Document Type : Research Paper
Authors
Karaj Islamic Azad University
Abstract
Background and Objectives: Pulp refining is considered as an essential unit operation in the development of the paper properties. However, it is intensive energy consumer in the era that world is struggling with energy shortage. Therefore, paper industry has been searching various alternative including application of chemicals to reduce refining energy. Also, during the refining stage, compressive and shear stresses cause swelling, flexibility, and internal and external fibrillation of the fibers, increasing the potential contact surface for fiber bonds. On the other hand, excessive refining can increase fiber shortening and fines production. The objective and aim of this research were concentrated on the application of cellulase enzyme as an environmental friendly process to optimize the refining energy and improve the properties of pulp fibers and paper.
Material and Methods: Two sequences of enzyme treatment and refining were used; first enzyme treatment then refining called ER and first refining then enzyme treatment call RE. Pulp mixture was composed of 70% hardwood kraft and 30% softwood kraft pulps. Three dosages of 200, 300, and 400 ppm (based on dry weight of pulp) enzyme and three reaction times of 60, 90, and 120 minutes were selected. Sample preparation and all tests were performed according to Tappi standard procedures. The freeness of the pulp of each of the 19 treatments (control and 18 treatments) was measured, hand sheet was prepared, and strengths and optical measurements were performed. The analyses included response surface models selected on the basis of leave-one-out cross-validation. Principal component analysis (PCA), hierarchical clustering, descriptive comparison of nine condition-matched pairs, rank correlation, and multi-response desirability analysis coupled with sensitivity analysis.
Results: Based on the average values of the results, the values of ER treated pulps compared to RE were varied as follow; burst strength index, 2.5 against 1.70 kPa.m2/g, tensile strength index, 51.43 against 42.16 N.m/g and brightness 82.88% against 80.05%. However, tear strength index was lower after enzyme treatment. The highest values burst strength index and tensile strength index values obtained applying ER300-120 treatment were 2.90 kPa.m2/g, and 60.14 N.m/g respectively. Principal component analysis (PCA) was performed on 14 complete, non-constant response variables after z-score standardization. Hierarchical clustering was conducted using Ward’s method and Euclidean distance. Given the nature of the available data, the statistical comparisons and conclusions were reported on a descriptive and exploratory basis.
Conclusions: The results of strength properties, freeness degree, and optical properties showed that the order of enzymatic treatment and refining is effective on pulp performance. The average values of the measured properties for ER treatment were higher than respective values for RE treatment. The values of burst strength index and tensile strength index were 66.7% and 43.5% respectively higher than control sample. The response of the RE treatment was not uniform and the average values of the tensile strength index was fairly higher than control sample, but the other properties were lower than control. The tear strength index of all treatments was lower than control which can be attributed to destruction of the fiber integrity. This finding necessitates the appropriate selection of variables to reach optimum results.
Keywords: Cellulase, Refining, Kraft Pulp, Freeness, Strength Properties, Optical
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