Optimising Polyethylene Recycling

The growth of plastic production and its lasting environmental damage is putting strain on industries to transition from a linear plastic economy to a closed loop system. A circular plastic economy will ease the dependence on the production volume of virgin plastics whilst allowing its demand to be met through post-consumer recycled polymers. This means the lifetime of plastics are extended by recycling in a continuous loop numerous times before it reaches its final stage in landfill or energy recovery.

This PhD project will focus on the mechanical processing of polymers, with emphasis on HDPE to analyse its performance under multiple extrusions. Although extrusion is the fundamental mechanism for recycling, it also gives rise to thermo-oxidative and shear-induced degradation of polymeric materials which weakens its mechanical properties. Variations between different grades of the same material can impact performance.

For example, HDPE can possess varying amounts of UV and thermal stabilisers which can affect its degradation behaviour. Furthermore, difference in molecular weight between HDPE grades will show variations in melt flow index and viscosity due to chain entanglement and molecular mobility. This in turn determines how the material will act when subject to extrusion conditions and recycling.