Appl. Sci. 2025 , 15 , 9160
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paper. However, the magnitude and outcome of these effects are highly dependent on the pulp source. Softwood kraft pulp (SwBKP) and hardwood kraft pulp (HwBKP), two widely used industrial pulps, differ markedly in fiber length, coarseness, and structure, which in turn shape their responses to mechanical treatment. Softwood fibers tend to impart strength and durability, while hardwood fibers improve surface smoothness and printability [2,5]. Previous studies have examined the effects of mechanical treatment on different pulp types. For instance, it has been reported that increased refining intensity improves the tensile strength of softwood pulp but at the cost of higher energy consumption [6,7]. In contrast, hardwood pulp requires less energy to achieve comparable levels of fibrillation, highlighting differences in refining efficiency between pulp types [8,9]. Some research on mixed pulp stocks has demonstrated that optimal mixing ratios can enhance both the strength and smoothness of paper products [10,11]. However, these studies also note the complexity of mechanical treatment effects on mixed pulps, which are influenced by factors such as fiber morphology and treatment intensity. The Valley beater, a laboratory-scale adaptation of the Hollander beater, is widely used for its ability to simulate industrial refining processes with high precision and control. It consists of a cylindrical roll fitted with metal bars or knives and a movable bedplate, which together apply shear, compression, and bending forces to pulp fibers, resulting in effective fibrillation and fiber shortening [3,5]. This equipment is particularly valuable for research and development due to its reproducibility and controllability. In contrast, industrial refiners—such as disc and conical refiners—are essential for large-scale papermaking due to their efficiency and scalability [1]. Disc refiners, which include single, twin, and double-disc configurations, use rotating discs with bars and grooves to impart mechanical forces to the pulp [5]. Conical refiners operate similarly but utilize a conical rotor and stator. Recent advancements in refiner technology have focused on improving energy efficiency and refining performance. For example, the development of a lightweight refiner plate for hardwood kraft pulp, resulting in enhanced refining efficiency and reduced energy consumption [11,12]. Similarly, the introduction of a novel lightweight vertical bar plate for softwood pulp further improves refining performance and contributes to energy savings [13]. In this study, an ultra-fine bar plate equipped with closely spaced, narrow bars was employed in the disc refiner to provide precise and controlled mechanical treatment. This design maximizes fiber-to-fiber contact while minimizing excessive cutting, promoting effective fibrillation and fiber bonding. The ultra-fine bar plate’s refined bar pattern allows for intensified refining intensity at low energy consumption, making it highly suitable for optimizing pulp properties in both softwood and hardwood kraft pulps. Combining softwood and hardwood pulps in various proportions is a common indus- trial practice to balance paper strength and quality [2]. However, the effects of beating and refining on mixed pulp stocks are complex and can be influenced by fiber morphology, re- fining intensity, and the specific equipment used [14,15]. Understanding these comparative effects is crucial for optimizing paper properties while minimizing energy consumption and production costs. This study aims to compare the effects of Valley beating and ultra-fine bar refining on softwood and hardwood kraft pulps, both individually and in mixed stocks. By analyzing changes in fiber morphology, paper strength, and related properties, this research seeks to identify optimal treatment conditions for achieving desired paper qualities. Addition- ally, the study will assess the energy implications of each process, providing insights for enhancing the sustainability of pulp and paper production. By elucidating the interplay between pulp type, mechanical treatment, and paper properties, this research contributes to a deeper understanding of the papermaking process. The findings are expected to
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