Sorption of xyloglucan onto cellulose fibers
Molinarolo, Susan L.
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Xyloglucan is a hemicellulose found in the primary cell walls of many plant species. Found adjacent to the cellulose, it is believed to function as a cementing material which contributes crosslinks and rigidity to the cellulose framework. The only noncovalent linkage reported in the primary cell wall cellulose-hemicellulose-pectic polysaccharide matrix of the cultured tissues is that between xyloglucan and cellulose. Therefore, the xyloglucan:cellulose association has been of great interest to researchers. Xyloglucan can be bound to cellulose in vitro to simulate this in vivo relationship. Previously, the sorption of xyloglucan fragments onto cellulose under non-physiological conditions had been studied, but little information was available on xyloglucan polymer sorption onto cellulose under more natural conditions. This thesis examined the sorption of the xyloglucan polymer isolated from Tamarindus indica onto cellulose fibers (cotton linters) in an aqueous environment. The structure of the xyloglucan isolated from Tamarindus indica in this thesis resembled that of other tamarind xyloglucans reported in the literature. Due to the milder isolation procedure employed, the molecular weight of this polymer was much larger than those previously found. No acetyl, pyruvate, methoxyl, or carboxyl groups were found. The molecular weight and certain structural features (e.g., no fucose units) also differed from the xyloglucan found in plant primary cell walls. When sorbed onto well characterized cotton linters, this xyloglucan exhibited equilibrium sorption within 24 hours. The equilibrium adsorption isotherm was defined. Monolayer sorption occurred. A maximum specific sorption value of 3.9 milligrams of xyloglucan sorbed per gram of cotton linters was calculated using Langmuir's adsorption isotherm theory. This value was compared with other values found in the literature for similar polymer adsorption studies. The effect of molecular weight on sorption equilibrium was also examined and found to be insignificant over the molecular weight range of the polymer isolated in this thesis.