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50 SYNTHETIC FIBRES

CHAPTER 4

Synthetic Fibres

4.1 SYNTHETIC FIBRES
This chapter on the manufacture and properties of synthetic fibres reinforces the
principles of polymer chemistry introduced in Chapter 3. Synthetic fibres are
produced from simple organic chemicals, obtained mainly from petroleum. They are
thus distinct from natural fibres and those made from regenerated natural polymers
such as cellulose. In particular, the dyeing of synthetic fibres is quite different from
that of natural fibres and the progress of each synthetic fibre has involved new
dyeing technologies.

The major polymers used for synthetic fibres are polyamides (nylons), polyesters
and polyacrylonitrile. The first two are products of polycondensation reactions, and
the latter of radical addition polymerisation. Figures 3.2 to 3.4 show the structures of
these polymers. Synthetic fibres have many excellent textile properties and comprise
over 40% of all fibres consumed (Figure 1.9). Each type is available in a wide variety
of modifications to suit market requirements. These include mono- or multi-
filaments, or staple fibre, of any denier or length, and with a variety of different
physical and chemical properties. One of the advantages of synthetic fibres is the
relative ease with which physical and chemical modifications are possible. The
favourable economics of the mass production of nylon, polyester and acrylic fibres
are the result of solving many technical problems for their production and use. The
introduction of new types of synthetic fibre in the foreseeable future is often
considered unlikely, but such pessimism may not be warranted [1].

Research on polymer formation at DuPont, under the direction of W H Carothers
in the 1930s, led to the first fully synthetic textile fibre of commercial significance:
nylon 6.6, introduced in 1940. This polyamide is prepared by condensation of the
bifunctional monomers adipic acid (1,6-hexanedioic acid) and hexamethylene-
diamine (1,6-hexanediamine) (Figure 3.3). Both these compounds have 6 carbon
atoms per molecule, hence the name ‘nylon 6.6’. Very shortly thereafter, nylon 6 was
produced in Germany by polymerisation of caprolactam. Caprolactam is the lactam
(cyclic amide) of 6-aminohexanoic acid, a single monomer with just 6 carbon atoms
(Scheme 4.1). After the Second World War, polymer chemistry and engineering
rapidly developed and the unbranched polyester polyethylene terephthalate (PET,

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