Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596386
Title: Nuclear magnetic resonance studies of soft-solid extrusion
Author: Barnes, E. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2005
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Abstract:
Extrusion is a low cost, versatile process widely used in industry for the production of a broad range of products of various shapes, including foodstuffs, pharmaceutical pellets and catalysts. The primary tool used to study the extrusion process in this work is Nuclear Magnetic Resonance (NMR). An extruder system made from PEEK and aluminium, suitable for use in strong magnetic fields, has been designed and commissioned. It has been used to acquire fully-quantitative spatially resolved real time NMR velocity measurements of two soft-solid materials representative of those commonly extruded in industry; a mixture of 5 cSt polydimethyl siloxane (PDMS) added to a commercial soap (DoveTM), and a stiff biscuit dough. Flow patterns were found to be material dependent, with the soap and PDMS mix exhibiting a much flatter velocity profile than that of the biscuit dough. These spatially resolved velocity profiles are reliable and extensive, providing data suitable for evaluating theoretical models. Comparison of the experimentally determined velocity profiles with velocity profiles predicted from geometric and CFD models highlighted the limitations of these existing models, none of which proved to be entirely satisfactory. Self-diffusion measurements were used to investigate extrusion induced changes in the distribution of PDMS within soap and PDMS mixtures prepared by (i) warm-mixing and (ii) cold-mixing. Before extrusion the PDMS exists in domains of ~ 6mm diameter. Extrusion of the warm-mixed sample leads to a ~17% reduction in domain size, whereas extrusion of the cold-mixed sample causes elongation of the domains but not reduction in domain size. NMR has also been used to make in situ measurements of the extent of rejoining of two streams formed during ram extrusion through a die with a slit obstruction, and of the filling of a cylindrical mould following ram extrusion.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.596386  DOI: Not available
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