Improvement of water sensitivity, mechanical properties and utilization of hemicellulose based polymeric materials

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2015
Akkuş, Merve
Hemicelluloses are sustainable resources of biopolymers with a huge potential to be converted into materials substituting petroleum-based products, but their hydrophilic characteristics pose a challenge to their industrial adoption. The main aim of this study is to decrease the water sensitivity of alkaline extracted xylan-based corn cob hemicelluloses (xylans) by heat-treatment and acetylation also by addressing their extrusion processing with sorbitol, glycerol and blends. Heat-treatment resulted in extruded strips with less moisture uptake, less normalized water vapor transfer rate (NWVTR) and enhanced mechanical properties, but without any significant change in their water solubilities. Acetylation was studied by exploiting the potassium acetate (KAc) salt that is formed during the alkaline extraction, which is usually removed. Moisture uptake, water solubility, and NWVTR of KAc containing acetylated xylans decreased significantly, with an increase in mechanical properties and thermal stability, showing that acetylation with KAc is an efficient method without salt purification steps and toxic catalysts like pyridine. Extrusion of xylans with sorbitol and glycerol was studied alternative to the plasticization by moisture conditioning where both plasticizers rendered xylans extrudable. Similar to the effect of KAc, vi acetylation carried out in the presence of sorbitol and glycerol resulted in reduced water solubilities; however the mechanical properties were only enhanced for glycerol containing strips. Xylan-and-polyvinyl alcohol (PVA) blends and their heat treatment and acetylation were also studied to reduce their water sensitivity. Extrusion of xylan/PVA blends was successful which might increase the industrial utilization of xylans, but their heat treatment and acetylation resulted in brittle strips