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Arundo donax L. reed: new perspectives for pulping and bleaching, part 3: ethanol reinforced alkaline pulping.

APPLICATION: This study investigated the influence of process variables on yield and properties of the ethanol-alkali pulps from Arundo donax to identify optimal cooking conditions.

A recent comparative analysis on the applicability of different organosolv processes to giant reed (Arundo donax L.) showed the advantages of ethanol reinforced alkaline pulping (ethanol-enhanced or ethanol-alkali pulping). Screened yield, brightness, and papermaking properties of the ethanol-alkali pulps were superior to those for kraft and other tested organosolv pulps, while the content of residual lignin was lower.

This report investigates the influence of cooking variables on yield and properties of the ethanol-alkali pulps from A. donax. The reaction medium alkalinity was a controlling factor of delignification, strongly affecting pulping selectivity. Increasing alkali charge from 5% to 35% (as NaOH on o.d. reed), at a fixed ethanol content of 40% by volume, led to a drop in residual lignin content from 20% to 3%. It also caused substantial degradation of carbohydrates and loss in pulp yield from 72% to 47%. Adding ethanol to the alkaline solution had a positive effect on carbohydrates preservation. The retention of 3.6% (on o.d. reed) non-cellulosic polysaccharides in pulps resulted from increasing ethanol content in the pulping liquor from 20% to 60% (by volume), at a fixed alkali charge of 25%. Pulp yield increased from 44% to 49% with this range of ethanol concentrations, while the content of residual lignin decreased from 5% to 3%. Changing the liquor-to-reed ratio from 5/1 to 8/1 mL/g did not reveal any appreciable influence on pulping results. Only uronic acid moieties showed some tendency to degradation with reduced ratios on pulping.

Kinetic analysis revealed three stages in the ethanol-alkali delignification. The major portion of lignin (about 71%) was removed in the rapid initial stage, actually taking place during the impregnation and heating-up periods. The second (bulk) stage was comparatively short and removed only 15% of lignin. Progressive delignification with minimal carbohydrate losses resulted when the pulping duration was extended from 60 to 180 min under 140[degrees]C. View this paper online at http://www.tappi.org/index.asp?pid=28652

Anatoly A. Shatalov and Helena Pereira are with Centro de Estudos Florestais, Universidade Tecnica de Lisboa, Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa Codex, Portugal. Email Shatalov at anatoly@isa.utl.pt.
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Title Annotation:Nonwood Pulping
Publication:Solutions - for People, Processes and Paper
Date:Feb 1, 2004
Words:387
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