Mechanical Recycling of Engineering Thermoplastics using Alloying Techniques

Abstract: The aim of this thesis is to indicate routes by which recycled engineering thermoplastics (ETP) can be upgraded using alloying techniques. Recycled ETP have often been subjected to long-term service-induced degradation, so that the residual properties of recycled ETP need to be improved.

Recycled ETP are often commingled, containing incompatible components. Great effort is required to separate them. Polymer alloying techniques, such as compatibilization and toughening, are the primary tools used in this work for upgrading recycled mixed ETP. A compatibilizer is an important modifier for raising the interfacial strength in an incompatible polymer blend. An impact modifier is critical for retaining the impact strength of the polymer blends. A core-shell impact modifier functioned both as impact modifier and compatibilizer for recycled ABS/PC blends. Since many ETP contain functional groups, it was of interest to utilise reactive compatibilization techniques. Reactive compatibilizers containing maleic anhydride, epoxide and oxazoline functional groups were shown to be effective compatibilizers for ABS/PA-, ABS/PBT- and ABS/PET-blends. Co-continuous structures and corresponding fibrillar structures in fracture surfaces obtained at low deformation rates were observed and discussed. Commercial polymer blends can be used as compatibilizing agents for ETP recycling. Different types of blends based on five recycled ETP from dismantled Volvo cars, including ABS, ABS/PC (30/70) blend, PMMA, glass-fibre-reinforced PA and mineral-filler-reinforced PA, could be upgraded using small amounts of compatibilizers and impact modifiers.

Toughness is an important material property. Different types of toughness measurements may give different or even contradictory test results. It is recommended that the toughness properties should be evaluated by two or more complementary methods. The J-integral method and the common Charpy impact test constitute such a pair.

A recycled polymer may exhibit poor surface appearance and poor mechanical properties. Co-injection (sandwich) moulding employs two different materials forming a core-skin structure. The possibility of using recycled ETP as the core material in co-injection moulding was investigated. The interfacial strength is important for co-injection moulding products. Its influence on the impact strength was of particular interest in this work.