A new method of measuring the flexibility of high-yield pulp fibres wa
s developed in order to characterize two different types of mechanical
pulp: CTMP and TMP. This method is based on the Bauer McNett classifi
cation and the average fibre lengths obtained with a Kajaani FS100 app
aratus. The determination of the average fibre length of each fraction
from the Bauer McNett classifier and the correlation between the Kaja
ani lengths and the theoretical McNett lengths allows a dynamic and a
static flexibility coefficient to be defined. This flexibility measure
ment is applicable to all sorts of lignocellulosic fibres. Flexibility
coefficients are affected by refining, bleaching, the wood species an
d the mechanical pulping process. Flexibility is an important paramete
r in the development of the optical characteristics and strengths of t
he pulps. This method is rapid and can be used for laboratory control
purposes in pulp production. It is one way to characterize high-yield
pulp fibres and to better understand the way the fibre evolves during
the production process.