Retention of cellulose, xylan and lignin in kraft pulping of eucalyptus studied by multivariate data analysis: influences on physicochemical and mechanical properties of pulp

Abstract

Um planejamento fatorial completo foi empregado na investigação dos efeitos das variáveis de polpação kraft de eucalipto nas retenções de carbohidratos e lignina. As influências da retenção desses componentes nas propriedades físico-químicas e mecânicas da polpa foram avaliadas usando o método de Análise de Componentes Principais. O álcali ativo (AA) foi a variável que mais afetou a degradação macromolecular da celulose e as retenções de xilana e lignina. A retenção da celulose não foi afetada. O uso de baixo nível de AA na polpação favoreceu todas as propriedades mecânicas da polpa, porém apresentou efeito negativo na alvura ISO e número kappa. O grau médio de polimerização da celulose apresentou relação com o módulo elástico e com o índice de tração enquanto que a xilana apresentou relação com densidade aparente das folhas. O índice de rasgo apresentou influência positiva do comprimento médio das fibras e dos ácidos urônicos, que foram preservados na xilana possivelmente devido a combinação de baixo AA, baixa espessura dos cavacos e curto ciclo de polpação. A característica, mais do que o conteúdo de xilana na polpa, foi sugerido como fator relevante ao índice de rasgo.Effects of pulping variables on the retention of carbohydrates and lignin in fast kraft pulping of eucalyptus were investigated using a complete factorial design. Influences of pulp chemical composition on physicochemical and mechanical properties were evaluated using Principal Component Analysis. Active alkali (AA) significantly affected the macromolecular degradation of cellulose and retention of xylan and lignin. Cellulose retention was unaffected. The use of low AA in pulping improved all mechanical properties, but increased the kappa number and reduced ISO brightness. The degree of polymerization of cellulose was related to tensile index and elastic modulus while xylan affected the apparent sheet density. Tear index had a positive influence of fiber length and uronic acid groups, which were preserved in xylan by a combination of low AA, thin wood chips and a short pulping cycle. The characteristics, rather than the content of xylan, were suggested to be relevant to tear index. Keywords: eucalyptus, alkaline degradation, carbohydrates, lignin, multivariate data analysis IntroductionKraft pulping and its improved versions are widely used in pulp production due to its simplicity compared to other processes, high strength of the pulps and tolerances to variations in the wood species and quality. Chemicals such as NaOH and Na 2 S are employed in pulping liquor to separate fibers from wood at high temperatures, leading to different extents of degradation of lignin and carbohydrates.1 Hemicelluloses are more susceptible to alkaline hydrolysis than cellulose due to their low degree of polymerization, amorphous state and accessibility to the pulping liquor. The degradation, dissolution, and retention of fiber components during pulping are the main factors affecting the unbleached pulp chemical composition.2 In fact, degradation and retention are dis...

Effects of kraft pulping on the interfacial properties of Eucalyptus pulp fibres

“…It should be mentioned that the variation of AA aiming at changing the fibre chemistry was based on previous experiments using a factorial design and fast pulping cycles. 24 The effects of AA on the surface composition of pulps were assessed by FTIR-ATR combined with PCA. The average sampling depth of this technique is 1 μm, what corresponds to an external layer of 17% of the fibre wall thickness of eucalyptus kraft pulp.…”

“…Other explanation may be the sorption of relocated xylan onto fibre surfaces after removal of its side groups by reactions in the pulping liquor. 24 Additionally, the surface charge results indicated that the formation of metasaccharinic acids in cellulose 29 appeared to occur in inner regions of the fibre wall. This was reasonable considering that the penetration of cooking liquor is believed to be through the fibre lumen.…”

“…The utilization of fast pulping cycles, low AA and thin eucalyptus chips was suggested to reduce the xylan relocation, improving fibre wall swelling and flexibility and thus contributing to fibre-to-fibre bonding. 24 More recently, it was also suggested that surface extractives can be detrimental to mechanical properties due to reduction of fibre-to-fibre bonding. 35 Hence, according to the hypothesis presented here, any strategy to be developed for fibre modification or even optimization of pulping, bleaching and refining conditions should consider the migration and relocation of extractives onto fibre interfaces.…”

Optimization of Xylanase Production byThermomyces lanuginosusin Solid State Fermentation

“…23,49) Xylanase preparations suited to such an application should retain activity at elevated temperatures and alkaline pH and be free of cellulases. [50][51][52] Thermomyces lanuginosus is a thermophilic fungus that is a cellulase-free, single-xylanase producer. 13) A single xylanase from T. lanuginosus 195 has been purified 9.3-fold from a crude koji extract, with a specific activity of 6,182 U/mg of protein.…”

Influences of surface chemical composition on the mechanical properties of pulp as investigated by SEM, XPS and multivariate data analysis

“…A strategy combining retention of polysaccharides in pulping and chemical modification of fibre surfaces seems to be a good alternative for improving strength properties. Retention of carbohydrates by using fast pulping cycles and preservation of non-relocated xylan was recently suggested 38 and is expected to improve the strength at the nanocomposite level and the fibre flexibility. Different methods for surface modification 39 or addition of mannans 40 were recently reported to increase the fibre-tofibre bonding, even for commercial pulps.…”