The influence of the counter-ions to the charged groups on the refinability of never-dried bleached pulps (original) (raw)
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It has earlier been shown that the counter-ion to the charged groups in the fibre has a significant effect on the beatability of fibres, but large-scale investigations of this effect are scarce in the literature. The objectives of the present study were therefore to develop a technique to ion-exchange large quantities of industrial pulp into the Na +-form using complexing agents and to study the effect of industrial-scale refining on pulp fibres in the Na +-form and how the fibres respond to industrial-like papermaking. The results show that ion-exchange can indeed be conducted on a pilot-scale using complexing agents such as DTPA. The study further indicates that an energy reduction of 50% at a given WRV or tensile index may be achieved if the fibres are converted to Na +-form prior to pilot-scale refining. By applying these techniques in full-scale production, it should thus be possible to save significant amount of energy, especially in the case of papers made from unbleached pulp that usually demands a higher degree of beating to achieve sufficient strength.
Holzforschung, 2004
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A partial cationization of cellulosic pulps has been suggested to enhance the retention of fillers and fines in the paper and board manufacturing industry. The challenge is the highly crystalline structure of cellulose and the mass transfer limitations of softwood fibers, which are long and resistant to and hinder the chemical reactions. In the present paper, it was demonstrated that refining (leading to decrystallization) and alkaline treatments facilitate the subsequent cationization process with quaternary ammonium groups. Cationization was performed with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) at 120°C for 2 h, and degrees of substitution above 0.3 were achieved. Beating to 4000 or 4500 PFI revolutions was found to be an optimum to achieve these high degrees of substitution. Mixing a small percentage (4%) of cationized pulp (with a charge density of approximately 0.8 meq g−1) with the untreated pulp could compensate for the negative surface charge of the orig...
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The requirement for high quality pulps which are widely used in paper industries has increased the demand for pulp refining (beating) process. Pulp refining is a promising approach to improve the pulp quality by changing the fiber characteristics. The diversity of research on the effect of refining on fiber properties which is due to the different pulp sources, pulp consistency and refining equipment has interested us to provide a review on the studies over the last decade. In this article, the influence of pulp refining on structural properties i.e., fibrillations, fine formation, fiber length, fiber curl, crystallinity and distribution of surface chemical compositions is reviewed. The effect of pulp refining on electrokinetic properties of fiber e.g., surface and total charges of pulps is discussed. In addition, an overview of different refining theories, refiners as well as some tests for assessing the pulp refining is presented.
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This article presents the impact of a degree of polymerization on the papermaking potential of paper. Bleached pinewood kraft pulp from one of paper mills was used for research purposes. The main objective of this work was to investigate the influence of a degree of polymerisation of pulp on the properties of fibres such as water retention value (WRV) and the fines content etc. Different degrees of polymerization were obtained as a result of the pulp drying at different temperatures (105 ̊C, 130 ̊C and 150 ̊C) for a period from 1 hour up to 150 hours. During the drying process, a visible decrease in a degree of polymerization of cellulose in hornified fibres occurs. Significant differences in pulp properties can be observed in particular in case of pulps dried at a very high temperature (150°C) and in case of a long drying time (150 h).
Holzforschung, 2000
The influence of alkaline peroxide treatment has been characterized on elementally chlorine-free (ECF) bleached softwood (SW) kraft pulp. The results indicate that fiber charge increased with an increase in peroxide charge: a maximum fiber charge increment of 16.6% was obtained with 8.0% more peroxide charge on oven-dried (0.d.) pulp at 60.0°C. Two primary bleaching temperatures of 60.0°C and 90.0°C were investigated during peroxide treatment. Copper number decreased for peroxide charges of 0.5% and 1 .O% at 60.0°C and 90.0°C, respectively, then increased with increasing peroxide charge. Both fiber charge and copper number approached constant values when 4.0% or higher peroxide charge was applied. Peroxide treatment on a bleached kraft pulp at 90.0eC resulted in lower fiber charge and lower intrinsic viscosity compared to treatment at 60.0°C. Sodium borohydride (NaBHJ pretreatment was able to protect the fibers from being degraded during peroxide bleaching. Fiber charge and copper number were compared after peroxide treatment of ECF bleached kraft pulp to NaBH,-reduced ECF bleached kraft pulp. The results indicate that the carbonyl group content of fibers is favorable for improving fiber charge after peroxide treatment.
Bulk and surface characterization of unbleached and bleached softwood kraft pulp fibres
Cellulose Chemistry and Technology, 2008
The main difficulties in wood and pulp fibre characterization arise from the numerous components of the different chemical structures. The processing of wood determines some structural modifications in its components, depending on the wood type and on the applied procedure. In-bulk and surface methods (ATR-FT-IR, XPS, SEM, XRD, DSC, TG) have been applied to analyze unbleached and bleached softwood kraft pulp fibres, and the differences between the samples have been established. The bands corresponding to the allomorph phases I and I in cellulose were identified in softwood kraft pulp fibres. The crystallinity degree was determined from the absorbance FT-IR ratio (1280/1200) and XRD data. The increase in the apparent crystal size (ACS) and crystallinity index of the cellulosic fibres, determined after bleaching by XRD, evidenced a lower number of small crystallites, which improved fibre crystallinity, a reaction which was also due to the removal of amorphous hemicelluloses and lignin during bleaching. The differences between unbleached and bleached softwood kraft pulp fibres referred to characteristic temperatures and mass losses during various thermogravimetric steps, lower overall activation energies being recorded in the first step and higher, respectively, in the other two steps of the bleached softwood kraft pulp fibres, comparatively with the values registered in unbleached pulps. The ATR-FT-IR and XPS results supported the idea that the amount of oxygen atoms was higher on the surface of the bleached kraft pulp fibres than on that of the unbleached kraft pulp ones. The decrease in the O/C ratio and the increase in the C ox /C unox suggest the removal of the carbon-containing compounds from the pulp fibre surfaces after bleaching. The unbleached material was quite heterogeneous, with intact individual fibres, while, after bleaching, the surface of the individual fibres changed, becoming smooth. It was also observed that cellulose aggregates were running in fibre direction and that, after bleaching, the diameter of the cellulose fibres was smaller.
On the importance of oxidizable structures in bleached kraft pulps
After cooking, kraft pulps always contain not only residual lignin but also significant amounts of hexenuronic acid and other non-lignin structures oxidizable by permanganate under the standard kappa number determination conditions. These here referred to as false lignin. Like ordinary lignin, the false lignin also consumes bleaching chemicals, thus increasing both the production costs and the environmental impact of bleach plant effluents. The false lignin also has an effect on pulp properties such as brightness stability. This necessitates the development of efficient experimental routines for the determination of false lignin in different types of unbleached and bleached kraft pulps, together with studies of its formation, chemical behaviour, and ultimate fate.
Determination of fiber charge components of Lo-Solids unbleached kraft pulps
Journal of Colloid and Interface Science, 2004
Four different titration methods for measurement of fiber charge were used in this study. Each method gave different fiber charge values depending on the acidity of the end point and the interaction between the fiber chemical components and the titrant. Also, the interactions between the ionizable groups on the fiber had significant effects on the interpretation of these results. The conductometric titrations showed trends similar to the results obtained from the potentiometric titration. The conductometric titrations with NaOH produced higher fiber charge values, higher than the titrations with NaHCO 3 . The differences between the results obtained from the potentiometric and polyelectrolyte titrations, which were associated with the dissolved fiber components during the delignification, were linearly related to the Kappa number of pulps. The positive intercept of this linear relationship indicated that the kraft pulping process not only removed the ionizable groups associated with the dissolved components, but at the same time provided conditions to form new ionizable groups in the fibers. The polyelectrolyte titration results indicated that the lignin content in the fibers did not affect the fiber surface charge. Data extracted from the FTIR spectra of protonated fibers were highly correlated with the fiber charge values obtained from the conductometric titration with NaOH. 2004 Elsevier Inc. All rights reserved.
Cellulose, 2020
Reactivity of dissolving pulp is one of the main parameters to determine its availability to be transformed into viscose. It is related to the use of carbon disulphide (CS2). An industrial sequential totally chlorine free bleaching process is used as case study. It is carried out in two stages: 1) Alkaline extraction (EOP) and 2) peroxide bleaching (PO). In order to assess how to decrease the use of carbon disulphide, several experiments were performed at laboratory scale for the two stages mentioned before by modifying the operating conditions: NaOH and H2O2 dosages, time and temperature. Reactivity using a modified Fock's method and pentosan content was analysed along with quality pulp parameters: α-cellulose, viscosity and lignin content (kappa number). Results showed that reactivity increases through the bleaching process and varies with the chemical dosage in both stages. Pulp obtained at the best conditions had the following characteristics: reactivity, 95.3 %; α-cellulose 91.17 %; intrinsic viscosity, 448 mL/g; kappa number, 1.81 and pentosan content 2.86 %, and as a result, CS2 usage was reduced by 11.88 %. At the best conditions obtained in this work, NaOH dosage in PO stage was reduced to zero and temperature was slightly lower, when compared with industrial operating conditions.