STABILIZATION AND MODIFICATION OF CELLULOSE DIACETATE - Photochemical Reactions in Heterochain Polymers - page 70

CDA, and, at last, the whole additive passes into aggregates, which fade slower owing to the
effect of concentration suppression.

2.6. L IGHT S TABILIZATION OF CDA BY P OLYCONJUGATED
A ZOMETHINE C OMPOUNDS

Use of low-molecular stabilizers has essential shortage - protective effect duration time
under working conditions, as they are quickly consumed at ultraviolet irradiation, washed out
from the polymer and they are lightly volatile products.
In this connection there rises a question about use of highmolecular light-stabilizers.
However, very little attention is paid to these stabilizers in literature. Besides, there are not
enough systematic investigations of mechanism of the action of polymer light-stabilizers in
literature. Polyconjugated azomethine compounds (PAC) attract attention from the set of
potential highmolecular light-stabilizers; stabilizing activity of PAC regarding CDA has been
found by I.Ja. Kalontarov with his helpers [176].
Interesting results have been obtained during investigation of lightfastness of products
from cellulose diacetate by the way of using additives of polyconjugated azomethine
compounds, their characteristics are presented in Table 15, and studying the mechanism of
these compounds effect on CDA transformations on photooxidative destruction. Absorption
ability of PAC-products at ultraviolet irradiation is in the range of 253 - 368 nm, that
supposes presence of shielding mechanism of polymer protection at introducing of these
chemicals - additives.
Measurement of acetic acid accumulation at ultraviolet irradiation of stabilized and
unstabilized CDA film were carried out for quantitative evaluation of stabilizing activity of
PAC as ultraviolet absorbers. Relation of the rates of acetic acid in the absence (W o ) and
presence (W st ) of additives was recognized as characteristic of phototransformation [10].
Effect of well-known industrial ultraviolet absorbers of Tinuvine and 2-oxy-4-
methoxybenzophenone type, that were not inhibitors of radical processes, was investigated
for comparison [162]. Being measured values of the rate of acetic acid accumulation were
obtained with regard to corrections for shielding.

Table 15. Characteristics and light-stabilizing properties of PAC

Stabilizer

Average molecular mass Т melt 0 С

λ, nm
in С 2 Н 5 ОН

Conservation in
% spec.

ХХХI 400 140-145 261;360 81,0

XXXII 800 180-186 266;350 85,0

XXXIII 1400 116-120 352 82,5

XXXIV 600 90-95 253;372

XXXV 1000 110-115 263;368 84,0

XXXVI 1200 210-215 258;372 77,0

XXXVII 1680 103-105 277;315

From Table 16 it follows that tinuvine II and 2-4-methoxybenzophenone decrease the rate
of CTA phototransformation at rather large concentrations, while, as in the case XXXV, the