1993 Volume 2

The impact of fines from various sources on selected physical and mechanical properties of paper has been examined.

In the first of two experiments, the influence of fines was determined by producing two fines free pulps from furnishes which had been refined to 600 ml and 290 ml CSF. Fines removal had a detrimental effect on most properties at a given level of densification including: formation, in-plane and out-of-plane elastic properties, and normal span tensile strength. Densification either by refining, wet pressing, or fines addition resulted in an increase in sheet roughness; this is tentatively attributed to an increase in nonuniform shrinkage in the thickness direction of the sheet. Fines removal gave a more porous sheet particularly at the higher level of refining. Zero span strength or the ultimate strength of the sheet increased with sheet densification, being largely independent of how that densification was produced.

Fines type and addition level were investigated in the second set of experiments. Fines, up to a level of 30%, were added to a fines-free furnish 740ml CSF. Primary fines are those present in an unrefined virgin pulp, and secondary fines are those produced by refining. “Primary” fines are those fines present after repulping recycled paper, and include both primary and secondary fines. “Secondary”fines are the fines generated by refining a fines-free “primary” pulp.

It was inferred, from drainage measurements, that the secondary fines had a greater hydrodynamic surface area and were, therefore, more effective than primary fines in enhancing sheet densification and some properties. Furthermore, “secondary”(H)fines, which had been produced from handsheets which had undergone more extensive wet pressing and drying, were, surprisingly, even more effective than the control fines and “secondary” fines. The behavior of newprint fines from preconsumer waste was similar to that produced by primary fines.

It is clear that fines, defined as material passing a 200 mesh screen, are inadequate to characterize their impact on paper properties. This agrees with the findings of Hawes and Doshi (L6).

NA

Mill-made deinked pulp fibres for news print were compared with virgin single pulps in terms of pulp properties. The results showed that fundamental fibre properties ,which had been proposed by many researchers, were useful for the characterization of deinked pulp, provided their fractions were compared. Possible reason for this is that fractionation sorts the fibres, and in this way helps to characterize the complicated fibre composition of deinked pulp. Notable characteristics of long fibres of deinked pulp seemed to be fibre coarseness , wet fibre flexibility and curl or kink as well as fibre swelling. These results suggested that the characterization of mill-made deinked pulps with these fibre properties should be carried out by taking the fibre types into account. For this reason, a new method for the determination of fibre composition has been proposed. It provides good results within a certain range of pulps, but further studies are required to devise a more sophisticated method

Modern high yield pulps, typified by chemithermomechanical pulp (CTMP), are likely to be used increasingly for printing, writing and publication grades where longevity is a major consideration. This paper reports an investigation of the ageing of papers containing CTMP, and sized both with rosin/alum and alkyl ketene dimer(AKD) systems, using paper made specially for the study on a pilot papermaking machine. Emphasis was placed on mechanical properties, in view of the concern of librarians and archivists with the embrittlement of paper due to acid hydrolysis of the cellulose. The results show that use of CTMP has a negligible effect on rates of loss of strength; in a series of papers containing various proportions of CTMP with a bleached softwood sulphate pulp, sized with AKD, the rate of degradation was very similar, and acceptably low. Naturally, the papers containing CTMP are not initially as strong, and will become yellow on exposure to light; in judging whether or not such papers are acceptable for long term use, all these factors need to be considered with respect to particular applications.