STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 12

1.1.5. Polymer Dyeing in Mass
At usual surface dyeing, based on the diffusion process of dye penetration into fibre,
inverse process - yield of dye from polymer matrix - is realized in one way or another, and
this causes reduction of the products dyeing intensity. But because of structural
inhomogeneity of fibres (presence of crystalline and amorphous regions) the dye is distributed
in them nonuniformly, resulting in uneven painting and deteriorating colour indexes.
Diseconomy of bath dyeing process owing to incomplete sampling of the bath and need in
carrying out additional finishing operations should be noted too.
Since there are data on stabilizing activity of dyes at photo - and thermal destruction of
PCA [86] introduction of such dyes-stabilizers by the method of mass dyeing, that is adding
the dye into polymer at any stage of its production or forming the fibre is of great interest.
Coincidence of polymer synthesis or shaping fibres from them with dyeing is a
progressive method in technologycal and economic respect by which fibres in completed
marketable state may be directly obtained at chemical fibres plants. It should be noted that
mass dyeing, being practically wasteless production, acquires great significance, compared
with other methods, in connection with stern measures adopted nowadays in the field of
environment protection. Besides, there is no longer any necessity for sewage treatment of
textile-finishing manufacture from different pollutions (dye, surface-active agents, salts and
so on) because of the service water shortage. The most important is the fact that dyes for mass
dyeing in the majority of cases, provide painting with high stability indexes to all actions,
often unachievable at usual dyeing methods. Dyes used for mass dyeing do not have a bad
effect on fibre strength, but in some cases they are able to protect it from photochemical
destruction.
Methods of Mass Dyeing of Polycaproamide
The process of thermoplastic polymers production and shaping is carried out at high
temperatures, achieving 300 0 C, which, in its turn, puts strict restrictions to the choice of dyes
and their assortment because the most part of the used dyes for PA - fibres dyeing do not
withstand long action of high temperature and agressive melt medium. That is why, for PA -
fibre dyeing in the process of polymer production and shaping there may be applied only
those dyes which meet definite requirements, namely:
(a) to be resistant to high temperatures (250-300 0 C) throughout the whole process of
production from the melt; to be resistant to agressive melt medium, chemical action
both on the part of separate components, included into the melt, and products of their
chemical decay and physical action in the process of polymer processing;
(b) to dissolve and coincide with the polymer, and in the case of pigment - to disperse
quite well;
(c) to impart stable to physico-chemical action paint to the fibre.
The dye introduced into reaction mass at the stage of polymer synthesis is in much more
rigid conditions. At this time this dye is exposed to the action of monomers which, as a rule,
are more reactive that the polymer.