The technology and economics of recycling scrap rubber.

The purpose of this project is to make a detailed technological and economic analysis of the current UK situation regarding the use of scrap rubber in order to identify the most effective processes and products. The scope of the investigation is restricted to the re-use of scrap rubber as a primary raw material for rubber product manufacture. The thesis emphasises the following aspects : (i) the structure of the rubber processing industry and the role of the rubber recycling sectors; (ii) property relationships in rubber compounds incorporating scrap rubber crumb, with particular attention to material mechanics; (iii) the estimation of curing agent distribution in a crumb incorporated rubber vulcanizate; and (iv) the economics of the cryogenic grinding of scrap rubber tyres.The property relationships of vulcanizates incorporating recycled rubber have been studied using several mathematical models : Gent, simple law of mixtures, Mooney-Rivlin models, and a non-Gaussian model based on a simplified form of inversed Langevin function. It was found that; (i) for some compounds the elastic modulus and strength could be described well by the law of mixtures for composites, (ii) the reduction in strength caused by the incorporation of crumb decreased with decreasing particle size but there is little advantage to be gained by reducing the size below 20 pm, (iii) different modes of failure may be operative, i.e. adhesive and cohesive, according to the strength of the matrix rubber.The redistribution of curing agent in our whole tyre crumb-rubber vulcanizates has been studied using the SEM and EDAX techniques.Although qualitative and quantitative evidence for the migration of cure agent from matrix to crumb is given, no evidence was found for an interfacial layer between the two phases which is depleted of cure agent.Little detailed information on the economics of the majority of commercially operated processes is available. Data has been obtained for the cryogenic grinding of scrap rubber, a technology which seems to show potential for commercial exploitation, and a thorough economic analysis performed. The result showed that, under currently depressed crumb prices and low demand, the most feasible of the plants considered is just marginally economically viable. It was found that the most important cost input to the cryogrinding process is the cost of cryogenic material (liquid nitrogen) and that the most important factor which governs the economic viability of the process is the price of the rubber crumb output. Socio-environmental and resource conservation factors indicate the desirability of Government support.