The Influence of Processing on the Aesthetic, Morphological and Mechanical Properties of Structural Foam Mouldings of High-Impact Polystyrene

The production of large plastic parts, in small series and at low cost, requires the development of alternative tools and materials. Structural foams (SF) are an appropriate solution, when the production of thicker parts with superior properties is specified. They allow the production of lightweight parts with high stiffness and excellent dimensional stability, due to their sandwich-like structure consisting of a cellular core and two solid skins. The porous core is the result of the addition of a blowing agent in the polymeric matrix. These materials are applied in the urban furniture, automotive, nautical and aerospace industries. The most commonly used process to produce SF is low pressure foam moulding, which is a short-shot process, with impression pressures below 4 MPa. Therefore, the use of hybrid moulds with moulding blocks obtained by rapid prototyping routes is seen as a viable alternative for SF injection moulding. This work reports a study of the influence of processing conditions on the aesthetic, morphological, and mechanical properties of SF mouldings of high-impact polystyrene (HIPS-SF). The results compare the effect of the use of hybrid moulds to conventional moulds on the surface aspect of the circular centre-gated mouldings. Furthermore, the influence of the moulding temperature is ascertained in terms of the resulting cellular morphology, the flexural stiffness of the plate mouldings, and the impact resistance in the instrumented drop weight test.