Correlation of regenerated fibres morphology and surface ... - Lenzing

Lenzinger Berichte, 82 (2003) 83-95
p 2
γ m (13)
s =
d 2
γ b (14)
s =
Results and discussion
X-Ray analysis
Small angle X-ray scattering SAXS. All types of
regenerated cellulose fibres exhibit a welldefined
maximum on the meridional SAXS
diagram (Figure 3) indicating periodical
structures due to alternation of crystalline and
amorphous regions along the fibre axis. The
long period values were calculated (Table 3)
2θ 2 .I(2θ) 2θ 2 .I(2θ) 2θ 2 .I(2θ)
88
from the peak position and are almost similar
for all untreated fibres (approx. 13.5 nm). This
This This finding is in good agreement with the
values reported [8,17]. Fibre’s treatment in
alkaline solution or a bleaching medium causes
distinct changes. In the case of viscose fibres an
increase of the long spacing for about 15%
occurs regardless of the treatment conditions
applied. Modal fibres show a significant change
of long spacing (by about 15%) only in case of
alkaline treatment. The opposite effect was
observed with lyocell fibres showing a decrease
of long spacing of about 10% (bleaching) and
5% (mercerisation).
2θ 2θ 2θ
Figure 3. Plot of 2θ 2 . I(2θ) vs. 2θ of meridional SAXS curve for the untreated viscose, modal and lyocell fibres,
respectively.
Viscose fibres are of low crystallinity but
highly accessible to different media due to their
mainly amorphous molecular arrangement and
an extensive inner surface. This morphology
enables a better sorption of water and low
molecular species, compared to the two other
fibres [11,28] causing major structural
reorganization shown by the changes in long
spacing.
Cellulose molecules in CMD fibres are well
oriented, have a higher degree of
polymerisation and are densely packed. A nonextensive
void system is formed because of the
spinning process at high drawing ratios [9].
This structural parameter is the reason for the
lower hydrophilic capacity of modal fibres in
comparison to viscose or lyocell fibres.
Mercerisation is the only treatment process that
causes significantly increased long spacing and
promotes the swelling process.
Lyocell fibres have a more complicated
structure. They show high hydrophilicity
caused by the fibres larger void system
(comparable with viscose) and not by the
fibre’s superstructure. It was shown that water
swollen solvent spun fibres contain more
separated elementary fibrils and less nonswelling
clusters than fibres spun from
cellulose derivates [17]. The interstices that
separate single elementary fibrils, the
interfibrillar and intrafibrillar voids are
accessible to water, sodium hydroxide and
other treating media. The dense fibre inner
structure prevents major structural
reorganization if the lyocell fibres are bleached
or mercerised without tension. Swelling does
not create new voids nor do existing voids
disappear; only the voids diameter is increased
[16]. In the case of viscose and modal fibres the
increase of long spacing is accompanied by a
more pronounced crystallinity increase that
could additionally influence changes in the
periodical structure.