Dual-adsorption of poly(allylamine hydrochloride) and lignosulfonate onto recycled cellulosic fibers

The effects of the dual-polyelectrolyte adsorption of poly(allylamine hydrochloride) (PAH) and lignosulfonate (LS) on a recycled unbleached softwood kraft pulp were studied and the method used for the determination of LS concentration was discussed. Adsorption isotherms of LS on untreated and on previously PAH-treated pulps at neutral pH, and different ionic strengths were built, and the effects of the amount of PAH on LS adsorption were considered. It was found that even at low dosages of PAH, for which fibers remain anionic, high levels of LS adsorption at room temperature and short adsorption time can be achieved. Besides, it was found that the increase in ionic strength also increased the amount of LS adsorbed. The highest values on papermaking properties were obtained using only PAH. Nevertheless, when compared to the reference pulp, the PAH/LS system clearly improved the wet tensile strength and the compressive strength, avoiding paper non-uniformity or charge-reversal problems