Kraft Pulping of Wheat Straw

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.