The document discusses gel spinning of polyethylene and polyacrylonitrile fibers. It finds that high deformation rates during polyethylene gel spinning can introduce defects, resulting in weaker fibers. Higher spinning temperatures and avoiding spinline stretching can prevent defect introduction. Properties depend on factors like molecular weight distribution and polymer concentration. Gel spinning polyacrylonitrile results in fibers with more circular cross-sections and homogeneous structures than dry-wet spinning. Gel-spun fibers also achieve better mechanical properties than dry-wet spun fibers after drawing.

1. Gel Spinning
Presented by
Arka Das

2. Influence of spinning temperature and spinline
stretching on morphology and properties of
Polyethylene gel spun fibre
 The tensile strength of gel-spun polyethylene fibres
hot-drawn to the maximum draw ratio depends on
the spinning conditions such as spinning speed,
spinline draw ratio and spinning temperature.
 High deformation rates during spinning introduce
defects and fibres with poor ultimate properties are
produced.
 These defects are already present before the hot-
drawing step and can be detected indirectly by
wide-angle X-ray scattering, since they are
accompanied by preferential c-axis orientation
parallel to the fibre axis and a shish-kebab structure.

3. Experimental procedure
 The linear polyethylene sample used
throughout this study was Hifax 1900 with
Mn, = 2 x 10^5kg/mol and Mw = 4 x
10^6kg/mol
 5wt% of this polyethylene was dissolved in
paraffin oil.
 Upon cooling, this solution formed a gel
which was fed to the spinning apparatus.
 The gel was extruded into a filament at
temperatures varying from 170 to 250ºC
with a spinning speed of 1 or 100m/min.

4. Results and discussion
 Freely extruded
filament have tensile
strength same at all
temperature.
 The tensile strength
of fibre drawn in the
spinline to a draw
ratio of 50 increases
considerably with
increasing spinning
temperature.

5.  Fig. 2 shows clearly that
at a given spinning
temperature the
unfavourable effect of spin
line stretching is
enhanced at higher draw
ratios.
 As in the case of a
spinning speed of 1
m/min , the effect of spin
line stretching diminishes
at higher spinning
temperatures.
 Again the ultimate tensile
strengths for different
winding speeds merge at a
spinning temperature of
about 250°C
Results and discussion

6. Results and discussion

7. Results and discussion
 In Figure 3 maximum filament strength is observed
at 100 m/min.
 Again the ultimate tensile strengths for different
winding speeds merge at a spinning temperature of
about 250°C (Fig. 3)
 In Fig. 4 this measure of the degree of preferential
c-axis orientation parallel to the fibre axis is presented
as a function of the spinning temperature for freely
extruded fibres and fibres drawn in the spinline to a
ratio of 50.

8. Results and discussion
 In Fig. 5 the degree of
preferential c-axis orientation
parallel to the fibre axis is
presented as a function of the
winding speed for different
spinning temperatures.
 The efficiency of creating c-
axis orientation parallel to the
fibre axis created by a flow-
field and trapped by
crystallization is determined
by the deformation rate
(elongation or shear), the
exposure time to the
orientational action of the
flow-field, and the relaxation
time.

9. Results and discussion

10.  In our case this
combination shows
that the amount of
shish-kebab structure
increases with
increasing preferential
c-axis orientation
parallel to the fibre
axis.
 pictures of the inside
of the fibre, clearly
prove that the whole
fibre consists of a
shish-kebab
structure.

11.  Fig. 9 shows the stress-
strain curves of the
extracted fibres spun under
different spinning
conditions.
 Fibres containing
preferential c-axis
orientation parallel to the
fibre axis (Curve (a)) have
an elongation at break of
about 10 to 30% and no
yielding is observed.
 On the other hand fibres
with no preferential c-axis
orientation parallel to the
fibre break at much larger
strains (up to about 900%,
Curves (b) and (c)).

12.  The tremendous
influence of the
presence of preferential
c-axis orientation
parallel to the fibre axis
on the stress-strain
behaviour is
demonstrated more
clearly in Fig. 10.
 It shows a very steep
drop of the draw ratio
at break of the
extracted fibres with
increasing preferential
c-axis orientation
parallel to the fibre
axis.

13. Influence of polymer concentration and molecular
weight distribution on morphology and properties of
Polyethylene gel spun fibre
In addition to spinning temperature,
spinline stretching and spinning
speed, the properties of gel-spun
polyethylene fibres hot-drawn to the
maximum draw ratio also depend on
the polymer concentration, molecular
weight and molecular weight
distribution.

14. Experimental details
 Two samples of linear polyethylene Hifax 1900
were used, one with a broad molecular weight
distribution (Mw = 4 x 10^6 kg/mol , Mw/Mn =
20; referred to as HifaxA) and one with a
smaller molecular weight distribution (Mw =
5.5 x 10^6kg/mol, Mw/M n ~ 3; referred to as
HifaxB).
 1 to 5 wt % polyethylene solutions in paraffin
oil were prepared (containing 0.5wt% DBPC
anti-oxidant) at 150°C
 The gel was extruded into a filament at
temperatures varying from 170 to 250°C With
an extrusion rate of 1 or 100m/min using a
conical die with an exit of 1 mm

15. Result & Discussion
 Fig. 1 where the tensile
strength at break for
fibres obtained from a 2
and a 5 wt. % gel and
spun under various
spinning conditions are
compared.
 However, 2wt % is
already close to the
minimum
concentration at which
gel-spinning is still
possible.

17.  Fig. 4 presents this
ratio for 2 wt %
solutions of HifaxA
and HifaxB as a
function of the
spinning temperature
for an extrusion rate
of 100 m rain-i and a
winding speed of
500m/min .
 As expected, the
degree of preferential
c-axis orientation
parallel to the fibre
axis decreases, with
increasing spinning
temperature.

21. • One of the problems encountered during gel-
spinning polyethylene solutions is the adsorption
of the polyethylene on the wall of the die. This
results in fibres with poor properties, because
stretching the entanglement network at one end
while the other end is anchored by the adsorbed
layer on the wall of the die leads to rupturing of
the entanglement structure.
• Adding 1 wt. % aluminium stearate to the
polyethylene solution.
• A second way to suppress adsorption is to reduce
the residence time of the polymer solution in the
spinneret below the time required for adsorption.
• Finally, the adsorption can also be suppressed by
raising the spinning temperature

22. In studying gel-spinning of ultra-high molecular
weight polyethylene (U~WPE) we came across an
interesting effect due to adding 1 wt % of
Aluminiumstearate to the spinning solution
Whereas without this additive, drawing of the gel
directly afterleaving the die, resulted in a rapid
decrease in tensile strength of the ultimate fibre,
the additive enabled us to pull the extrudate with
speeds exceeding 300 m/min while the strength
of level was still maintained at about 3 GPa. This
unexpected phenomenon induced some further
investigations into the influence of additives on
the spinnability of polyethylene solutions.
Effects of Additives on Gel-Spinning of Ultra-High
Molecular Weight Polyethylene

23. Results and Discussions
 Drawing the gel-
filament composed of
only 5 wt % UHMPE in
paraffin oil gave rise to
a lowering in the
tensile strength from 3
GPa at 1 m/min to 0.5
GPa at 25 m/min
 Adding 1 wt % of
Aluminium-stearate
showed no decrease in
tensile strength far
beyond drawing rates
of 70 m/min

24.  Gels containing also I
wt % of EPDM
rubber,the winding
speeds up to 75 m/min
have no influence on
the tensile strength.

26. Gel-spun polyacrylonitrile fiber from pregelled
spinning solution
 Polyacrylonitrile (PAN) fibers have been gel
spun from pregelled PAN spinning solution.
The pregelled solution had network
structure with elevated spinnability, the as-
spun fiber from which had more circular
cross-section and reduced skin-core
difference. Drawing was more effective in
inducing the segmental orientation and
crystallization in gel-spun fiber than in dry–
wet spun fiber. The mechanical properties of
the gel-spun fiber were better than those of
the dry–wet spun fiber after multi-stage
drawing.

27. Fiber Spinning and Drawing
 Certain amounts of PAN copolymers were
dissolved in the mixture of 94.8/5.2 (w/w)
DMSO/water to produce a viscous
PAN/DMSO/water spinning solution with the
PAN concentration of 23 wt%.
 The solution was deaerated for 3 h at 70°C in
a vacuum oven.
 In gel spinning, the pregelled spinning
solution was prepared by keeping a fresh
solution in a thermostatic spinning barrel at
25°C for 2 h.
 The pregelled solution was extruded through a
spinneret.

28. Results and Discussion
The pregelled
solution is
more elastic
and it is thus
less likely to
deform during
fiber spinning.
Hence the
resultant fibers
are more likely
to have circular
cross-section.

29. Surface Morphology and Physical Properties

30. The pattern of the dry–wet
spun fiber (drawn to 60
times) was similar to that of
the gel-spun fiber drawn to
45 times, suggesting that
the segments in gel-spun
fiber were more easily
aligned in the direction of
drawing.

31. Dry–wet spun fiber’s tenacity and Young’s
modulus were much lower than that of the gel-
spun fiber drawn to 90 times and were only
comparable to those of the gel-spun fiber drawn to
45 times.

32. The gel-spun fiber drawn to
90 times exhibited the
highest tenacity, whereas the
dry–wet spun fiber drawn to
60 times had the lowest
tenacity and breaking
elongation.

33. Conclusions
 Stretching during spinning introduce defects in the
filaments resulting low strength fibre.
 Gel spinning of polyethylene only leads to fibres with
good ultimate properties if the introduction of defects
is prevented. The stresses should be kept below the
threshold value for the introduction of defects by
avoiding spinline stretching and/or increasing the
spinning temperature. If these conditions are not
satisfied.
 various properties of gel-spun polyethylene fibres
depend strongly on the molecular weight distribution
and polymer concentration in solution.
 Compared with the dry–wet spun fiber, the gel-spun
fiber was more likely to possess circular cross-
section and homogeneous structure with reduced
skin-core difference.

34. Thank You