MORPHOLOGICAL ASPECTS OF INJECTION-MOLDED POLYPROPYLENE WITH METALLIC PIGMENTS Isabel O. Santos, António J. Pontes, Carla I. Martins Institute for Polymer and Composites/I3N, University of Minho, Guimarães, Portugal Abstract Innovation, design freedom, cost and weight reduction are some factors for the replacement of metals by plastics. Plastics continue to offer attractive solutions for design engineers. The metallic effect obtained by incorporation of metal particles in polymers by injection molding has the advantage of eliminating post-processing techniques such as painting or metallization. Moreover, it reduces production costs and time to get a superior part quality. Nevertheless, undesired defects in the final appearance of parts are common, such as flow lines and weld lines. These defects occur due to inhomogeneous orientation and anisotropy of the metal particles. Very few studies are reporting the influence of metallic particles on the morphology development of PP parts. Therefore, this study is focused on the production of parts made of PP/metallic pigments (aluminum, bronze and copper) by injection molding in order to understand the influence of metallic particles on the aesthetic and morphological properties of the parts. Introduction In recent years, new materials and new technologies have been developed to eliminate the existing gaps in terms of aesthetic products. The metallic effects of the plastics came to revolutionize the automotive industry, packaging and appliances, replacing the metal by plastic in various components. Thus, attributing the quality and prestige of the metal and adding value to products [1]. Metal particles have different sizes and shapes. Those having a plate like shape promote the increase of reflected light in a specular way, increasing the luster and metallic appearance of surfaces [2]. However, the use of smaller particles or particles with a significant distribution in their size have resulted in increased light scattering (by increasing the edges, for the same surface area), so that the gloss of the part is reduced. The defects caused by the incorporation of metallic pigments in a polymeric matrix are due to the orientation and anisotropy of the particles in the region of the weld [2, 3]. Therefore, it is essential to understand the behavior of metal particles within a polymeric matrix. The welded line results from the meeting of two front lines, where particles tend to have a perpendicular orientation to the surface [4]. These defects can be minimized by adjusting the processing conditions. An increase of mold and injection temperatures causes the disorientation of flakes, which in turn, attenuates weld/flow lines. The changing of size and size distribution of metal particles are alternatives to minimize these defects [3, 5]. Large particle sizes ranging from 60-330 μm minimize the appearance of flow and weld lines [2]. Brightest metallic effects are also found in the aluminum pigments with large particle size, due to their highest reflectivity. Typically, 1.5-2wt% of aluminum pigments and 0.5-1wt% of bronze pigments [5, 6] is necessary to achieve a metallic look appealing by polymers. Materials and methods Polypropylene (PP) copolymer powder from ICORENE with specific gravity of 0.9 g/cm 3 and a melt flow index of 13 g/10 min (190ºC, 2.16 kg), was used in this study. The pigments used were: (i) aluminum with two different dimensions, (ii) bronze and (iii) copper. The pigments references are described in Table 1. The aluminum and bronze pigments were provided by Poliversal S.A. Table 1. Metallic pigments. A previous study [5] indicated that both Al and bronze particles had a flake like shape, whereas copper had a spherical like shape. The injection molding test geometry was a two gated box of dimensions: 152 mm width, 73mm length, 16 mm height and 1.5 mm thick. The injection molding was carried on a Ferromatik-Milacron K85, using the processing conditions reported in Table 2. Metallic pigments Reference Particle size Al 75 21075 aluminum pigment (master batch) 75 microns Al 27 Sparkle silver 880-30 (master batch) 27 microns Bronze Bronze powder 7600 rich pale gold (powder) 15 microns Cu Copper R0402 (powder) -