Refining and the development of fibre properties

The development of fibre length and coarseness with refining was examined, and both were observed to decrease with refining. However, it was found that the changes in the length-weighted fibre length did not correlate with changes in the number of long fibres per unit mass, indicating that the length-weighted fibre length was not accurately tracking the reduction in fibre length with refining. This is mainly because its value is affected by the production of fines during refining. A number of sheet properties were also measured in an attempt to correlate the measured tensile strength with that predicted from the Page equation. It was found that only a relatively poor fit between the theory and experiments could be obtained using the measured values of fibre length and coarseness. This is because these measured values are affected by the presence of fines generated during refining. A better fit with the Page equation was actually obtained by assuming no change in coarseness and fibre length for the refined pulps. The major source of improvement in the tensile strength of the sheets was an increase in their relative bonded area.