The oxidation of acrylic fibres for the formation of carbon fibres.

The chemistry of the thermal reactions of polyacrylonitrile have attracted attention since the use of the polymer as a textile fibre. The discovery that high performance carbon fibres could be easily made from acrylic fibres added another dimension to the scene -the morphology of the fibres during the thermal reactions. This thesis attempts to combine chemical analysis with mechanical analysis in order to determine why acrylic fibres are so suitable for the formation of carbon fibres. Firstly, apparatus for the heat treatment and carbonisation of acrylic fibres was constructed, and experimental conditions for the production of high performance carbon fibres, from Courtelle fibres, were established and proved. By analysing Courtelle fibres taken from various stages in the production, the pertinence of the work was ensured. The analytical procedures used were elemental, infra-red and mechanical. Because the spectrum of Courtelle was complicated by the comonomers, which contained oxygenated groups, the homopolymer was synthesised and used for comparison. Additionally, in order to obtain quantitative measurements from the infra-red spectra, films of homopolymer and Courtelle were produced and a technique for correlating fibres and film was developed. The work was concentrated on the preliminary stages of the heat treatment process where the foundations of the carbon fibre structure are laid. The most important result of this work is that reasons have been described for the necessity of the oxidation stage in the production. These reasons centre on the formation of high energy bonding and the introduction of potential cross-linking ability, both without disruption to the oriented macromolecular structure. This thesis also points out the more significant anomalies in the theories. Perhaps the least understood area is the relation between the extent of precursor oxidation and the development of high performance properties in the carbon fibres. It seems appropriate to finish this summary on a negative note as although the suggested theories seem basically sound, the anomalies are of such gravity that it would be conceited to say that the process of producing carbon fibres from acrylic fibres, is well understood