Tensile Modulus of Paper Wet-Stiffened by Crosslinking

Abstract

The mechanism of the wet tensile performance of paper is described in terms of the hydrogen bond theory of paper. Distinctions are made between the action of wet strength agents and the stiffening action of crosslinks. Chemical crosslinks improve the wet stiffness of paper by reducing the moisture sensitivity of the cellulose network to the swelling action of water. Below the fibre saturation point, the effect of water in reducing the tensile modulus of crosslinked paper is quantitatively the same as in uncrosslinked paper. Wet stiffening arises only from the reduction in the fibre saturation point that the crosslinks create. The role of crosslinks as load-carrying elements is not important in wet stiffening. Rather, crosslinks function as swelling restraints to the network, so that a larger fraction of the pre-existing hydrogen bonds function to retain a larger fraction of the paper’s dry tensile modulus. In this respect, even crosslinked paper can be considered a hydrogen-bond-dominated solid.