Comparison of the effect of mixing unbleached Kraft pulp from date palm rachis and empty fruit bunch in improving the quality of recycled old corrugated containers (OCC) pulp

Background and Objectives: Enhancing the use of recycled paper in the production of liner and corrugated paper is a vital strategy within the papermaking industry, driven by both economic and environmental considerations. Over time, recycled fibers tend to lose their strength due to repeated use. Consequently, some studies have explored the effects of incorporating virgin fibers into the recycled fiber mixture to improve the strength and quality of the resulting paper. Due to restrictions on the use of virgin forest fibers and the implementation of environmental policies, the pulp and paper industries have increasingly turned to non-wood plant fibers and agricultural lignocellulosic waste as sustainable and cost-effective resources. This study investigates the effects of incorporating varying percentages of virgin fibers derived from two types of lignocellulosic waste from date palms—rachis (R) and empty fruit bunch (E)—into the pulp obtained from recycled old corrugated containers (OCC). The research evaluates and compares the impact of this addition on the quality of the produced paper, ultimately highlighting the usability of these two types of waste.
Materials and methods: Date palm lignocellulosic wastes (R) and (E) were collected from plantations located in Dashtestan, Bushehr Province, Iran. The wastes were air-dried, crushed, and separately pulped using the kraft process under an effective alkali charge of 20%, sulfidity of 25%, and a cooking temperature of 165 °C. The cooking durations were set at 120 min for rachis and 20 min for empty fruit bunch. The resulting unbleached kraft pulps were characterized by determining kappa number, yield, and freeness. OCC pulp was obtained from Golestan Persia Paper Mill (Gorgan, Iran). Each type of virgin pulp derived from date palm wastes (R) and (E) was separately blended with the OCC pulp at substitution levels of 10%, 20%, 30%, 40%, and 50%. Standard laboratory handsheets with a grammage of 120 g/m² were prepared from these mixed pulps in accordance with TAPPI standard procedures. The physical, mechanical, optical, and barrier properties of the produced papers were evaluated according to TAPPI standard methods using the available instruments in the Pulp and Paper Laboratory of Gorgan University of Agricultural Sciences and Natural Resources.
Results: Blending unbleached kraft pulps derived from date palm lignocellulosic wastes (R) and (E) with recycled OCC pulp significantly enhanced the physical and mechanical properties of the resulting papers. Increasing the proportion of virgin pulp in the furnish resulted in significant improvements in tensile and burst indices, as well as ring crush (RCT) and folding endurance. Overall, the papers incorporating virgin pulp from (E) demonstrated superior performance compared with those containing (R) pulp. An increase in sheet density and a decrease in air permeability were also observed in samples containing virgin pulp, indicating the formation of denser and more cohesive paper structures. In contrast, a reduction in brightness was detected in treatments containing virgin pulp, which can be attributed to the presence of residual lignin in the unbleached pulps. Moreover, the tear index showed lower sensitivity to pulp composition than the other properties, which is likely due to the direct influence of fiber length and the uniform refining conditions among the treatments.
Conclusion: Despite its environmental and economic advantages, the paper recycling process presents challenges such as diminished fiber quality and lower durability of the final product. In many regions, abundant lignocellulosic waste from date palms particularly (R) and (E) is often disposed of or incinerated without full utilization, leading to notable environmental repercussions. The findings of this study indicate that incorporating unbleached kraft pulp derived from these lignocellulosic wastes, especially (E) into the recycled pulp composition significantly enhances the physical and mechanical properties of recycled paper.