Preparation and characterisation of high performance rubber vulcanizates loaded with modified aluminium oxide

Purpose - A new method for modifying the properties of aluminium oxide had been developed which allowed alumina to be used as a white, reinforcing filler in various rubber composites to replace carbon black, producing high performance white rubber vulcanizates comparable to those loaded with carbon black that could be coloured if needed. Design/methodology/approach - Alumina was treated with small amounts of ammonium molybdate. Characterisation of modified aluminium oxide was carried out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Also, evaluation of the pigments prepared, in terms of oil absorption, specific gravity; and bulking value using international standard testing methods was performed. The morphology of the natural rubber composites loaded with the new modified alumina were studied using SEM. Kraus equation was used to analyse the extent of polymer-pigment interaction, while Mooney-Rivlin relation was employed to study the near equilibrium stress-strain behaviour. Findings - The results showed that, the pigment had a significant effect on the theological characteristics (scorch, cure time, etc.), mechanical properties, stress and strain at yield and at rupture of white rubber vulcanizates prepared resulting in high performance. Research limitations/implications - As concentration of molybdenum oxide increased in the alumina crystals, the reinforcing effect in rubber composites also increased till an optimum concentration where such a reinforcing effect reversed. However, investigation of the application of these pigments in other systems such as an anticorrosive pigment in paint formulations and reinforcing filler in polyester composites could also be interesting. Practical implications - The pigments prepared could be used as reinforcing filler in plastic composites and also as anticorrosive pigment in paint formulations. Originality/value - Aluminium oxide is a cheap compound. The originality of the work lay in the finding that by adding trace amounts of molybdenym to it, aluminium oxide's properties changed dramatically resulting in more effective action in reinforcing rubber composites filled with such modified alumina, producing white rubber composites with comparable properties to those loaded with carbon black, and may exceed them in some cases. This allowed the preparation of coloured rubber with good theological and physical properties.