Surface Chemistry of Fibres and Fillers

SURFACE CHEMISTRY OF FIBRES AND FILLERS Surface Chemistry of Fibres 

The surface character of fibres influences their affinity towards various chemical additives by, for example, their adsorption properties and also in their tendency to flocculate. Cellulosic fibres, because of the presence of acidic groups which are introduced during chemical pulping and bleaching, are mildly anionic. These acidic groups may be carboxylic (COOH) or in some cases sulfonic acid (S03H) and they are able to dissociate to leave a net negative 

As pulping progresses, the lignin content decreases and the acid group content also decreases. Lignin is not usually measured directly but by the degree of oxidisability of the pulp using, for example, 

The surface charge of a fibre has an important influence on its interaction with chemicals (both particulate and soluble) which are added to the aqueous fibre suspension. Their anionicity gives them a high affinity towards cationic additives, and many additives are produced in a cationic form in order to maximise their retention. The pH of the aqueous paper-making system is also important in these interactions. The surface charge of cellulose, because it arises from the dissociation of acidic groups, is dependent upon pH (see 

Many inert pigments (often known as fillers) are incorporated into paper in addition to the cellulosic fibres. They may be added to improve certain optical properties—in particular opacity and brightness—or simply as a cheap replacement for costly fibre. The two most common pigments are kaolin (china clay) and chalk (limestone), but talc and speciality pigments such as titanium dioxide are also used. The particle size for general purpose fillers is normally expressed as an equivalent spherical diameter (esd) and this is determined from sedimentation data. Values for the common paper- 

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