In the present study, only mechanical treatment (i.e. refining) was used to
increase the fibre strength.
Figures 19 show the effect on tensile index and tearing resistance of refining
of the two pulps used in Paper I, softwood and abaca. It can be seen that the
tensile index of both the softwood and the abaca pulp increased sharply with
refining at the beginning of the sequence. Both pulps then reached a plateau
where the tensile index remained at a fairly constant level when the refining
was further increased. At the end of the refining study the tensile index
seemed to start to decrease, which would be a result of fibre weakening and
shortening. The tear index showed a different behaviour. For the softwood
pulp, there was first a sharp increase and then a sharp decrease at a low
dewatering resistance level. When the dewatering resistance was over 20 SR,
the tear index slowly decreased with increased refining. Abaca showed a sharp
decrease in tear index with increased refining up to about 30 SR and then a
moderate decrease up to about 40 SR. Thereafter the tear index seems
unaffected by the refining up to a dewatering resistance of about 70 SR after
which the tear index again apparently decreased.