Chemistry Reference
In-Depth Information
With the help of DTA method effect of interesterification and polycondensation catalysts
on PETP stability at thermooxidation [214] has been studied. Thermooxidative destruction is
accelerated by the presence of metal catalysts.
Labile structures initiating polymer decay [215] are formed during the process of
thermooxidation in the air. Thermooxidation rate is defined by the rate of oxygen diffusion
into polymer. Constant of destruction rate in the air compared with inert medium increases,
and activation energy decreases [216]. However, in some cases active energy increases; this is
connected with the contribution of physical phenomena of heat and mass transition together
with chemical processes into the total kinetics of destruction.
It is supposed that PETP decay during oxidation goes mainly along ester bonds by their
hydrolysis with water, formed at hydroperoxide decay [217].
In the work [218] there have been found hydroperoxide sections being formed during
oxidative destruction and responsible for thermal stability of PETP. It is shown in the work
that prediction of antioxidative behavious of PETP directly depends on the quantity of
hydroperoxide radicals being formed.
Depolymerization of polymer macromolecules runs as a result of sample destruction,
moreover the greatest rate of depolymerization is observed at the temperature 533-543 K and
pressure 9,0-11,0 MPa [219]. Products of depolymerization were analysed with the help of
gas-liquid and gas chromatography.
Absorption of considerable amounts of oxygen at high temperature oxidation of PETP
shows that oxygen takes part not only in initiation but in further stages of radical-chain
process [34].
So, all works on investigation of the mechanism of thermal and thermooxidative
destruction suppose that these processes have radical nature and run by the way of formation
and decay of peroxide radicals and hydroperoxides. Together with oxidative decay of
aliphatic part, as a result of which polymer chain decomposes with volatile products liberation
and formation of new end groups, there are also changes in aromatic part-jointing of polymer
takes place.
3.1.
P
HOTO
-
AND
P
HOTOOXIDATIVE
D
ESTRUCTION OF
PETP
PETP is quite resistant to ultra-violet irradiation but at long action of sun-light
destruction becomes visible. Light stability of PETP depends on irradiation conditions, and
irradiation intensity and wave length are the most important factors here. Length is also
important and so energy of light waves being absorved by the fibres during insolation is
important too. Thus, effect of irradiation and its intensity are defined by the energy of light
waves.
PETP destruction under atmospheric conditions, as a result of photochemical reaction,
flows mainly under the action of ultra-violet rays with λ=300-330 nm [220]. Energy of these
waves is about 1% of the total energy of the sunlight. Authors connect this fact with the
presence of absorption maximum of PETP itself in this region of the spectrum.
Considerable changes take place in PETP structure at ultra-violet irradiation. So M.S.
Kuligin with his research workers found increase of absorption bonds intensity in the region
1620 cm
-1
in infrared spectra of irradiated PETP, characterizing the presence of double bonds
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