Indian Journal of Fibre & Textile Research
Vol. 37, December 2012, pp. 326-330
Production of polypropylene melt blown nonwoven fabrics: Part II —Effect of
process parameters
Zhao Boa
College of Textiles, Zhongyuan University of Technology, Henan, Zhengzhou, 450007, P R China
Received 7 October 2010; revised received and accepted 21 September 2011
The effects of processing parameters on the fibre diameter and the web weight unevenness of melt blowing nonwovens
fabrics produced by dual slot inset sharp die have been investigated. It is observed that the effects of processing parameters
on fibre diameter and web weight unevenness are not similar. The results show that the web weight unevenness increases
with the increases in polymer throughput rate and accessory air pressure; the web weight unevenness decreases initially and
then increases with the increase in air initial pressure and die-to-collector distance. The fibre diameter decreases with the
increases in air initial pressure and accessory air pressure and reductions in air initial pressure; the fibre diameter decreases
initially and then increases with the increase in die-to-collector distance. It is concluded that the polymer throughput rate,
accessory air pressure, air initial pressure and die-to-collector distance are the key factors in controlling the web weight
unevenness of melt blowing nonwoven, and the lower polymer throughput rate, larger air initial pressure, larger accessory
air pressure and die-to-collector distance will be of benefit to produce finer fibre diameter.
Keywords: Melt blowing, Dual slot sharp die, Nonwoven, Web weight unevenness, Fibre diameter, Polypropylene
1 Introduction
The melt blowing technology1-5 is a one-step
process in which high velocity air blows a molten
thermoplastic resin from an extruder die tip onto a
conveyor or take-up screen to form a fine fibrous and
self-bonding web. In this process, high velocity hot
air streams impact upon a stream of molten polymer
as the polymer issues from a fine capillary. The result
of this impact is that the polymer is rapidly attenuated
into fibre as fine as 1µm in diameter. The melt
blowing products are suitable for medical materials,
oil spill absorbents, filtration media and so on. The
web weight unevenness and the fibre diameter of melt
blowing nonwovens, therefore, are strongly affected
by the air jet flow field developed from the dual slot
inset sharp die. In this work, the effects of the
processing parameters on the web weight unevenness
and the fibre diameter are discussed. Moreover, we
analyze the relationships between the processing
parameters and the fibre diameter and the web weight
unevenness.
2 Materials and Methods
The polypropylene(Y-3500) was used with a melt
flow rate of 34.2 g/10 min.
____________
a
E-mail: zhaobohenan@sina.com / zhaobohenan@163.com
2.1 Test Methods
The melt flow index (MFI) experiments of
polypropylene (PP) were performed with a
temperature of 230°C, load capacity of 2.160 kg,
aperture of capillary tube of 2.095 mm and length of
capillary tube of 8 mm on RL-11B type melt flow
indexer at ambient room temperature conditions.
The methods used to analyze the web weight
unevenness are the subsample weight measurement.
The balance used to measure weight of the subsample
is JN-B precise torsion balance, having the weight
range of 0-5 mg and scale of 0.01 mg. All the samples
tested were conditioned for 24 h at 65% RH and 20°C
before evaluation.
The image analysis method was employed to
measure the fibre diameter. The images of nonwoven
samples were acquired with a Questar threedimensional video frequency microscope (Questar
Corp., New Hope, PA) with an enlargement factor of
600 and depth of focus of 1 mm and then processed
with Image-Pro Plus image analysis software(Media
Cybernetics, Inc., Silver Spring, MD) to measure the
fibre diameter. The image processing includes
enhancement, smoothing, binarization, and filtering.
The fibres of the melt blowing nonwoven are
regarded as cylinders because their cross-sections are
nearly round. Twenty fibres are chosen to measure
ZHAO BO: PRODUCTION OF POLYPROPYLENE MELT BLOWN NONWOVEN FABRICS: PART II
327
their diameters in each grid, so altogether there are
200 fibres to be measured in 10 grids. The mean value
of the diameters of 200 fibres was considered as the
fibre diameter of the polypropylene (PP) nonwoven
sample.
2.2 Process Parameters
The melt blowing processing parameters
concerned are the polymer throughput rate (0.0150.24g/min/hole), polymer melt initial temperature
(290-335°C), air initial pressure (0.1-0.80 MPa),
accessory air pressure (0.1-0.4 MPa) and die-tocollector distance (600-1800 mm). To condense the
discussion and comparison, a group of fundamental
parameters was assumed during the computations,
such as a polymer throughput rate 0.046g/min/hole, a
polymer melt primary temperature 300°C, an air
initial pressure 0.3 MPa, an accessory air pressure
0.2 MPa and a die-to-collector distance 1000 mm.
When one of the processing parameters was varied,
the fundamental values of the other process
parameters were kept constant.
Fig. 1—Schematic diagram of melt blowing equipment
2.3 Dual Slot Blunt Die Parameters
The parameters of dual-slot sharp die of melt
blowing process were angle between the slot and the
cross-sectional of β=60°, a die head b=2.06 mm wide,
a slot e=0.65 mm wide, an air gap d=0.84 mm wide,
and an inset distance a=0.5 mm.
2.4 Production Application and Structure Properties of Melt
Blowing Nonwoven Processing
Fig. 2—Schematic diagram of melt blowing principle
Figures 1 and 2 show the schematic diagrams of the
melt blowing equipment and melt blowing process
principle respectively. A typical melt blowing process
consists of extruder, metering pump, die assembly,
web formation, and winding.
The extruder and metering pump provide uniform
polymer melt delivery to the die assembly. The die
assembly is the most important element of melt
blowing process. The die assembly has three distinct
components, namely polymer feed distribution, die
nosepiece and air manifolds. The polymer feed
distribution system delivers uniform polymer melt to
the die nosepiece.
The air manifolds supply the high velocity hot air
through the slots to the top and bottom sides of the die
nosepiece. The high velocity air is generated using an
air compressor. As soon as the molten polymer is
extruded from the die holes, high velocity hot air
streams attenuate the polymer streams to from
microfibres. As the hot air stream containing the
microfibres progresses toward the collector screen, it
draws a large amount of surrounding air that cools
and solidifies the fibres. The solidified fibres
subsequently get laid randomly onto the collecting
screen, forming a self-bonded nonwoven web. The
fibre in the melt blowing web are held together by a
combination of entanglement and cohesive sticking.
The fibres are generally laid randomly because of the
turbulence in the air stream, but there is a small bias
in the machine direction due to some directionality
imparted by the moving collector. The collector speed
and the collector distance from the die nosepiece can
be varied to produce a variety of melt blowing webs.
Usually, a vacuum is applied to the inside of the
collector screen to suck the hot air and to enhance the
fibre laying process.
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INDIAN J. FIBRE TEXT. RES., DECEMBER 2012
3 Results and Discussion
3.1 Web Weight Unevenness
3.1.1 Effect of Polymer Throughput Rate
Figure 3(a) shows the effect of polymer throughput
rate on nonwoven web weight unevenness6. The web
weight unevenness increases with the increase in
polymer throughput rate. The web weight unevenness
corresponding to a polymer throughput rate of
0.12g/min/hole is larger than that corresponding to a
polymer throughput rate of 0.03g/min/hole. As can be
seen, the quality of the web gets worse in terms of the
web weight unevenness, with the increased polymer
throughput rate. This is primarily due to the fact that
the fibre diameters in the web increase with the
increasing polymer throughput rate. Therefore, when
the nonwoven web basic weight is kept constant, the
fibre number in the web weight decreases with the
increase in fibre diameter, leading to the increasing
web unevenness.
3.1.2 Effect of Air Initial Pressure
Figure 3(b) illustrates how the changes in air initial
pressure cause changes in the rate of web weight
unevenness7. It first decreases with increase in the air
initial pressure and then increases with further increase
in the air initial pressure. For the conditions in Figure
3(b), when the air initial pressure increases to
0.35 MPa, the web weight unevenness is 28.9%
smaller than that when the air initial pressure is 0.1
MPa. But when the air initial pressure increases to
0.55 MPa, the web weight unevenness is 13.8% larger
than that when the air initial pressure is 0.35 MPa. This
may be explained by the following facts that the
primary increasing air initial pressure leads to the
decreasing fibre diameter, and then the decreasing web
weight unevenness. However, when the air initial
pressure increases continually though the fibre
diameter decreases continually, the high air pressure
influences the path of fibre, landing to the collector and
leads to more uneven fibre distribution in the web.
3.1.3 Effect of Accessory Air Pressure
Figure 3(c) shows how the web weight unevenness
changes with the varying accessory air pressure. As
can be seen, the effect is significant. The web weight
unevenness increases when the accessory air pressure
Fig. 3—Effect of polymer throughput rate, air initial pressure, air initial pressure, and die-to-collector distance on web weight unevenness
ZHAO BO: PRODUCTION OF POLYPROPYLENE MELT BLOWN NONWOVEN FABRICS: PART II
is increased. This is mainly attributed to the fact that
when the accessory air pressure is too high, the fibres
will be very disheveled and entangled before they
land to the collector, leading to an unevenness web.
3.1.4 Effect of Die-to-Collector Distance
Figure 3(d) reveals the significant effect of the
die-to-collector distance (DCD) on the web weight
unevenness7. It first decreases with the increase in
DCD and then increases with the further increase in the
DCD. This is primarily due to the fact that when the
DCD is short, the fibre tends to cling to each other
before collected on the collector surface due to the
short solidifying time. However, when DCD exceeds a
certain extent, the long travel time of the fibre before
collection causes the fibre to entangle more severely,
and the produced web presents to be more uneven. It is
concluded that a high DCD or a small DCD contributes
little to increase the quality of the web.
3.2 Fibre Diameter
3.2.1 Effect of Polymer Throughput Rate
Figure 4(a) illustrates the effect of the polymer
throughput rate on fibre diameter. As expected,
decreasing the polymer throughput rates produces a
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finer fibre. For the conditions in Figure 4(a), the final
fibre diameter for a polymer throughput rate of
0.03g/min/hole is 23.9% smaller than the final fibre
diameter for the high polymer throughput rate of
0.11g/min/hole. The reason is that the lower polymer
throughput rate gives much more rapid attenuation
and gives finer fibres.
3.2.2 Effect of Air Initial Pressure
Figure 4(b) shows how the fibre diameters change
with varying attenuating air pressure. As can be seen
from Figure 4(b), the increasing air pressure strongly
reduces fibre diameter over the observed range of air
pressure. The higher the air initial pressure, the finer
is the fibre. When the air initial pressure is 0.55 MPa,
the fibre diameter is 19.8% smaller than that when the
air initial pressure is 0. 1 MPa. This may be explained
by the facts that the velocity difference between the
air and the fibre increases, resulting in a higher
drawing force exerted on the fibres, causing the
formation of finer fibres.
3.2.3 Effect of Accessory Air Pressure
Figure 4(c) shows the effect of accessory air
pressure on fibre diameter. As expected, a larger
Fig. 4—Effect of polymer throughput rate, air initial pressure, accessory air pressure, and die-to-collector distance on fibre diameter
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INDIAN J. FIBRE TEXT. RES., DECEMBER 2012
accessory air pressure yields smaller fibre diameter.
When the accessory air pressure is 0.325 MPa, the
fibre diameter is 11.6% smaller than that when the
accessory air pressure is 0.15 MPa. Plots in this figure
show that an increase in accessory air pressure,
analogous to an increase in airflow rate, reduces fibre
diameter.
3.2.4 Effect of Die-to-collector Distance
Figure 4(d) shows the effects of the die-to-collector
distance on the fibre diameter. It is revealed that the
die-to-collector distance have an obvious influence on
fibre diameter over the experimental range
researched. A larger distance causes the fibres to be
attenuated much more. When the distance increases to
1050mm, the final fibre diameter is 28.2% smaller
than that when the distance is 750 mm. Moreover,
when the distance increases to 1250 mm, the web
thickness unevenness is 11.3% larger than that when
the distance is 1050 mm.
4 Conclusion
In this paper, the effects of polymer throughput
rate, air initial pressure, accessory air pressure, and
die-to-collector distance on web weight unevenness
and fibre diameter of melt blowing nonwoven fabric
are investigated, which do not show similar variation
trends. The experimental results indicate that the web
weight unevenness increases with the increase in
polymer throughput rate and accessory air pressure,
respectively. The web weight unevenness decreases
initially and then increases with the increase in air
initial pressure. The air initial pressure first decreases
with the increase in die-to-collector and then increases
with the further increase in die-to-collector. The
results also show that the fibre diameter decreases
with the increase in air initial pressure and accessory
air pressure and reductions in air initial pressure; the
fibre diameter decreases initially and then increases
with the increase in die-to-collector distance.
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