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Due to environmental concerns and increasingly for economic reasons due to punitive legislation that is being currently introduced world-wide, there is extensive interest in materials recycling. The work undertaken and presented in this thesis focuses on the recycling of rubber materials. Extensive previous research has investigated ways of reclaiming rubber materials and some research has focused on measuring the behaviour of materials that incorporate some quantities of recycled material. This project will concentrate upon the reuse of ground-up rubber granulate mixed within a virgin material.
Reusing granulates derived from old tyre stock and other sources in high tech engineering applications is still considered a high risk option as typically it reduces the strength of the whole composite. This work aims to develop techniques to identify the rubber granulates, develop techniques to predict the behaviour of the final composite and to explore in detail the reduction of strength properties resulting from the incorporation of granulates.
This work shows that addition of granulates increases the intrinsic flaw size of a finished product. The flaw size plays a vital role in determining the fatigue life and the strength of the finished product, with larger flaws producing a weaker material. A technique that can compare the strength of the interface between the granulate and the virgin material with the basic strength of the virgin stock and the granulates is developed. This thesis also looks at volume changes that take place in the matrix-granulate composite as a result of cavitation phenomena at the interface when the rubber is subjected to cyclic loading. The development of these new techniques allows an informed evaluation of the effect of reincorporating granulates to be established, so that tailored interfaces that maximise the performance of rubber granulate-virgin rubber composites can be optimised in the future.