Making an impact with nanocomposites

Nanoclays can improve the performance of injection-molded polypropylene components likely to be subjected to impact in servic

Yield, impact and fracture performance of injected metallic looking polypropylene parts

Innovation, 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 moulding has the advantage of eliminating postprocessing techniques reducing production cost and time. Nevertheless, undesired defects in the final appearance of parts are common. 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 (aluminium) by injection moulding in order to understand the influence of metallic particles on the aesthetic, morphological and mechanical properties of the parts

Fracture toughness of injection moulded organoclay reinforced polypropylene composites

The fracture behavior of polypropylene reinforced with different amounts of PP/50% organoclay masterbatch was studied. Test pieces were prepared using a two-gated hot runner injection mould. Morphology of final pieces was analyzed by polarized optical microscopy, Xray diffraction and transmission electron microscopy. Fracture toughness was evaluated under quasi-static conditions at different positions in the molded pieces. The brittle mode of failure of PP became more ductile with increasing the amount of clay. However, the midthickness region (core) of “ductile” samples underwent brittle fracture while the surface layers (skin) behave in a ductile way, exhibiting elongation, necking and ductile tearing, probably due to differences in thickness and crystalline structure found in skin layers of composite pieces. Different Fracture Mechanics approaches were applied to characterize the fracture behavior: fracture toughness initiation value was assessed by means of the stress intensity factor at 5% non-linearity, KIq, and fracture toughness propagation value was obtained by means of the propagation strain energy release rate, Gcp. It was found that fracture initiation neither depends on clay content nor on test piece location. On the other hand, clay reinforcement increased fracture propagation values away from weld line region. This toughening effect was found to be dependent on the clay content and reinforcement orientation induced by the processing technique

Microestructura y desempeño de compuestos de PP/nanoarcilla producidos por técnicas de inyección no convencionales

Fundação para a Ciência e a Tecnologia (FCT)CONyCET (Argentina

Impact behavior of injected PP/nanoclay parts

This work attempts to contribute to bridge the gap between scientific challenges and industrial stakes regarding PP/nanoclay composites. Pieces of nanocomposites were obtained by direct injection of commercial PP mixed with a commercial MB of PP with 50% of organoclay, with a double-gated hot runner mould, which produced mouldings with a weld line. The moulding microstructure was assessed by POM and XRD, while the distribution and exfoliation grade of clay was evaluated by TEM and XRD. The typical skin-core structure was found, with a skin thickness wider in bulk than in weld line zones. Regarding clay platelets mostly intercalated structures were seen. The impact properties at room temperature were assessed by means of tensile and biaxial tests. Properties were monitored at different sites of the mouldings. At the weld line zone less energy was consumed under tensile conditions and exhibited higher apparent impact toughness under biaxial conditions than the bulk zone. Visual inspection of biaxially impacted samples showed that the orientation of polymer molecules and clay platelets induced by melt flow prevailed, and the weld line was not the determinant of the toughness of the mouldings. An optimum in impact performance was found for moulding with 3% of clay, since at larger clay contents platelets agglomerated and acted as stress raisers

Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings

Polypopylene/nanoclay three-dimensional parts were produced without intermediate steps by direct injection molding to explore the influence of flow features and nanoclay incorporation in their impact performance. The nanocomposite was obtained by direct compounding of commercial PP with nanoclay masterbatch. The as-molded morphology was analyzed by X-ray and TEM analyses in terms of skin-core structure and nanoclay particle dispersion. The nanoclay particles induced the reduction of b-form spherulites, a known toughener. The impact behavior was assessed in tensile and biaxial modes. The PP nanocomposite molding toughness was practically unaffected by the processing melt temperature and flow rate. Conversely the nanoclay presence is influent in the impact performance. Under biaxial stress impact, the regions close to weld lines are tougher than the bulk and the fracture develops with main crack paths along the flow direction and the weld line. Cracking along the weld line results from less macromolecular interpenetration and chain entanglement, and unfavorable nanoparticle orientation. It seems that a failure mechanism which involves nanoclay delamination and multiple matrix crazing explains the toughening of PP in the directions where the nanoparticle orientation with respect to loading is adequate.Contract grant sponsors: CONICET, ANPCyT from Argentina, MINCyT (Argentina) - FCT (Portugal), Universities Nacional de Mar del Plata and Minho

Surface property effects of compounding a nanoclay masterbatch in PP injection moulding

Indicado para o prémio de melhor artigo mais inovador.The interest on the use of nanofillers in injection mouldings has been going on for more than a decade but a real breakthrough has not been achieved yet, especially in that mechanical properties are concerned. The nucleating effect of nanoclays in semicrystalline polymers suggests that surface effects may result interesting especially during processing. This paper includes some information on the surface properties of an injection moulding grade of polypropylene mixed with a commercial masterbatch of PP and 50% of organoclay. They were moulded as plates for testing in a prototype device for determining the coefficient of friction in as-moulding conditions. The surface was also characterised by depth sensing indentation tests. The through thickness microstructures of the mouldings were assessed by optical microscopy and differential scanning calorimetry, while surface morphology was assessed by X-ray diffraction. It was observed that independently of MB content, its addition caused a slight increase in elastic modulus and hardness in the skin layer.The friction properties directly associable to the product performance showed a slight improvement in terms of the dynamic friction coefficient. Conversely the static friction coefficient that is relevant in processing was no affected by the presence of the nanoclay

Synergistic effects of nanoclay and SGF on tribological and dynamic properties of polypropylene composites

In recent year’s polymer/layered silicate (PLS) nanocomposites have attracted great interest, both in industry and in academia, because they often exhibit remarkable improvement in materials properties when compared with virgin polymer or conventional micro and macrocomposites. These improvements can include high moduli, increased strength and heat resistance, decreased gas permeability and flammability, and increased biodegradability of biodegradable polymers. However these properties are strongly influenced by how the clay is dispersed in the polymer. In this study the synergistic effects in PP+short glass fiber+nanoclay systems in the tribogical and dynamic properties in injection mouldings were analysed. The materials used were a Polypropylene Homopolymer, Nanoclay (montmorillonite layer silicate) for Polyolefin Nanocomposites in percentages of 2%, 6% and 10% and a Polypropylene Homopolymer with content of 10% and 30% of glass fiber reinforced. The various materials systems were characterized in terms of dynamic properties and tribological properties. Several tests were conducted which includes the measurements of coefficient of friction in conditions similar to the ejection phase in injection moulding process. The microstructure of the mouldings was characterized by DSC. Polymer properties are determined by the incorporation of nanoclays, SGF and by processing. Moreover influencing the microstructure of the mouldings and a synergistic effect of the nano and micro reinforcements are also observed