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The water and fuel absorption and desorption characteristics have been studied of aircraft fuel tank sealants. The sealants were an epoxy-cured polythioether and a MnO 2 -cured polysulphide. The effect of the water and fuel exposure on the glass transition temperature was also investigated. Water diffusion was found to be Fickian for the polythioether sealant and the equilibrium plateau level was found not to be dependent on the immersion temperature. On the other hand, the polysulphide sealant demonstrated a clear non-Fickian water uptake characteristic, with large uptake levels, which were attributed to water droplet formation in the volume of the bulk sealant. The glass transition temperature of the polythioether sealant was not affected by the presence of water ($ 4% by weight) while that of the polysulphide was increased by $ 88C for a water uptake level of $ 50% by weight. Fuel absorption followed a very similar trend for both sealants with the weight gain demonstrated an early maximum followed by a subsequent weight decrease, indicating leaching of fuel soluble fractions, until equilibrium was reached. The presence of fuel acted as plasticizer for the sealants; depressing their glass transition temperature by $ 108C. Tests on dried samples have shown that the effect on the glass transition temperature was reversible.

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The peel performance of two aircraft fuel tank sealants was comprehensively investigated by means of a modified peel specimen previously developed. Experiments were carried out at five different peel angles in the range from 90 to 180 • using seven sealant layer thicknesses in the range from 0.1 to 5 mm. The effect of the peel rate was also investigated at a fixed peel angle and sealant layer thickness. The results were analysed in terms of the peel energy. Both peel angle and sealant layer thickness were found to affect significantly the measured peel energy of the sealants in a coupled way. In particular, it was found that the peel energy increased linearly with the sealant layer thickness, for the range considered in this study, and the rate of this increase was also found to increase as the peel angle was varied from 90 to 180 • . For very small sealant layer thicknesses (0.1 mm) there was no effect of the peel angle on the measured peel energy. The results were explained in terms of the amount of energy these materials dissipated upon deformation up to fracture and a relationship for the prediction of the peel energy was proposed. The peel rate was found to affect only slightly the measured peel energy, in the range studied.

The effect of a range of organic additives on the thermal stability of poly(vinyl chloride), both with and without a chloroparaffin extender, was studied using a number of experimental techniques. Of the additives used the best overall balance was provided by pentaerythritol, which increased stability when the extender was present and had no effect when it was absent. The congo red test emerged as the most suitable technique, being consistent and inexpensive and able to screen several additives simultaneously. Isothermal differential thermal analysis correlated with the congo red test but required more expensive equipment, was time‐consuming and demanded good mixing of the poly(vinyl chloride) compound to give reproducible results. Thermogravimetry was not sufficiently sensitive and the heat stability test was the least useful of all.