STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 42

may be related to stabilizing action of the latter. Similar effect is probably connected with
shielding action, as in the case of AC.
Kinetic curves of oxygen absorption at constant temperature 200 0 C were obtained to
discover the effect of DTCU additives on thermooxidative stability. Curves of oxygen
absorption by modified and initial PCA before and after ultra-violet irradiation are given in
Figure 1.18. Analysis of curves (Figure 1.18) shows unified mechanism of PCA oxidation. A
bit larger oxygen absorption by initial PCA is probably connected with larger specific internal
surface of polymer, whereas surface of modified polymer is filled by DTCU additives. Hence
it follows that ultra-violet irradiation increases resistance of modified PCA to
thermooxidative destruction. Similar effect was observed earlier [137] during studying
thermooxidative destruction of natural silk fibration. This effect may be explained both as
antioxidative activity of DTCU additive [138], and activating effect of ultra-violet irradiation
on DTCU, which is quite proved by data on kinetics of oxygen absorption by DTCU itself
before and after irradiation (Figure 1.19). Activating effect of ultra-violet light is probably
due to the fact that at severe irradiation paramagnetic centres are formed in DTCU which is
proved by electronic paramagnetic resonance (EPR) spectra (singlet on EPR curve with
g=0,002, showing presence of radicals). EPR signal was not observed in unirradiated DTCU
samples.
Thus, one may come to a conlusion that PCA modification by introducing DTCU into
polymer and irradiation by ultra-violet light leads to increase of its thermooxidative stability.
Hexaazocyclanes (HAC) and their salts (iodine and bromine) (LV + 2J − ), (LV + 2Br − ) may
be other possible thermostabilizers of PA. Taking into account the possibility of long
utilization of polymers at high temperatures we studied kinetics of PA destruction during
isothermal heating at 200 0 C during 6 hours in the air.
Figure 1.18. Oxygen absorption by PCA with DTCU additives before (1, 5, 6) and after (2-4)
irradiation. DTCU content from PCA mass: 2-0,5%, 3-1%, 4-3%, I-0,5%, 5-1% (before irradiation).