Adsorption of polysaccharide wet-end additives in papermaking systems

Abstract

The adsorption of polysaccharide guar gum and starch additives and their interactions with cellulosic fiber and fines, as well as soluble and colloidal carbohydrates, present in wood pulp suspensions were investigated by employing HPLC and spectrophotometry. A unique phenomenon, i.e. carbohydrate uptake or ‘substraction’, was observed to occur in a variety of cellulosic systems [whole pulp, washed/screened pulp, alkali-extracted pulp, fines suspension and microcrystalline cellulose (MCC)] upon addition of uncharged and cationic polysaccharides. The adsorption and aggregation behaviors which take place in aqueous pulp suspensions are not only affected by the surface physicochemical characteristics of the cellulosic substrates but are also strongly influenced by the nature (charge type and degree of substitution) of the polymeric additives. It is evident that there is a complexation or aggregation of soluble and colloidal carbohydrates with the polysaccharide molecules that are then adsorbed on fines and/or retained on cellulosic fibers upon addition of the polysaccharides at very low dosages corresponding to those used in industrial practice. This correlates to the maximum fines retention, drainage and paper strength observed in industrial applications. The interactions that can take place among the various cellulosic components of pulp suspensions and polysaccharide additives are discussed in order to provide a better understanding of the intricate phenomena that occur in the wet end of paper manufacturing systems.