Notes Bull. Korean Chem. Soc. 2014, Vol. 35, No. 6 1901

http://dx.doi.org/10.5012/bkcs.2014.35.6.1901

Preparation and Characterization of Polypropylene Non-woven Fabrics

Prepared by Melt-blown Spinning for Filtration Membranes

Kong-Hee Chu, Mira Park, Hak-Yong Kim, Fan-Long Jin,†,‡ and Soo-Jin Park‡,*

Department of BIN Fusion Technology, Chonbuk National University, Chonju 561-756, Korea†Department of Polymer Materials, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China

‡Department of Chemistry, Inha University, Incheon 402-751, Korea. *E-mail: sjpark@inha.ac.kr

Received January 27, 2014, Accepted February 14, 2014

Key Words : Polypropylene, Nonwoven fabrics, Melt-blown, Plasma, Tensile strength

Polypropylene (PP) non-woven fabrics have been widely

used as filtration membranes in wastewater purification with

industrial applications due to their low cost, good mech-

anical strength, and high thermal and chemical stability. The

membrane fouling behavior depends strongly on the physi-

cal and mechanical properties of the membrane, including

pore size, porosity, morphology, and hydrophilicity.1-5

In general, PP non-woven fabrics have poor hydrophili-

city; this has limited their application in the biomedical field.

It is therefore necessary to develop PP non-woven fabrics

with improved surface hydrophilicity to increase the scope

of their use. Plasma treatment, an environmentally friendly

alternative to traditional chemical activation, only changes

the uppermost atomic layers of a membrane surface without

affecting the bulk properties of the polymer.6-12

To perform as a functional membrane, the PP non-woven

fabrics must have a porosity of ≤ 1 μm, remove > 95% of

impurities, and possess a morphology for surface filtration.

However, the porosity of traditional membranes prepared

from non-woven fabrics is ≥ 5 μm and exhibit a depth

filtration mechanism. The fibers prepared by melt-blown

spinning have usually 8-15 μm porosity, which is reduced to

1-2 μm after heat treatment.13-15

In this study, PP nonwoven fabrics were prepared by a

melt-blown spinning process. To control the porosity and

impart hydrophilicity, the PP non-woven fabrics were treated

with heat and plasma processes. The mechanical properties,

contact angle, water flux, average pore size, average pore

pressure, and particle removal efficiency of these PP non-

woven fabrics were investigated.

PP non-woven fabrics were prepared by melt-blown spinn-

ing. However, the resulting PP non-woven fabrics have a

large pore size and low hydrophilicity, making them un-

suitable for use as filtration membranes. The PP non-woven

fabrics were subsequently treated with heat and plasma

processes to control porosity and impart hydrophilicity.16,17

Figure 1 shows SEM micrographs of the PP non-woven

fabrics before and after heat treatment. Figure 1 shows the

increase in the fiber sizes of the PP non-woven fabrics from

2-7 μm to 4-11 μm before and after the heat treatment. This

was due to the densification effect.18,19

Table 1 shows the mechanical properties of the PP non-

woven fabrics before and after heat treatment. The tensile

strength of the original PP non-woven fabrics was 2.8 MPa,

which increased to 9.1-9.4 MPa after heat treatment, due to

the increasing interfacial bonding strength induced by the

process.20 However, the heat treatment process reduces the

elongation of the PP non-woven fabrics from 103% to 28.2-

49.3%.

Table 2 shows the contact angle of the PP non-woven

Figure 1. SEM micrographs of PP non-woven fabrics before (a)and after heat treatment (b).

1902 Bull. Korean Chem. Soc. 2014, Vol. 35, No. 6 Notes

fabrics before and after plasma treatment. The contact angle

of the PP non-woven fabrics decreased significantly after

plasma treatment, indicating that the hydrophilicity of the

non-woven fabrics was improved. This can be attributed to

the formation of oxygen-containing functional groups at the

PP non-woven fabric surface by the oxygen plasma treat-

ment process.21-24

Yu et al. studied PP microporous membranes modified by

air plasma treatment.21 Their results indicated that the static

water contact angle decreased evidently from 128.5o to 35.0o

with increasing treatment time from 0 to 8 min. Jaleh et al.

showed that the surface of a PP membrane could be made

superhydrophilic by the oxygen plasma treatment, which

results in the formation of C=O, C−O, and O−C=O bonds at

the membrane surface.22 Similar results have been reported

by Wei and Mirabedini et al. using plasma treated PP fibers

and films.23,24

Figure 2 shows the water flux, average pore size, and aver-

age pore pressure of the PP non-woven fabrics before and

after the heat and plasma treatments. Figure 2(a) shows that

the water flux of the PP non-woven fabrics decreased signi-

ficantly after the heat treatment, but increased about two fold

after the plasma treatment. Oxygen plasma treatment leaves

active sites on the PP membrane surface, which is subject to

further activation-reactions; oxygen-containing functional

groups can be introduced on the PP membrane surface after

breaking the C−C and C−H bonds. The uppermost atomic

layer of the surface is activated to improve wettability with-

out affecting the bulk properties of the polymer, thus signi-

ficantly enhancing the water flux.22

Figure 2(b) shows that the average pore size of the PP

non-woven fabrics decreased significantly after the heat

treatment. The open pores in the PP non-woven fabrics were

partially filled with PP consequently, reducing the average

pore size and open porosity.25 The average pore size of the

PP non-woven fabrics after heat treatment was 0.7 μm, a

nano-sized pore size. The average pore size of the PP non-

woven fabrics was not altered after the plasma treatment.

Figure 2(c) shows that the average pore pressure of the PP

non-woven fabrics increases significantly after the heat

treatment, owing to low permeability induced by the pro-

cess.26 The average pore pressure of the PP non-woven fabrics

was not altered after the plasma treatment.

Figure 3 shows particle removal efficiency of the PP non-

woven fabrics after the heat and plasma treatments. The

particle removal efficiency was 97.2% for a particle size of 1

μm, 98.6% for 2 μm, and 99.4% for 3 μm, demonstrating

excellent particle removal efficiency.

These results show that PP non-woven fabrics prepared by

melt-blown spinning, following by heat and plasma treat-

ments, have nano-sized pores, high hydrophilicity, improved

mechanical properties, and excellent particle removal effici-

ency, making them suitable for use as filtration membranes

for wastewater purification.

In conclusion, PP non-woven fabrics were prepared by

melt-blown spinning, followed by heat and plasma treat-

Table 1. Mechanical properties of PP non-woven fabrics

SampleBefore heat

treatment

After heat

treatment

Tensile strength (MPa) 2.8 9.4

Elongation at break (%) 103 28.2

Table 2. Contact angle of PP non-woven fabrics before and afterplasma treatment

SampleBefore plasma

treatment

After plasma

treatment

Contact angle ( o ) 114 96

Figure 2. Water flux (a), average pore size (b), and average porepressure (c) of PP non-woven fabrics before and after heat andplasma treatments.

Notes Bull. Korean Chem. Soc. 2014, Vol. 35, No. 6 1903

ments. After heat treatment, the PP non-woven fabrics dis-

played decreased water flux, increased tensile strength,

decreased elongation, and an average pore size of 0.7 μm.

The hydrophilicity of the PP non-woven fabrics was improv-

ed by plasma treatment. The water flux of the PP non-woven

fabrics increased about two fold after the plasma treatment.

The particle removal efficiency was determined to be 97.2-

99.4% for 1-3 μm sized particles, demonstrating a high

particle removal efficiency.

Experimental Section

Materials. The PP used in this study (purchased from

PolyMirae Co. of Korea), possessed a melt index of 900-

1100 g/min and density of 0.9 g/cm3. The PP non-woven

fabrics were prepared using a melt-blown spinning techni-

que under an extruder inlet/outlet temperature of 120 oC/230oC, through-put of 0.1 g/min, air pressure of 0.3 kg/cm2, and

die to collector distance of 150 mm.

Heat and Plasma Treatments. The PP non-woven fabrics

were heat (densification) treated using a calendar at a

pressure of 60 psi, line speed of 4 m/min, press spacing of

0.02 mm, and roll temperature of 120 oC. The PP non-woven

fabrics were plasma treated for 5 min under 100% oxygen at

a total gas flow rate of 300 cm3/min.

Characterization and Measurements. The surfaces of

the non-woven fabrics were investigated using a scanning

electron microscope (HITACHI S-3000N).

The tensile strength test was conducted using an Instron

mechanical tester (LRIOK model) at a tensile speed of 20

mm/min. All of the mechanical property values were obtain-

ed as the average of five experimental values.

The contact angle of the PP non-woven fabrics was mea-

sured using a contact angle tester (Dataphysics DCTA 21

model) with de-ionized water as the wetting liquid.

The water flux of the non-woven fabrics was measured

using a permeation cell tester (Amicon Model 8050) at pre-

ssure of 1 bar and temperature of 30 oC.

The average pore size of the non-woven fabrics was mea-

sured using a capillary flow porometer (Porous materials,

Inc. CFP-1200-AEL).

The particle removal efficiency of the PP non-woven

fabrics was measured using a particle efficiency tester with

ISO 12103-A standard particle at a concentration of 3 ppm

and flow rate of 11.4 L/min.

Acknowledgments. This work was supported by the

Carbon Valley Project by Ministry of Trade, Industry and

Energy, and the Eco-Innovation Project by Ministry of

Environment, Korea

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Figure 3. Particle removal efficiency of PP non-woven fabricsafter heat and plasma treatments.