crosslinking reaction were also evaluated.</p> <p>Furthermore, gelatinized starch with processing additives was crosslinked with and without natural sisal fiber using sodium trimetaphosphate within a co-rotating intermeshing twinscrew extruder. The produced biocomposites were characterized using infrared spectroscopy, sessile drop contact angle measurement, moisture content determination and tensile mechanical testing. Comparison of experiment data and calculated values from modified Tsai-Halpin model confirmed crosslinkages formed between the crosslinked starch matrix and sisal fibers. The mechanical properties of the biocomposites were significantly improved, but the moisture sensitivity was increased due to reduced crystallinity caused by crosslinking.</p> <p>Finally, hydrophobicity of the starch biocomposite was improved by surface modification with Hydrores 266MB dispersion. Improvement of hydrophobicity is essential to maintaining superior mechanical properties of the biocomposites in surroundings with high relative humidity.</p>