Abstract
Heartwood and sapwood of Scots pine were procured and chipped using a newly developed pilot drum chipper, which for the heartwood resulted in a combined fraction of pin chips and fines of ~ 3%. Heartwood wood chips were processed using a set of 15 different reaction conditions that differed with respect to impregnation and cooking procedures. The result was evaluated with regard to absorption of impregnation liquid, pulp yield, fraction of reject, viscosity, kappa number, brightness, fiber properties, and chemical composition measured using two different techniques (compositional analysis using two-step hydrolysis with sulfuric acid and Py-GC/MS). The chemical analyses provided detailed information about how all main organic constituents of the wood, cellulose, hemicelluloses, and lignin, were affected by operational parameters. Inclusion of a pressurized (9 bar) impregnation step resulted in a more efficient cook, but the duration of the impregnation step (five minutes and four hours were compared) was not decisive for the outcome. Omission of the impregnation step or using low-pressure impregnation resulted in high fractions of reject, poor delignification, and, with a cooking time of two hours, no advantages with regard to fiber length and fraction of fines. The results indicate that the conditions used during impregnation, such as pressure, temperature, and acidity of impregnation liquid, warrant further attention in future studies.
Highlights
The sulfite process has been of considerable interest for the development of forest-based biorefineries, where one possible product is dissolving pulp that can be utilized for textile production and production of cellulose derivatives
It was clear that the wood chips from heartwood were significantly (p ≤ 0.01) thicker
The trend that wood chips from heartwood were thicker than wood chips from sapwood was supported by the thickness distribution data (Fig. 2b)
Summary
The sulfite process has been of considerable interest for the development of forest-based biorefineries, where one possible product is dissolving pulp that can be utilized for textile production and production of cellulose derivatives. Even though the production of dissolving pulp peaked in 1975, the demand has typically increased since 2000. The global production, 4.5 million metric tons in 2010, was lower than the 5.3 million metric tons in 1975, but higher than the 2.3 million metric tons in 2000 [1]. The increase is mostly due to an increasing demand for highly pure cellulose fibers for textile applications, and for manufacture of cellulose acetate for high value-added films, plastics, and coatings, cellulose ethers, and cellulose powder [2]. One advantage with the acid sulfite process is the high recovery rate for the cooking chemicals
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