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Itim, Bachir (2015) Influence of Polyolefin Contamination on the Thermal Characteristics of Bottle Grade Recycled Polyethylene Terephthalate. Doctoral thesis, London Metropolitan University.
During the mechanical recycling, especially during the sorting and separation process of bottle grade PET, cross contamination with polyolefin is inevitable. Very small number of polyolefin bottles, caps and closures pass through the separation process and get recycled with PET bottles and affect the final characteristics of the recyclate. The effect of this cross contamination and the influence of polyolefin contamination on the overall characteristics of bottle grade recycled PET, especially the thermal characteristics with emphasis on crystallinity, were thoroughly investigated. The investigation showed that the inclusion of polyolefin contamination influenced the overall characteristics of the bottle grade rPET matrix and indicated incompatibility of polyolefin contaminants and rPET-bg. This influence had an impact on the viscosity, elasticity and strength of the rPET-bg matrix. Furthermore, the crystallinity of the rPET-bg matrix showed the impact of polyolefin contamination as a result of variation of cooling rates and that cross-linking and chain branching predominated over chain scissions as a result of repetitive extrusions. The crystallisation process of the non contaminated rPET-bg and rPET-bg contaminated with polyolefin depended on many influencing factors, such as impurities, cross-linking, chain branching, chain scissions, cooling rates and repetitive extrusion cycles. Also, the crystallisation mechanism fully depended on the nucleation and growth rates and that competition between nucleation and molecular mobility was influenced by the variation of cooling rates and repetitive extrusion cycles. As a result, the thermal characteristics were greatly influenced by the inclusion of polyolefin contamination, especially crystallinity, as shown and validated by the Avrami and Ozawa models and that the findings are a step forward and an original insight on the influence of polyolefin contamination at industrial scale.
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