Gas Evolution During Stabilization

Although the main evolution of volatiles takes place in the subsequent high temperature treatment (carbonization. Sect. 3.4), small amounts of gas are evolved during the stabilization treatment in air ( 250 °C), and concomitant weight losses are reported, both increasing with the temperature (see e.g. Bell and Mulchandani 

At temperatures below 240 °C, there is essentially no gas evolution, with the exception of some HjO after long heating time. In the range 250-300 °C, small amounts of low hydrocarbons (AN, MAN, propionitrile) evolve. These compounds are supposed to proceed from depolymerization of uncyclized parts of the polymer. Hydrogen cyanide starts to evolve after 70 min at 250 °C and after 30 min at 300 °C. The early evolution of HCN has frequently been ascribed to dehydrocyanation (analog to dehydrochlorination from polyvinylchloride), either within a molecule, leading to unsaturation  

This suggestion is corroborated by the observation that, in PAN, the hydrogen cyanide starts to evolve only after some time of heating, which would allow for cyclization and aromatization to have taken place. 

Huron and Meybeck did not find ammonia among the principal products of degradation of PAN in air. Earlier authors have reported the formation of NHj, perhaps under somewhat different reaction conditions (e.g. Bell and Mulchandani ). The evolution of NH3 has been interpreted as the consequence of deamination of chain ends from CN oligomerization, or of coupling of two such chain ends (Hay 

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