a b s t r a c tThe effect of ageing in a sweet oil environment on the tensile properties, apparent crosslink density, CO 2 diffusion and Shore hardness of a typical carbon black reinforced hydrogenated nitrile butadiene rubber (HNBR) is presented. Different ageing conditions yielded materials with different properties, attributed to varying degrees of apparent crosslinking. These results showed that, with increasing apparent crosslink density, tensile stiffness and hardness increased, while CO 2 diffusivity and saturation swelling in chloroform decreased. The relationships between these properties suggests that geometry independent tests (such as solvent swelling) may be performed on parts retrieved from service in order to predict properties (such as tensile stiffness or gas diffusion) which cannot normally be measured on retrieved parts due to geometrical constraints.

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This paper presents a study of traditional netting materials subjected to disinfecting chemicals during fish farming and treatment of net cages. A series of tests were performed in order to study the effect of various concentrations of disinfecting chemicals on the tensile strength of Raschel knitted Nylon netting materials. Simulated spill of diluted hydrogen peroxide to the jump fence during de-lousing did not affect the strength of the applied new and used knotless nylon netting samples. Hydrogen peroxide reacted with biofouling forming gas bubbles, but this did not result in reduced netting strength. The performed tests did not indicate any effect on netting strength from a simulated single, traditional bath disinfection as performed at service stations applying the disinfectant Aqua Des containing peracetic acid. However, increasing the Aqua Des concentration from 1 to 10 % resulted in a strength reduction of 3–6 %. Simulated spill of concentrated Aqua Des on the jump fence of a net with copper coating residuals resulted in a severe reduction in strength of 45 %. This strength loss was probably a consequence of chemical reaction between copper and Aqua Des, and uncoated netting did not experience any loss in strength subjected to the same chemical exposure. These findings from application of Aqua Des should also apply to other peracetic acid disinfection chemicals with trade names as for example Perfectoxid and Addi Aqua.

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