Chemistry Reference
In-Depth Information
Chapter 1
S
TABILIZATION AND
M
ODIFICATION OF
P
OLYCAPROAMIDE
1.1.
P
HOTO
-
AND
T
HERMAL
D
ESTRUCTION OF
A
LIPHATIC
P
OLYAMIDES
Aliphatic polyamides (PA) and products on their base are polymers with low stability to
ultra-violet irradiation and under the effect of solar radiation they destruct less than in a year
[1]. In natural conditions ultra-violet part of solar spectrum with wave-length 290-350 nm is
more dangerous for these polymers, though aliphatic PAs in this field have very weak
absorption of chromophore amide group [2, 3]. That is why while examining the problem of
PA phototransformations, unlike other polymers, both possibility of light absorption by
impurities and self-absorption should be taken into consideration [4].
As it is seen from the work [5] long-wavelength absorption for extra free amides is
characterized by low coefficient of extinction
ε=0.02 l/mole
and by maximum of absorption
λ=300 nm.
Besides, more long-wavelength absorption, caused by impurities, is observed in
solid PA in comparison with model compounds; as impurities there may be products of PA
oxidation and initial monomers [6]. Hence, theoretically possible absorption of light by amide
group is limited by wave length
λ=350-360nm
, that is photo-transformation of PA may be
only sensitized and initiated by impurities, products of oxidation and special additives, in
natural conditions PA destructs during 2-3 months and this allows to come to a conclusion
that there is possibility for both direct and sensitized transformation of PA under sunlight
action.
Many works are devoted to investigation of aliphatic PA light ageing. However,
interpretation of obtained results was still contradictory and, as a rule, all investigations come
to accumulation of quantitative information about phenomenon of PA light ageing and
differences in carrying out experiments (time of irradiation, size of samples, spectral
composition of active light and so on) were leading, in their turn, to changing not only
relation between product of oxidation, but also composition of products. For example,
presence of carbon dioxide and hydrogen and also hydrocarbon in products of oxidation was
observed only in some cases. So, formation of hydrogen, characteristic for conditions of
photolysis [7] was only lately explained by diffusion restriction of oxygen penetration into
polymer [8], and, in its turn,
CO
2
content increased in the presence of oxygen, but H
2
was not
