Abstract. The metallic effect obtained by incorporation of metal particles in polymers by injection molding has the advantage of eliminating post-processing techniques reducing production cost and time. Nevertheless, undesired defects in the final appearance of parts are common. In this work PP/aluminum pigments were obtained by direct injection molding and the influence of metallic particles on the aesthetic, morphological and mechanical properties of the parts was assessed. Aesthetic aspects could be improved by manipulating processing conditions: high melt temperatures diminished differential shrinkage and made weld lines less noticeable. Also at high melt temperatures Al particles increased thermal conductivity of PP generating a thicker skin, which combined with an inherent gradient temperature and typical shear stresses developed during injection molding, induced the formation of !-PP phase. Mechanical performance of parts showed to be dependent on PP morphology. Distinct deformation behaviors were seen according to the presence of PP polymorph, !-PP counteracting the detrimental effect of not bonded Al flakes, and making PP-Al moldings to have similar toughness as PP moldings with the added value of metallic looking.

Polypropylene (PP) is a low-cost plastic commodity, which currently is in a transition zone between massive use and engineering applications due mainly to its limited mechanical properties, such as low tensile and impact resistance. That is the reason why PP is usually modified with additives and particles to improve its mechanical and thermal performance and thus meet the requirements demanded by engineering applications. Besides, PP composites are suitable materials to be processed by a simple, fast, automatic, and massive technique such as injection molding. This makes PP composites attractive for several applications. However, it is important to keep in mind that PP composites' performance depends not only on their intrinsic properties but also on processing conditions. This chapter will summarize the relationship between processing and performance of several PP composite-micro, nano, and hybrid-injected parts with the aim of generating a bridge between technologic knowledge and scientist knowledge.

The effect of distinct morphologies induced by shear controlled orientation in injection moulding (SCORIM) in the mechanical and fracture performance of polypropylene (PP) and PP/nanoclay mouldings is examined in this work. The effect of high shear conditions applied during processing was assessed. Samples exhibited a range of fracture stability ranging from a modest non-linearity to a quasi-stable regime depending on material type and injection conditions. Neat PP showed non-linear brittle behaviour while nanocomposites exhibited quasi-stable behaviour induced by the large deformation capability of the skin layer. Despite the fracture initiating at practically the same loading levels, the propagation energy varied with processing conditions and nanoclay content. The reduction of the core layer achieved by the SCORIM processing along with the differences between the skin and core favoured by the presence of nanoclay are responsible for the toughening of the SCORIM PP/nanoclay thick mouldings.

Summary One of the most valued and required features of new polymers are a high level of stiffness combined with good toughness. In this way, it seems useful to combine nanoclay reinforcement with rubber toughening to balance end use performance. In this work, the feasibility of producing this kind of nanocomposites by direct injection molding is evaluated. The performance of actual injected pieces of polypropylene (PP) compounded with thermoplastic vulcanizate (TPV) and organoclay (MMT) is analyzed and compared. Ternary composite presents low warpage and so better final quality. Morphology developed in actual pieces is influenced both by processing and by MMT presence, this morphology giving place to alternative deformation mechanisms and crack arrest. Also, a good impact resistance compared with neat PP is observed. Weld lines are diluted and they do not act as stress concentrators, this being of mechanical and aesthetical interest. The use of PP/TPV/MMT seems to be promising for injected moldings.