Pulp and paper
Arman Sadafi Ardejani; Esmaeil Rasooly Garmaroody; Pyam Ghorbannezhad sorkhkolaei
Abstract
Background and purpose: Cellulose fiber has an anionic property to some extent due to having acid groups created during the chemical cooking and pulp bleaching. These acid groups may be carboxylic groups (COOH) which have more activity and reactivity compared to the hydroxyl groups present on the carbohydrates ...
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Background and purpose: Cellulose fiber has an anionic property to some extent due to having acid groups created during the chemical cooking and pulp bleaching. These acid groups may be carboxylic groups (COOH) which have more activity and reactivity compared to the hydroxyl groups present on the carbohydrates of lignocellulosic materials. If it is possible to increase the number of these groups on the fiber surface, it can improve the strength of the final paper. This research was done in order to improve the characteristics of kraft pulp from Chuka pulp and Paper Company by using acid oxidation method with hydrogen peroxide.
Materials and methods: In this research, kraft pulp, which was collected from Chuka Company, was used as a raw material. In this regard, first, kraft pulp were subjected to acid oxidation treatment using hydrogen peroxide the rate of 1, 3, 5 and 10% at 85 °C, in 90 min., pH = 4 and consistency of 2.5%. At the end of this step, the pulps were thoroughly washed with distilled water and used for the next steps. Then the structural characteristics of the fibers such as kappa number, WRV, carboxyl groups, viscosity and FT-IR analysis were evaluated and compared with the control sample of Chuka kraft pulp. SPSS software was used for the statistical analysis of this research and the data were statistically analyzed using the analysis of variance technique. The comparison between different samples and treatments was done based on the grouping of averages and by Duncan's test method at a confidence level of 95%.
Results: The results showed that the oxidized pulps with up to 3% peroxide consumption had the lowest kappa, carboxyl groups and viscosity and the highest WRV. Increasing the consumption of peroxide the rate of greater than 3% has caused an increase in Kappa number, carboxyl groups and viscosity, and instead they have faced with the decrease in WRV. These changes were also confirmed by FT-IR evaluations. The reason for the decrease in kappa number up to 3% concentration is due to the removal of lignin from the fiber wall, and the reason for its increase in concentrations at more than 3% peroxide, is probably due to the creation of acidic hexuronic groups during the oxidation process, which usually cause errors in the measurement of kappa. In addition, the removal of lignin improved the WRV properties of the fibers and further reduced this property. The content of carboxyl groups for both alkaline and acidic conditions seems to be more or less unchanged, which means that in C6, most aldehydes are converted into carboxyl groups, and in C2 and C3, oxidation often causes the formation of ketones. On the other hand, it seems that increasing the carboxyl groups in treatments above 3% has led to an increase in the molecular weight of cellulose, which has increased the viscosity.
Conclusion: The evaluation of the results showed that the oxidation of acidic hydrogen peroxide has modified and improved the characteristics of kraft pulp, and its effects are expected to be positive on the characteristics of the final papers. In this regard, 1% and 3% acid oxidation treatments with hydrogen peroxide seems more suitable for paper production.
