Date

2015

Author

Doğu, Berk

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The purpose of the first part of this thesis was to investigate the effects of microcrystalline cellulose (MCC) content on the properties of polylactide (PLA) biocomposites; including the influences of maleic anhydride (MA) grafted PLA copolymer (PLA-g-MA) compatibilization. PLA/MCC biocomposites were produced by industrially compatible production techniques, i.e. twin-screw extrusion melt-mixing for compounding and injection molding for shaping of bulk specimens. SEM analysis and mechanical tests indicated that use of 3 wt% MCC resulted in very uniform distribution and consequently improved properties especially in terms of ductility and toughness. For instance, compared to neat PLA, the increases in the values of %strain at break and fracture toughness were 78% and 31%, respectively. After MA compatibilization, these increases became as much as 82% and 55%, respectively. Moreover, DSC and TGA indicated that use of MCC resulted in no significant changes in the transition temperatures and thermal degradation temperatures of PLA. The purpose of the second part of this thesis was to reveal effects of accelerated weathering in neat PLA and its 3 wt% MCC biocomposite. Weathering conditions were applied via consecutive steps of UV irradiation and humidity in accordance with ISO 4892-3 standards for 200 hours. Various characterization techniques and mechanical tests indicated that photolysis, photo-oxidation and hydrolysis were the main degradation mechanisms leading to significant decrease in the molecular weight of PLA via main chain scission. Consequently, except elastic modulus other mechanical properties; strength, ductility and fracture toughness of PLA and PLA/MCC decreased substantially. However, after comparing the mechanical properties of the neat PLA and PLA/MCC biocomposite specimens having 200 h of accelerated weathering, it was concluded that; for the outdoor applications use of PLA/MCC biocomposite (with only 3 wt% MCC) was extremely beneficial compared to using neat PLA.

Subject Keywords

Cellulose., Polylactic acid., Maleic anhydride., Composite materials.

URI

http://etd.lib.metu.edu.tr/upload/12619024/index.pdf
https://hdl.handle.net/11511/24979

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Graduate School of Natural and Applied Sciences, Thesis