*2.1.4. Wool*

Wool is the most important animal fiber used in manufacturing nonwoven bonded fabrics. It is used mainly as reclaimed wool or cuttings because of its high price. The variation in quality and the impurities in reclaimed wool as well as the chemical and physical properties deter‐ mined by its provenance impose restrictions on its use [17].

Wool is a suitably stiff and permanently crimped bi-component fiber. The distinct variations in thickness are in most cases favorable to produce nonwovens [16]. Wool fiber is initially used to make felt. The wool fibers are then pressed into a flat sheet and subjected to moisture, heat, and agitation. The scaly structure of the wool fiber causes the fibers to interlock and mat. Weaving or knitting in the production of such felts and simple mechanical interlocking of fibers in the production of such felts and simple mechanical interlocking of fibers in a batt structure is capable of producing a dimensional stable fabrics with densities, up to 0.7 g/cm3 . Animal felts have been used since ancient times. Traditional felting method is still used for producing clothing item such as hats, slippers, interlinings and handbags. In addition to traditional felting method, modern pressed felting techniques are used in a wide range of industrial applications. These products are used for polishing metals, optical surfaces plastics, and jewelry, and in manufacturing seals, gaskets, washers, felt nibs and markers, air and liquid filters, oil wicks, piano cushion felts, shoes, toys, pennants, table covers, notice boards, bookbinding, furniture components and orthopedic appliances. [11,18,19].

Wool is not only used for producing felts but also used for producing needle-punched, hydroentangled, thermally and chemically bonded fabrics. In recent years, the production of serviceable, lightweight wool fabrics of 70-150 g/m2 for apparel applications using a process known as hydroentanglement has been commercialized. Man-made fibers such as polyester, polypropylene, viscose rayon, and blends containing cotton, wood pulp, and other fibers can be used for producing hydroentangled bonded fabrics in the medical and hygiene industries. However, in recent years, wool is used hydroentanglement process [20].

For example, while producing hydroentangled fabrics, at firstly the web is transported by a porous belt or a drum is passed below a series of injector heads (typically 6-8 heads in total depending on requirements), which produce single or multiple rows of closely spaced, fine columnar water jets of about 60-140 µm diameter as required. Commercially, these jets operate at pressures of about 25-250 bar, although much higher pressures up to 1000 bar are now possible depending on the machine design. The jet pressures used depend on web weight line speed and fiber properties, and normally, the pressure is profiled so that it tends to increase as the web passed toward the machine exit. Usually, the web is treated face and back to achieve a homogeneously bonded structure, although single-sided treatments are possible using lightweight webs [20]. At each injector, suction is applied from below to remove excess water from the surface of the conveyor. The design and surface structure of the conveyor belt influence the resulting fabric structure. Bonded fabric is taken away from the belt and is dried, wound, and slit according to the required width. Chemical and thermal bonding can be done before and after drying. While producing nonwoven fabrics by the hydroentanglement method, a large volume of water is used. Water has to be recirculated and filtered to remove particulates before entering to the injectors. Recirculation and filtration account for a consid‐ erable part of the total cost of a hydroentanglement facility [20].
