Page 108 - Advances in Textile Biotechnology

Enzymatic hydrolysis and modifi cation of core polymer fi bres 89

control, its effect being not only limited to surface degradation but also to
other parts of the polymer, and therefore it has less potential for commer-
cial application.

Nylon oligomers degradation
During polymerization reactions, some molecules fail to polymerize and
remain as oligomers, and others undergo head-to-tail condensation to form
cyclic oligomers. These nylon oligomers are the byproducts from the nylon
factories, and, thereby, contribute to the increase in industrial waste materi-
als. Biochemical studies revealed that hydrolases from Flavobacterium sp.,
namely 6-aminohexanoate-cyclic-dimer hydrolases are able to degrade
6-aminohexanoate oligomers (Fischer-Colbrie et al., 2006; Kakudo et al.,
1993; Kato et al., 1994; Kinoshita et al., 1981; Negoro, 2000; Negoro et al.,
1983, 1984). Negoro and co-workers have recently performed the x-ray
crystallography of this enzyme as well its mutational analysis (Negoro et al.,
2005, 2007; Ohki et al., 2006). Some work has been done on the isolation of
a 6-aminohexanoate oligomer hydrolase from Agromyces sp. and Kocuria
sp. (Yasuhira et al., 2007). Other reports describe oligomer degradation by
Pseudomonas sp. (Prijambada et al., 1995).

Methods to quantify enzymatic hydrolysis

Enzymatic modification of polyamide materials involves the limited hydrol-
ysis of amide bonds. The resulting changes in surface properties can be

easily quantified by tensiometry or hydrophilicity measurements (Silva
et al., 2007a). The corresponding chemical changes are measured in terms
of formation of hydrophilic groups. The functional groups (e.g. amino
groups) can be quantified at the surface of the treated materials by means

of coloration with an α-bromoacrylamide reactive dye, which reacts spe-

cifically with amino groups (Silva and Cavaco-Paulo, 2004). The hydrolysis
products released to the liquid treatment are quantified by colour change

using 2,4,6-trinitrobenzenesulfonic acid (Silva and Cavaco-Paulo, 2004).
The use of enzymes to modify polyamide materials requires limited hydrol-
ysis at the surface of the polymer, leading to the production of new func-
tional groups. High levels of hydrolysis can increase the amount of products
released, therefore increasing materials degradation. A compromise
between levels of hydrolysis and polymer degradation must be achieved
(Silva and Cavaco-Paulo, 2008).
When hydrolysis leads to the solubilization of the resulting smaller frag-
ments, HPLC (high performance liquid chromatography) can be used to
quantify them (Heumman et al., 2006). Attenuated total refl ectance- Fourier
transform infrared spectroscopy (ATR-FTIR) and scanning electron micro-
scopy (SEM) have been used to analyse surface hydrolysis of polyamide

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