Material extrusion of SEEPS blended isotactic PP for possible application as automotive bumper: Performance analysis through Finite Element Simulation

Abstract

3D processing of isotactic polypropylene or PP based composites through material extrusion is evolving globally as an advanced product development tool for highly specialized sectors like aerospace, biomedicals and automobiles. Conversely, pristine PP shows a severe drawback of exhibiting higher warping compared to other thermoplastics following higher crystalline shrinkage. These have prohibited the wider acceptance of virgin PP in 3D processing for product development. The current investigation is primarily aimed to overcome these disadvantages through mixing with amorphous Poly (styrene-co-(ethylene-co-(ethylene-co-propylene)-co-styrene)) or SEEPS in various mass percentages starting from 10 wt% to 30 wt% in melt before printing. The target was to make a tougher PP with retention of its original strength by reducing the shrinkage; In addition, it is also aimed to predict the usability of such material by virtual testing as a potential alternative to pristine PP for constructing an automotive bumper, designed using an AutoCAD. The printed product (dumbbell) demonstrated a higher toughness and resistance to shrinkage than pristine PP but the tensile strength and modulus decreased significantly beyond 10 wt% loading of SEEPS. Parallelly, at 10 wt% loading, the tensile strength and toughness of the printed products were found to be superior than the compression molded sample. In addition, the printed sample at this loading also possessed lower specific heat (4.79 J/g °C) than the pristine one (5.83 J/g °C) and was more thermally stable (lower degradation rate) than both the pristine and the corresponding higher blend compositions. Due to partial similarity in chemical structure between SEEPS and PP, the former had produced autonomic compatibilization with PP and formed a partially miscible blend. A car bumper was designed from this blend composition (10 wt%) using AutoCAD and its resistances to withstand against the collision stress at high (60 km/h) and low (45 km/h) car speeds were evaluated and compared virtually through Finite Element Simulation (FES) with virgin PP. Due to advantageous properties like retention of tensile strength, higher toughness and thermal stability and lower specific heat, the 10 wt% composition exhibited lesser tendency towards failure by predicting higher deformation than virgin PP. Thus it was found suitable as a bumper material which can be prototyped/finally prepared using materials extrusion technique.