In the fractionation of hardwood chemical pulp using a hydrocyclone, charac
terization of the separated fibre fractions has been a major hurdle to over
come in understanding how the fractionation process occurs. In this study,
image analysis and confocal microscopy are used to determine fibre cross-se
ction dimensions. These in turn are used to calculate the apparent density
of the fibre. Measurements on rejects and accepts fractions show clearly th
at this apparent density is one of the major factors controlling hydrocyclo
ne separation. The fibre measurements obtained are also consistent with and
help to explain the differences in physical properties of handsheets made
from the accepts and the rejects fractions.