The effect of crosslinking agents on thermal stability of elastomers
Thermogravimetry was used in the studies on the effect of various vulcanizing systems on thermal stability of hydrocarbon, silicone, chlorine-containing and fluorine-containing elastomers. Thermal stability was evaluated by means of several thermal indexes obtained from the corresponding thermogravimetric curves, namely from the TG and DTG curves. It was found that substances and vulcanizing systems introduced into hydrocarbon, polydiene, and heteroatoms-containing elastomers substantially influence their thermal stability indexes, but they do not cause, except for polychloroprene (CR) changes in the character of thermal decomposition. A considerable decrease in the weight loss on set temperature T0 and in the T5 index (i.e. temperature at which weight loss is equal to 5%) was observed. It is understood that this factis connected with the decomposition of organic peroxides and accelerators in the vulcanizing system. Radicals formed during this decomposition cause not only crosslinking, but also simultaneously initiate degradation and destruction of polymers. Crosslinking of elastomers results in a considerable improvement of the thermal stability of the elastomers studied. In the case of CR the effect of the vulcanizing system (ZnO, MgO, ethylenethiourea) manifests it self above all in a considerable lowering of the temperature and rate of dehydrochlorination reaction. It is indicative of a catalytic effect of the vulcanizing system on this reaction. It was demonstrated that ZnO is the only component of the vulcanizing system with such catalytic activity.
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