Mid Sweden University

The dry tensile strengths of bleached kraft pulp handsheets were measured as functions of the cationic charge density and hydrophobic substituents on 2 million Dalton dextran adsorbed onto the fibers before sheet making. The charge density controlled the maximum amount of dextran that could be adsorbed by the fibers which, in turn, influenced tensile strength. The lower the charge density, the higher were both the dextran adsorption capacity of fibers and the tensile strength of the resulting paper. Butanoic and hexanoic acid when condensed onto dextran gave hydrophobic domains which lowered paper strength linearly with hydrophobic content. An extension to the Page equation gave a semi-empirical model which predicted the major effects of hydrophobic substitution on paper strength.