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

Lenzinger Berichte, 82 (2003) 83-95
Sorption properties show a behaviour, which
can be correlated with the differences in
morphology. CV is able to adsorb the greatest
amount of solvent and low molecular weight
species (iodine). This is caused by a large
amount of amorphous phase (crystallinity index
= 0.25), and a large volume, diameter, and inner
surface of voids. The polar component of SFE
indicates a similar great number of accessible
polar groups as in the case of CLY, which are
able to interact with polar liquids.
CMD adsorbs the smallest amount of solvent
and low molecular weight species; has the
largest contact angle, and the smallest polar
component of SFE. This is caused by the rather
dense structure; the smaller void volume and
inner surface area even if the degree of
crystallinity is smaller than that of CLY.
CLY fibres sorption velocity is higher than
CMD; they have contact angles and polar
components of SFE similar to CV. The high
hydrophilicity is caused by the fibres void
system and not by the fibres superstructure,
nevertheless the void system is less accessible
for iodine adsorption.
The applied conventional treatment processes
influence the fibres fine structure, increasing
the crystallinity index and decreasing the
tenacity. The changes in fine structure are
especially pronounced in CV and CMD due to
the chemical changes caused by alkali
treatment. Crystallinity index increases as much
as 51%. Lyocell fibres have a more complicated
structure and are less affected with respect to
the crystallinity index. The dense fibre inner
structure prevents major structural
reorganization. These findings are also reflected
by the iodine adsorption. The influence on the
crystalline orientation differs, it increases in the
case of the less oriented CV and CLY, but
decreases in case of the most oriented CMD
fibres.
Mercerisation has the biggest influence on the
sorption properties of all three types of fibres.
The tensionless alkali treatment most likely
causes an increase of the inner surface and the
number of polar groups accessible for polar
liquids. Hence an increase of the sorption
94
velocities (≈115%) and the total SFE of the
fibres follows, mainly due to the increase of the
fibre ’ s SFE polar component (≈48%).
Bleaching causes less changes in fibres supramolecular
structure but it increases the SFE´s
polar component by 20%. This is the
consequence of the increased number of polar
groups created by the oxidation process [5].
A good correlation between iodine adsorption
and structural changes was observed. The
increase in crystallinity decreases the
accessibility of fibres and, thereby, the sorption
of iodine becomes lower. The observed
structural changes are not pronounced enough
to significantly influence fibre’s mechanical
properties, with the exception of alkali treated
CMD and CLY fibres where a significant
decrease of tenacity was observed.
Viscose fibres (raw and treated) have the fastest
sorption velocities, the lowest contact angle and
the highest polar part of the SFE, and are
therefore the most hydrophilic among
regenerated cellulose fibres due to their
structure (the greatest volume, diameter, and
inner surface of voids) and above all due to the
highest contribution of the accessible groups
which are able to interact with polar liquids.
References
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