Rheology of concentrated suspensions

• Various aspects of alkyd emulsion technology have been investigated. Firstly, the influence of alkyd oil length, acid value and hydroxyl number, as well as the type of surfactant used as emulsifier, on shear stability of alkyds emulsions have been studied. It was found that the acid value was the most important alkyd parameter, the stability increasing with increasing oil length. It is also shown that anionic surfactants give emulsions with small droplet sizes down at lower concentrations than nonionics. Secondly, polymerizable nonionic surfactants have been tested as emulsifiers and compared with conventional surfactants of the same HLB. It was found that surfactants capable of participating in the autoxidative curing process give faster drying and improved film hardness compared with non-reactive surfactants. Thirdly, the distribution of driers between the alkyd phase and the water phase has been investigated. It was found that low pH and the use of hydrophilic anionic surfactants, such as SDS, favour partitioning of cobalt into the aqueous phase which is unfavourable with respect to drying properties.

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