Chemistry Reference
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homolytical break of PCA macromolecules and inhibit secondary processes of polymer
destruction to a different extent.
There is opinion that stabilizing additives should be colorless [10, 76], on the other hand
fluorescent additives (optical bleach) are introduced into polymer in order to compensate
yellow painting, which appears at PA processing and also to increase luster and whiteness of
products. However, there are works in literature in which there is opinion that it is more
preferable to use dyes as stabilizers [77-81], especially if it is necessary to get dyed polymers.
New results are given in the work [77], where it is studied the effect of light spectral
composition and dye concentration on the efficiency of photooxidation in PA material, there
also studied action of the air oxygen. However, there are practically no data about the effect
of dyes and products of their photochemical decay on the polymer itself. Kalontarov and
Kharkharov [80] while investigating atmospheric stability of PCA-fibre, dyed by active dyes
of dichlortriazine series, have found that after 40-days testing in the atmosphere of Saint
Petersburg the given strength exceeds such value for dyed samples by 10-12%.
There has been voiced a supposition [81] that light stabilizing activity of dispersed dyes
regarding PA is displayed by the mechanism of PA excited states suppression, but mechanism
of ultra-violet shielding does not contribute greatly into the total effect of light protective
action. It is also supposed that inhibition of free radical transformations in polymer matrix by
dyes may take place [82].
Effect of dyes of different class on light ageing of PA is studied more detailed in the
work [83]. It appeared that dyes, used by the authors, sensibilize PA photooxidation
according to radical mechanism, however the total action of the dye may be stabilizing owing
to shielding effect, and in some cases according to the mechanism of antioxidant action.
Investigation of the effect of the additives of azo dyes on the proceeding of radiation-
chemical processes of jointing, destruction, gas emission at irradiation of aliphatic PA in the
air and in vacuum has shown that introduction of dyes more effectively reduces the rate of
jointing and destruction at irradiation in vacuum, amount of gases at PA radiolysis decreases
[84]. According to the authors, protective action of azo dyes is in accepting primary products
of destruction and redistribution of absorbed energy between molecules of polymer and dye.
The same results were obtained by the authors of the work [85] who were studying effect
of modifier and azo dyes, formed directly in PCA-fibre itself, on photooxidative destruction
and photolysis of PCA. In this case azo dyes inhibit both photochemical decay of the fibre at
ultra-violet light in vacuum and destruction of dyed fibre.
However, enumerated stabilizers have one vital defect, being expressed in use in thermo-
unstable compounds (with some exception), owing to which their use for PCA stabilization is
limited according to technological reasons. The task of getting thermostable stabilizers for PA
is very topical today. Besides, taking into account the fact, that stabilizing additives are
introduced in the amount from 0,25 to 2,0% and only in some cases for coatings up to 10%, it
may be supposed that more perspective will be stabilizers acting according to complex
physico-chemical mechanism of stabilization including shielding, suppression and inhibition.
One of the most rational methods of PA stabilization may be introducing thermostable
stabilizing additives of dyes into polymer mass. In connection with the said above it is
necessary to consider modern state of PA mass dyeing.
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