Internal treatment of paper sheets from wood and bagasse pulps with polyvinyl alcohol

Mechanical strength and optical properties of paper sheets prepared from polyvinyl alcohol (PVA)-treated wood and bagasse pulps were investigated. The effects of the percentage of added PVA, the amount and type of polymer precipitant, and the manner of polymer addition (before or after the beating stage) on the properties of prepared sheets were presented. Studies were also carried out to compare the properties of loaded paper sheets produced from PVA-treated pulp and fillers (kaolin, TiO2, talc, and CaCO3), with those produced from conventional rosin-alum-filler loaded paper sheets. The obtained results show that 4% PVA (based on pulp) and 100% borax (based on polymer) were the optimum additives required to attain the maximum improvement in the strength properties of the paper sheets obtained from both pulps. It was found that the pH value of the pulp slurry has a profound effect on the filler retention and strength properties of produced sheets, whereas it has a weak effect on the optical properties of sheets. The optimum strength properties were noticed at pH 7.0. Also, the addition of PVA was more efficient for improving the strength and optical properties of paper sheets loaded with a high percentage of filler, especially kaolin, compared with conventional rosin-alum addition. However, the reverse trend was noticed in the case of the oil resistance property for all paper samples under investigation, except the case of paper sheets made from 4% PVA addition to bagasse pulp, as the beating additive, whereas its oil resistance property was nearly the same as the case of rosin addition.