Kelly, Nicole L. (2020) A multi technique characterisation approach to the analysis of polymers and biomaterials. PhD thesis, University of Warwick.

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Abstract

A multi technique characterisation approach is vital for the full understanding of a material and its properties. Through combining predominantly solid state nuclear magnetic resonance (NMR), wide-angle (WAXS), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and Raman spectroscopy, four different systems have been investigated.

The importance of the development of biopolymers cannot be understated, polylactide (PLA) is one such biopolymer that has a lot of focus due to its wide range of end uses through tailoring it’s physical properties. The characteristics and behaviour of PLA pre and post processing has been investigated. The degradation of four PLA samples with different ratios of D- and L- polylactide (PDLA/PLLA) has been tracked over the course of a year using the aforementioned techniques. The long range order does not change over the course of a year for all of the samples. There is however a potential rearrangement of the PLA helix but without an overall change in mobility.

The end product PLA materials were injection moulded and underwent tensile and impact testing. Two different mould temperatures were applied to investigate the difference between amorphous and crystalline products of the same starting composition. Additionally, the effect of nucleating agents has been investigated by the incorporation of talc. The crystalline products resulted in strong materials, with the addition of talc resulting in the introduction of crystalline regions even at low mould temperatures increasing the strength of the materials.

The multi technique approach has also been applied to a series of polyester and polyamide elastomers with a range of cis:trans ratios. The Young’s modulus is an important characteristic of any elastomer and is affected by crystallinity which in turn is influenced by the cis:trans ratio. The Young’s modulus for the polyesters increases with a greater cis content directly matching the increase in T1ρ times. This confirmed that an increase in crystallinity and a consequent decrease in molecular mobility increases the Young’s modulus. The effect of cis:trans ratio on polyamides is less pronounced than for the polyesters. The molecular weight has also been investigated and found to have little difference between ‘oligomers’ and ‘polymers’.

Finally, an additional technique, electron paramagnetic resonance (EPR) has been implemented for the analysis of coper doped calcium phosphate bioactive glasses. Copper is incorporated into bioactive glass structures as Cu+ and Cu2+. The combination of solid state NMR, EPR and Raman spectroscopy allows for the determination of how each of the Cu species incorporates into the bioactive glass network. Increasing the copper doping, even up to ~ 20 % copper, results in a continuous incorporation of Cu ions without saturation. There is no net depolymerisation of the bioactive glass network due to two competing processes. These are Cu+ forming CuO chain ends and Cu2+ ions forming linear arrangements causing repolymerisation. The Cu2+ ions can also form tetragonally distorted octahedral coordination between phosphate chains.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Biopolymers, Polylactic acid, Nuclear magnetic resonance spectroscopy, Small-angle x-ray scattering, Calorimetry, Solid state physics
Official Date:	September 2020
Dates:	Date Event September 2020 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Hanna, John V.
Format of File:	pdf
Extent:	xvii, 159 leaves : illustrations
Language:	eng

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