Search

Abstract??Carboxymethylcellulose (CMC) was prepared from nine commercial dissolving pulps with different origins, viscosities and S18-values. The rate of the etherification reaction and the final DS were studied with respect to the influence of pulp composition, pulp viscosity and S18-value, and with respect to the sodium hydroxide and sodium monochloro-acetate charges. The possible influence on the final DS-value of the CMC of the washing procedure after the etherification was also investigated. [ABSTRACT FROM AUTHOR]

Abstract  The influence of the solvent system used during the CMC manufacturing on the characteristics of CMC in different solutions was studied by producing CMC in ethanol, isopropanol or a mixture thereof. This paper shows that the solvent system used has an impact on the substituent pattern and this is especially the case during the mercerisation. When isopropanol is used in comparison with ethanol the distribution of the substituents along the cellulose backbone becomes more uneven and the amount of tri-substituted glucose units increases as well as the number the amount of substituents on the C-6 position. This affects the behaviour of CMC when dissolved in different electrolyte solutions. [ABSTRACT FROM AUTHOR]

The depolymerisation of laboratory-prepared kraft pulps from birch, eucalyptus and reed canary grass during acid hydrolysis was studied. The intention was to study especially the influence of xylan content on the levelling-off degree of polymerisation (LODP) and on the dissolution of carbohydrates during the acid hydrolysis. The xylan content in the pulps was varied by prehydrolysis prior to the kraft pulping or by alkali-extraction of the bleached pulps, and the levelling-off degree of polymerisation was compared with the amount of xylan left in the pulps at LODP. The dimensions of the original fibers in the pulps and of the fiber fragments after hydrolysis were also measured. It was found that the fiber fragments after hydrolysis were longer in the pulps containing a higher amount of xylan. Xylan thus appears to prevent degradation during acid hydrolysis, both on the fiber level and on the individual cellulose fibril level. [ABSTRACT FROM AUTHOR]

Four different spruce sulphite pulp samples were used for the preparation of carboxymethylcellulose (CMC). The characteristics of the unreacted fibre and particle residuals obtained in the CMC-preparation were used to establish a correlation between the hemicellulose in the pulp and the intrinsic viscosity, i.e.,␣cellulose chain length and the occurence of unreacted residuals. It was shown that the residual particles in the CMC consisted of fibres, fibre fractions and gel particles of different degrees of substitution. The results suggested that pulps with long cellulose chains, i.e., pulps with high intrinsic viscosities, resulted in particles that were more substituted and more swollen. These pulps also resulted in more substituted hemicelluloses in the CMC and more substituted residuals. It was also suggested that galactoglucomannan in the cellulose pulps is favourable for the swelling which results in more substituted hemicelluloses in the CMC and more swollen residuals. The amount of residuals was influenced mainly by the characteristics of the cellulose in the pulp. It is therefore believed that a combination of high viscosity and a suitable combination of hemicelluloses is the most favourable way of eliminating the occurrence of undissolved residuals in CMC. [ABSTRACT FROM AUTHOR]

Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose (CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage. It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity. [ABSTRACT FROM AUTHOR]

Abstract The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed kraft pulp. A model explaining the LODP-results is proposed. [ABSTRACT FROM AUTHOR]