*2.2.3. Polyamide*

**Moisture Regain (%)** <0.1 **Refractive Index** 1.49 **Thermal Conductivity (Btu-in/ft.hr.ºF)** 0.95 **Coefficient of Linear Thermal Expansion (ºF)** 4.0×10-5 **Heat of Fusion (cal/g)** 21 **Specific Heat (cal/g.c)** 0.46 **Heat of Combustion (Btu/Ib)** 19400 **Oxygen Index** 17.4 **Decomposition Temperature Range (ºC)** 328-410 **Dissipation Factor (0.1 MHz)** <0.0002 **Dielectric Constant (0.1 MHz)** 2.25 **Specific Volume Resistively (Ω Cm)** >1016

**Table 1.** Polypropylene physical properties [14]

**•** surface smoothness and hardness,

**•** resistance to micro-organisms,

**•** chemical resistance,

**•** good abrasion resistance,

**•** good bulk and cover, and **•** good stain and soil release.

overcome this problem,

**•** difficult to dye after manufacturing,

**•** high tenacity, **•** high shrinkage,

10 Non-woven Fabrics

**•** good resilience,

Advantages of PP fibers for nonwoven fabrics are [12,14] as follows:

**•** low melting point leading to significant energy conservation,

Disadvantages of polypropylene fibers [14] are as follows:

**•** high crystallinity and poor thermal conductivity,

**•** low density and specific gravity enabling lightweight fabrics to be produced,

**•** inherent hydrophobicity that can be modified using fiber finishes and other treatments,

**•** poor UV and thermal stability (requires expensive UV stabilizers and antioxidants to

Synthetic man-made fibers account for the largest part of the raw material used in manufac‐ turing nonwoven bonded fabrics. Polyamide fibers are the oldest ones that are used in production, and they also increase the serviceability of the product. This improved quality is of importance for various purposes (see Ref. [17]):


The pioneering work of Wallace Carothers of the DuPont Company in the USA led to the discovery of nylon 66 in the 1930s. This polymer was melt-spun to give to the world the first synthetic fiber. The fiber was introduced commercially by DuPont in 1939 using a patent of W.H. Carothers granted in 1938. The success of nylon 66 led to the vigorous growth of the synthetic fiber industry. Subsequently, Paul Schlack in Germany discovered nylon 6, which was produced through another method, in 1939. Both these fibers now occupy an important place among the commodity fibers and have had a far-reaching impact on the international fiber front [30].

Only a few of the many known polyamides have reached large-scale significance for produc‐ tion. Only polyamide 6 (PA6) and polyamide 6.6 (PA66) came to large-scale production. Polyamide 6 is known as perlon and polyamide 6.6, which is generally called nylon to distinguish it from perlon. The numbers after the word "polyamide" indicate the number of carbon atoms in each molecule that make up the polyamide [17]. The structural units of a polyamide are combined by an amide (-NH-CO-) group. A polyamide manufactured from aliphatic monomer(s) is commonly designated as nylon. However, the US Federal Trade Commission has defined nylon as a manufactured fiber where the fiber-forming substance is a long-chain synthetic polyamide in which less than 85 % of a amide linkages are attached directly to two aromatic rings, while a polyamide in which at least 85 % of the amide links are attached to two aromatic groups is known as an aramid [30].


\*Fibre does not have the usual round crosssection

**Table 2.** Typical values for normal polyamide fiber properties [6]

The most important values for the physical properties of normal spun polyamide fibers are listed in Table 2, which covers various fiber thickness, degrees of luster and cross-sectional forms. The term "normal" is of great importance for nonwoven bonded fabrics, because:

