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Nonwoven fabrics have long become an independent and technologically sophisticated industry in their own right and owe the industry's prosperity to a great multiplicity of raw material and process options. Non-woven fabrics can be classified in different ways by different classification systems. According to their manufacturing practices, non-woven fabrics can be divided into eight types in total.
1. Spunless nonwoven fabric
Spunless nonwoven fabric is an indispensable type of nonwoven fabric. Spunless nonwoven fabric may sound unfamiliar, but in fact, products made from this type of spunless nonwoven fabric are widely used such as wet wipes. The spunlaced process, also known as hydroentanglement, is a production system for nonwoven fabrics that use jets of water to entangle the fibers and thereby provide fabric integrity. The spunlace process is free from binders and therefore environmentally friendly. Nonwoven fabrics made with this process can retain their original properties. The fibers are not damaged, and the appearance is closer to traditional textiles than other types of nonwoven fabrics. Spunless nonwoven fabrics are characterized by high strength, low fluff, good absorbency and permeability, softness and washability.
2. Thermal bonding of nonwoven fabric
Thermal bonding can be performed in a number of ways, including a variety of heating methods. In through-air bonding, hot fluid or air is forced through a preformed web. When the temperature of the liquid or air is high enough, the fibers partially melt and bond where they come into contact. In infrared bonding, infrared light provides the heat needed to partially melt the fibers. In ultrasonic bonding, the ions between the friction fibers partially melt the fibers. In thermal point bonding, the preformed fiber web passes into heated calendar rolls that are either smooth or embossed with a bonding pattern. On a smooth calendar roll, bonding occurs where the fibers cross each other, while on an embossed calendar roll, bonding occurs primarily between raised areas. In all the processes mentioned above, the basic working principle is the same - the fibers are heated, bonded and then cooled. Thermal bonding is suitable for the production of nonwoven fabrics with thermoplastic fibers with low melting temperatures, including homophile and bicomponent fibers, which allows obtaining a wide range of fabric properties and aesthetics to meet a wide spectrum of needs. Thermal bonding is much less energy-intensive, kinder to the environment, and more economical. Effective thermal contact offers significant energy and water savings in contrast to latex bonding. It is more environmentally friendly because there is no residue to treat.
3. Air-laid nonwoven fabric
Air-laid refers to a manufacturing technology that creates a web of small fibers in an aerial way. Individually loose fibers and fine particles are uniformly dispersed in an air stream and laid on a metal mesh for bonding. Air-laid nonwoven technology typically uses latex emulsion, thermoplastic fibers, or some combination of both to bond the fibers of the web and increase the strength and integrity of the sheet. The process creates a paper-like fabric that is dense, soft and absorbent. Air-laid nonwoven fabrics boast more excellent tear resistance and tensile strength, especially when wet. These physical properties of air-laid nonwoven fabrics make them suitable for many disposable absorbent applications in the consumer, industrial and institutional sectors, such as household cleaning wipes and mops, adult incontinence products and baby diapers.
4. Wet lay nonwoven fabric
The working principle of wet-laying is generally similar to that of papermaking. The difference lies in the number of types of synthetic fibers present in wet-laid nonwoven fabrics. A thin slurry of water and fibers is deposited on a moving wire screen and drained to form a web. The web is further dried, consolidated and dried by pressing between rollers. Impregnation with binders is often included in later stages of the process. The strength of a randomly oriented web is somewhat similar in all directions in the plane of the fabric. A wide range of natural, mineral, synthetic and man-made fibers of different lengths can be used for the wet laying process.
5. Spunbond nonwoven fabric
Spunbond fabrics are produced by depositing extruded, chopped filaments on a collection belt followed by fiber bonding in a coordinated random manner. The materials used to make nonwoven fabrics using the spunbond technique are mainly terylene and polypropylene. Fibers are separated during the web-laying process by air jets or electrostatic charges. The collecting surface is usually perforated to prevent airflow from uncontrollably deflecting and carrying the fibers. Bonding imparts strength and integrity to the web by partially melting the polymer and applying heated rolls or hot needles to fuse the fibers. Since molecular orientation increases the melting point, fibers that are not drawn too much can be used as thermal binding fibers. Spunbond nonwoven fabrics are found in carpet backing, geotextiles, and disposable medical and hygiene products. Since fabric production is combined with fiber production, the process is generally more economical than using staple fibers to make non-woven fabrics.
6. Melt blown nonwoven fabric
Meltblown technology is one of the most effective ways to produce very fine, highly efficient filter media. The raw material is usually a thermoplastic synthetic material consisting of a very large number of tiny nozzles that are melted and forced through an extruder. Immediately after exiting the nozzle, the individual molten filaments are blown in the same direction by hot air while still in their semi-molten state, stretching them and forming very fine, continuous filaments within milliseconds. A melting fiber is less than 10µm in diameter, many times finer than human hair, which is 120µm in diameter.
7. Needle-punched nonwoven fabric
Needle-punched nonwoven fabrics are made in which the fibers are mechanically pressed together and abraded by repeated penetration of fine needle barbs. Needle-punched fabrics have characteristic periodicity in the structural architecture that results from the interaction of the fibers with the needle barbs. The fiber segments are rearranged and migrated from the surface of the web towards the interior of the fabric, forming a column of fibers oriented almost perpendicular to the plane.
8. Stitch-bonded nonwoven fabrics
Stitch bonding uses a cross-laid web, which is fed directly to the stitch bonder in a continuous process. The machine used in stitch binding is essentially a variation of a warp knitting machine, which binds the fabric by weaving columns of stitches down the length of the web. In some cases, the web is initially fed to a needle puncher to achieve a light needling operation, known as tacking, before the wool rolls are sent to a sewing board. Tacking enables easy unrolling of the fleece and improves mechanical interlocking between the fibers, which aims to provide adequate anchorage of the fibers to the fleece. Other measures to reduce this weakness include the use of longer staple length fibers and the inclusion of some relatively low melting point fibers, which can provide additional bonding during subsequent heat settings.
Source: Online/NNA
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