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).