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dc.contributor.advisorØye, Gisle
dc.contributor.advisorMartínez Urreaga, Joaquín
dc.contributor.authorSolvoll, Anne Marthe
dc.date.accessioned2016-09-01T14:01:49Z
dc.date.available2016-09-01T14:01:49Z
dc.date.created2016-07-18
dc.date.issued2016
dc.identifierntnudaim:14779
dc.identifier.urihttp://hdl.handle.net/11250/2403600
dc.description.abstractThe demand for plastic continues to increase, and the search for sustainable solutions has become crucial for the large demand the world is facing today. The biopolymer polylactic acid (PLA) has generated special interest, especially for packaging in the food industry, due to its optical and mechanical properties, biocompatibility, and biodegradability. The aim of this Master`s thesis was to examine the water uptake of mechanically recycled PLA, and consequently the hydrolytic degradation with the prospect of using the material as packaging material. It was compared with virgin PLA, to obtain information about the behaviour of the material in the recycled state. The primary challenge with PLA regarding its use in different applications is its facility to undergo hydrolytic degradation in the presence of water. In hydrolytic degradation the ester bonds of the molecules undergo hydrolysis, leading to a decrease in average molecular weight and a worsening of mechanical properties and the stability of the material, which may render it useless for some applications. Therefore, it was necessary to test the utility of mechanical recycling of PLA and its nanocomposites by studying its resistance to hydrolytic degradation in comparison with the virgin material. Commercial PLA pellets were purchased, which could be used just as they were, but a 2% Cloisite 30B clay was added to half of the PLA material. The pellets were prepared by extrusion and, half of the samples were exposed to accelerated ageing, cleaning and finally, mechanically reprocessed to simulate the recycling process. The PLA was immersed for different times in a buffer solution to maintain neutral conditions concerning hydrolytic degradation. UV-Vis spectroscopy of the immersion liquid presented spectra that illustrated three bands located at 228, 246 and 290 nm. These bands grow with increasing immersion time and can be assigned to oligomers of low molecular weight, lactide, lactic acid and lactoyllactic acid that are formed during the hydrolytic degradation of PLA. The PLA endured hydrolytic degradation, and the small molecules formed migrated to the liquid during this process. The FTIR analysis presented the existence of four types of interactions between water and polymer that can be distinguished as very strongly-, strongly-, weakly- and very weakly absorbed water. Fickian behaviour was assumed for the water diffusion up until two days of immersion and by this assumption, the diffusion coefficients were calculated. The diffusion coefficients for the recycled materials with and without clay were calculated to be 3.5·10-12 and 7.1·10-12 m2/s respectively. Clay caused increased water absorption in the material, due to its hydrophilicity, and when dispersed as layers in the polymer it acts as a barrier preventing the passage of water. Thus, the material with clay has a lower diffusion coefficient, which may be important to slow the absorption of water in early stages, extending the life of the materials made with PLA. The recycling of the material caused a small degradation, altering the molecular structure of the polymer and thus, providing faster diffusion of water. The measured intrinsic viscosity decreased with immersion time, and the degradation occurred more rapidly in the recycled material compared to the virgin material and even faster in the material with clay. Thermogravimetric analysis indicated that the thermal stability of the material is reduced with immersion time due to degradation and that the stability of the recycled material, is slightly inferior to the virgin material. The material with clay also showed to be inferior regarding the thermal stability, compared to the material without clay. The results obtained in this project provided information on the water absorption and hydrolytic degradation of PLA, and about the effect on factors such as the presence of a layered clay or mechanical recycling of the plastic. Recycling has a slight negative effect on the material, where it increases the diffusion coefficient compared to the virgin material. The presence of clay sheets well dispersed in the polymer may slow the absorption of water, which can slow the first stages of the hydrolytic degradation. The mechanical recycling, when no demanding cleaning steps are included in the process, gives materials with good properties, very similar to those corresponding to the virgin materials. The results obtained in this work appear to indicate that these recycled materials could be used in packaging. When a demanding cleaning step is included in the recycling process, the recycled materials show decreased stability, although the difference is small. These results support the feasibility of the mechanical recycling of PLA.
dc.languageeng
dc.publisherNTNU
dc.subjectIndustriell kjemi og bioteknologi, Kjemisk prosessteknologi
dc.titleEffect of Mechanical Recycling on the Hydrolytic Degradation of PLA used in Food Packaging
dc.typeMaster thesis
dc.source.pagenumber132


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