Kraft Pulping of Wheat Straw
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Date
2017-07
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Addis Ababa University
Abstract
In this paper, pulping of wheat straw with Kraft process was studied. Chemical and
morphological properties of wheat straw fibers were also investigated. Chemical properties
including cellulose (39.8%), hemicellulose (29.47%), lignin (20.98%), ash (6.27%) and
extractives (4.1%) were determined. Fiber length, diameter, lumen width and cell wall
thickness were 1210, 17.20, 8.40 and 3.80μm, respectively. Wheat straw has acceptable
Runkel ratio (0.9) and flexibility coefficient (48.8) in the range of non-woods.
Various pulping conditions including composition of cooking liquor (10, 15 and 20%) and
cooking temperature (130, 140 and 150oC) at reaction times (30, 60 and 120 min) were
studied systematically to determine the suitable pulping conditions. The influence of pulping
conditions on the pulp obtained (Yield and Kappa number) and paper strength properties
(tensile, tear and bursting strength) are analyzed by three-factor and orthogonal experiments,
and optimum pulping conditions are obtained. The best properties of the pulp and hand sheets
were obtained with 10% sodium hydroxide, in the cooking solvent, 136.9oC cooking
temperature and 30 min as cooking time. As a result of using the processing variables over
the variation ranges considered, the following optimum values of the dependent variables
were obtained: 33.91% (yield), 16.76 (kappa number), 4027m (breaking length), 8.96*10-3
Nm2g-1 (tear index) and 2.66 KNg-1 (burst index) for pulps and hand sheets. In general,
results based on chemical and morphological analysis indicated that wheat straw fibers are
promising fibrous raw material for the paper production.
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Chemical and Bio Engineering