The influence of properties in cellulose pulps on the reactivity in viscose manufacturing
This paper describes properties in cellulose pulps to adress the increased quality demands on pulps for viscose production. Several grades of cellulose pulps were selected to investigate their chemical reactivity based on pulping process, original wood type and intrinsic viscosity. In total, six sulfite pulps and four sulfate pulps were chosen, of which all but one sulfate pulp were of dissolving grade. The physical and chemical properties of the pulps were tested. The influence of these properties on xanthation and viscose manufacturing as well as their correlation to each of the three selection criteria was investigated by the use of multivariate data analyses. Two methods to describe cellulose reactivity were used: a laboratory scale viscose test method for cellulose reactivity (Fock) and a filter clogging test for viscose dope. It was shown that all pulps chosen in this investigation formed groups according to all three selection criteria using principal component analysis. The analysis shows that sulfite pulps, from both wood types, are strongly correlated to the variables Fock reactivity, pore size and concentration of extractives. Sulfate pulps, however, are separated into two groups, hardwood and softwood. Hardwood sulfate pulps are strongly described by the variables permeability, content of hemicelluloses and filter clogging value. Softwood sulfate pulps, on the other hand, are described by variables such as alpha cellulose content, R10 and R18. Partial least square regression showed that Fock reactivity is influenced by the following cellulose pulp properties, in order of importance: absorption rate with caustic, pore area, permeability and pore diameter. The main property affecting the filter clogging value of the viscose dope is pulp permeability, followed by pore diameter, content of hemicelluloses, R18 and pore area.
Available from: András Gorzsás
- "There is a wide array of dissolving pulps available on the market, with specific characteristics depending on the choice of wood type and pulping process for manufacturing these pulps. The refinement process of dissolving pulps to a specific derivative is intrinsically dependent on these characteristics, and knowledge about the pulp properties is thus important (Strunk et al. 2011). Many methods for the characterization of the properties of dissolving pulp are available and used today. "
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ABSTRACT: : Several grades of dissolving pulps have been analyzed using FT-IR, solid state 13 C NMR and two dimensional 1 H-13 C HSQC NMR spectroscopy to obtain an extensive data set for further characterization. The selection of the dissolving pulps with high cellulose purity was based on pulping process, wood type and, intrinsic pulp viscosity. Multivariate data analysis was used to investigate how information derived from the spectroscopic data correlate to each of the selection criterion: wood type, process type and viscosity. The spectroscopic methods were also compared with common dissolving pulp analyses to see to what extent spectroscopy can predict pulp analyses. Correlations were found between the spectroscopic data and the pulp characteristics process type and wood type, but not for intrinsic viscosity. A reason for a good correlation to wood type appears to be the hemicelluloses composition, expressed as the xylose:mannose ratio by 2D NMR spectroscopy. For process type, 2D NMR showed the most characteristic property to be the amount of reducing ends in the cellulosic samples, which in turn strongly correlates to lower molecular weight for the sulfite samples as determined by molecular weight distribution. Many common, yet expensive and time consuming, pulp analyses could also be predicted by the achieved models. It can be concluded that investigations of dissolving pulp characteristics, especially concerning different wood and process types, can take advantage of the methods and models presented in this study.
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ABSTRACT: Several grades of cellulose pulps were investigated for their influence on the product quality of a cellulose ether, ethyl-hydroxy-ethyl cellulose (EHEC). The selection of the pulps was based on pulping process, original wood type and intrinsic viscosity. In total, five sulfite pulps and four sulfate pulps were chosen, of which all but one sulfate pulp were of dissolving grade. The physical and chemical properties of the pulps were analyzed as well as important qualitative parameters of the final product EHEC. The influence of pulp properties on EHEC quality was investigated by multivariate data analyses. Principal component analysis showed that due to the influence of all variables, the pulps aligned in groups in accordance to the selection criteria pulping process and wood type. Partial least square regression revealed that high gel formation in EHEC is explained by the pulp properties high intrinsic viscosity and high Mw in combination with high caustic absorption rate and high total caustic absorption. The amount of hemicelluloses, in particular xylose, also contributed to gel formation. High cloud point for an EHEC solution was explained by a high MS EO and low DS Et of the EHEC molecules, where in turn a high MS EO could be predicted by a high pore area, high PD and a low caustic absorption rate. A low DS Et could on the other hand be predicted by a low hemicellulose content and hence a high R18. In a separate model, the same pulp properties explaining MS EO and DS Et also predicted cloud point directly. Fock reactivity and viscose dope filterability, both test methods originating from the viscose manufacturing, were shown to predict cloud point but have low predictability on other EHEC quality parameters. The models achieved can thus be utilized to predict final EHEC product qualities for new pulps within the design set of the chosen pulps.
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ABSTRACT: The dissolution of pulps with varying characteristic properties, for example cellulose chain length or content of hemicellulose, has been investigated in two alkaline solvent systems [sodium hydroxide (NaOH)/urea/thiourea (8:8:6.5 by wt.) and NaOH/zince oxide (ZnO) (9:0.5 by wt.)]. One standard paper pulp, two dissolving pulps and three pretreated pulps were selected for this study. The dissolution parameters in focus were the fiber dimensions, average degree of polymerization (DP), polydispersity, water retention value and content of hemicelluloses. The solubility was not influenced by the fiber dimensions. The only significant properties, according to variable importance plot, were DP and composition of the hemicelluloses. It was also established that mass transfer effects during the dissolution stage plays an important role in the dissolution of cellulose derived from pulp fibers.
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