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Sulphate and bisulphite pulp yields within wood growth zones of Picea mariana (Mill.) B.S.P. and Pseudotsuga menziesii (Mirb.) Franco Chiu, Shui-Tung

Abstract

Quantitative methods for sulphate and Na-base bisulphite micro-pulping and micro-analytical procedures were developed. Raw pulp and pulp carbohydrate yields were correlated with relative position within growth increments of black spruce and Douglas fir. Profiles varied at different pulp yield levels and with pulping process. No profiles were simply correlated with wood micro-specific gravities. Maximum raw pulp and pulp carbohydrate yields within growth increments shifted from earlywood to latewood as yield changed from high (80 ± 5%) to low (45 ± 5%) levels. Delignification rate differed within increments for both pulping processes. In the initial sulphate and Na-base bisulphite cooking stage, latewood lignin seemed to be more easily removed than that from earlywood. At high yield levels (80 ± 5%), the pulp residual lignin contents based on oven-dry pulp followed similar patterns in that maxima were found in early-wood, abruptly decreasing in the transition zone then slightly increasing in the latewood portion. At low yield levels (45 ± 5%), the residual lignin patterns varied slightly, or remained constant throughout the whole increment. Raw pulp yields, residual lignin contents and pulp carbohydrate yields (based on extractive-free water-free wood) were not significantly different for combined data of heartwood and sapwood, the two woods and two pulping processes, except for Na-base bisulphite pulp carbohydrate yields which showed significantly higher values for sapwood. Sulphate raw pulp yields and residual lignin contents obtained by combining data from all cooking levels and wood zones were not significantly different between the two species examined, except for Douglas fir carbohydrate yield which was significantly higher than that of black spruce. For Na-base bisulphite pulping, Douglas fir raw pulp yields and pulp carbohydrate yields were highly significantly greater than those from black spruce, whereas pulp residual lignin was not significantly different.

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