Graduate Thesis Or Dissertation
 

An investigation of the effect of dihydroquercetin and quercetin on bleaching of Douglas-fir groundwood

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  • Sapwood and heartwood groundwood samples were prepared separately from a second growth, coastal range, young Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). The bleaching responses of these two groundwoods to zinc hydrosulfite were examined, and the roles of both dihydroquercetin and quercetin in this bleaching reaction were investigated. Heartwood groundwood was identified to be the major culprit in the bleaching of Douglas-fir groundwood. For this particular sample, the bleachability of its heartwood groundwood was inversely linearly proportional to the pulp freeness at the lower freeness levels. The addition of pure dihydroquercetin to sapwood groundwood had a minor effect on both brightness and bleachability of this groundwood, but the addition of quercetin resulted not only in decreased unbleached brightness but also in insignificant brightness gain during groundwood bleaching with zinc hydrosulfite. Paper and gas chromatographies were employed for the quantitative determinations of dihydroquercetin present in heartwood groundwoods treated in various ways, such as bleaching and/or aging. The brightnesses and bleachabilities of these heartwood groundwoods showed poor correlation with their dihydroquercetin contents. The effect of aging and the bleached brightness reversion were similar for both sapwood and heartwood groundwoods. Solvent extractions did not improve either the unbleached or bleached brightness of heartwood groundwood. No commercially feasible method of improving the brightness of Douglas-fir heartwood groundwood to a commercially acceptable level has been developed in this research.
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