Using cationic polyvinyl alcohol (C-PVA) to improve the strength of wood-free papers containing high-yield pulp (HYP).

High-yield pulp (HYP) is gaining increasing interest in wood-free papers, because it can improve the bulk, formation, and opacity of papers. However, one of the challenges for the papermakers is the strength of papers when a large amount of HYP is replaced with hardwood kraft pulp. In this work, we explored the potential of using cationic-modified polyvinyl alcohol (C-PVA) in increasing the strength properties of HYP. Also, C-PVA was applied to the paper-sheets made of softwood/hardwood bleached kraft pulps (SBKP/HBKP) and HYP under various conditions, and the corresponding paper properties were evaluated. It was observed that C-PVA increased the strength properties of these paper-sheets, and the results obtained from using C-PVA were only slightly less effective than those obtained from using cationic starch (C-starch). Furthermore, the addition of C-PVA to HYP, and subsequently mixing with the blend of SBKP/HBKP (option no. 1) improved the tensile and burst indices, light scattering coefficient and apparent density of paper-sheets more significantly than did the addition of C-PVA directly to the mixed furnish of SBKP/HBKP/HYP (option no. 2). Additionally, atomic force microscope (AFM) analysis showed that the attraction force, developed between the AFM-tip and the fiber surface, was changed by the C-PVA modification. The tensile and burst indices of paper-sheets were improved by adding 10 mg g-1 C-PVA and substituting 30% of HYP for HBKP, whereas the tear index, apparent density, PPS-roughness, and brightness decreased. [ABSTRACT FROM AUTHOR]