Use of Fibers in Geotextiles:
Primary uses of geotextiles are separation or stabilization, drainage, erosion control and reinforcement of road sides or river banks. Different fibers from both natural as well as synthetic category can be used in the manufacture of geotextiles for various applications. Natural fibers can be classified based upon their origin, whether plant or vegetable, animal, or mineral. Plant fibers have the greatest potential for use in geotextiles because of their superior engineering properties; for example, animal fibers have lower strength and modulus and higher elongation than vegetable fibers. Mineral fibers are very expensive, brittle, and lack strength and flexibility. Moreover, tensile strength is an important property in order to carry out the reinforcement functions of geotextiles successfully; plant fibers thus exhibit the greatest potential for use in geotextiles.
On the other hand, synthetic fibers have been used as the main raw material for the manufacture of geotextiles. The four most common synthetic fibers used for the production of geotextiles are polypropylene, polyester, polyamide, and polyethylene.
Natural fiber-based geotextiles have found a particular interest for the last 2 decades as an increasing knowledge of natural fiber properties has been gained. Natural fibers in the form of paper strips, jute nets, wood shavings or wool mulch are being used as geotextiles. In certain soil reinforcement applications, geotextiles have to serve for more than 100 years. But bio-degradable natural geotextiles are deliberately manufactured to have relatively short period of life. They are generally used for prevention of soil erosion until vegetation can become properly established on the ground surface. The list of plant fibers that can be used in geotextile manufacture includes jute, sisal, flax, hemp, abaca, ramie, and coir.
The frequently used natural fibers in the manufacture of geotextiles are:
These are subtropical bast fibers, which are obtained from their plants 5 to 6 times a year. The fibers have silky luster and have white appearance even in the unbleached condition. They constitute of pure cellulose and possess highest tenacity among all plant fibers.
This is a versatile vegetable fiber which is biodegradable and has the ability to mix with the soil and serve as a nutrient for vegetation. Their quick biodegradability becomes weakness for their use as a geotextile. However, their life span can be extended even up to 20 years through different treatments and blendings. Thus, it is possible to manufacture designed biodegradable jute geotextile, having specific tenacity, porosity, permeability, transmissibility according to need and location specificity. Soil, soil composition, water, water quality, water flow, landscape etc. physical situation determines the application and choice of what kind of jute geotextiles should be used. In contrast to synthetic geotextiles, though jute geotextileas are less durable but they also have some advantages in certain area to be used particularly in agro-mulching and similar area to where quick consolidation are to take place. For erosion control and rural road considerations, soil protection from natural and seasonal degradation caused by rain, water, monsoon, wind and cold weather are very important parameters. Jute geotextiles, as separator, reinforcing and drainage activities, along with topsoil erosion in shoulder and cracking are used quite satisfactorily. Furthermore, after degradation of jute geotextiles, lignomass is formed, which increases the soil organic content, fertility, texture and also enhance vegetative growth with further consolidation and stability of soil.
Coir, jute, and flax fibers are mainly composed of cellulose, hemicellulose, pectin and lignin but coir fibers present an higher lignin percentage. Consequently, when submitted to the natural soil degradation performed by microbial population flax fibers will likely present higher sensitivity compared to coir fibers as lignin degrading organisms are less widespread than cellulolytic ones.
Flax tows from textile varieties and flax fibers from oleaginous varietiess are byproducts of the textile and vegetal oil industries respectively. From a mechanical point of view, flax fibers have higher tensile strength, compared to coir fibers. Up to now the highest properties are reported for flax and nettle fibers slightly above hemp. However, their weak point is their low antimicrobial activity.
This may be due to the low micro-fibrillar angles observed for flax and hemp (about 10 degrees and 6 degrees respectively as compared to coir 45 degrees). Indeed, high micro-fibrilar angles have for consequence to reduce the sensitivity to microorganism attack.
The four main synthetic polymers most widely used as the raw material for geotextiles are – polyester, polyamide, polyethylene and polypropylene. The oldest of these is polyethylene which was discovered in 1931 by ICI. Another group of polymers with a long production history is the polyamide family, the first of which was discovered in 1935. The next oldest of the four main polymer families relevant to geotextile manufacture is polyester, which was announced in 1941. The most recent polymer family relevant to geotextiles to be developed was polypropylene, which was discovered in 1954.
The commonly used synthetic fibers in the manufacture of geotextiles are :
- Polyvinyl chloride
- Ethylene copolymer bitumen
- Chlorinated polyethylene
Above synthetic fibers are described below:
1. Polypropylene (PP):
Polypropylene is amongst the most widely used fibers for the manufacture of geotextiles because of its low cost, acceptable tensile properties, and chemical inertness. The fiber has an added advantage as it has low density, which results in a very low cost per unit volume. The major disadvantages of polypropylene include its poor sensitivity to ultraviolet radiation.
Moreover, its properties can easily deteriorate under high temperature conditions and it exhibits poor creep characteristics.
Polypropylene is a crystalline thermoplastic produced by polymerizing propylene monomers in the presence of stereo-specific Zeigler- Natta catalytic system. Homo-polymers and copolymers are two types of polypropylene. Homo polymers are used for fiber and yarn applications whereas co-polymers are used for varied industrial applications. Propylene is mainly available in granular form.
Both polyethylene and polypropylene fibers are creep prone due to their low glass transition temperature. These polymers are purely hydrocarbons and are chemically inert. They swell by organic solvent and have excellent resistance to diesel and lubricating oils. Soil burial studies have shown that except for low molecular weight component present, neither HDPE nor polyethylene is attacked by micro-organisms.
2. Polyesters (PET):
The other important synthetic fiber used in the production of geotextiles is polyethylene terephthalate (PET), commonly known as polyester. It has excellent tensile properties along with high creep resistance and the geotextiles made from polyester fibers can be used under elevated temperatures. The main demerit of polyester fiber is that it is susceptible to hydrolytic degradation in soils which have a pH of more than 10.
Polyester is synthesized by polymerizing ethylene glycol with dimethyle terephthalate or with terephthalic acid. The fiber has high strength modulus, creep resistance and general chemical inertness due too which it is more suitable for geotextiles. It is attacked by polar solvent like benzyl alcohol, phenol, and meta-cresol. At pH range of 7 to 10, its life span is about 50 years. It possesses high resistance to ultraviolet radiations. However, the installation should be undertaken with care to avoid unnecessary exposure to light.
3. Polyamides (PA):
The other synthetic fibers such as nylon 6,6 and nylon 6 belonging to the family of polyamides are also used in small quantities for manufacturing geotextiles. Although polyamide is a common fiber-forming polymer and textile material, nonetheless, it is rarely used in geotextiles, where its cost and overall performance render it inferior to other polymers.
There are two most important types of polyamides, namely Nylon 6 and Nylon 6,6 but they are used very little in geotextiles. The first one an aliphatic polyamide obtained by the polymerization of petroleum derivative ε-caprolactam. The second type is also an aliphatic polyamide obtained by the polymerization of a salt of adipic acid and hexamethylene diamine. These are manufactured in the form of threads which are cut into granules. They have more strength but less moduli than polypropylene and polyester They are also readily prone to hydrolysis.
4. Polyethylene (PE):
Polyethylene can be produced in a highly crystalline form, which is an extremely important characteristic in fiber forming polymer. Three main groups of polyethylene are – Low density polyethylene (LDPE, density 9.2-9.3 g/cc), Linear low density polyethylene (LLDPE, density 9.20-9.45 g/cc) and High density polyethylene (HDPE, density 9.40- 9.6 g/cc).
5. Polyvinyl chloride (PVC):
Polyvinyl chloride is mainly used in geo membranes and as a thermo plastic coating materials. The basic raw materials utilized for production of PVC is vinyl chloride. PVC is available in free- flowing powder form.
6. Ethylene copolymer Bitumen (ECB):
Ethylene copolymer bitumen membrane has been used in civil engineering works as sealing materials. For ECB production, the raw materials used are ethylene and butyl acrylate (together forming 50-60%) and special bitumen (40-50%).
7. Chlorinated Polyethylene (CPE):
Sealing membranes based on chlorinated poly ethylene are generally manufactured from CPE mixed with PVC or sometimes PE. The properties of CPE depend on quality of PE and degree of chlorination.
- Handbook of Technical Textiles – 2nd Edition Volume 2: Technical Textile Applications Edited by A. Richard Horrocks, Subhash C. Anand
- Handbook of Natural Fibres Volume 2: Processing and Applications, 2nd Edition Edited by Ryszard M. Kozłowski
- Geotextiles: From Design to Applications by Robert M. Koerner
- Jute Geotextiles and their Applications in Civil Engineering by Tapobrata Sanyal
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.