Effects of titania particles on the behaviours of polylactide based composites

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2018
Can, Ulaş
In the first part of this thesis, the main aim was to compare influences of various contents of the micron (200 nm) and nano (50 nm) sized titania (TiO2) particles especially on the mechanical performance of the polylactide (PLA) biopolymer. Micro and nano composites were prepared by twin-screw extruder melt mixing, while the specimens were shaped by compression molding. SEM analyses and mechanical tests revealed that due to the most uniform distribution in the matrix, the best improvements in the strength, elastic modulus and fracture toughness values could be obtained either by 5 wt. % micro-TiO2 or by only 2 wt. % nano-TiO2 particles. The secondary aim of this part was to investigate influences of using maleic anhydride (MA) grafted copolymer (PLA-g-MA) compatibilization on the performance of one nanocomposite composition. Due to the improved chemical interfacial adhesion, use of PLA-g-MA compatibilization for the specimen of PLA/2 wt. % n-TiO2 composition resulted in the highest improvements in the mechanical performance of neat PLA. The improvements were 14% in tensile strength, 20% in flexural modulus and as much as 67% in fracture toughness. Thermal behavior of all specimens were also analysed by DSC and TG analyses. In the second part of the thesis, the purpose was to investigate mechanical and thermal performance of 2 mm thick PLA specimens against UV irradiation; first when only adding benzotriazole based organic UV absorber (UVA), micron and nano sized TiO2 particles alone, and then to reveal possible synergism when they are added together. Specimens prepared by the same techniques were exposed to UV irradiation under fluorescent lamps (UVB-313) with 0.50 W/m2 for the periods of 12 and 24 days. Changes in the performance of UV irradiated specimens were evaluated in terms of % weight loss, changes in color and chemical structure, including the decreases in the mechanical and thermal properties. Various tests and analysis conducted in this part revealed that synergistic benefits of using micro and nano TiO2 particles together with benzotriazole type UVA were not only due to the effective stiffening, strengthening and toughening actions of titania particles but also due to their very significant “UV screening” actions absorbing the photons of the UV irradiation, thus decreasing the degree of the detrimental photodegradation reactions leading to chain scissions in their PLA matrix.

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Citation Formats
U. Can, “Effects of titania particles on the behaviours of polylactide based composites,” M.S. - Master of Science, Middle East Technical University, 2018.