Novel high added value materials from mixed post-consumer polymer waste

Bainbridge, Clint (2013) Novel high added value materials from mixed post-consumer polymer waste. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Increasing awareness of the impact of today’s ‘disposable society’ has highlighted the finite nature of mankind’s resources. As such, there is increasing impetus on ‘the three Rs’ – Reduce, Reuse, Recycle. While many sources such as metals, glass and plastic bottles (high density polyethylene (HDPE) and poly(ethylene terephthalate) (PET)) are widely recycled, mixed polyolefins require resource-intensive separation and are rarely recycled as a comingled feedstock. Furthermore, these mixed polyolefins may be in the form of multi-material items such as food packaging which comprises of many layers of bonded materials which are impossible to segregate. This thesis discusses a method of processing comingled mixed polyolefin waste streams by use of a compatibilising system which negates the necessity of separation. The outcome of adopting this approach resulted in the significant improvement of the mechanical properties of the materials, whilst also reducing cost by means of adding the compatibiliser system via a surface-treated filler. Calibration curves were developed using differential scanning calorimetry (DSC) and attenuated total reflectance fourier-transform infra-red spectroscopy (ATR-FTIR) data to calculate the polyolefin ratios of unknown samples. Binary polyolefin blends of HDPE and polypropylene (PP) were also produced to investigate the associated interactions and behaviour of the systems to understand how the morphology contributes to the mechanical behaviour observed. A commercial coupling agent know as Lubrizol Solplus C800® was used via a calcium carbonate filler as a compatibiliser in the polyolefin wastes, and in most instances significantly improved the mechanical response of the materials. Through solvent extraction and subsequent TGA analysis, it was suggested that the mechanism by which compatibilisation occurred was through the formation of an amorphous rubbery interfacial region close to the filler surface. While it was found that Solplus C800® goes a significant way in compatibilising mixed polyolefin wastes, it was suggested that an increased functionality coupling agent would be the next logical step in this line of research. However, initial work in this area has suggested that the complexity of this topic may provide a basis for subsequent research and development.