Graduate Thesis Or Dissertation
 

Molecular weight distribution analysis of wood pulp cellulose by size exclusion chromatography

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  • Automated size exclusion chromatography with a differential refractometer detector was employed to study the molecular weight distribution patterns in various types of wood pulp cellulose. The results obtained were correlated with the conventional methods of measuring these properties. The dissolution of pulp celluloses in N,N-dimethylacetamide-lithium chloride solvent was optimized. This procedure solubilized the cellulose components directly without prior extraction or derivatization, processes that could lead to degradation of high molecular weight components. Stable cellulose solutions were obtained. The optimum dissolution conditions in the solvent system was highly dependent on the molecular weight, crystallinity and lignin content of each pulp cellulose sample. The molecular weights and molecular weight distributions of the pulp cellulose solutions were analyzed by size exclusion chromatography. A series of polystyrene standards were dissolved in the solvent and used as reference materials. The chromatographic data revealed whether depolymerization has taken place uniformly or non-uniformly during the pulp processing operations. The dilute solution intrinsic viscosity of the celluloses in N, N-dimethylacetamidelithium chloride solvent system was measured by capillary viscometry. Likewise, viscosity in cupriethylenediamine solution was analyzed. The measured viscosity values correlate well with the molecular weight data determined by size exclusion chromatography. The effect of acid hydrolysis on the molecular weight distribution pattern of cellulose was likewise studied. Results showed that each acid treatment provided different development of the molecular weight distribution curve, possibly due to the selectivity of hydrolytic attack on the cellulose components. The experimental data showed that dissolution in N,N-dimethylacetamide-lithium chloride solvent system and solution analysis by size exclusion chromatography can be a powerful tool in detecting differences among pulp cellulosic samples of widely different molecular weight and molecular weight distribution.
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