3.5. The fractionation index of Olson et al.
Given that the aim is to separate the long fibres from the short fibres, Olson et al. (2000) suggest that length fractionation can be quantified by a fractionation index, Φ. This can be defined — in terms of fractionation yield as defined above — as the yield of long fibres in the reject minus the yield of short fibres in the reject:
If the long fibres are defined as equivalent to the Bauer-McNett R30 fraction (fibres retained on a 30-mesh wire) and the short fibres to the P30 fraction (fibres passing through a 30-mesh wire), then the fractionation index will be:
