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Title: Degradation of polypropylene and novel blend formulations, and the release of hazardous chemicals
Author: Kassam, Zara
ISNI:       0000 0004 6423 1967
Awarding Body: Kingston University
Current Institution: Kingston University
Date of Award: 2017
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Plasticisers and additives are used for their effectiveness in improving flexibility in plastics, for many commercial applications ranging from the medical to the food industry. Human exposure to additives such as bisphenol A (BPA) and phthalates such as bis(2-ethylhexyl) phthalate (DEHP), have been found at harmful detectable levels in the humans, where concerns of their potential health risks may arise from chronic exposure. This thesis presents a brief history and an overview of the traditional plasticisers currently obtainable in the global market, as well as the complications associated with the end uses of these plasticisers, and reviews recent scientific approaches to resolve these problems. The polymers themselves were found to have thermally degraded after repeat exposure to microwave irradiation; this was revealed by using X-ray diffraction analysis, which indicated a drastic reduction in crystal size from 7.94 nm to 2.62 nm. Changes in the polymer surfaces was identified using scanning electron microscopy (SEM), where it was be noted that as the polymer underwent an increased number of reheating cycles, the morphology of the polymer was disrupted. Attenuated Total Reflectance-Infrared Spectroscopy (ATR-IR) was used to identify structural property changes due to solvolysis and hydrolysis on exposure to microwave irradiation; with the main distinctive features being a strong OH peak in the 3500 cm-1 region, as well as a strong C-O peak present at 1346 cm-1 and a C=O peak at around 1725 cm-1 , the chemical changes were verified using gravimetric analysis where the mass of the polymer increased from 5.5 % to 40%. As the polymer degraded, the phthalates and additives incorporated during the polymerisation process were prone to leaching; a Gas ChromatographyMass Spectroscopy (GC-MS), selected ion monitoring method was developed in order to identify and quantify specific leachates and the quantities leaching. Dimethyl phthalate was the first compound to be identified and quantified, and was found to be at a concentration which is almost five times higher than safe levels stated by the National Institute for Occupational Safety and Health (NIOSH); also benzyl butyl phthalate (BBP) at about 30 times the safe level. Initially the phthalates and additives were tested on Caco-2 human colorectal cells to investigate how they responded when exposed at concentrations corresponding to the leachate amounts collected through GC-MS analysis. An assay carried out showed the effects on cell proliferation. BPA exposure was found to decrease the cell viability from the lowest concentration (0.1 μg/l). The number of viable cells at this concentration had a 10% average decrease from the control cells and when the cells were exposed 0.4 μg/l the cell viability decreased by 90%. The development of natural plasticisers for application in packaging is one of the great challenges of research in material science. In this project soybean oil, rapeseed oil and coconut oil were successfully epoxidised to produce alternative plasticisers, with the identification of the epoxidised oils being carried out using ATR-IR spectroscopy and nuclear magnetic resonance (NMR). Poly(lactic acid) is a biodegradable and bioactive thermoplastic aliphatic polyester, which was synthesised from anhydrous lactic acid with Dimethylaminopyridine (DMAP) and N,N'-Dicyclohexylcarbodiimide (DCC). Poly(lactic acid) was melt blended along with polypropylene (PP) and various ratios of epoxidised oils in order to produce a polymer with the same characteristics as those produced by the harmful alternatives. Poly(propylenegraft-maleic anhydride) (PP-g-MA) was incorporated into the polymer blend to functionalise the polypropylene, and improve the compatibility of the polymer blend. ATR-IR was used for identification of the successful blend; The CH3 stretch of Poly(lactic acid) is identified at 2983 cm-1 , the peak distinctive for O-C=O is shown at 1190-1080 cm-1 . At 1734-1740cm-1 the C=O of poly(lactic acid) can be observed. The epoxidised oils display small intensity signals at 950-850cm-1 , and around 1250cm-1 this is an important characteristic for the C-O-C stretch of the epoxide. The interaction between the PLA and epoxy group through hydrogen bonding resulted in enhanced morphological properties providing the desirable characteristics provided by the harmful plasticisers and additives. Poly(propylene-graft-maleic anhydride) can be identified by its strong peaks between 1800 cm-1 and 1700 cm-1 and can be assigned to symmetric C=O stretching of anhydride functions grafted on polypropylene. Confirmation of the blend components interaction in this study was observed by representing the ester linkage at 1756-1755 cm-1.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry