Abstract
Non-fibrous materials used in papermaking are considered under the headings of colloids (positive or negative, hydrophilic or hydrophobic), surfactants (cationic, anionic or non-ionic), electrolytes and other non-polymeric materials. Their effects on flocculation of fibres are discussed in terms of entanglement, bridging and electrokinetic theories of fibre interaction. Various methods of measuring the heterogeneity of pulp suspensions and papersheets are reviewed and it is concluded that the beta-ray scanning method offers several advantages for paper studies. In this work, the heterogeneity of handsheets made from short-fibred and long-fibred pulps has been determined with a beta-ray scanner (Pm14’7 source). The experimental results showed that flocculation was more pronounced in the long-fibred pulps, but that the reduction in paper strength with increasing heterogeneity is greater in the short-fibred paper. Scanning across the handsheet diameter revealed that in some sheets the observed heterogeneity is partly due to systematic variation. In the study of electrokinetic properties of fibre/water interfaces, two parameters-zeta-potential and ionic charge density in the double layer-have been evaluated for alum-treated and polyamide-treated pulps. The results indicate that the variation in zeta-potential with additive concentration is primarily related to charge on the fibre surface for the polyamide-treated pulps and to electrolyte concentration for the alum-treated pulps. The effect of nonfibrous materials on consolidation is considered in terms of surface tension, fibre collapse and hydrogen bonding. Preliminary work on the erect of cationic starch on fibre strength is reported and a method of obtaining lateral load/compression curves of single fibres is described. The curves can be compared to those observed with tubes of differing wall thickness and elastic modulus. Experiments on the effect of modified starches and starch fractions on inter fibre bonding are also described; these lead to the conclusion that the bonding efficiency depends on the state of dispersion of the colloid, the internal cohesion of the dried colloid film and the adhesion at the colloid/fibre interface.
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