STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 24

From the data of Table 4 it follows that stabilizing action of XLY compound depends on
its concentration in polymer, besides when concentration increases up to 1 mass %
conservation of molecular mass rises, but at further growth of the concentration it decreases a
little.
All this is displayd in Figure 1.4, where concentration dependence of the number of
breaks of PCA macromolecules for XLY compound is presented.
Such shape of a curve may be explained by the fact that at increase of additive content
first, light absorption increases (as content of chromophore groups increases), secondly,
supermolecular structure of polymer itself changes. Similar investigations were carried out
and with dyed PCA fibres, obtained during additive introduction into polymer melt.
Table 5. Conservation of molecular mass of PCA fibres stabilized by bis -
aroilenbenzimidazoles (1,0 mass %) after 24-hours irradiation by mercury-quartz lamp

Additive
concentration
%

[ή] Molecular mass Conservation

of molecular
mass, %

A number
of break

Before
irradiation

After
irradiation

Before
irradiation

After
irradiation

PCA initial 1,02 0,53 35200 15000 42,7 1,34

PCA +
additive XL

1,04 0,95 35900 32300 89,8 0,11

-//- XLI 0,97 0,92 32800 30700 93,4 0,07

-//- XLII 1,00 0,89 34300 29400 85,6 0,17

-//- XLIII 1,10 1,00 38800 34400 88,6 0,13

-//- XLIV 1,07 1,00 37600 34500 91,7 0,09

-//- XLV 1,02 0,98 35400 33400 94,3 0,06

-//- XLVI 1,05 0,97 36700 32800 89,4 0,12

As it is seen from the data of Table 5, initial polymer loses more than 40% of initial
molecular mass after 24 hours irradiation. All additives have stabilizing effect, expressed in
conservation of molecular mass from 85,6 up to 93,4% depending on dye structure.
Comparing similar by “bridge” groups compounds of benzoilenbenzimidazole (XL -
XLII) and naphthoilenbenzimidazole (XLIY - XLY) series we note that bridge group, but not
chromophore part, exerts great effect on stabilizing action. This is proved by close value of
indexes of conservation of molecular mass and breaking numbers accordingly for compounds
XL-XLIY, XLI-XLY, XLII-XLYI. Compounds with oxygen bridge have more intensive light
protective effect. Compounds with oxygen bridge possess greater mobility around 0 - atom,
then benzidine derivatives XL-XLIY, and at the same time greater degree of conjugation,
then compounds with methylene bridge XLII-XLYI.

1.3. P HYSICO -M ECHANICAL C HARACTERISTICS OF S TABILIZED
PCA F IBRES AT P HOTOOXIDATION

PCA fibres, in one way or another, bear mechanical load in real service conditions. That
is why, strength indexes and, in the first place, rupture stress and extension are of great