Manufacturing and Characterization of Filled Polymeric Systems

Doctoral thesis, 2013

The physical properties are changed if fillers are added to a polymeric material. In this work a highly filled model system for power injection moulding (PIM) and graphite nanoplatelet (GNP) based nanocomposites have been manufactured and characterized. Powder injection moulding is an important and accepted industrial technique for producing net-shaped components which combines the advantages of injection moulding and powder metallurgy. An accurate characterisation of the feedstock properties are of great significance in many situations, e.g. when simulating moulding of PIM-components. In the present work, a model system, consisting of steel powder, poly(ethylene glycol) and wax, is used in order to illustrate how the rheological properties as well as thermal properties of the system can be related to the corresponding properties of the polymeric binder system. In a similar way, the pvT (pressure-volume-temperature)-behaviour of the model system is analysed and discussed. With the model system described above and a medium-pressure injection-moulding machine, the mould filling phase was studied in situ with a special mould equipped with a sight glass using a high speed camera. Effects of features such as the mould temperature, the melt temperature, the surface roughness of the mould cavity, the gate dimensions, the mould design and the flow rate on the filling behaviour were demonstrated. The experimentally determined mould filling behavior was compared with predictions from numerical simulations. The agreement between the experiments and the predictions was in most cases quite fair or good. The manufacturing strategy is of prime importance for the appropriate incorporation of fillers into a polymeric material, and this particular refers to nanofillers. In this work graphite based nanoplatelets have been incorporated in both polystyrene and ethylene-butyl acrylate copolymer using different mixing methods. The as-received filler material contained microscopic size agglomerates formed by nanoscopic size graphite nanoplatelets. Refining of the agglomerates and dispersion of the nanoplatelets during the production of the composites are the key factors for achieving high quality nanocomposites. The nanocomposites manufactured have been studied by microscopical techniques in order to evaluate the efficiency of the different mixing methods. Also electrical and rheological properties of the composites have been assessed and used to further investigate the dispersion and deagglomeration of the filler particles. The effects of carbon black on the electrical and rheological properties of the GNP/ethylene-butyl acrylate composite have also been studied and positive synergistic effect on the electrical percolation threshold was observed.