(2019) 1:6
Omer et al. BMC Chemical Engineering
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strengths are highly correlated to a high proportion of hemicelluloses [30, 31]. The dominating source of darkening, however is defin- itely the condensed and degraded lignin. Nevertheless, too high alkali concentrations must be avoided especially at the end of the cooking procedure. Otherwise, over- proportional degradation and dissolution of hemicellu- loses and cellulose might take place, resulting in reduced yield and viscosity. The combination of low yield but good papermaking properties suggested that okra pulps could be used in blends with the short-fibered hardwood pulps. Conclusion The okra stalks has multiple purposes and could be promising raw material for pulp and paper production as agricultural waste. The use of soda-AQ pulping accel- erated the delignification and beating rate, increased yield and viscosity and gave pulp with superior proper- ties and highest alkali charge. The screened yield of 32.2% was achieved with negligible amount of rejects, at bleachable Kappa number 22.2 and viscosity 1065 ml g − 1 during application of high alkali charge 21% as NaOH. Decreasing this alkali charge to 18% gave screened yield 28% with very low rejects 1.5% kappa number 27.8 and viscosity 1045 ml g -1. The rejects were increased to 7% during application of 15% NaOH with high Kappa num- ber 29.6 and viscosity 1010 ml g − 1 . The fiber dimensions and morphological indices represented okra stalks as in range of tropical non woody plants. The chemical com- position of okra gave indication of suitability of soda-AQ cooking for these agricultural residues. The pulps produced are suitable for production of printing and writing papers. Due to relatively low screened yield and good papermaking properties, it is advisable to blend these pulps with other high yield pulps.
Fig. 3 Screened yield and rejects of Abelmoschus esculentus okra stalks versus chemical charge% as NaOH
It is well known that tensile strength, burst and double folds increase with increase in freeness level, this clearly reflected during application of freeness 25 and 50. The high tensile strength, which mainly based on the good bonding ability of the fibers, results from high pentosans content due to the high stability of xylan and cellulose in the outer cell wall layers. The high hemicellulose con- tent also improved the beating [25, 29]. In paper production the primary role of hemicelluloses is to imbibe water and thus to contribute to fiber swell- ing. This leads to internal lubrication of the fiber and improves its flexibility and ease of beating. The swelling pressure contributes to loosening of the structure and fibrillation. The hemicelluloses being amorphous and adhesive in nature tend to hornify as the fiber shrinks and dries. Thus hemicelluloses serve as a matrix binding substance between fibers in a pulp. Burst and tear
Additional file
Additional file 1: Physical properties of Abelmoschus esculentus (Okra plant). (DOCX 795 kb)
Acknowledgements Authors grateful for the Cellulose Chemistry and Technology Research Unit- National Centre for Research (NCR) – Khartoum, Sudan for using of research facilities. The lab work done by students Rashid Hamid Edris, Hadiel Ibrahim Ahmed and Fakhreldin Alfadil Rahmatallah.
Funding Not applicable.
Availability of data and materials We have already included most of data in the manuscript, the lab and data, some data not included in the manuscript attached as Additional file 1. Authors ’ contributions SHO and SKS were carried out, supervised the chemical analysis, soda-AQ pulping and revised the draft manuscript. OTE did the fibers dimensions and
Fig. 4 Prepared hand sheet from pulp of Abelmoschus esculentus okra stalks for physical properties evaluation
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