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
Sample Before 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 after plasma treatment
Sample Before plasma
treatment
After plasma treatment
Contact angle (o) 114 96
Figure 2. Water flux (a), average pore size (b), and average pore pressure (c) of PP non-woven fabrics before and after heat and plasma 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/230
oC, 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 fabrics after heat and plasma treatments.
