Page 208 - Basic Principles of Textile Coloration
P. 208
197
CHAPTER 11
Dyeing theory
Dyeing theory covers a wide range of subjects mainly in the area of physical
chemistry. As for all theory, the aim is to provide a set of hypotheses that explain
the behaviour of known dyeing systems, and which are capable of predicting what
will happen in a new situation. Dyeing theory has many qualitative aspects that
are useful in explaining practical dyeing, but the physico-chemical measurements
on dyeing processes that provide quantitative data are often far removed from
actual dyeing practice. Some of the subjects included in dyeing theory are:
(1) the state of dyes in solution and in the fibre during and after dyeing;
(2) the rates of dyeing processes and how these are influenced by mass-transfer of
dye from the bath solution to the dye–fibre interface, and by diffusion of the
dye from the interface into the fibre;
(3) the phenomena occurring at the dye–fibre interface such as dye molecule
adsorption and the effects of surface potentials;
(4) the nature of the interactions between dye and fibre molecules, which are the
origin of substantivity;
(5) the treatment of dyeing as a thermodynamic equilibrium and its description
in terms of thermodynamic variables;
(6) the theory of fibre structure and how this influences dyeing rates and
equilibria.
Many of these subjects are discussed briefly, and qualitatively, in other chapters of
this book. This present chapter will introduce some of the more quantitative
aspects of dyeing equilibria and kinetics.
11.1 DYEING EQUILIBRIA
In the study of dyeing equilibria, the fibre and dye solution are heated at constant
temperature until a state of equilibrium is reached. After the initial increase in the
degree of exhaustion, it eventually becomes constant, but a true equilibrium
implies that the dye is also uniformly distributed throughout the fibres. On heating
for the extended period required to reach a true equilibrium, there is always a risk
of some decomposition of the fibre, or of the dye.
197
