Optimisation of the production of commingled recycled plastic materials.

The recycling of post-consumer plastic waste is a challenging task due to the commingled nature of the waste composition. Commingled plastic recycling is one of the most economically viable ways to manufacture plastics waste into commercial products. Similar to virgin polymers, fillers can be added to recycled plastics to improve engineering properties of the final products. The common operations of commingled plastic recycling however lack in depth knowledge in relation to the selection of the appropriate fillers, additives, and optimum processing variables. This project aimed to investigate three types of mineral fillers, talc, wollastonite and gypsum, for their abilities to modify the mechanical properties of commingled recycled plastic composites. The effectiveness of the fillers to improve the mechanical properties was considered to be influenced by interface bonding (between the filler and matrix) and extrusion variables. These factors were also investigated in this research. Mechanical test results showed that the talc reinforced composites were significantly better in mechanical properties compared to the gypsum and wollastonite composites (tensile strength and modulus improved by 170% and 20%, respectively at 0.26 v/v loading). Scanning electron microscopy (SEM) showed that gypsum formed large agglomerates in the matrix leading to inferior mechanical properties. The interface adhesion between filler and matrix was evaluated using several established models. The tensile or flexural strength of the composites was satisfactorily predicted using Turcsanyi and Nicolais-Narkis equations. For the tensile and flexural modulus of the composites the Einstein equation was found to give a good correlation. In attempt to enhance the adhesion, the mineral fillers were pre-treated with silane coupling agents, 3 methacryloxypropyltrimethoxy silane (γ-MPS) and 3-aminopropyltriethoxy silane (γ-APS) before being blended with the plastics. This did not result in any significant improvement to the material properties. The γ-APS treatment, however, increased the tensile properties of the composites by approximately 5% compared to the γ-MPS treatment. The SEM investigations showed that the γ-APS treatment provided better adhesion of filler particles and hence voids were less likely to form in the matrix compared to the γ-MPS composites. Extruder parameters like screw rotation and barrel temperature did not have a significant influence on the mechanical properties of filler-recycled plastic composites.Thesis (M.Eng.Sc.) -- University of Adelaide, School of Chemical Engineering, 200