Abstract
The low temperature stabilisation reaction is an important stage in the production of carbon fibres from polyacrylonitrile. The resultant structure contains cyclised sequences, which enable the fibres to withstand carbonisation without disintegrating. In this thesis a technique has been developed to cyclise polyacrylonitrile using chemical additives. The reactions have been carried out under closely controlled experimental conditions at temperatures between 273 and 333 K. The reaction of polyacrylonitrile solutions with n-butyllithium has been investigated for a series of experimental conditions. Isolation of the reaction products at various stages enabled a cyclisation mechanism to be proposed, from qualitative studies,using spectroscopic and thermal analysis techniques. Quantitative analyses established the relationship between the reduction in nitrile concentration and n-butyllithium concentration, as a function of reaction time. The extent of cyclisation was determined to be directly proportional to the residual enthalpy, recorded when the partially cyclised products were analysed using differential scanning calorimetry. A reaction model was developed, invoking a simple two stage reaction to describe the cyclisation of polyacrylonitrile with n-butyllithium. Both stages were found to be first order with respect to nitrile concentration. The chemical cyclisation reaction in polyacrylonitrile has also been proposed to be a possible substitute for the low temperature stabilisation reaction, as a precursor to carbon fibre production.