Influence of rosin resin acids amides on the strength of interfiber bonds in paper in the z-direction

Resin acid amides of rosin, depending on the structure, can have both a hydrophobizing and hardening effect on paper pulps. It has been established that the developed products of rosin modification (adhesive rosin composition TMAS3N and polyamide resin ProChem DUO) containing amides of resin acids, when introduced into paper pulps made from fibrous suspensions of sulphate cellulose (unbleached and bleached) of coniferous and broad-leaved species and waste paper, different in the degree of grinding (25, 40 and 70 °ShR), contribute to the increase in the strength of interfiber bonds in paper in the z-direction. The effect of the TMAS-3N emulsion was compared with the traditionally used TM and AKD sizing emulsions. The introduction of the TMAS-3N emulsion into paper pulps (0.40 % of a. d. w.) provides the maximum increase in the strength of interfiber bonds in paper in the z-direction made from cellulose, equal to 16.7–88.6 %, and from waste paper – 19.4–75.4 %, which is 1.6–6.4 and 2.3–4.5 times more compared to TM emulsion, respectively. The achieved positive effect is due to the presence in the TMAS-3H emulsion of particles of the dispersed phase of hydroxyethylamides and aminoethyl ethers capable of forming hydrogen bonds with hydroxyl groups on the mating surfaces of cellulose fibers. Sizing paper stocks with AKD emulsion reduces the strength of interfiber bonds in paper in the z-direction over the entire range of paper content studied. Polyamide resin ProChem DUO, which is a polyaminoamide of rosin resin acids, at its content in paper stocks of 0.10 %, increases the strength of interfiber bonds in paper in the z-direction, made from cellulose and waste paper suspensions, by 50.0–92.3 and 44.4–63.5 %, respectively. The obtained results of increasing the strength of interfiber bonds in paper in the z-direction by resin acid amides of rosin are in full agreement with the mechanism of bridged bonds and the theory of hydrogen bonds.