STABILIZATION AND MODIFICATION OF POLYCAPROAMIDE - Photochemical Reactions in Heterochain Polymers - page 39

In ultra-violet region the picture is a little different - stabilizing effect of the dye XLYII
is extremely small in comparison with initial PCA-fibre and dyed by the dye XLY.
Hence, aroilenbenzimidazoles do not show protective action and even become
sensibilizers outside the limits of absorption regions of acting light and all this requires
individual approach to the synthesis of additives for PCA depending on on the range of acting
light during the use of products from this polymer.

1.8. T HERMOOXIDATIVE D ESTRUCTION OF M ODIFIED PCA

PCA warming-up in the presence of oxygen or in the air leads to great changes in
polymer chemical composition, which is accompanied by the loss of positive service
properties of PCA materials. These changes allow to registrate complex thermogravimetric
method of analysis.
So, investigations of effect of bis-(1', 8' - benzoilen - 1, 2 - benzimidazoles) and bis -
(1,8 - naphthoilene - 1,2 - benzimidazoles) on thermooxidative PCA destruction in
conditions of dynamic and isothermic heating have been carried out in this connection.
Data of complex thermogravimetric analysis showing that introduction of bis-
aroilenbenzimidazole derivatives into PCA shifts temperature of beginning of PCA
depolymerization by 10-25 0 C into the region of higher temperatures are given in Table 11.

Table 11. Thermal characteristics of PCA fibre dyed by derivatives of bis-
aroilenbenzimidazole

Fibre sample T melting,

0 C

T-beginning of
decomposition, 0 C

Temperature of mass loss,

5% 10% 25%

PCA - initial 216 325 347 368 407

PCA + additive XL 216 338 356 380 410

PCA + additive XLI 217 352 358 385 412

PCA + additive XLII 215 333 355 379 408

PCA + additive XLIII 215 335 350 373 405

PCA + additive XLIV 218 341 363 386 415

PCA + additive XLV 217 364 365 390 418

PCA + additive XLVI 217 336 356 382 412

Similar effect is probably connected with structural changes in PCA, taking place at
addition of compounds XLY-XLYI into polymer and their possible inhibiting effect on PCA
thermooxidative destruction.
Performing differential thermal analysis of the processes taking place in the field of
polymer melting (T=215-220 0 C) has disclosed great differences in dyed and undyed
samples. Initial polymer (Figure 1.16) has wide peak of exoeffect in temperature range of
160-215 0 C before melting peak (endoeffect at 220 0 C), which is practically absent in its dyed
analogs.
Such difference is explained by the effect of XLY-XLYI compounds on the ordering of
PCA supermolecular structure during the period of its formation as it comes from the results