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Nonwovens / Technical Textiles


Geotextiles provide important benefits in civil engineering and agricultural applications.

Jürg Rupp, Executive Editor

F rom the beginning, people have tried to master hydraulic power. The separation of water and land is one of the oldest requirements of mankind. Geotextiles have been used for thousands of years. They were used in roadway construction in the days of the pharaohs to stabilize roadways and their curbs. These early geotextiles were made of natural fibers, fabrics or vegetation mixed with soil to improve road quality, particularly when roads were constructed on unstable soil. In medieval times, levees were first constructed to create more usable land or to protect against flooding. Today, they are made using geotextiles. If the geotextiles are not properly applied, failures occur, such as the levee failures after Hurricane Katrina in 2005.

Parallel with the development of modern man-made fibers, geotextiles became essential for modern civil engineering. Geotextiles are nonvisible, permeable fabrics used in civil engineering construction projects such as paving, dams, embankments and drains for the purpose of soil reinforcement and stabilization, sedimentation and erosion control, support and drainage, and many other applications.

Gigantic projects such as the man-made Palm Jumeirah Islands in Dubai can only be built with the use of extremely durable nonwovens.

Barrier And Filtration
Geotextiles serve mainly as barrier and filtration materials to permanently separate the soil from water and ultimately to prevent water pressure buildup, therefore preventing the water's flow from causing erosion. Geotextiles also are used effectively for optimizing the productivity of crops, gardens and greenhouses. Their protective nature reduces the need for pesticides and keeps manual labor to a minimum.

Geotextiles serving as barrier and filtration materials permanently separate soil from water and ultimately prevent water pressure buildup, thereby preventing the water's flow from causing erosion.

Geotextiles may be used in place of soil nailing as an effective and less expensive reinforcement of slopes, retaining walls or excavated areas. Such reinforcement allows for landscaping of steep slopes, for example, to enhance aesthetic value.

The most important factors that dictate the construction or strength of a geotextile product are the force with respect to hydraulic pressure exerted on the fabric by the soil, and the fabric's porosity, which determines the product's barrier or filtration capabilities. Therefore, a defined machine direction:cross direction (MD:CD) ratio is of outstanding importance. Depending on the requirements, the products primarily are woven, needlepunched or chemically bonded.

Most major breaches in the New Orleans levee system after Hurricane Katrina in 2005 were caused by flaws in design, construction and maintenance.

Needlepunch Technology
For geotextiles, needlepunch technology is in the forefront of production, thanks to its sophisticated machinery and the easy treatment of all kinds of virgin and recycled fibers. Geotextiles and filter media, along with bicomponent fibers for every conceivable quality of composite, occupy the limelight.

Throughout the textile chain, the term "sustainability" is no longer an empty phrase, and recycling is of growing significance. As the majority of thermoplastic man-made fibers are easy to recycle, products formerly consisting of various components have now been restructured to enable recycling of textile waste.

Agricultural Applications
Geotextiles are tailor-made products, and the list of applications is never-ending. Here are some examples in which geotextiles are in use for agricultural purposes:
•    crop covers;
•    plant protection;
•    seed blankets;
•    weed-control fabrics;
•    biodegradable plant pots;
•    capillary matting;
•    landscape fabric; and
•    protection from frost and insects.

Fibers Used In Geotextiles
The main man-made polymer materials used to make geotextiles are polypropylene and polyester, but for some applications, natural fibers such as coir or jute are used. Natural-fiber-based erosion-control geotextiles are subject to decomposition and have a limited useful life before their inherent durability suffers. Onsite use of natural-fiber blankets degraded in this way can result in an ineffectual installation. Man-madepolymers have the advantage of not decaying under biological and chemical processes, but being petrochemical-based products, they are made from nonrenewable resources; and they also cause environmental pollution in their manufacture and use, and have associated health risks.

Ideally, vegetation can provide the best erosion control, but this may be difficult to establish. The use of hydroseeding or seed-impregnated fabric can be an effective method to establish vegetation. Hydroseeding, sometimes referred to as hydromulching, is a fast, efficient and economical process of planting grass. A mix is made of fibrous mulch, seed, fertilizer, and water. Different fibers will degrade at different rates - for example, coir geotextiles degrade in two to three years, and jute in one to two years. Coir is therefore useful in situations where vegetation will take longer to establish, and jute is useful in low-rainfall areas because it absorbs more moisture.

The rate of erosion depends on factors such as climate and temperature as well as the consistency of the soil. Experts estimate that some 40 percent of the world's agricultural land is seriously degraded due to erosion. The applied nonwovens must be tailor-made and configured according to the consistency and the fineness of the soil: the finer the particles, the finer the fabric  required. Most nonwoven geotextiles are used in road construction as a barrier fabric and to support the road construction between the stone and gravel layer and the tarmac. As mentioned before, water is of great importance to erosion processes and the reason for many problems around the world. Geotextiles are especially suitable for reinforcing slopes to prevent erosion caused by water.

Any modern harbor construction is underlaid with geotextiles. The way it functions is easy to explain: Imagine standing on the beach with your feet in the shallow water. After one minute, your feet are covered with sand. If you stand on a towel, your feet are still visible because the towel is acting like a geotextile respectively as a barrier fabric to provide the free flow of the water.

Most of the major breaches in the New Orleans levee system after Hurricane Katrina were caused by flaws in design, construction and maintenance. It has been reported that lives may have been lost because mistakes were made and safety was exchanged for cutting corners and reducing costs. Some parts of the system could still be unstable even after the current round of repairs by the US Army Corps of Engineers.

Agrotextiles Reduce Chemical Use
The use of nonwoven crop covers on the land increases yields and improves crop quality. Very light, flexible sheets are laid over seed beds, creating a microclimate in which the heat and humidity are controlled. Plant growth is accelerated, and the plants are protected from adverse weather conditions and vermin. In capillary mat applications, nonwovens promote the healthy growth of flowers and vegetables in greenhouses by offering soilless growing methods.

The spaces among the intersecting fibers of nonwoven sheets are big enough to allow air and water to penetrate the fabric and reach the crop, but small enough to keep out insects. The protection allows plants and crops to grow without the need to use pesticides and herbicides.

With the further improvement of raw materials, such as fibers, coating material, composite constructions and other products; and, last but not least, with modern machinery and equipment, the end-uses for all kinds of geotextiles have expanded considerably. The products also have appeared on the market under such names as geogrids and geonets.

January/February 2009