Cellulose composite structures – by design

Winkworth-Smith, Charles G. (2015) Cellulose composite structures – by design. PhD thesis, University of Nottingham.

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Abstract

The aim of the work presented in this thesis was to investigate different mechanical and chemical pre-treatments which can dramatically change the properties of native cellulose and add alternative routes to structure formation. Ball milled cellulose, which had a reduced crystallinity, degree of polymerisation and degradation temperature, was rehydrated in excess water resulting in recrystallisation. Fully amorphous samples recrystallised to the more thermodynamically stable type II polymorphic crystal structure. Flash differential scanning calorimetry (DSC), which allows thermal transitions to be scanned at much higher rates than conventional DSC, was able to register a glass transition temperature for amorphous cellulose. The next stage of the study focussed on the production of freeze dried galactomannan foams. Cellulose fibres provided reinforcement to the foams. The level of reinforcement was related to fibre content, size, crystallinity and surface roughness. Microfibrillated cellulose (MFC) provided the greatest reinforcement due to its much higher surface area and fibrillated structure. Extrusion was found to be a useful alternative to homogenisation for the production of MFC and to create foams using alternative processing to the freeze drying routes.

A novel molten salt hydrate, LiCl/urea/water, was found to swell native cellulose and reduce its crystallinity. A weak gel-like structure was formed at ambient temperature. Micro DSC results showed that this structure was melted out at 60oC but the process was reversible indicating hydrophilic to hydrophobic conformational changes on the surface of the cellulose fibres, although these were likely to be dependent on the celluloses having a low degree of polymerisation. In these solvent conditions starch granules were eroded from the outside rather than being swollen as has been found for some ionic liquids and underwent total dissolution in LiCl/urea/water. Fenugreek and xyloglucan, which are both highly branched, were found to increase in viscosity in LiCl/urea/water relative to water, possibly due to the breakage of all intramolecular associations whereas the viscosity of konjac which is predominantly unbranched did not change. Locust bean gum (LBG) had a lower viscosity in LiCl/urea/water compared to water due to the disruption of aggregates. Confocal microscopy showed that fenugreek and LBG are able to bind to cellulose in water, however, the conformational change of fenugreek in these solvent conditions inhibited it from binding to cellulose in LiCl/urea/water whereas conformational change allowed xyloglucan to bind to cellulose in LiCl/urea/water whilst it was unable to bind in water. Konjac did not bind to cellulose in either solvent system. The pre-treatments shown in this work will enable the creation of novel cellulose composites.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Foster, T.J.
Subjects: Q Science > QK Botany > QK710 Plant physiology
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 28823
Depositing User: Winkworth-smith, Charles
Date Deposited: 22 Sep 2015 10:07
Last Modified: 13 Sep 2016 11:43
URI: http://eprints.nottingham.ac.uk/id/eprint/28823

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