Agro-Waste Derived Additives for Polylactide and Tapioca Starch
Abstract: Development of materials from renewable resources is one of the big challenges facing our world. In this thesis agro-industrial waste derivatives were developed and evaluated as additives for two common renewable polymer matrices, polylactide (PLA) and starch. Two waste products, wood flour (WF) and rice bran (RB) were evaluated in different forms. Milled WF and RB were either used directly to prepare PLA and starch biocomposites or they were liquefied by acid catalyzed hydrolysis to low molecular weight products. The complex polyol mixtures from liquefaction were tested directly as PLA and starch additives or utilized as monomers for synthesis of esters. The synthesized esters were evaluated as plasticizers for PLA and starch. The effect of different additives on tensile properties, miscibility, surface chemistry and morphology were evaluated by Instron, DSC, FTIR, FTIR imaging and SEM. In the case of polylactide films the influence of additives on hydrolytic degradation rate and process was evaluated by following the weight loss, surface changes, compositional changes and/or water-soluble migrants and degradation products by FTIR, SEM, pyrolysis-GC-MS and ESI-MS. The most marked difference in mechanical properties was observed in the case of PLA modified with liquefied wood flour derived ester plasticizer (PWF). Addition of 10 and 30 weight-% plasticizer increased the strain at break from a few percent for pure PLA to over 100 and 300%, respectively. The liquefied rice bran based ester, however, did not form miscible blends with PLA and it did not function as plasticizer. In some cases the impact of additives on the following degradation process was significant. Depending on the used additive, they could either concentrate in the matrix during the hydrolysis of polylactide or they were rapidly released to the surrounding water. In some cases clear hydrolysis catalyzing effects were observed. Liquefied rice bran in combination with mineral fillers and/or traditional plasticizers seemed to have the best potential as starch plasticizer.
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