Paper and Surface Chemistry – Part 1-Fiber Surface and Wet End Chemistry

Abstract

Paper manufacturing and converting involves a multitude of surface chemical interactions. Beating, stock preparation, coating and converting processes are steps where surface phenomena play an important role for product consolidation and performance. Interactions between fibers and colloidal particles, polymers, minerals and, dyes are fundamental in papermaking and most of them are complex and not very well understood. Thus, many paper formulations are designed according to an empirical trial-and-error approach. This work is a critical literature review of some of the interactions present in papermaking, coating, and printing. In the first part, the current models for fiber surfaces and their interactions in the wet end are discussed. Limitations concerning the fiber surface definition and the available models based on direct observation, DLVO theory, and a combination of qualitative and quantitative approaches are highlighted. Complexity factors such as surface composition heterogeneity, contamination from manufacturing processes, and surface mobility are suggested to be considered. Surface interactions present in the wet end, with focus on reversible and irreversible flocculation as well as on the flocculation mechanisms concerning fibers, polymers and micro-particles are also discussed. The role of the fiber surface chemical composition on flocculation and flock size and the influence from the chemical medium in the paper machine is reviewed. Papermaking is suggested as being a fiber surface modification process once polymers and other chemicals are used to change the surface energy and chemical composition. Modification by formation of cellulose esters or attachment of aluminum abietate onto surface anionic groups is believed to occur during sizing. Modification which affects the fiber-fiber bond with the aim of improving the wet and dry strength properties is also discussed. Accessibility of anionic groups in pulp fibers to the chemicals during the short time scale of papermaking process as well as competition for the same charged sites are still not clear and its implications are reviewed. Comments are made on the limitations regarding the present process monitoring using measurements with no specificity. A combination of different sorption and chemical microscopy methods is suggested as a suitable approach to clarify surface interactions. Why does a paper formulation need such a number of additives? Where are they attached on the fiber? Questions of this nature are challenges not only in the scientific point of view, but also to market perspectives, demanding critical research work. Another idea presented in this review is the application of surface engineering to pulp fibers. Surface engineering is a concept traditionally applied to development of coating for metals and its main goal is the modification of material surfaces in order to achieve desired properties. This concept has a good potential for eucalyptus based pulp and paper, especially for improving strength and absorbing properties. The strategic application of surface chemistry in the pulp and paper industry can also be a useful tool, not only for patents and product development, but also to improve troubleshooting and customer support.

Keywords: Papermaking, pulp fibre, surface chemistry, flocculation, surface engineering