بهبود خواص مقاومت خشک و تر خمیر کارتن کنگره ای کهنه بازیافتی با استفاده از پلیمر های مختلف Improving wet and dry strength properties of recycled old corrugated carton (OCC) pulp using various polymers

۱٫ Introduction In recent years, the availability of wood-based pulps has been of great concern. Extensive research has focused on exploring a suitable substitute for conventional forest based materials used in papermaking manufactures (Fatehi, Tutus, & Xiao, 2009). Among the possible alternatives, the development of pulp and paper using recycled paper is currently at the center of attention (Ghasemian, Ghaffari, & Ashori, 2012). Today, the application of waste paper is steadily increasing inthe world,due to the environmental concerns, population growth and the shortage of wood supply. Old corrugated carton (OCC) paper is the most significant category of waste papers for recycling, based on the percentage of recovery rate and by tonnage (Ashori & Nourbakhsh, 2008). However, by increasing the number of cycles in the fiber recycling, the strength of papers is gradually reduced, which is mainly due to the decrease in the fiber bonding strength through the hornification phenomenon (Hamzeh, Najafi, Hubbe, Salehi, & Firouzabadi, 2012). It has been claimed that the strength of such recycled fibers is not sufficient to meet the industry’s demand; thus, the strength should be improved. One approach to improve the strength of recycled fibers is to use dry strength additives. They are usually water soluble, hydrophilic, natural or synthetic polymers. The most common chemicals used commercially are cationic starch (CS) and polyvinyl alcohol (PVA). Dry-strength polymers can interact with fibers in a number of ways. In order of increasing bond strength, these interactions are generally termed as van der Waals forces, hydrogen bonding, ionic attractions and covalent bond formation. The majority of paper strength additives function on the first two of these energy levels, relying primarily on multiple hydrogen bond formation for their retention and effectiveness. Starch, for example, which has sufficient molecular size to span inter-fiber distances and also has a proclivity for forming hydrogen bonds with cellulosic materials, clearly functions by increasing the number of low energy bonds betweenfibers.Inorder to gaingood retentionand improve the efficiency of starch utilization on papermaking fibers, cationic starch was developed (Malton, Kuys, Parker, & Vanderhoek, 1997), which promotes strong adsorption onto fibers, fines and fillers through electrostatic attraction to the anionic groups on the surface of the fibers and particles. Controlled penetration, high binding strength, and reduced effluent loads are important benefits that are often derived from the use of cationic starch (Glittenberg & Becker, 1998). Poly (vinyl alcohol) (PVA), which is one of the most dominant polymers, has several applications in papermaking processes. PVA is widely recognized as one of the strongest binders available in the paper industry, and depending on its molecular weight, can be 3–۴ times stronger than starch (Fatehi et al., 2009). Due to the presence of hydroxyl groups in every repeating unit of PVA, it appears to be one ofthe best polymers to reinforce cellulose fibers (Pelton, 2004). In addition, it has excellent film forming potential (Lertsutthiwong, Nazhad, Chandrkrachang, & Stevens, 2004). PVA can tie down the fines and help bind filler particles to the fiber, both of which are advantageous in printing papers. In papermaking, PVA is used for surface sizing to form films with very high tensile strength and high degree of transparency, flexibility and oil resistance (Briscoe & Luckham, 2000). PVA can also be mixed with starch and applied at a size press (Zakrajsek, ˇ ۲۰۰۸). In papermaking, chitosan has been found to be effective as dry and wet strength agent(Laleg & Pikulik Ivan, 1991; Lertsutthiwong, Chandrkrachang, Nazhad, & Stevens, 2002; Ashori, Jalaluddin,Wan, Zin, & Mohd Nor, 2006) as well as in coating (Kjellgren, Gällstedt, Engström, & Järnström, 2006), sizing (Laleg & Pikulik Ivan, 1992; Lertsutthiwong et al., 2004; Ashori, Raverty, Vanderhoek, & Ward, 2008), and retention (Li, Du, & Xu, 2004a). Chitosan, a biodegradable, nontoxic, antibacterial, as well as renewable resource, is the second most widespread natural polysaccharide (Li, Du, Xu, Zhan, & Kennedy, 2004b). It is the acid-soluble deacetylated derivative of chitin, prepared by reacting chitin with an aqueous hydroxide solution (Fig. 1a and b). Chitin and chitosan belong to a very interesting family of -(1–۴) linked polysaccharides. This kind of glycosidic linkage leads to relatively extended and rigid structures in the solid stage, particularly in the dry state (Kumar & Majet, 2000). The primary structure of chitosan is similar to cellulose except that the C-2-hydroxyl group of cellulose is replaced by an amino group (Laleg & Pikulik Ivan, 1993). Chitosan is insoluble in water under alkaline conditions, but because of its primary amino groups it is soluble in acidified water (Fig. 1c). The first and important goal of the paper production is to make a product with the customer demanded quality specifications as economically as possible. This requires a good runability of paper machine thatis oftenevaluated by thenumber of web breaks inproportion to production speed. Mostfrequently,the paper web breaks occur after couch roll when weak wet web is transferred unsupported between two machine parts in a so-called “open draw”. Wet web strength can be developed by increasing the fine and long fiber proportion in furnish, pulp refining, and solid content of sheet (Ferreira & Guimarães, 2003). Despite the significant effect of wet-web strength of runability of paper machine, in the past very few attempts have been made to increases the wet-web strength (WWS) of paper by chemical additives (Laleg & Pikulik Ivan, 1991, 1992). The improvement of wet paper web strength, and consequently enhancing paper machine runability through the various chemical additives, has received a great attention in recent years both from academics and papermakers (Tejado, Miro, & van de Ven, 2011; Kataja-aho, Haavisto, Asikainen, Hyvärinen, & Vuoti, 2011). In this work, different dosages of chitosan, PVA, and cationic starch were individually added to the OCC furnish and the handsheet properties in terms of dry and wet tensile and stretch properties were investigated. In addition, various sequences of combination of polymeric additives were examined to find the optimal combination for improving both wet and dry strength.