Cooling behaviour of particle filled polypropylene during injection moulding process

The effects of thermal properties of various fillers (magnetite, barite, copper, talc, glass fibres and strontium ferrite) in various proportions on the cooling behaviour of polypropylene matrix composites are investigated in an injection moulding process. A thermocouple in the cavity of the mould records the temperatures at the surface of the composite during injection moulding. From the slope of the cooling curves the thermal diffusivities of the composites are estimated and compared with thermal diffusivities at room temperature and elevated temperatures measured with a transient technique. The cooling curves show different merging sections affected by the after pressure, the diffusivity of the composite and the diffusivity of polypropylene matrix. The cooling behaviour depends on the anisotropic thermal diffusivity of the used composite, which is caused by the alignment of filler material due to the injection moulding process and the interconnectivity of the filler particles. The thermal diffusivity shows the highest value for 30 vol% talc filled polypropylene, whereas the shortest cooling time was found for 35 vol% copper filled polypropylene. The knowledge of the systematic variation of thermal transport properties of composites due to different filler material and filler proportions allows to optimize the mould process and to customize the heat flow properties. Furthermore, the strongly anisotropic thermal transport properties of talc filled polypropylene allow the design of composites with a predefined maximum heat flow capability to transport heat in a preferred direction.