Novel blend of biorenewable wet-end paper agents

Abstract

Recent studies have shown potential for a designed biorefinery product, polylactic acid (PLA), to increase the strength-to-weight ratio of paper produced from conventional kraft pulp and kraft pulp made from hot-water extracted hardwoods (biorefinery pulp). These results indicated that, after surface-treatment with 2 % PLA (per ovendry [o.d.] fiber basis), paper made from sugar maple biorefinery pulp could be equivalent to or even greater in strength than paper made from sugar maple conventional kraft pulp, while retaining its higher bulk. In the current study, we present the results of reinforcement of the pulps with PLA applied in the wet-end in combination with a known environmentally friendly dry strength agent, cationic starch. The preliminary results obtained with amylopectin-based starch of relatively high nitrogen content (starch B) were encouraging since strength, including wet strength and stretch, of paper reinforced with a blend of 0.5% starch B and 0.5% PLA was higher than strength of paper reinforced with 1% starch B. Moreover, based on the compatible strengths of paper reinforced with 0.6 % PLA-starch B blend (1/5) and of paper reinforced with 1% starch B, we hypothesize that there is a synergistic effect of PLA and starch B on tensile strength of paper. The hypothesis was tested using pulps of different lignin content (Norway spruce thermomechanical pulp [TMP], hardwood unbleached kraft pulp, and softwood bleached kraft pulp). Tensile strength increased for papers made from these pulps. The effect was pronounced in the case of lignin-rich pulps, where tensile strength in the presence of 0.6% PLA-starch blend (1/5) exceeded that in the presence of 1% starch B. This result is in accordance with a higher attraction of lignin-rich fibers to hydrophobic PLA and indicates a promising approach in increasing strength-to-weight ratio of paper made from relatively hydrophobic pulps like TMP or unbleached kraft pulp. Accordingly, paper made from unbleached hardwood kraft pulp with 0.6% PLA-starch B blend (1/5) exhibited an improved resistance to water penetration.