Types of nonwoven fabrics: Nonwovens, depending on the production process can be divided into:
• Materials produced by physicochemical methods; and
• Mechanically produced materials.
Materials produced by physicochemical methods
Most nonwoven materials, are made by binding fibers with adhesives. The most common glued materials are those based on fibrous cloth (a layer of textile fibers whose weight is 10–1000 gsm 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.
A fibrous cloth is usually made of cotton, a mixture of viscose and polyamide fibers or the waste products of textile manufacture, including unspun fibers. The most common method of producing bonded nonwoven materials are to impregnate the cloth with a liquid adhesive or spraying/printing the adhesive over the surface of the cloth. Gluing the fibers includes saturate bonding and spray bonding or a latex adhesive is applied to the fibers and then the fabric is dried. The impregnated material is dried and treated in chambers heated by hot air or infrared radiation. The nonwoven materials made in this fashion (at a rate of 50 m/min and more) are used as interlacing and sealing materials, as heat and sound insulation materials for upholstery, bedding and drapery liners.
Melting fibers together can only be accomplished with synthetic, thermoplastic fibers or with a blend of fibers containing thermoplastic fibers or fusable powders. These methods include thermal bonding (heat applied to the web with or without pressure) a carded web, ther-mobonding a spunlaid web with a calendar, thermobonding a melt blown or flash spun web with a calender, thermal bonding a carded or air laid high loft web in an oven.In the hot-pressing process, the fibers are bonded by thermoplastics such as polyamides, polyethylene, and polyvinyl chloride at pressures of up to 2 mega newtons 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 or after its formation.
In the spunbonded 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.
Mechanically produced materials
Stitch bonded Nonwovens
According to the maliwatt technique in the German Democratic Republic [GDR] and the Arachne technique in Czechoslovakia, stitched nonwoven materials are made by joining fibers into the fabric, which is moving through a knitting-stitching machine, stitching with threads placed and joined like foundation stitches on a knitting machine. Such nonwoven materials are used as thermal insulation or packing material or as the foundation in the manufacture of quilts, blankets and jackets.
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 for towels. Especially useful are thread-stitched materials with pile loops (half-loops), which can compete successfully with woven shag fabrics. Sheet-stitched nonwoven materials are made by stitching a pile-woven textile sheet with napped yarn which facilitates improved structure and properties of the sheet. 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. 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 or linings for rugs and carpets and blankets.