Taguchi analysis of shrinkage and warpage of injection-moulded polypropylene/multiwall carbon nanotubes nanocomposites

This paper focuses on the effect of multi-walled carbon nanotube (MWNT) addition on shrinkage and warpage properties of polypropylene (PP) injection mouldings before and after annealing. A Taguchi design of experiments has been implemented to highlight the influence and optimise processing conditions such as injection flow rate, holding pressure, back pressure and screw speed. The addition of 2 wt% of carbon nanotubes into PP significantly reduces the shrinkage and warpage of injection-moulded parts as compared to the neat PP. Skrinkage reduction up to 48% (respectively 33%) is noticed in the flow direction before (respectively after) annealing, whereas warpage reduction exceeds 55%. The sensitivity of the injection-mouldings dimensional properties to processing parameters remains roughly the same in case of neat PP and PP/MWNT nanocomposites when shrinkage is considered. It is even significantly reduced by carbon nanotubes addition when warpage is considered. Furthermore, the Taguchi method provides an efficient and effective tool to study the effects of process parameters on the warpage and shrinkage of injection moulded parts. The additive model used works well for predicting the warpage and shrinkage behaviour of PP and PP/MWNT composites.