Page 120 - Advances in Textile Biotechnology

Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 101

the United States, as manufactured fibres in which the fi bre-forming sub-
stance is any long-chain synthetic polymer composed of at least 85% by
weight of acrylonitrile units (Guillen, 1987). In 2006, acrylic production was

6.8% of that of total chemical fibres (Yarns and Fibres Exchange, 2007).
Acrylic fibres impart warm, natural-like aesthetics to most fabrics as

opposed to the cold, plastic handle of polyester and nylon fi bres (Lulay,
1995). According to a study performed to evaluate qualitatively the proper-

ties of several fibres, consumers considered acrylic as having moderate
performance on highly desirable properties like abrasion, wrinkle and pill
resistances, strength and wash-wear. Nylon and polyester were considered
to have a better performance for those properties. Therefore, there is a
continued effort to improve acrylic properties to compete with other syn-
thetic fibres. Several methods have already been tested, including incorpo-

ration of comonomers and modification of the spinning process and/or

finishing treatments (Frushour and Knorr, 1998).

The term acrylic fibre covers a broad range of products, more diverse in

composition than any other synthetic fibre (Masson, 1995). The major
reason for this is that acrylonitrile can copolymerize with many different
monomers with an ethylene unsaturated group, by free radical polymeriza-
tion (Fig. 5.2). The comonomers are used in order to increase the solubility
of the polymer in the spinning solvents and improve the rate of dye diffu-
sion into the fibres (Frushour and Knorr, 1998). Acid and basic comonomers

are also used to create additional sites for dye fixation and to provide a

hydrophilic component in water-reversible crimp bicomponent fi bres
(Frushour and Knorr, 1998; Masson, 1995). Halogenated comonomers,
usually vinylidene chloride, vinyl bromide and vinyl chloride, can be used
to impart flame resistance to the acrylic textiles (Frushour and Knorr, 1998;

Masson, 1995).
The pendant group in PAN molecules is therefore the nitrile group. The
distinguishing feature of the nitrile group is the large dipole moment,
making it one of the most polar organic functional groups (Frushour, 1995).
It is believed that these protuberant nitrile groups are responsible for the
net attraction between adjacent PAN polymer chains and the ability of this
vinyl polymer to form fi bres with some degree of structural order, which is

essential for its use as a textile fibre. Consequently, if the choice is to act on
the nitrile group as a primary target in order to alter the acrylic properties
or to add new functionalities, it is mandatory that these modifi cations
happen at the fibre surface leaving intact the core structure that is essential

for the resistance and integrity of the acrylic fibres. Current methods for

the addition of functional groups or transformation of existent nitrile groups
on the surface of acrylic fibres involve the action of chemical or physical

agents, like hydrogen peroxide, concentrated acid and bases, or radiation
and plasma (Battistel et al., 1995; Gübitz and Cavaco-Paulo, 2008). However,

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