**6. Structure–property relationship**

2 cos g q

> b

where *θ* is the contact angle between the liquid surface and the capillary wall and *β* denotes

**Figure 7.** a) A tube (*L*) of a radius *r* is suspended in a liquid source. The distance travelled by the liquid along the

<sup>2</sup> cos cos 4 8

s

The parameters, *r, γ, θ, μ, σ, g and β* remain constant for a given system, so Eq. (5) can be

= - *dl a <sup>b</sup> dt l*

where a and b are constants. When the penetration of liquid is horizontal (β = 90°), the effects of the gravitation field are negligible and the acceleration g vanishes and therefore the second

 m  b

*dt l* (13)

Substituting, Eqs. (11) and (12) in Eq. (10) and expressing the volume *V* as *πr* <sup>2</sup>

g q

m

= - *dl r r g*

term (*b*) can be neglected. Finally, the wicking length (*l*) can be solved as [47, 48]:

cos *<sup>b</sup> p lg* (12)

(11)

*l*, we can obtain

 =*<sup>a</sup> p r*

> = s

the angle between the tube and the vertical axis (Figure 7a).

capillary axis is *l*. (b) Liquid transport on the surface of a textile substrate

the Lucas–Washburn equation to express the flow rate as:

simplified to:

176 Non-woven Fabrics

Although different nonwoven materials such as needle-punch, melt spun, thermal bonded, etc. are used as padding, this chapter focuses more on the needle-punch structures. A needlepunch structure is obtained from the entanglement of fibres which is achieved via mechanical punching using needle beds [3, 4]. The structure is decided by the fibres and the processing parameters, for example, fibre size and distribution, depth of needle penetration, amount of feed, layering factor, and needle punching frequency. As an example, the results of a set of nonwoven samples made from 100% polypropylene fibres are described. The varying parameters are the fibre linear density (expressed as denier ̶ weight of 9000 m length of fibre), mass per square meter (g/m2 ) and needling density (punches/m2 ) of the nonwoven. Three levels of fibre denier (2.5, 6 and 15) are taken for comparison. The gram per unit area and needling density (punches/m2 ) of the nonwoven samples can be obtained by changing the machine parameters. The effect of different levels for the mass per square meter (100, 200, 300 and 400 g/m2 ) and needling density (50E4, 130E4 and 210E4 punches/m2 ) is explained on the pressure and comfort performance of padding product.
