Characterization and filtration performance of pressed non-woven
fabric membrane
T. Oike
Kyushu Institute of Technology, JapanAbstract— Low cost membranes for water treatment using non-woven fabric membrane are proposed. The non-woven
fabric membranes are applied in the novel separation technologies that are the pore diffusion separation and the flow
fractional separation. The compression ratio, surface roughness and pore size of the membrane were evaluated in thecorrelation of their filtration performance. It was able to reduce the membrane thickness, the surface roughness and theaverage pore size of the non-woven fabric membrane by pressing in wet state. It was confirmed the particles with morethan 10 μm could be removed completely and it was maintained almost stable between two days (3000 minutes) and almost
no clogging was observed.

I. INTRODUCTION
Due to the increase in the world population and theeconomic development, the water shortage has becomea serious problem. To solve the water shortage, manytechnologies of water treatment have been developed.
The water treatment required for developing countries
must be small size, easy to handle and low cost, since it
is not easy to build large-scale infrastructure. A problem
of a centralized city is also needed to concern. Due toold facilities of domestic infrastructure, it will be goodchance to convert them to such small-scale equipments.
In the case of installing small devices, the operation
system must be simple, because the local people has tooperate them. A membrane separation may be the mosteffective. The membrane separation device currently on
the market is very expensive. The reason of the priceincreases is the high production cost of the membrane.
In this paper, one of the low cost membranes forwater treatment is proposed. The membrane using
non-woven fabric is manufactured by mass production.
The authors think the non-woven fabric membrane canbe applied for water treatment and it is possible todevelop a novel separation membrane having a micronpore size.
The pore diffusion, defined as the diffusion of a
substance in a pore of a membrane, is the technique toseparate the large particles and water[1]. Water
molecule passes through the inside of the membranewith a multilayer structure by diffusion and also isfiltered through a bulk flow. The particles shift theirposition to the place where shows the higher flow rate.
The particles cannot be entered to the internal pores ofthe membrane, and then, is separated from water. Oneof the features of the pore diffusion is high level ofparticle removal ability. On the other hand, slow
filtration rate is a disadvantage. Non-woven fabricmembrane can be satisfied for the demand of low costin membrane technology.
The flow fractionation separation has been proposed
for the porous membrane[2]. The separation mechanism
is based on the flow fractionation effect (or thecollection axis effect) that occurs by quickened flowrate[3] (Fig.1). The flow fractionation effect is observedin blood flow within the human body[4]. By the use ofthis effect we may maintain a stable long-term filtration
performance. For example, red blood cells moves to thecenter of the blood vessel by the effect resulting thestable filtration[5][6]. When we use this effect in thefiltration prosecc of aqueous solution, it is possible toseparate particles and water by low pressure filtration.
The flow fractionation effect is observed only in thecase of the shear stress to the particles exceed over thecritical value that originates the rotational motion of theparticles in a flow stream. This indicates that the flow
stream of a given aqueous solution must be the laminarflow and the flow should give the shear rate to theparticles. The shear rate, τ, is given by the following
equation (1).
τ =V/t(1)

Where V is the flow rate (mm/s), t is the width of theflow path (mm). When the particles size are a
sub-micron, more than 20 sec-1 shear rate works
effectively on the rotational motion of the particles.

Fig.1: The flow fractionation effect diagram

Even in the case of the non-woven fabric membrane,
the flow fractionation is available and also the porediffusion is applicable. We can expect the developmentof the novel low cost and small scale equipment forwater treatment.
In this paper, we will prepare a prototype non-woven
fabric membrane by pressing a commercial available
non-woven fabric. The pressed non-woven fabric maybe evaluated compression ratio, surface roughness andan average pore size. The wastewater containing
particles of a certain particle size may be employed andthe separation performances including particle removal
ability and filtration speed may be evaluated. We intend
to evaluate the potential application for the novel
separation technology.
II. METHODS
A. Non-woven fabric membrane
Regenerated cellulose filament non-woven fabric(The non-woven fabric membrane) was prepared bycopper ammonium process (100g / m² basis weight, 390
μm thickness, Ra=21.1 μm surface roughness), androller pressed or hot pressed in a wet condition. Hotpress was operated by hand with a heated iron. Roller
press machine was used for the roller press. The
average pore size of the original regenerated cellulose
filament non-woven fabric was about 100 μm including
support mesh pore size.

D. Average pore size
Average pore size of the membrane, more than 50%
compression ratio, was measured by the filtration rate of
distilled water by the following formula (3).

(3)

Where J is the flow rate (mL / min), d is the thickness(μm), ⊿ P is pressure difference (mmHg), A is themembrane area (m2). These are using the measuredvalues. Prρ is "1 - (cellulose density / membranedensity)". η is the viscosity.
E. Evaluation of filtration performance
The separation performance was evaluated byfiltering waste water through the non-woven fabricmembrane. The waste water includes the large particle
of toxic flocculated materials by using flocculating
agent (nucleating agent). The flocculated materials,
about 20 μm particle size (measured by DLS, Dynamic
light scattering. See Fig.3), were stirred by a pump of
the flow fractionation separation unit and crushed byshear force to smaller particles about 10μm to be around.
The particles were filtered through the pressed
non-woven fabric membrane.

B. Compression ratio
The compression ratio was calculated with thethickness of the membrane before and after pressing.
Compression ratio is given by the following equation(2).
Compression ratio = (T1-T2)/T1×100(2)

Where T1 is the thickness of non-woven fabricmembrane before pressing, T2 is the thickness afterpressing.
C. Surface roughness
The surface roughness of the pressed non-woven
fabric by the roller press was measured. The surface
roughness is represented by the average roughness Ra.
When the highly of the surface of the fabric isexpressed in y = f(χ), in micrometers (μm), Ra value
was determined by the equation shown in the figure
below the roughness curve.

Fig.2: Surface roughness Figure

Fig.3: Particle size distribution of the flocculatedmaterials (nm)III. RESULTS AND DISCUSSION
A. Non-woven fabric membrane
Regenerated cellulose filament non-woven fabric bycopper ammonium process was pressed by roller pressmachine at 30 C in wet condition.
The cross-section of the pressed non-woven fabricmembrane was observed with a microscope.
Distribution of fiber was measured as a function of thedistance from the surface of non-woven fabric and total
fiber number per cross-sectional area unit. The numberof fiber cross-section present in the layer of 500 μm
length and 50 μm depth of the cross-sectional view wasmore than 10 in any layer. Pulsation of the number had
been within 2 times of the number and the averagenumber of 0 and those values are the number of fibercross-section present in the layer at 500 μm length 10μm depth cross-sectional direction also. The pulsation
indicates that non-woven fabric membrane has alaminated multilayered structure. This multilayered
structure is one of the most important factors for theseparation by the use of a membrane. Thus thisprototype non-woven fabric membrane can be expectedhaving a certain separation performance.

2520

15

10

50

1

2

34

Fig.6:Surface roughness Ra. 1.Original, 2.Hot press,
3.Rollar press (center), 4.Rollar press (edge)

Fig.4: Cross-sectional view of the non-woven fabricmembrane (left: original, right: pressed)

D. Average pore size
Pressed non-woven fabric membranes were preparedin industrial scale under the conditions of 52.6%
compression rate. The average pore size of themembrane was measured through the water filtration
rate method. The average pore size was about 8 μm
degree, as shown Fig.6.

Pore size (um)B. Compression ratio
Compression ratio of the pressed non-woven fabricmembrane was measured. The observed compression
rate of the hot pressed membrane was 11.8%. The edgeof the Roller Pressed membrane was 52.6% and at thecenter of it was 43.2%.

60.0%
50.0%

9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0

60

40.0%

80100120

140

Membrane thickness (um)

30.0%

Fig.6: Change in pore size with thickness ofmembrane; prepared by compression rate 52.6 %

20.0%
10.0%

23

Fig5: Compression ratio of membrane prepared bypressing; 1.Hot press, 2.Rollar press (center),
3.Rollar press (edge)
C. Surface roughness
Surface roughness was measured before and after thepress of the non-woven fabric membrane. The original
non-woven fabric was Ra (μm) = 21.1, the hot Pressed
membrane was Ra (μm) = 13.9, roller pressed (center)
Ra (μm) = 17.1, (edge) Ra (μm) = 7.7. For water
treatment, it might be necessary to make the surface
roughness small as like less than Ra = 10 to realize
laminar flow. It is necessary to clarify the condition of
the edge of the roller pressed non-woven fabricmembrane in order to get the reproducible
manufacturing. Fig.6 represents the value of Ra for four
membranes.

E. Evaluation of filtration performance
By using the non-woven fabric membrane preparedin industrial scale, a wastewater was filtered and its
separation performance was evaluated. After filtration,
large particles with more than 10 μm in the waste water
were almost cleared by visual inspection.
The filtration rate in this filtration experiment could
maintain at a stable filtration rate about two days (3,000minutes) and almost no clogging was observed.
90

80
70

60
50

40
30

20
1005120
235
350
465
580
695
810
925
1040
1155
1270
1385
150016151730
1845
1960
2075
2190
2305
2420
2535
2650

1

V /L･m 2-1 ･h-1

0.0%

t /minFig.7: Filtration performanceIV. CONCLUSION
It was possible to compress and reduce the thicknessof the non-woven fabric membrane in the wet state.
It was able to reduce the surface roughness and theaverage pore size of the non-woven fabric membrane bypressing.
It was confirmed the particle removal performancefor 10 μm particle size. The performance maintained
almost stable between two days (3000 minutes) andalmost no clogging was observed under the flow
fractionation and the pore diffusion.
V. ACKNOWLEDGEMENTS
We are deeply grateful to Mr. Takeuchi, Asahi
Kasei Fibers Corp. for his enormous supports suchas providing membrane samples and helpfulcomments. Also, we would like to thank FAIS,
Kitakyushu Foundation for the Advancement ofIndustry, Science and Technology, for his financial
supports.

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S. Kim, S. Lee, C. Kim, J. Cho, “A new membrane performanceindex using flow-field flow fractionation (fl-FFF)”, Desalination,
vol. 249, 2009, pp. 169-179
N. Maeda, “Microcirculation of Erythrocytes in Relation toTheir Rheological Properties”, Fluid Dynamics Research, vol.
21, 2002, pp. 129-134
N. Maeda, “Blood Flow Structure Related to Red Cell Flow”,
Jpn. J. Physiol., vol. 51, 2001, pp. 19-30T. Pan, T. Wang, “Dynamical Simulation of Red Blood Cell
Rheology in Microvessels”, Int. J. of Numerical & Modeling,
vol. 6, 2009, pp. 455-473