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TRANSCRIPT
Structure Regulation and Properties of Melt-electrospinning Composite
Filter Materials
Ying Shen1, Sainan Xia1, Pengfei Yao1, R. Hugh Gong2, Qingsheng Liu1,2*, Bingyao
Deng1,* 1Key Laboratory of Eco-Textiles (Ministry of Education), Jiangnan University, Wuxi 214122,
China 2The School of Materials, The University of Manchester, Manchester, United Kingdom
*Corresponding authors:
Qingsheng Liu, E-mail: [email protected], Tel: +86-13771087025, Fax:
+86-0510-85912009
Bingyao Deng, E-mail: [email protected], Tel: +86-13806185561, Fax:
+86-0510-85912009
Running Heads: Structure Regulation and Properties of Filter Materials
Abstract: Two kinds of composite filter materials were prepared by regulating the structure of
melt-electrospinning polypropylene (PP) webs. The self-designed multi-nozzle melt-
electrospinning device was used to produce PP webs which deposited on PP spunbonded
nonwoven. Firstly, the composite filter materials with different thickness and ratios of coarse/fine
fibers were prepared, and the effect of the thickness and the ratio of coarse/fine fibers on filtration
properties were studied. The results showed that the filtration efficiency and pressure drop
increased as thickness increased. In addition, compared with the general filters which were
composed of coarse or fine fibers, the filters with coarse/fine fibers had “low pressure drop”
under the similar filtration efficiency. In the case of the ratio of coarse/fine fiber about 2:2, this
filter achieved optimal performance. When the thickness was 0.42 mm, its filtration efficiency for
particles more than or equal to 2.0 μm could reach more than 95%. Its pressure drop and air
permeability were 18.13 Pa and 54.69 mm/s, respectively, while those of general filter were 38.67
Pa and 10.02 mm/s, respectively. After that, the composite filter materials composed of various
angles of oriented webs were produced. The results showed that the filtration efficiency for
particles with the size of more than or equal to 2.0 μm was higher than that of filters composed of
one angle of oriented webs. In addition, the lower the orientation was, the lower the pressure drop
was.
Key words: melt-electrospinning; polypropylene; filters; structure regulation; filtration property
Introduction
The nonwoven filters have attracted much attention due to high specific surface area, high
porosity and softness. They have been widely used in different kinds of fields in modern society,
such as environment, health-care, aerospace industry, and so on. Among the usual manufacturing
methods of filters, such as spun-bonded, melt-blown, spunlaced, needle-punched nonwoven
technology and electrospinning [1], electrospinning is widely used for producing air filter
materials because it is the most effective and simplest methods for preparing ultrafine fibers [2]. It
includes solution electrospinning and melt electrospinning [3]. Compared with solution
electrospinning, melt electrospinning has distinct advantages over it, such as solvent free, safe,
environmental friendly, high production, etc. [4]. The webs produced by this way have a broad
future in biomedical, filters and many other fields [2].
One commercial application of melt-electrospinning webs is as filters which were used to
filtrate air or water. Li et al. [5-6] produced microfiber membrane via melt-electrospinning
technique on the surface of traditional Polyester (PET) spunlaced nonwoven. The filtration
efficiencies of composite filter materials were higher than that of PET spunlaced nonwoven. Lee
and Obendorf [4] developed melt-electrospinning PP laminates which had high barrier
performance. Li et al. [1] produced polyvinyl alcohol (PVA)/PP composite filters for water
purification by using solution and melt electrospinning. The rejection ratio to 500 nm particles of
filters could reach more than 96%. Given the above, the study on melt-electrospining filters
focused mainly on the relationship between fiber diameter and filtration efficiency.
However, some reports showed that the structures of filters had very important influences on
the filtration properties. Yan et al. [7] produced the filter with gradient structure. The “low
resistance and high filtration efficiency” of gradient filter was showed through the result of test.
Li et al. [8] prepared carbon-nanotube/quartz-fiber films with gradient nanostructures. This filter
showed a high efficiency compared with general structure filter. In addition, the fiber orientation
also has significant effect on pore size and filtration efficiency of filter. The oriented web
prepared by solution electrospinning showed much smaller mean pore size and higher filtration
efficiency than random web [9]. In addition, the influence of arrangement for oriented webs on
filtration efficiency was significant. The more uniform the interval angle of adjacent web was, the
greater the pure water flux and rejection ratio would be [10].
To sum up, the structure has a major impact on filtration properties of filter materials.
Therefore, in order to decrease the pressure drop of composite filter materials under the same
filtration efficiency, new PP composite filter materials were prepared via melt-electrospinning
technique in this paper. There were two types of composite filter materials: one contained coarse
and fine fibers and the other one was compounded of various angles of oriented webs. The
structures and filtration properties of filters were studied.
Experimental
Materials
PP (Fiber-grade) with melt flow rate (MFR) of 1100 g/10min (230 oC, 2.16 kg) was
produced by Poly Mirae Co., Korea. The PP spunbonded nonwovens of 25 g/m2 were obtained
from Changzhou Accessories Market, China.
Composite filter materials with coarse/fine fibers
The composite filter materials were prepared by the combined melt-electrospinning and hot
pressing machine as shown in Figure 1. This machine is consisted of melt electrospinning device
and hot pressing device. The melt electrospinning device is consisted of five major components: a
variable high voltage power supply (Tianjin High Voltage Power Supply Plan, China) with
a voltage range of 0-45 kV, an air compressor, cone-shape nozzle of 0.6 mm inner
diameter, temperature controller and a collector. The two key design features of the combined
device are as follows. (1) The melt electrospinning device has four spinneret holders and each
of them has eight spinnerets. In addition, each spinneret holder has its own temperature
controller. (2) The spinneret holders can be moved in longitudinal direction and the PP
spunbonded nonwovens can be moved in horizontal direction under the effect of winding
device, which realize continuous spinning. The PP master batch was placed into the spinneret
hopper and the air in the spinneret hopper was exhausted by the air compressor (the air
velocity was 0.5 kPa). After that, the air compressor was closed. The PP master batch was
heated to be melted, stretched into filament and deposited on the PP spunbonded nonwoven
substrate. During the experiment, the high voltage was imposed on the collector. The output
voltage was imposed on the spinneret, which was grounded for operation.
Insert Figure 1
The preparation process of composite filter materials with different ratios of coarse/fine
fibers was as follows. Firstly, the other conditions were kept stable (spinning voltage 41
kV, tip-to-collector distance 7 cm and spinneret diameter 0.6 mm), six spinning temperatures
(180, 195, 210, 225, 240 and 255 oC) were selected to obtain different fiber diameters via
melt-electrospinning equipment of the combined device (as shown in Figure 1). Secondly, the
suitable spinning temperature was selected in accordance with the fiber diameter. Finally, the
different thickness filters with different ratios of coarse/fine fibers (0:4, 1:3, 2:2, 3:1 and 4:0)
were online prepared by regulating spinning time and the number of spinneret holder. Each
composite filter material was prepared at the condition of 90 oC hot pressing temperature, 0.4
MPa hot pressing pressure and 3.25 cm/min rolling-up speed. In addition, the ratio of coarse/fine
fibers was 0:4, which means that all of the spinneret holders were used for spinning fine fibers,
and the prepared filter was named F0:4. The ratio of coarse/fine fibers was 1:3, which means that
one out of fore spinneret holders was used for spinning coarse fibers and three out of fore
spinneret holders were used for spinning fine fibers, and the prepared filter was named F1:3, and
so on. After that, these filters above were characterized by the thickness, pore size, porosity,
filtration efficiency, pressure drop, air permeability, etc.
Composite filter materials with various angles of oriented webs
This kind of filter was also prepared via the combined melt-electrospinning and hot pressing
machine as shown in Figure 1. The motion direction of spinneret holder was set to 0o, and the
angle of fiber increased slowly from 0o to 450 by regulating rolling-up speed. The spinning
temperature was 240 oC, spinning voltage was 41 kV, tip-to-collector distance was 7 cm
and spinneret diameter was 0.6mm in the course of the experiment. At first, the angles of
orientation
and filtration properties of filters were studied under different rolling-up speeds (3.3、6.6、9.9、
13.2、16.5 and 19.5 cm/min). Based on the research results, three kinds of speeds were selected:
3.3 cm/min, 9.9 cm/min and 16.5 cm/min. And the composite filter materials composed of
various angles of oriented webs were prepared. The spinning time used for each layer was 27 min.
Each composite filter material was prepared at the condition of 90 oC hot pressing temperature
and 0.4 MPa hot pressing pressure
Fiber morphology and diameter
The structural morphology and diameter of electrospinning PP fibers were characterized by
Fiber Fineness Analyzer (YG002C, Nanjing Beike Testing Instrument Co., China). Fiber
diameters and their standard deviation (SD) were calculated from 100 measurements of random
fibers at each spinning condition.
Physical properties
Thickness and areal density
The thickness of the composite filter materials was measured according to ASTM D 5729-
95 [11] using Fabric Thickness Gauge (YG141D, Wenzhou Da Rong Textile Instrument Co., Ltd.
China). The used pressure foot area, overburden weight and overburden time were 100 mm2, 50
cN and 10 s, respectively. And 50 readings were taken for calculating the average thickness.
The areal density of the composite filter materials were measured according to ASTM D
3776 [12] using an electronic balance. According to the actual conditions, the test surface area was
5 cm × 20 cm and the average areal density was calculated from 3 measurements in this study.
Angle of orientation
The angle of orientation was calculated through the ratio of rolling-up speed to spinneret
holder movement speed:
v arctan
1 (1)
v2
where α respects the angle of orientation, v1 respects the speed of rolling-up roller in horizontal
direction, v2 respects the speed of spinneret holder in vertical direction.
Measurement of pore size and porosity
The pore size and pore size distribution are important for filters and transport applications.
In this paper, the pore size and pore size distribution were measured by Capillary Flow
Porometry (CFP-1100A, Skei do Will Co., USA) using the bubble-point method. The diameter of
the capillary could be calculated by determining the pressure necessary to force liquid out of the
capillary. The theoretical relationship between the pressure and the pore size is [3]:
D 4 cos p
(2)
where D is the pore size; γ is the surface tension of the liquid; θ is the liquid-solid contact angle;
p is the bubble-point pressure.
The porosity [13] of the composite filter materials are defined as:
n 1 m 100
%(3)
where n is porosity; m is the areal density of the material; ρ is fiber density; δ is the thickness of
material.
Measurement of filtration property
The filtration efficiency (flow rate 84 L/min), pressure drop (flow rate 84 L/min) and air
permeability (pressure difference 5 Pa) of composite filter materials were measured by using
Filtration Material Comprehensive Performance Test Bench (LZC-H, Suzhou Hua Da instrument
and Equipment Co., Ltd., China). The experimental set-up was shown in Figure 2. The filtration
efficiency and pressure drop are defined as Eq (4) [14] and Eq (5) [15], respectively.
1CdownCup
(4)
where Cdown and Cup are the number concentration of particles at filter upstream and downstream,
respectively.
R Q
A (5)
where R is the air permeability of the measured materials; Q is the air flow under 5 Pa pressure
difference; A is the test area used in this test, which is 50 cm2.
Insert Figure 2
Result and discussion
Composite filter materials with coarse/fine fibers
Structural morphology and diameters of PP fibers
In the experiment, the tip-to-collector distance was 7 cm, the spinning voltage was 41 kV,
and the nozzle diameter was 0.6 mm. The spinning temperature increased from 180 oC to 255 oC
with 15 oC increment. The structural morphology and diameters of PP fibers are listed in Figure 3.
It can be seen from Figure 3 that the average fiber diameter decreased from 13.92 μm to 6.18 μm
when spinning temperature increases from 180 oC to 255 oC. The standard deviation of fiber
diameter is relatively large. At the temperature of 240 oC, the standard deviation of fiber diameter
is the smallest. It can be seen that the relationship between fiber diameter and the spinning
temperature is the same as our previous study [16].
Insert Figure 3
Morphology and physical properties of composite filter materials
The selected spinning temperature and fiber diameter were 210 oC, 8.74 μm and 240 oC,
6.18 μm, respectively. After that, the composite filter materials with different structures and
thickness were prepared by varying the number of spinneret holders and spinning time (15, 30, 45,
60 and 75 min). The morphology, thickness and areal density of these filters are tested and the
results are listed in Figure 4, Table 1 and Table 2, respectively. In addition, the areal density of the
filters with different structures are named m0:4, m1:3, m2:2, m3:1 and m4:0, respectively. It can be
seen from Table 1 and Table 2, the thickness and areal density of these composite filter materials
increase with the increase of spinning time.
Insert Figure 4, Table 1 and Table 2
Pore size and porosity of composite filter materials
The effect of thickness and ratio of coarse/fine fibers on pore size of filters were studied in
this part and the results are listed in Figure 5 and Figure 6, respectively. From Figure 5, it can be
seen that the pore size and standard deviation of pore size decrease as the thickness increases. It
means that increasing thickness can make distribution of the pore size more uniform. It also can
be concluded from Figure 5 that the pore size of F0:4 decreases from 92.21 μm to 26.04 μm when
the thickness increases from 0.21 mm to 0.42 mm. It can be explained that the content of fibers
deposited on PP spunbonded nonwoven increases with the increase of thickness, as shown in
Table 2. However, other filters, especially F2:2, show small decrease in pore size. The reason for
this is that there are coarse fibers in these filters.
Insert Figure 5
It can be seen from Figure 6 that the pore size and standard deviation of pore size of F2:2 and
those of F0:4 are the largest and the smallest, respectively. The rule becomes more obvious with
the increase of thickness. The reasons are as follows. Under the same thickness, the web prepared
by coarse fibers possesses large pore, while the web prepared by fine fibers possesses small pore.
Compared with F0:4, F2:2 contains coarse fibers which result in physical separation to fine fibers
and size difference between pores.
Insert Figure 6
The porosity of the composite filter materials with different thickness and ratio of coarse/fine
fibers are calculated from Eq. (3) by knowing m, ρ and δ, and the results are listed in Figure 7.
The porosity of filters decreases as thickness increases due to hot-pressing, as shown in Figure 7.
In addition, the porosity of F1:3, F2:2 and F3:1 is greater than that of F0:4 and less than that of F4:0.
The reason is that there are coarse and fine fibers in F1:3, F2:2 and F3:1. The structure of the loose
arrangement between coarse/coarse fibers and tight arrangement between fine/fine fibers of filters
are neutralized. The physical separation happens between coarse and fine fibers, and the space
between fibers increases.
Insert Figure 7
Filtration properties of composite filter materials
The effect of thickness on filtration efficiency was studied in this part and the results are
listed in Figure 8. For each structure, as the thickness increases from 0.21 mm to 0.42 mm, the
filtration efficiency of composite filter materials increases to a certain value, as shown in Figure 8.
This conclusion can be explained by the pore size. The average pore size of filters decreases
rapidly and then slowly with the increase of thickness (Figure 5). It means that filtration
efficiency increases as the thickness increases, and kept constant when thickness reaches a certain
level.
Insert Figure 8
Figure 9 shows the effect of ratio of coarse/fine fibers on filtration efficiency of composite
filter materials. For each thickness, the F2:2 has maximum filtration efficiency and F4:0 has
minimum filtration efficiency. In addition, the ratio of coarse/fine fibers has no significant effect
on filtration efficiency for particles smaller than 0.5 μm. However, there is a significant effect on
filtration efficiency for particles more than 1.0 μm. The reason is as follow. There are more
irregular pores in the filters which have coarse and fine fibers. The particles smaller than 0.5 μm
are difficult to be captured when the air passes through the filter because of diffusion manner.
However, the particles larger than 1.0 μm are easy to be intercepted due to inertial impaction. It
also can be seen from Figure 9 that the prepared composite filter materials have low filtration
efficiency for particles smaller than 0.5 μm. The main reason is that the diameters of fibers spun
via melt-eletrospinning technology are not thin enough.
Insert Figure 9
Figure 10 shows the pressure drop and air permeability of the composite filter materials with
different thickness and ratio of coarse/fine fibers. As shown in Figure 10, a negative relationship
exists between pressure drop and air permeability. As the thickness increases from 0.21 mm to
0.42 mm, the pressure drop increases obviously. The reason to cause this phenomenon is that the
path of particles passing through filter increases with the increase of thickness, which increases
the contact area between filters and particles. The pore size and porosity of filter decrease as
thickness increases. In addition, it also can be seen in Figure 10 that the pressure drop of F2:2 is
the smallest and its air permeability is the largest. The reason is that the pore size and porosity of
F2:2 are the largest (Figure 6 and Figure 7).
Insert Figure 10
Composite filter materials with different orientated webs
Effect of rolling-up speeds on structures and filtration properties of filters
The structures and filtration properties of filters prepared under different rolling-up speeds
were tested and the results are listed in Figure 11, Table 3 and Table 4. The web prepared under
3.3 cm/min rolling-up speed is named M3, and the filter composed of substrate and M3 is named
SM3, and so on.
Insert Figure 11, Table 3 and Table 4
As shown in Figure 11, microfiber coating reduces the pore size of substrate. It also can be
seen that increasing the rolling-up speed can increase the pore size and deteriorate pore size
distribution. The reason for this is that the content and orientation of fibers deposited on the
substrate decrease with the increase of rolling-up speed [9], as shown in Table 3. This causes the
increase of spaces between fibers. It can be seen from Table 4 that the filtration efficiency and
pressure drop decrease as rolling-up speed increases. The cause of this phenomenon is that the
pore size increases, as shown in Figure 11.
Structure design and preparation of composite filter materials
The angles of orientation of fibers in those webs, which were chosen to prepare composite
filter materials, were 3.7o, 11.0o and 18.0o, respectively. Table 5 lists the structures and names of
designed composite filter materials. Remarkably, in the preparation process, the spinning time of
each layer is 27min to keep each layer in the same areal density. The layer with orientation angle
of 3.7o is named W3.7, and so on. The letter S stands for substrate. In addition, the prepared filters
are named L3.7-11-18-S, L3.7-18-11-S, L3.7-11-S-18, L3.7-18-S-11, L3.7-S-11-18, L3.7-S-18-11, L3.7-3.7-3.7-S, L11-11-11-S and
L18-18-18-S, respectively. The structures of these filters are listed in Table 5.
Insert Table 5
Structure parameters of composite filter materials
The thickness, areal density, pore size and pore size distribution of filers were tested and the
results are listed in Table 6 and Figure 12. As shown in Table 6, the composite filter materials
composed of various angles of oriented webs have nearly the same thickness and areal density.
However, the composite filter materials composed of one angle of oriented webs (L3.7-3.7-3.7-S,
L11-11-11-S and L18-18-18-S) have nearly the same areal density and different thickness. Their
thickness increases with the orientation decreases.
Insert Table 6
The six kinds of filters composed of various angles of oriented webs have nearly the same
average pore size of about 58 μm, which is bigger than that of L3.7-3.7-3.7-S, L11-11-11-S and L18-18-18-S,
as shown in Figure 12. The reasons are as follows. The orientation of each layer of the six filters
was different. However, each layer of L3.7-3.7-3.7-S, L11-11-11-S and L18-18-18-S has the same orientation,
which decreases the gaps between fibers. In addition, it also can be seen that the pore size of
L3.7-3.7-3.7-S, L11-11-11-S and L18-18-18-S decreases with the decrease of orientation.
Insert figure 12
Porosity of composite filter materials
The porosity of the composite filter materials with different oriented webs are calculated
from Eq. (3) by knowing m, ρ and δ, and the results are listed in Figure 13. It can be seen from
Figure 13, the porosity of the six filters with different oriented webs are about 85.9%. The reason
is that their thickness and areal density are nearly same. However, the porosity of L3.7-3.7-3.7-S,
L11-11-11-S and L18-18-18-S increases from 81.8 % to 87.4 % with the decrease of orientation. The
reason for this is that their thickness increases from 0.30 mm to 0.44 mm, as shown in Table 6.
From Eq (3), the porosity increases with the increase of thickness under the same raw material
and areal density.
Insert Figure 13
Filtration properties of composite filter materials
Differences of filtration efficiency in different filters composed of various oriented webs are
small. The cause of this phenomenon is that these six filters are prepared on line and there is
difference in maximum and minimum pore size of filters. It also can be seen from Table 7 that the
filtration efficiency for less than or equal to 1.0 μm particles of previous six filters is lower than
that of L3.7-3.7-3.7-S, L11-11-11-S and L18-18-18-S. However, their filtration efficiency for particles more
than or equal to 2.0 μm is bigger than that of L3.7-3.7-3.7-S, L11-11-11-S and L18-18-18-S. The reasons are
as follows. The previous six filters are composed of various angles of oriented webs, which result
in the formation of irregular pores. As we all know [17], the particles less than or equal to 1.0 μm
are captured through diffusion deposition, and particles more than or equal to 2.0 μm are captured
through gravitational settling. In addition, the filtration efficiency of L3.7-3.7-3.7-S, L11-11-11-S and
L18-18-18-S increases as orientation decreases. It can be explained that their thickness increases and
pore size decreases with the decrease of orientation, as shown in Table 6 and Figure 12. Although
the filtration efficiency of L18-18-18-S is the biggest, its pressure drop is not the biggest. The reason
is that L18-18-18-S had the largest porosity among these three filters (L3.7-3.7-3.7-S, L11-11-11-S and L18-18-
18-S), as shown in Figure 13. Therefore, it can be concluded from the investigation that when the
filters have the same areal density, the lower the orientation is, the lower the pressure drop is.
The smaller the interval angle of adjacent web is, the greater the filtration efficiency for particles
less than or equal to 1.0 μm of filter is.
Insert Table 7
Conclusion
In this study, a combined melt electrospinning and hot pressing device was introduced to
fabricate two kinds of composite filter materials by regulating the structures of melt-
electrospinning PP webs. The structures and filtration properties were tested. The results
were as follows.
The first kind of composite filter materials contains coarse and fine fibers. As the thickness
of filters increases from 0.21 mm to 0.42 mm, the areal density and pressure drop increases
obviously. The filtration efficiency increases gradually, but the increase rate tends to reduce. At
the same time, the pore size, porosity and air permeability decreases obviously. Experimental
results also shows that the pressure drop of F0:4 and F4:0 are the largest and smallest,
respectively. Among F1:3, F2:2 and F3:1, the pressure drop of F2:2 is the smallest and its air
permeability is the largest. In addition, the filtration efficiency for particles less than 2.0 μm of
F2:2 is the largest. Therefore, F2:2 has high filtration efficiency and low resistance. Its filtration
efficiency for particles more than or equal to 2.0 μm could reach 95.3%. Its pressure drop is
18.13 Pa under flow rate of 84 L/min while that of general filter is 38.67 Pa. Its air permeability
is 54.69 mm/s under pressure difference of 5 Pa while that of general filter is 10.02 mm/s. It
means that regulating the ratio of coarse/fine fibers can be useful in designing composite filter
materials which own higher filtration efficiency and lower resistance. The second prepared
composite filter materials are composed of various angles of oriented webs which have the same
areal density. This structure has significant effect on filtration efficiency for particles more than
or equal to 2.0 μm. The pressure drop of this kind filters decreases as the orientation of webs
decreases. The smaller the interval angle of adjacent web is, the greater the filtration efficiency
for particles less than or equal to 1.0 μm is. In addition, the maximum filtration efficiency for
particles more than or equal to 2.0 μm of the filters with different oriented webs is 89.1%. It
means that the filtration efficiency of the second filter is lower than that of the first filter.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51403084),
the Jiangsu Overseas Research Training Program for University Prominent Young and
Middle-Aged Teachers and Presidents, the National Key Research and Development Project of
China (2016YFB0303200, 205), the Natural Science Foundation of Jiangsu Province
(BK20130142), and the Priority Academic Program Development of Jiangsu Higher Education
Institutions.
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Table legends and Figure captions
Table 1. The thickness of composite filter materials
Table 2. The areal density of composite filter materials
Table 3. The thickness and angle of the webs
Table 4 The filtration efficiency of filters
Table 5. The structures of filter materials
Table 6. The thickness and areal density of the filter materials
Table 7. The filtration properties of composite filter materials
Figure 1. Combined melt-electrospinning and hot pressing device
Figure 2. Experimental set-up for testing filtration efficiency
Figure 3. Optical microscope figures and diameter distribution of melt electrospinning PP fibers
Figure 4. SEM images of composite filter materials with different structures
Figure 5. The effect of thickness on pore size of composite filter materials with different
structures
Figure 6. The effect of ratio of coarse/fine fibers on pore size of composite filter materials with
different thickness
Figure 7. The porosity of composite PP material
Figure 8. The effect of thickness on filtration efficiency of composite filter materials
Figure 9. The effect of ratio of coarse/fine fibers on filtration efficiency of composite filter
material
Figure 10. The pressure drop and air permeability of composite filter materials
Figure 11. The pore size and pore size distribution of filters
Figure 12. The pore size and pore size distribution of the filter materials
Figure 13. The porosity of the filter materials
Table 1 The thickness of composite filter materials
Spinning time /min 15 30 45 60 75
Thickness /mm 0.21 0.26 0.30 0.36 0.42
Table 2 The areal density of composite filter materials
Spinning time/min
15 30 45 60 75
Areal density/(g/m2)
m0:4 31.60 38.40 49.20 73.80 92.40
m1:3 30.89 38.27 47.98 69.51 89.62
m2:2 29.80 37.60 46.60 57.80 76.20
m3:1 28.42 37.30 45.57 58.70 75.30
m4:0 28.00 36.00 44.00 58.40 73.40
Table 3 The thickness and angle of the webs
Sample Substrate M3 M6 M9 M13 M16 M19
Spinning time/min - 27.00 13.50 9.00 6.75 5.40 4.57
Thickness/mm 0.19 0.04 0.04 0.03 0.02 0.01 0.01
Angle of orientation/o Random 3.7 7.4 11.0 14.6 18.0 21.3
Table 4 The filtration efficiency of filters
Sample Particle size/μm Substrate SM3 SM6 SM9 SM13 SM16 SM19
≥0.3 10.2 24.4 13.9 12.5 15.9 11.3 9.6
≥0.5 11.9 30.1 15.6 14.1 19.3 14.3 12.1
≥1.0 24.6 54.7 33.2 30.1 37.2 34.2 30.3Filtration efficiency /%
≥2.0 41.2 79.9 67.3 62.2 60.8 59.1 54.6
≥5.0 24.0 81.7 73.1 68.3 58.7 69.1 66.8
≥10.0 -39.3 75.4 75.6 75.7 39.5 83.6 81.0
Pressure drop /Pa - 1.0 7.0 5.5 5.0 4.0 3.8 3.0
Air permeability- ＞332.4 222.7 282.5 282.5 289.2
＞ ＞
/(mm/s) 332.4 332.4
Table 5 The structures of filter materials
Air flow direction Filters Layer No. 1 2 3 4
L3.7-11-18-S W3.7 W11 W18 S
L3.7-18-11-S W3.7 W18 W11 S
L3.7-11-S-18 W3.7 W11 S W18
L3.7-18-S-11 W3.7 W18 S W11
L3.7-S-11-18 W3.7 S W11 W18
L3.7-S-18-11 W3.7 S W18 W11
L3.7-3.7-3.7-S W3.7 W3.7 W3.7 S
L11-11-11-S W11 W11 W11 S
L18-18-18-S W18 W18 W18 S
Table 6 The thickness and areal density of the filter materials
Filters Thickness/mm Areal density/(g/m2)
L3.7-11-18-S 0.40 50.82
L3.7-18-11-S 0.39 49.80
L3.7-11-S-18 0.39 50.21
L3.7-18-S-11 0.39 49.56
L3.7-S-11-18 0.39 49.40
L3.7-S-18-11 0.40 50.00
L3.7-3.7-3.7-S 0.30 49.15
L11-11-11-S 0.37 50.40
L18-18-18-S 0.44 50.76
Table 7 The filtration properties of composite filter materials
Particle L3.7-11-18 L3.7-18-11 L3.7-11-S L3.7-18-S L3.7-S-11- L3.7-S-18 L3.7-3.7 L11-11-11- L18-18-1
Samplesize/μm -S -S -18 -11 18 -11 -3.7-S S 8-S
≥0.3 31.2 31.4 32.1 30.2 30.3 29.5 34.6 34.3 39.4
≥0.5 41.9 42.2 43.8 41.1 39.9 39.3 45.8 45.6 50.9
Filtration ≥1.0 71.5 70.3 71.6 71.2 69.3 71.5 72.7 73.3 76.1
efficiency/% ≥2.0 89.1 87.0 89.8 88.1 87.2 90.4 88.8 89.1 89.1
≥5.0 92.3 91.0 93.1 91.3 91.2 93.1 90.4 91.6 91.9
≥10.0 93.4 89.3 92.6 92.1 93.6 91.2 78.9 91.5 92.8
Pressure drop/Pa - 20.8 20.2 21.0 21.3 19.6 20.0 17.3 21.7 18.0
Air permeability- 39.3 43.4 36.7 37.9 45.6 44.0 75.2 34.2 60.6
/(mm/s)
3
2 4
7
56
Figure 1. Combined melt-electrospinning and hot pressing device
1
1. Air compressor 5. .Rolling-up roller2. Rolling-back roller 6. Hot pressing roller3. Spinneret holder and Temperature controller 7. High voltage4. Substrate
13 12 3 8. Test Filter 9. Particle Counter10. Flow-meter 11.ID Fan 12.Gas-water Removal Filter 13.Oilless Compressor
Figure 2. Experimental set-up for testing filtration efficiency
ream
9
Dow
9
1. Otomizer-pump 2. Aerosol Valve3. Solenoid Valve 4. Oil Otomizer5. Collector 7. Cylinder Clamp6. Filter Differential Pressure Indicator
HEPA
11
nstream7UpstAir
8DEHS5
4
61
32
HEPA10
180oC 195oC 210oC
225oC 240oC 255oC
Figure 3. Optical microscope figures and diameter distribution of melt electrospinning PP fibers
F0:4 F1:3
F2:2
F3:1 F4:0
Figure 4. SEM images of composite filter materials with different structures
F0:4 F1:3 F2:2
F3:1 F 4:0
Figure 5. The effect of thickness on pore size of composite filter materials with different
structures
0.21 mm 0.26 mm 0.30 mm
0.36 mm 0.42 mm
Figure 6. The effect of ratio of coarse/fine fibers on pore size of composite filter materials
with different thickness
Figure 7. The porosity of composite PP material
F0:4 F1:3 F2:2
F3:1 F4:0
Figure 8. The effect of thickness on filtration efficiencies of composite filter materials
0.21 mm 0.26 mm 0.30 mm
0.36 mm 0.42 mm
Figure 9. The effect of ratio of coarse/fine fibers on filtration efficiency of composite filter
material
Figure 10. The pressure drop and air permeability of composite filter materials
Substrate
SM3 SM6 SM9
SM13 SM16 SM19
Figure 11. The pore size and pore size distribution of filters
L3.7-11-18-S L3.7-18-11-S L3.7-11-S-18
L3.7-18-S-11 L3.7-S-11-18 L3.7-S-18-11
L3.7-3.7-3.7-S L11-11-11-S L18-18-18-S
Figure 12. The pore size and pore size distribution of the filter materials
Figure 13. The porosity of the filter materials