Characterization and Optimization of Soda-Anthraquinone Pulping of Teff Straw for Paper Making Process

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Date

2019-07

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Addis Ababa University

Abstract

The aim of this research was to investigate the important features of teff straw and its utilization in the pulp and paper industry via soda-anthraquinone pulping process. Morphological characterization indicated that the average length of teff straw fibers (1230μm), average fibers width (15.28μm), cell wall thickness (3.83μm), lumen diameter (21.28μm) and acceptable derived indices of slenderness ratio (80.78), Runkle ratio (0.36), flexibility coefficient (138.7) and wall rigidity coefficient (25) which were comparable to the most non-wood plants and Eucalyptus. The chemical composition of teff straw showed that the cellulose content (39.4%), hemicellulose (29.6%), lignin (14%), extractives (7.2%) and ash content (6.78%). It contained lower lignin and higher hemicellulose contents than most of non-wood plants which reflected that teff straw requires mild cooking conditions. For experimental design, Response Surface Methodology/Central Composite Design was used to compare the effects of cooking temperature (130, 140 and 150℃), cooking time (60, 90, and 120 minutes) and active alkali concentration (10, 15, and 20%) on pulp yield and Kappa number. The results indicated that sodium hydroxide concentration had a higher significant influence on both pulp yield and Kappa number followed by cooking time and temperature respectively. Greater interaction effects (temperature-time, temperature-active alkali concentration and time-alkali concentration) of factors were also seen on pulp yield and Kappa number both positively and negatively. Over cooking, extended time pulping and high active alkali concentration gave the lower pulp yield. The optimization results of pulping processes gave the optimal operating condition of 13.76% active alkali at 145.13℃ for 71.5 minutes and 33.15% pulp yield (based on oven dried teff straw) of 25.85 Kappa number. The paper hand sheets of 60 g/m were prepared from the pulps produced at optimum conditions and tested for its mechanical properties that showed breaking length (4294 m), tensile strength (11.6 kN/m), tensile index (42.1 Nm/g), tear index (5.2 mN.m 2 /g) and burst index (1.41 kPa.m 2 2 /g), and porosity (19.5 se/100 air). The results indicated that the tested strength properties were acceptable and make teff straw an alternative material for pulp and paper application.

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Keywords

Teff Straw, Soda-Anthraquinone, Characterization, Pulping, Paper Making Process

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