Chemistry Reference
In-Depth Information
Complete disappearance of PCA luminescence peak and appearance of true dye glow is
being observed at dye concentration of 3,5
10×
mole/kg and higher, moreover its further
content leads to decrease of dye luminescence intensity. This may be classified as the process
of concentration of self-supression, which is a positive factor, retarding consumption of the
dye in the process of irradiation.
Additives, having really used concentrations, provide protective effect, though
luminescence on the wave-length 420-430 nm has been already suppressed by them, so there
are no reasons to connect protective effect only with the process of suppression. This means
that polymer protection over shielding effect needs explanation through chemical action of
additives being used. Study of this photooxidation process must be the subject of separate
invesrigation.
The totality of these results shows, that:
3
(1)
obtained protective effects does not come to shielding effect: used dyes by no means
play the role of suppressors of polymer excited states, however, protection over
shielding cannot be explained mainly by processes of suppression;
(2)
since literature data, related to used irradiation conditions, do not allow to consider
protective role of possible effect of additives on supermolecular polymer structure,
then one may come to a conclusion that there is considerable contribution of
chemical inhibition of polymer photooxidation by applied additives in observed
protective effects;
(3)
chemical mechanism of protective action of applied additives needs additional
investigation, necessary for scientifically well-founded selection of much more
effective light-stabilizing compositions.
1.7.
E
FFECT OF
L
ONG
-W
AVE
I
RRADIATION ON
D
YED
PCA-F
IBRE
Since PCA-products are subjected to influence of wide spectrum of light radiation then it
is interesting to study the effect of long-wave irradiation on PCA-fibres dyed by bis-
aroilenbenzimidazole compounds. It should be noted that in the region with λ
abs
MAX
more than
480 nm additives XLIY-XLYI practically do not absorb acting light.
Data on dependence of viscosity change of undyed PCA-fibres and dyed by additive
XLY on the wave-length of acting light are given in Figure1.15. As it is seen from it, additive
XLY shows both stabilizing and sensibilizing properties depending on wave-length of acting
light.
During irradiation of PCA-fibre dyed by additive XLY by full spectrum of day-light lamp
LDTs - 80 it has been found that with increase of exposure time intensity of additive
absorption at λ
abs
=420 nm decreases and already after 8 days of irradiation the dye is
consumed practically completely.
Taking as a basis these facts one may come to a conclusion that total effect of
suppression, shielding and sensibilizing is realized in ultra-violet region. They act as
sensibilizers outside the limits of absorption spectrum of bis-aroilenbenzimidazole itself,
where there are practically no effects of shielding and suppression. The last conclusion was
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