Hydrophobicity in polysaccharide gelation

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dc.contributor.advisor Morris, E. R.
dc.contributor.author Jones, Amanda Kay
dc.date.accessioned 2010-10-04T14:31:49Z
dc.date.available 2010-10-04T14:31:49Z
dc.date.issued 1992-11
dc.identifier.uri http://dspace.lib.cranfield.ac.uk/handle/1826/4595
dc.description.abstract The role of hydrophobic substituents on the gelation mechanism of highly esterified pectin and the cellulose derivatives methylcellulose and hydroxypropylmethylcellulose (HPMC) has been explored by monitoring the behaviour of the amphiphilic polysaccharides in varying combinations of an ethylene glycoVwater solvent. The gelling ability (mechanical spectroscopy, visual observation) of very highly esterified (- 100%) pectin in high concentrations of ethylene glycol (>60%) is greatly reduced, however, the polymer still undergoes conformational ordering (CD, OR). A model for gel formation involving a two stage process has been proposed, comprising adoption of the ordered structure stabilised by hydrogen bonding between OH groups of contiguous polysaccharide chains, followed by (or coincident with) aggregation of the ordered sequences by 'hydrophobic' clustering of the fundamental structural subunits to form the three dimensional gel network. It has been found that ethylene glycol promotes the fIrst stage (ordering) but is antagonistic to the second (aggregation). The reversibility (mechanical spectroscopy) of the thermo-gelling cellulose derivatives can be largely abolished in the presence of ethylene glycol (40% for methylcellulose, 10% for HPMC) , attributed to solubilisation of the proposed ordered 'bundle' structure at low temperatures removing the enthalpic advantage (DSC) of gel melting. The increased sensitivity of HPMC to modification of the solvent environment is due to the presence of the polar hydroxypropyl substituent causing an inceptive destabilisation of the 'bundle' structure. It is suggested that gelation is driven by the entropic advantage of melting-out 'cages' of structured water surrounding the hydrophobic groups giving rise to intermolecular 'hydrophobic' aggregation. en_UK
dc.language.iso en en_UK
dc.publisher Cranfield University en_UK
dc.title Hydrophobicity in polysaccharide gelation en_UK
dc.type Thesis or dissertation en_UK
dc.type.qualificationlevel Doctoral en_UK
dc.type.qualificationname PhD en_UK

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