Properties of polylactide / montmorillonite nanocomposites: before and after weathering

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2015
Sarı, Burcu
The aim of the first part of thesis was to investigate the effects of montmorillonite (MMT) type nanoclay content and maleic anhydride (MA) grafted polylactide (PLA) copolymer compatibilization on the properties of PLA nanocomposites. Nanocomposites have compounded by twin-screw extrusion melt-mixing followed with injection molding for shaping of bulk specimens. Successively intercalated and exfoliated structures of the nanocomposites were observed by XRD and TEM analysis, including the interactions with FTIR. Mechanical tests indicated that use of only 1 wt% MMT resulted in significant improvements in many mechanical properties of PLA. Increases were only 14% in flexural modulus and 6% in flexural strength, but more than 6 times in ductility and as much as 85% in fracture toughness values. After MA compatibilization these improvements were higher, being more than 22 times in ductility and 119% in fracture toughness. On the other hand, no significant changes in the transition temperatures and thermal degradation temperatures of PLA were observed in DSC and TGA thermal analyses. The aim of the second part of this thesis was to compare accelerated weathering performance of neat PLA and its 1 wt% organically modified MMT nanocomposite. Accelerated weathering test system applied consecutive steps of UV irradiation and humidity in accordance with ISO 4892-3 standards for 200 hours. Chain scission actions of weathering degradation mechanisms photolysis, photooxidation and hydrolysis resulted in significant decrease in the molecular weight of PLA; consequently certain reductions in the modulus, strength, ductility and toughness of the specimens. However, it can be deduced that, after comparing mechanical properties of PLA and PLA/MMT before and after 200 h accelerated weathering, use of PLA with only 1 wt% MMT was extremely beneficial not only for “indoor applications” but also for “outdoor applications”. For example, the benefit gained in flexural strength was 6% before weathering, but after weathering the benefit gained was 88%. The reasons of this increments are the effective reinforcing and barrier actions of intercalated/exfoliated MMT layers.
Citation Formats
B. Sarı, “Properties of polylactide / montmorillonite nanocomposites: before and after weathering,” M.S. - Master of Science, Middle East Technical University, 2015.