Nonwoven Materials

Nonwoven Materials

 

textiles made from fibers or threads joined together without weaving.

Large-scale industrial production of nonwoven materials began in the 1940’s. Modern nonwoven materials are one of the main types of textiles produced in many countries. In 1972, world output of nonwoven materials was more than 3 billion sq m.

Materials produced by physicochemical methods. Most non-woven materials—the bonded materials—are made by binding fibers with adhesives (glues). The most common glued materials are those based on fibrous cloth (a layer of textile fibers whose weight is 10–1,000 g/m2 and more). The cloth is most often formed mechanically from several layers of combed fibers passing through the dotting drum of a combing machine. Fibrous cloth may be produced by the aerodynamic method in which the fibers are removed from the drum of the combing machine by a stream of air and transferred to a mesh drum (condenser) or a horizontal mesh with a maximum speed of up to 100 m/min, or by water dispersion of the fibers on the mesh of a paper machine.

There are several methods of producing bonded nonwoven materials, depending on the peculiarities of bonding of the fibers.

The most common method is based on impregnation of the cloth with a liquid adhesive, a synthetic latex. The cloth is immersed in a bath of the adhesive, or the adhesive is sprayed over the surface of the cloth. Sometimes the impregnation process is similar to the printing method of applying a design to the surface of a fabric. The impregnated material is dried and treated in chambers heated by hot air or infrared radiation. The fibrous cloth is usually made of cotton, a mixture of viscose and poly-amide fibers, or the waste products of textile manufacture, including unspun fibers. The nonwoven materials made in this fashion (at a rate of 50 m/min and more) are used as interlacing and sealing materials, as filters, and as heat- and sound-insulation materials in the automotive industry.

In the hot-pressing process, the fibers are bonded by thermoplastics (such as polyamides, polyethylene, and polyvinyl chloride) at pressures of up to 2 meganewtons per sq m (MN/m2), or 20 kilograms-force per sq cm (kgf/cm2), at high temperatures, usually on special calenders. The bonding is preceded by thermal treatment of the fiber layer, which contains an adhesive that is applied to the fibrous cloth during its formation (in the form of easily fusible fibers, meshes, or threads) or after its formation (in the form of a powder).

In making nonwoven materials with a paper machine (at a rate of 100 m/min or more), the adhesive (latices, easily fusible fibers, and so on) are applied to the slush entering the machine or to the previously poured sheet. Such nonwoven materials are cheap and are widely used to make disposable goods (bedding for hotels; towels, tablecloths, or first-aid dressings).

In the spun-bonded method, synthetic fibers are formed as they leave the spinnerets of spinning machines and pass through troughs in which they are stretched in an air current; they are then placed on a conveyor belt and form a sheet. The material formed in this way is most often bonded with an adhesive; in some cases the stickiness of the fibers themselves is sufficient.

In the structure-forming method of making nonwoven materials, the use of fibers may be avoided. The sheets are formed by a condensed phase from solutions or aerosols of polymers (in the form of porous, sometimes fibrous sediment, which may contain a filler that is later washed away); the sheet may also be formed by solidification of a foam. Such nonwoven materials “breathe” like woven fabric. They can be used as fabric or paper substitutes in industry (for example, as filters) or in daily use.

Mechanically produced materials. In making stitched non-woven materials (the maliwatt technique in the German Democratic Republic [GDR] and the Arachne technique in Czechoslovakia), the fibers are joined into the fabric, which is moving through a knitting-stitching machine, by being stitched with threads placed and joined like foundation stitches on a knitting machine. Such nonwoven materials are used as thermal insulation (instead of woven quilting) or packing material or as the foundation in the manufacture of synthetic leather. The output of a single unit is 3–8 m/min.

Thread-stitched nonwoven materials (Malimo materials; GDR) are made by stitching with one or more thread systems. They are used for decoration, for beach wear or outer clothing, or for towels. Especially useful are thread-stitched materials with pile loops (half-loops), which can compete successfully with woven shag fabrics (of the frotté type).

Sheet-stitched nonwoven materials are made by stitching a pile-woven textile sheet with napped yarn (Malipol material; GDR), which facilitates improved structure and properties of the sheet. Malimo material and woven fabric are used for this purpose. Nonwoven materials for overcoats and skirts are stitched with wool worsted; foundations for tufted carpets (550 cm wide) are stitched with carpet yarn, using needles to pull it through the fabric. On the return motion of the needle, the worsted is caught on a hook, and a loop is made. To secure the loops, an adhesive is applied to the reverse of the carpet. Machines for this process can produce 5 m2/min and more.

Threadless nonwoven materials are made on knitting-stitching machines (Voltex material in the GDR and Arabeva in Czechoslovakia). Such materials may consist of fabric and cloth made of staple fibers. After the cloth fibers are pulled through the scrim, sturdy loops are formed on the reverse of the material, and a deep, fluffy pile is formed on the front. Such materials are used as thermal stuffing in athletic clothing and light overcoats or for making headwear or warm shoes.

Needlepunched nonwoven materials are the most promising; they are made by twisting the fibers in the cloth and stitching them with notched needles. The material is punctured as a board with the needles moves downward (to the limiter). As it is raised again the material moves forward (the machine can produce 5 m/min). Such nonwoven materials are used for carpets that complete successfully not only with woven carpets but also with tufted carpets, since yarn is not required for their manufacture. Needlepunched materials are also used as blankets, felt for paper machines, and filters.

Rolled felt is also a type of nonwoven material. The ability of the fibers to become matted is used in its production; the matting takes place mechanically or by treatment with heat and water. Such nonwoven materials sometimes have a scrim. The technique for making such materials has a long history (for example, felt boots are made in this manner).

REFERENCES

Tekhnologiia proizvodstva netkanykh materialov. Moscow, 1967.
Tikhomirov, V. B. Khimicheskaia tekhnologiia proizvodstva netkanykh materialov. Moscow, 1971.
Perepelkina, M. D., M. N. Shcherbakova, and K. N. Zolotnitskaia. Mekhanicheskaia tekhnologiia proizvodstva netkanykh materialov. Moscow, 1973.
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