*2.2.4. Rayon*

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

> **Relative Wet Strength (%)**

45-55 50-60 80-90 10-15 4

40-50 65-75 80-90 10-15 4

40-50 55-65 80-90 10-15 4

30-40 70-80 80-90 10-15 4

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:

**•** the filaments used in spun-laid methods are produced under different conditions than the textile or technical man-made methods with regard to their production conditions;

**•** very strong and excellent tear strength fibers are not used in nonwoven bonded fabrics,

**•** fibers which react differently when dyed can be used together, for example, in needle floor

**•** these fibers find application in high-performance wipes, synthetic suede, heat insulators,

**•** fibers have excellent physical properties like polyester fiber, and it has a high melting point,

whereas they are used in tarpaulins, conveyor belts, and tires,

**•** nylon fibers are used as nonwovens separators in Ni/H and Ni/Cd batteries;

**Water Retention Value (WRV) (%)**

**Water Content at 20 ºC and 65 % Rel.Humidity (%)**

attached to two aromatic groups is known as an aramid [30].

**Maximum Elongation (%)**

1.6 dtex/40 mm bright 50-60 45-55 80-90 10-15 4

**Maximum Tensile Strength (cN/tex)**

**Polyamide Fibers**

12 Non-woven Fabrics

3.0 dtex/40 mm semidull

17 dtex/ 80 mm semidull

22 dtex/80 mm semidull

> 35 dtex/100 mm bright prof

coverings;

\*Fibre does not have the usual round crosssection

**•** co-polyamide fibers can also be used;

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

battery separators and specialty papers [14];

which conveys good high-temperature performance [14];

Rayon, which is one of the oldest manufactured fibers, is a regenerated cellulose fiber with a wide spectrum of properties. Historically, rayon faced a strong challenge from synthetic fibers like nylon, polyester, and acrylics, which came much later, but in spite of this competition, it has retained its place as a major textile fiber. The important considerations in favor of rayon are that the essential raw material for its production, namely cellulose, is abundantly available and a renewable source. Moreover, its hydroscopicity and easy dyeability characteristics are additional assets. Furthermore, rayon fibers can be produced with a wide range of properties, particularly mechanical properties, so far unmatched by any other fiber, natural or manufac‐ tured [31].

Dissolved cellulose method was first explored at the end of the 19th century. The first fibers were produced by dissolved cellulose in cuprammonium hydroxide solvent and tiny orifices were dissolved into a bath containing reagents. Regenerated filaments form cellulose and break tiny orifices into a reagent bath to remove solvent [31].

Some of the advantages of rayon fibers based on their properties are as follows:

