GEOLOGICAL SOCIETY OF THE PHILIPPINES
Preliminary Studies on the Development of Nano-Engineered Filtration Geotextiles
Over the years, geotextiles have played significant roles in erosion control and subsurface drainage. Today’s geotechnical civil engineering firms are now considering geotextiles as an alternative to natural materials. These filter fabrics, made of polymeric materials, can be used together with granular soils to improve filtration.
With regard to this, a novel approach of producing geotextiles has been conceptualized. With the increasing utilization of nanofibers to filtration, reduction of the geotextile fibers to the nano-scale level will be investigated. Several studies claim the potential of electrospun nanofibers for filtration applications.
This research aims to investigate on the potential of electrospun polypropylene nanofiber nanocomposite for filtration geotextile. Melt electrospinning, a cost-effective and environment friendly method of producing nanofibers, shall be employed in the fabrication of woven and nonwoven geotextiles.
Organo-modified montmorillonite, extracted from the bentonite deposit of Albay will be compounded to the polymer melt to enhance the mechanical strength of the nanofibers. Using Scanning Electron Microscope (SEM) the fibers will be characterized in terms of fiber morphology and diameter. Following American Standards for Testing Materials (ASTM), the patented geotextile will be evaluated in terms of its physical, mechanical and hydraulic properties.
This paper will conclude by reviewing a new way of producing geotextiles by examining the implication of emerging nanofiber technologies for the next generation of geotextiles.
Geotechnical problems were solved originally using natural materials such as soils and rocks. This traditional approach is relatively expensive, not always readily available and difficult to install. As a response to more economical geotechnical demands, geotextiles were developed. Along with the advance of polymers, a low cost alternative to natural materials became at hand. Today, geotextiles are readily accepted as a standard solution to geotechnical and hydraulic engineering problems. These textiles had proven their efficiency in soil stabilization, pavement rehabilitation, revetment filtration, basal and soil reinforcement, erosion control, etc (Tencate Geosynthetic Seminar, May 2007). They had rapidly revolutionized in the past 30 years due to the vast number of applications that they can perform.
Filtration is the oldest and most commonly used function of geotextile (TM 5-818-8/AFJMAN 32-1030, 1995). This function restricts the migration of soil particles but allows water movement or flow. Filtration geotextiles are very handy filter mediums that can retain soil particles of fill materials in place, while allowing the release of accumulated hydraulic pressure. With regard to this, a novel approach of producing geotextiles is conceptualized. The customary fabrication techniques were accomplished by two basic steps: (1) by making linear elements such as fibers and yarns and (2) by combining these to make planar structure designated as a fabric (Rao and Raju, 1990). These manufacturing methods produce a variety of geotextiles, and can be classified into woven, nonwoven and knitted. In this study, fiber production would be brought down to the nanoscale level. Nanofibers are suitable for filtration applications because of low density, large surface area to mass, high pore volume and tight pore size they offer (Tsai, 2001 in Hedge et. al. 2005 and Ko, 2004). Earlier researchers have proven the potential of nanofibers for filtration usage. Wordwide efforts of investigating the potential of nanofibers for air filtration (Grafe and Graham, 2003) had already been conducted, but rarely for soil filtration for geotechnical purposes.
In this work, melt electrospinning, which is an environmentally benign (Zhou, et. al. 2006) and cost effective method of producing nanofibers, would be employed to patent the geotextile. Compared to solution electrospinning, this method has a higher production rate, of about 10 to 50 times (Warner, et. al. 2006). Health risks associated with the use of more aggressive chemicals to dissolve the polymer to be used would be eliminated.
Polypropylene is the polymer to be electrospun because it is an "economical material that has an outstanding combination of physical, chemical, mechanical, thermal and electrical properties not found in any other thermoplastic" (quoted from San Diego Plastics, Inc., 1996). In addition, this material has dominated other polymers in geotextile manufacturing, of about 85% use worldwide (Koerner, 1998).
When fibers are in the nanometer range, the survivability is a problem (Chung, 2006). In order to enhance the mechanical properties, nanoclay would be compounded with the polypropylene melt. Note that nanoparticles, such as nanoclay can serve as matrix reinforcement for base materials (Kim, et. al. 2002; Alexander and Dubois, 2000 in Silvera Batista and Archer, 2005). Basilia (2004) developed a nanocomposite with improved tensile strength. Organo-modified montmorillonite, extracted from the bentonite deposit of Albay, Philippines was blended with recycled PET. The organo-modifed montmorillonite used by Basilia (2004) would be the nanoclay to be used in this study. The effect of nanoclay compounding to the geotextile fabric strength would be studied by varying the percentage of nanoclay to be blended in the polymer melt.
Currently, the melt-electrospinning apparatus is being set-up is and is being tested if it effectively produces nanofibers. The apparatus is composed of a micro pump controlled glass syringe, bounded by a nozzle heater to provide the heat. The glass syringe has a circular cross section of one inch diameter, with its longitudinal axis oriented vertically/ horizontally. Attached to the tip of the syringe is a needle. Positive terminal of a high voltage source of 20 kV capacity is be attached at the tip of the syringe, positioned 2 to 12 inches away from the grounded collector. The grounded collector is enclosed by a guided heating chamber, to avoid rapid solidification of fibers. A hot plate is used to provide heat to the guided (glass/wood) heating chamber. Two grounded collector will be utilized, a rotating collecting drum for the woven filtration geotextile and an aluminum collecting plate for the nonwoven filtration geotextile. After producing the nanofibrous woven/nonwoven geotextile, the fibers will be characterized in terms of fiber morphology and diameter using Scanning Electron Microscope (SEM). Following American Standards for Testing Materials (ASTM), the patented geotextile will be evaluated in terms of its physical, mechanical and hydraulic properties.
This paper concludes by reviewing a new way of producing geotextiles by examining the implication of emerging nanofiber technologies for the next generation of geotextiles.
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