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

Lenzinger Berichte, 82 (2003) 83-95
morphological characteristics, the increased
degree of crystallinity, high degree of
polymerisation and molecular orientation and
the smallest void system.
Fibre
Sorption
velocity ∗
(g 2 /s)
Contact
angle
( o )
p
γ s
(mJ/m 2 )
d
γ s
(mJ/m 2 )
Raw viscose 0.089 80.66 25.54 8.24
STDEV 1.6E-03 1.16 0.28 0.25
Mer. viscose 0.175 69.26 39.95 5.46
STDEV 5.0E-04 0.89 3.16 3.13
Raw modal 0.052 82.38 25.01 7.99
STDEV 1.0E-04 2.36 3.40 3.13
Merc. modal 0.150 72.92 35.43 5.26
STDEV 1E-04 1.69 3.11 2.93
Raw lyocell 0.063 81.06 25.36 8.03
STDEV 9.5E-05 2.87 3.34 3.11
Merc. lyocell 0.157 71.52 36.69 5.41
STDEV 1.0E-04 1.29 3.16 2.96
Table 4. Sorption velocities, contact angles, polar and
disperse components of the SFE of the raw and washed
slack-mercerised viscose, modal and lyocell fibres.
∗ -calculated in the linear part of the slope
Due to the inner surface, diameter, and volume
of the mercerised lyocell fibre’s voids, they are
able to adsorb more water then CMD fibres,
beside the fact that they have the most
crystalline structure [11]. In comparison to raw
fibres, the mercerised lyocell fibres have a 5
times higher sorption velocity and after water
absorption their weight increases by 133 %.
Comparing all three types of fibres,
mercerisation caused an increase of absorption
speed and amount and reduced the time needed
to complete fibre wetting. The adsorption speed
is almost identical; this correlates with the fact,
that mercerisation reduces the differences in
crystallinity index and crystalline orientation.
The amount of adsorbed water correlates with
the voids systems volume.
Contact angles
Contact angles were determined from the
measured sorption velocities and using the
modified Washburn Equation 1 [4]. The values
of the contact angles define the wetting
behaviour of the measured fibres (Figure 11,
Table 4). Results are presented as average value
of 10 parallel measurements.
92
Contact angle (°)
85
80
75
70
65
raw bleached washed /
bleached
viscose modal lyocell
washed / slackmercerised
Figure 11. Water contact angles of raw and treated
viscose, modal, and lyocell fibres as affected by the
applied treatment.
Viscose fibres have the lowest degree of
polymerisation, the lowest degree of
crystallinity [9], and a large amount of
amorphous regions [11,9], therefore showing
the best wetting and sorption properties. Modal
fibres have the smallest sorption ability because
of a higher degree of crystallinity and crystallite
orientation and a smaller ratio between
crystalline and amorphous phases in
comparison to viscose [9]. Lyocell fibres have,
in comparison to viscose fibres, a higher degree
of crystallinity, better orientation, and higher
proportion between the crystalline and the
amorphous phases (9:1) [9,9]. The lyocell fibres
are, with regard to wetting and sorption ability,
almost similar to viscose fibres despite the
higher amount of crystalline phase.
Bleaching and mercerising decreased the
contact angles (Figure 11), while the sorption
velocities increased (Figure 10), resulting in a
better sorption behaviour of the fibres. The
result of bleaching is a 9% decrease, the use of
mercerisation results in a 14% decrease of the
contact angles. The reason of the contact
angle’s decrease is due to changes in the fibres
structure. Mercerisation probably enlarges the
area accessible for the aquatic medium, the
bleaching process generates new groups
(aldehyde, ketones, carboxyl), which are able to
provide increased polar interactions with polar
liquids.