Softwood kraft pulp fines: application and impact on specific refining energy and strength properties

Abstract

Along with the emergence of micro and nanofibrillated celluloses and their application in papermaking, the influence of the so called fines fraction of pulps on both process and product properties has received increasing research interest in recent years. Several researchers have experimented with primary and/or secondary pulp fines to assess their effects on paper properties with not always consistent results. Our work focuses on the targeted application of the primary fines fraction of an unbleached softwood kraft pulp. The primary fines are separated from the pulp to be subsequently added to achieve blends of $$5\%, 9\%$$ 5 % , 9 % and $$12\%$$ 12 % primary fines content. These blends were then refined in a PFI mill to evaluate the effect of the primary fines on refining as well as on paper properties of hand sheets prepared from these pulps. It is shown that the addition of primary fines enhances tensile strength in the unrefined and slightly refined state, while the maximum tensile strength of the highly refined reference pulp is not increased. A slightly increased dewatering resistance (Schopper Riegler) at comparable air permeability (Gurley) for a given tensile strength was also observed. The linear relationship between tensile index and apparent sheet density seems to be affected in the unrefined and slightly refined state where the breaking length of the fines enriched samples is higher for a given apparent density.

Understanding polyamidoamine epichlorohydrin (PAAE) retention in paper

“…Lower press solids result in increased drying demand, which results in speed reductions for dryer limited machines. Another reason that the papermaker avoids excessive refining is that the process severely shortens, curls, and cracks the fiber (Gharehkhani et al 2015;Mandlez et al 2020). In this study the fiber length was reduced by 31% from 531 to 280 mL freeness (Table 3).…”

“…The fines increased from 4.24% to 15.0% as the freeness decreased. The refining process is known to generate fines, shorten the average fiber length, and lead to a more negative surface charge (Bhardwaj et al 2007;Banavath et al 2011;Gharehkhani et al 2015;Mandlez et al 2020).…”

“…Fiber modification usually promotes high tensile strength and smoothness of the sheet. In addition, the refiner modifies the freeness of the pulp, generates fines, affects fiber length, and more importantly changes the surface charge of the fibers (Ntifafa 2021;Bhardwaj et al 2007;Banavath et al 2011;Gharehkhani et al 2015;Mandlez et al 2020).…”

Polyamidoamine epichlorohydrin (PAAE) wet-strength agent: Generations, application, performance, and recyclability in paperboard and linerboard

“…The addition of carboxymethyl cellulose (CMC) enhances the amount of the carboxylic groups in the pulp, which in turn improves the retention of the wet strength resin. With the multilayering approach, opposite charged polyelectrolytes are adsorbed onto the fiber surface, which in turn favors large amount of PAE retention (Smith 1992;Hawes and Doshi 1986;Lindström et al 2005;Sandberg and Andreasson 2004;Gharehkhani et al 2015;Fischer et al 2017;Mandlez et al 2020). In addition, oxidizing the fiber or oxygen delignifying the fiber will increase the availability of carboxylic groups, which will enhance the formation of PAAE-fiber bonding (Hirosawa et al 2001;Dang 2007;Xu et al 2022).…”