Chemistry Reference
In-Depth Information
Hydroperoxide is not only the main branching agent but also forerunner of all lowmolecular
products and breaks of molecular chains, leading to the change of molecular mass and
molecular - mass distribution (MMD).
Oxidative processes are localized in amorphous interlayers, in interfibrillar regions and
others. Crystallinity and crystals sizes increase at initial stages of oxidation [303]; it also
means that oxidation is localized in amorphous part. Destructive decay of passing
macromolecules in amorphous interlayers release them and facilitates folding of chains into
crystals. Destruction and amorphicity of crystals takes place only at deep stages of oxidation.
Solubility of oxygen in polymer depends not only on polymer crystallinity but on
microstructure of amorphous or defect sections.
At samples heating in the presence of oxygen of the air exothermic and endothermic
effects, corresponding to oxidation reactions and polymer destruction, are seen on DTA
curves. In our case, much more differences than in melting region are observed on DTA
curves in the region of 400-500 ºC where complex process of oxidation and PETP decay take
place.
As it has been found, microphotographs show that hexaazocyclanes decrease the amount
of amorphous phase, that is why it should be expected that introduction of additives of these
compounds into PETP ought to break polymer oxidation, as fastdecomposing hedroperoxide
is in amorphous part of polymer.
Both decrease and increase of intensity and position of exothermic effect maximum at the
temperatures above melting temperature, caused by intensive polymer oxidation are marked
on DTA curves of modified PETP samples comparing with DTA curves of initial ones.
Increase of temperature maxima of oxidation peaks (Figure 3.11 curves 2, 3; Figure3.13
curves 6,7,8) is observed for PETP - fibres dyed by HC-1, HC-2, HC-5, HC-6, HC-7.
Opposite effect - temperature of oxidation maximum decreases - is observed on DTA curves
in the fibres with additives HC-3 and HC-4 (Figure 3.12 curves 4, 5). Besides, increase of
intensity of decay peak and shifting of decay temperature in the direction of higher
temperatures takes place in fibres modified by HC-1, HC-2, HC-5 (Figure 3.11 curves 2 and
3; Figure 3.13 curve 6). Increase of intensity of oxidation peak takes place on thermograms of
the fibres, modified by HC-3 and HC-4 (Figure3.12 curves 4, 5), besides temperature of
oxidation maximum decreases. Decrease of intensity of decay peak takes place in samples
with additives HC-6 and HC-7 on DTA curve (Figure 3.13 curves 7, 8), though decay
temperature increases in comparison with initial sample. Opposite effect is observed in fibres
with additives HC-3 and HC-4 on DTA curves (Figure 3.12 curves 4 and 5) in comparison
with fibres dyed by HC-6 and HC-7. Increase of decay peak is observed in fibres modified by
HC-3 and HC-4, but in addition maximum of this effect is shifted in the direction of lower
temperatures.
From the analysis of DTA curves one may come to a conclusion that introduction of
hexaazocyclanes have different effect on thermal and thermooxidative stability of PETP.
Supermolecular structure of fibres is little studied by itself and it is difficult to predict and
explain its dependence on the structure of modifier at the given stage of investigation.
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