**4.4. Knitting**

which causes a jet of the solution to be drawn towards a grounded collector. The fine jet stretches and elongates as it travels under energy field and is collected as a nonwoven nanoweb structure [103]. Various publications indicate that the voltage required to produce fibers range from 5 kV to 30 kV [104]. This range of voltage is good enough to overcome the surface tension of the polymeric solution and to produce very fine charged jets of liquid towards a grounded target. This charged jet before hitting the target undergoes splitting and drawing and forming fibers with different sizes and shapes before evaporating to form a nonwoven nano-web structure. The electrospinning system consists of two separate entities, a sprayer and a collecting device. The sprayer essentially consists of a glass spinneret, which holds the polymer solution. One of the metal electrodes from the high voltage supply is given to the solution, which serves as the positive terminal. A collector, which collects the fibers is given

Olry [80] developed a 3D nonwoven process based on the needling method. The method is essentially the same as 2D nonwoven process except for the usage of multiple nonwoven webs for fabric production. These webs are stacked one on top of another and needled in thickness direction to form a thick 3D structure. Figure 39 shows 3D flat and circular nonwoven machines schematically. Fukuta developed a hydroentanglement process where fluid jets are used to

**Figure 39.** (a) 3D flat non-woven machine (b) 3D circular non-woven machine [80, 81] (c) Schematic view of 3D biaxial‐

The 3D nonwoven structure is formed by using a warp knitting machine. Warp yarns are fed by one or more guide bars. Weft yarns are inserted between the warp yarns and the nonwoven web, whereas bias yarns are laid over the warp layers. Multiple compound needles insert the stitching yarns to lock the nonwoven web with warp, weft and bias yarns (Figure 39) [56, 57].

the other end of the electrode, which serves as the negative terminal [105].

*4.3.2. Three-dimensional nonwoven fabric*

produce 3D nonwoven fabric [81].

*4.3.2.2. By stitching method*

ly reinforced nonwoven structure made by warp knitting machine [57].

*4.3.2.1. By needling method*

114 Non-woven Fabrics
