A study of polyisobutylene and its derivatives at high temperatures

In recent years fuel injection equipment (FIE) has had to rapidly evolve to meet ever more stringent emission standards with developments such as higher fuel injection pressures and smaller injection orifices. The latest FIE technology, however, has been found to be more susceptible to deposit formation in injectors and filters which can be detrimental to the performance of the engine. The chemical resistivity, non-toxicity and high thermal stability of Polyisobutylenes (PIBs) makes these suitable precursors to polymeric dispersants which are engineered to help prevent deposit formation. The PIB molecules can be functionalised with succinimide/polyamine groups which facilitate adsorption of the polymers at the surface of carbonaceous materials which precipitate out of the fuel. Despite the fact the majority of processes involving these polymers occur at high temperatures almost all previous studies into the dispersancy behaviour of PIB and its derivatives are based at ambient or near ambient temperatures. Using high temperature analytical methods to investigate PIB type dipersions containing deposit surrogates will therefore allow insight into the dispersancy mechanism in the temperature range in which they normally operate. High temperature rheometry and 1H NMR have successfully been used in combination to study the fluidity of coal samples during coking and the pyrolysis of biomass polymers. This research presents for the first time a study of PIB type dispersions using these high temperature techniques. The aims of the project are (1) to establish a reproducible methodology for both the sample preparation and analysis of PIB type dispersions using high temperature rheometry and 1H NMR, (2) to investigate the structure activity relationships of the polymers through the utilisation of various PIB derivatives, and (3) to investigate the effects of changing the deposit surrogate on the dispersion behaviour at high temperatures. A reproducible methodology for both the sample preparation and the analysis has been established. Characterisation of PIB, and two functionalised derivatives, PIB succinic anhydride (PIBSA) and PIB succinimide (PIBSI), demonstrates that the viscoelastic and hydrogen mobility measurements of dispersion can be an indication of the strength of the interaction between the polymer and carbon particles. The range of PIBSI type molecules has been expanded to investigate the structure activity relationships which include the effects of the number of amines in the head group and the length of the PIB hydrocarbon chains. The results indicate that the size of amine head groups have the most dominant effects on the viscoelastic and molecular mobility behaviour. The effect of changing the carbon type was investigated using 1H NMR where a number of dipersions containing various types of commercially available carbons (that had previously been utilised as reference carbons in comparison with actual injector deposits) were analysed. The results show that changing the type of carbon used in a dispersion sample can significantly affect the measured mobility of the sample. It was indicated that the properties of the carbon material on the surface, such as the level of carbon and oxygen surface %, and the level of graphicity / amorphicity were the more dominant factors in effecting the mobility measurements as opposed to other factors such as particle size and surface area. This gives additional support that this method of high temperature measurement of dispersions can provide an indication of the strength of the interaction between the polymer and deposit surrogate particles rather than simply being controlled by the inherent physical properties of the polymers or carbons themselves