A precise study on the feasibility of enzyme treatments of a kraft pulp for viscose application

Abstract

The development of efficient process steps to convert paper-grade to dissolving pulps was investigated as part of the work programme to improve the process economics. The challenge of pulp refinement comprises the selective removal of hemicelluloses and the precise adjustment of the pulp viscosity, while maintaining the reactivity of the pulp as required for viscose application. The purpose of this study was to investigate the effects of various enzyme treatments on a commercial oxygen-delignified Eucalyptus globulus paper-grade kraft pulp in the course of a total chlorine free bleaching sequence in combination with refining techniques following the principle of Modified Kraft Cooking (Sixta et al. 2007). The objectives were to assess its applicability as viscose pulp besides the reduction of chemical consumption in alkaline and ozone bleaching steps by means of xylanase pretreatment and the controlled adjustment of final pulp viscosity utilizing endoglucanase post-treatment. Xylanase pre-treatment combined with cold caustic extraction at reduced alkalinity efficiently removed the hemicelluloses from the pulp and clearly increased the pulp brightness by extensive removal of hexenuronic acid side chains. The xylanase pre-treated pulp showed increased reactivity towards xanthation and high viscose dope quality in terms of particle content. The dependence of cellulose chain scission on the applied endoglucanase concentration was analyzed in detail, and this allowed precise viscosity reduction as well as reactivity increase. The differently treated pulps, with and without xylanase pre-treatment, were of very narrow molecular weight distribution and the quality of the spun fibers were very similar to those viscose fibers from commercial dissolving pulps.

Hot water treatment of hardwood kraft pulp produces high-purity cellulose and polymeric xylan

“…Several methods have been studied to remove the hemicelluloses from paper pulps, including enzymatic hydrolysis and cold caustic extraction (Gehmayr et al 2011;Ibarra et al 2009;Köpcke et al 2008), nitren extraction (Janzon et al 2006(Janzon et al , 2008, and ionic liquid extraction (Froschauer et al 2013;Roselli et al 2014). Despite their varying success in producing a high-purity pulp for dissolving applications, their high operational costs and/or their toxicity have limited the utilization of these methods in industrial scale.…”

Purification of cellulosic pulp by hot water extraction

“…In addition to a good quality rayon pulp, the SEW process allows high flexibility in terms of raw materials, short cooking times, and a significant recovery of sugars from the pulping liquor (Iakovlev and Heiningen 2012;Sixta et al 2013). The production of viscose-grade pulps has also been investigated by applying a CCE stage to paper-grade pulps, which allows the removal of substantial amounts of shortchain hemicellulosic sugars while preserving the yield of cellulose (Gehmayr et al 2011;Schild and Sixta 2011). Recently, the novel IONCELL process has been shown to be successful in the conversion of paper-grade pulps to dissolving pulps.…”

Comparative evaluation of the action of two different endoglucanases. Part I: On a fully bleached, commercial acid sulfite dissolving pulp

“…This spectrum suggests a small 426 presence of cellulose II and this cellulose polymorph is more susceptible to enzymatic 427 hydrolysis by endoglucanases (Krässig 1993 The outcomes of the F cellulase treatments were examined in greater detail 441 (Table 3). The water retention value (WRV) provides information about the integral pore 442 volume of a pulp and the content of hydrophilic groups (Gehmayr et al 2011). Fines are 443 thought to increase WRV improvement since these particles have more accessible -OH 444 groups and plays a major role in dewatering.…”