Pulping Potentialities of some Non-Woody Plants from Sudan

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Date
2015-06-22
Authors
Tarig Osman, Khider
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Publisher
University of Khartoum
Abstract
About 92 % of the total paper consumption in Sudan is purchased from abroad, only 8% is locally produced, Sudan has most of the basic factors required to establish a pulp and paper industry: availability of water, energy and fibrous materials such as hardwoods and agricultural residues, Against the background of fast depletion of traditional fibrous raw materials for the paper industry, such as softwoods and hardwoods, which are all forest based, and the need to stop deforestation for ecological reasons, the pulp and paper industry is looking for unconventional fibrous raw materials for producing different kinds of paper and boards, Among the unconventional raw materials agricultural residues hold an important position. In the present study, the pulping properties of Hibiscus cannabinus-kenaf bark, core and whole stalk, Musa sp. (banana) stems, Hyphaene thebaica (doum palm) rachis and Phoenix dactylifera (date palm) rachis and leaves have been investigated. The fibre dimensions, morphological indices and chemical composition of the raw materials were determined. The soda, soda-AQ, AS-AQ, and the ASAM process were applied and some of the produced pulps were bleached according the TCF bleaching method. Testing of the papermaking properties included blending of different kinds of pulps. Fibre dimensions were evaluated by microscopy. The fibres studied were very short (1mm kenaf core and doum palm rachis), short (1.5 mm date palm rachis and leaves) or of moderate length (banana stems and kenaf bast fibres). The fibres of the agricultural residues had thin to medium thick cell walls in the range of 3.1 µm for date palm leaves to 4. 5 µm for kenaf bark. The differences in morphology of these fibres could be well illustrated by the morphological indices calculated. According to the flexibility index, which is very important for fibre bonding they were classiufed in third (doum palm rachis), second (date palm rachis and leaves kenaf bark and banana stems) and first (kenaf core) category according to the Istas classification, Accordingly, the fibres studied, except for doum palm rachis, were expected to collapse easily during pulping and beating providing good fibre bonding. The stiff fibres of doum palm rachis were expected to be less suited for papermaking. The chemical composition of these raw materials is typical for tropical non-wood plants. They had high contents of ash, especially silica (except kenaf) and low lignin contents (especially kenaf bark). Only the date palm leaves had very high lignin content. The high to very high cellulose content of most raw materials studied predicated good to very good pulp yield. On the other hand date palm leaves had very low cellulose content. The overall chemical composition indicated the suitability of alkaline methods for pulping with reasonable alkali charges and predicted acceptable yields. This was demonstrated by cookings with alkali charges of 17-19% as Na2O for soda, 10-17% as Na2O for soda-AQ, 14-19% as Na2O for AS-AQ and 17% as Na2O for ASAM process. The cooking time was 90 to 120 min. at maximum temperatures between 165-175 °C. Kappa numbers in the range of 12.5 to 32.8 were reached. By addition of only 0.1 % AQ the accepted yield obtained by the soda pulping was significantly increased by 4.2-11.5%. ASAM cooking of kenaf core, whole kenaf stalk, doum palm rachis and date palm rachis resulted in high yields, low kappa numbers and excellent strength properties. Due to the low residual lignin content and high initial brightness, pulps from whole kenaf stalk and date palm rachis showed very good bleachability. AS-AQ pulps showed better viscosity and brightness compared to soda and soda-AQ pulps. Even better results with regard to Ins. viscosity and brightness were attained in ASAM pulping. The bonding strength of pulps was considerably improved by AQ addition. Despite of the superiority of the ASAM pulps, all pulping methods yielded pulps with good to very good strength properties except those pulps from doum palm rachis, which had inferior strength properties .The AS-AQ process, was suited for pulping of banana stems. Using this process banana could be delignified to low kappa numbers. Initial brightness, viscosity and strength properties exceeded those of conventional soda pulps by far. On the other hand soda–AQ pulping method also resulted in an increased yield and gave pulps with better properties compared to soda cooking without AQ .The date palm leaves gave pulps with low yield, but excellent papermaking properties, which could be used in blends in the same way as long-fibre softwood pulps. The optical properties of all unbleached pulps studied were characterized by high LSC of 18-36 m2/kg for soda and soda-AQ and 17-43 m2/kg for AS-AQ and ASAM pulps. The kenaf bark soda-AQ and AS-AQ pulps were blended with other raw materials in two ratios of 10:90 and 30:70. Blending improved all properties of these pulps, especially tear strength. The ratio of 30:70 showed better results. This might enhance the chances of kenaf bark pulp as strong contender to meet part of additional fibre supply requirement. Kenaf bark fulfils high quality and high yield options. TCF bleaching with the OQl (PO) Q2P sequence was applied to whole kenaf stalk and date palm rachis pulps (soda-AQ, ASAM and AS-AQ). The bleached pulps reached a final brightness of 81-88% ISO at kappa numbers between 2.7-7.6 and viscosities between, 737-994 ml/g the overall bleaching losses were 3.6 to 6.4 %. The application of 0.1-0.2%. EDT A in the Q stages was necessary to remove transition metal ions which otherwise would consume high amounts of hydrogen peroxide in the (PO) and (P) stages and would led to a dramatically reduced bleaching effect. The results achieved in the pulping and bleaching experiments show that, except doum palm rachis, all non-wood raw materials available in Sudan are suited for production of paper pulp. Pulping can be performed with low chemical charges under mild conditions. The corresponding pulps show good bleaching response and can be bleached to acceptable brightness in a TCF sequence. There are reasonable prospects for the commercial production of paper pulp from these raw materials. Feasibility study, concerned with plantation, harvesting, and collecting of these non-woody raw materials is required to utilize them in pulp and paper industry.
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Keywords
sudan;woods;chemical composition;Hyphaene thebaica;economical evaluation
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