Problem definition and objectives: Among high-yield pulps, chemimechanical pulp (CMP) from hardwoods is widely used in the production of printing and writing papers. However, the low optical and mechanical properties of papers derived from CMP remain a major challenge for its industrial application. In this study, the optimal conditions for the application of nanocellulose, nano chitosan, optical brightening agent (OBA), and cationic polyacrylamide were investigated to improve these properties. The main objective was to achieve desirable optical and mechanical characteristics in CMP-based papers. To this end, linear analysis and evaluation of the interactive effects of the variables were employed. The findings of this study provide a scientific basis for improving the papermaking process and enhancing the quality of CMP-based papers in the paper industry.
Methodology: In this study, bleached CMP pulp was used to improve the optical and mechanical properties of paper. nano chitosan, (0.1 and 2%), cationic polyacrylamide (0, 0.5, and 1%), and optical brightening agent (OBA) (0, 0.5, and 1%) based on the dry weight of pulp were added to the pulp suspension. Experimental design was carried out using the Box–Behnken method, and response surface modeling (RSM) was performed with Design Expert V13 software. A total of 15 experiments were designed, considering nano chitosan, polyacrylamide, and OBA as independent variables, while the optical and mechanical properties of the paper were regarded as dependent variables. Laboratory handsheets with a basis weight of 60 g/m² were prepared and their properties were measured. The data were analyzed using analysis of variance (ANOVA) and response surface methodology. The results led to the development of a mathematical process model and the determination of optimal additive conditions to achieve the highest quality of optical and mechanical properties in the paper.
Results: The analysis of variance (ANOVA) indicated that the quadratic model exhibited the best fit to the experimental data (R2=91.66), demonstrating its high accuracy and predictive capability. The results showed that the independent variables, nano chitosan and OBA, had statistically significant effects on enhancing the properties of the hand sheets. In contrast, the addition of polyacrylamide did not have a statistically significant impact on the optimal paper properties. For nano chitosan, increasing its concentration up to 1% improved the optimal properties of the paper. However, concentrations exceeding 1% led to a decline in these properties. Similarly, increasing the OBA concentration up to 0.75% resulted in a significant enhancement of the paper's properties. Beyond this level, further increases (up to 1%) caused a slight reduction in optimal properties. OBA was identified as the most influential factor in improving the response variables. These findings underscore the critical role of precise optimization of nano chitosan and OBA concentrations to achieve the highest optical and mechanical quality in the hand sheets.
Conclusion: This study aimed to investigate and optimize the effects of nano chitosan, optical brightening agent (OBA), and cationic polyacrylamide on the optical and mechanical properties of bleached CMP pulp using response surface methodology (RSM). The results indicated that OBA had the greatest positive effect, while cationic polyacrylamide showed the least impact on improving paper properties. The optimal conditions were identified as 1.21% nano chitosan, 1% OBA, and 0.2% cationic polyacrylamide, which maximized the combined index of optical and mechanical properties (1.04). Accordingly, these findings provide a practical strategy for enhancing the quality of CMP-based papers and overcoming the limitations associated with their application in the paper industry.