Microinjection of polipropylene with nanoclays

Polypropylene (PP)/montmorillonite (MMT) nanocomposites micro samples was produced by micro injection molding at concentrations 2, 6 and 10% of Nanomax. The dispersion of the nanoclay particles in polypropylene was characterized using optical microscopy in polarized light, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) and the mechanical characterisation was performed using the tensile test. The results of x-ray diffraction indicated the formation of nanocomposites with partially exfoliated or intercalated structures, depending on the concentration of clay, with a maximum basal spacing of 6.217 nm. The micrographs obtained by scanning electron microscopy of fractured nanocomposite showed good dispersion of clay in polymer matrix without the presence of clusters. The tensile strength of PP/MMT is not much improved compared with pure PP but deformation increased significantly

Fiber reinforced thermoplastics compounds for electromagnetic interference shielding applications

Market demands for lightweight and lower cost products drive manufacturers to improve current product portfolios. In the case of electronic devices, the most significant weight originates from the enclosure, traditionally in steel or aluminum, that ensures excellent mechanical and electromagnetic shielding performance. The use of thermoplastics filled with electrically conductive fibers, such as carbon or stainless steel, was investigated as a lightweight and cost-effective alternative to steel sheet for creating electromagnetic interference (EMI) shielding enclosures for electronic devices. This paper presents an EMI shielding analysis workflow for the development of plastic enclosures for an electronic device. The workflow starts by measuring the fiber-reinforced thermoplastic compounds shielding effectiveness (SE) with an experimental method in the 30 MHz–3 GHz frequency band. This analysis helps to filter a vast list of materials with a wide range of shielding performance, 20–100 dB, and allows to obtain empirical data for the second phase of the workflow, computer simulations. Simulations with experimentally adjusted material properties were used to validate the design concept of an enclosure in its early development phase. Results from this study showed that the selected material has better EMI SE performance than a steel sheet venting grid.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by Portugal Incentive System for Research and Technological Development, Project no 36265/2013

Model to predict shrinkage and ejection forces of injection moulded tubular parts of short glass fiber reinforced thermoplastics

This work presents a model to predict shrinkage and ejection forces for glass fiber reinforced thermoplastics of tubular geometry. This mathematical model was based in Jansen’s Model to predict shrinkage and residual stresses in fiber reinforced injection molded products and Pontes’s Model to predict ejection forces for tubular parts of pure PP. The model used the modified classical laminate theory applied to injection moulding and it uses the fiber orientation state, temperature and pressure field as input and which predicts the shrinkage and ejection forces. The fiber orientation state was determined experimentally and the temperature and pressure fields were obtained by MOLDFLOW simulations. The model to predict ejection forces considers also the fiber orientation state, friction coefficient between steel and polymer, elastic modulus of polymer, both in the ejection temperature and diametrical shrinkage. The model is validated by experimental results

Assessment of the shrinkage and ejection forces of reinforced polypropylene based on nanoclays and short glass fibre

In this study the influence of nanoclay and glass fibre in the shrinkage and ejection forces in polypropylene matrix in tubular parts moulded by injection moulding were analysed. An instrumented mould was used to measure the part surface temperature and ejection forces in tubular parts. The materials used were a polypropylene homopolymer Domolen 1100L nanoclay for polyolefin nanocomposites P-802 Nanomax in percentages of 2%, 6% and 10% and a polypropylene homopolymer with content of 10% of glass fibre Domolen P1-013-V10-N and 30% of glass fibre Domolen P1-102-V30-N with 2% of nanoclay. The shrinkage and ejection forces were analysed. The results show that the incorporation of nanoclays decreases the shrinkage and ejection forces whereas glass fibre decreases the shrinkage and increase ejection forces due to the increase of the elastic modulus. The nanoclays decrease the ejection force when compared with glass fibre and pure PP. The effects of nanoclays are less pronounced than those of glass fibre. The effect of the mould temperatures on the ejection forces in the mouldings produced with the mentioned materials were also analysed. The ejection force decreases with the increase of the temperature of the mould

Functionalized carbon nanotubes-polyamide composites produced by microinjection moulding

Polymer composites containing carbon nanotubes (CNT) have attracted much attention due to the possibility to obtain electrically conductive and reinforcing materials at relatively low CNT concentrations, and for their potential applications in electronics, and chemical and biological sensing. Microinjection molding (μIM) is an emerging efficient and cost-effective process for the large-scale production of thermoplastic nanocomposite microparts. The present work reports the dispersion of CNT in polyamide 6 (PA 6) for the production of nanocomposites with different amounts of functionalized and non-functionalized CNT. The nanocomposites were microinjection molded under specific conditions and the electrical and mechanical properties of the specimens obtained were measured.Fundação para a Ciência e a Tecnologia (FCT) - POCI/QUI/59835/2004, bolsa de doutoramento T. Ferreira (SFRH/BD/39119/2007)

Composite materials with MWCNT processed by Selective Laser Sintering for electrostatic discharge applications

Selective Laser Sintering (SLS) is an additive manufacturing technology that enables the production of polymeric parts for end-use applications. Despite the great potential of conventional materials, carbon-based reinforcements have been widely considered to contradict the electrically insulating nature of polymers, allowing the applicability of SLS in novel applications within electronics industry. However, the laser-sintering processing of such materials still encompasses a number of limitations including agglomeration problems, weak interparticle adhesion, low parts resolution, high processing time and costs. Therefore, this research reports the development of functional composite materials for SLS capable of being considered for the production of components that are in direct contact with electrostatic discharge (ESD) sensitive devices. To do so, composite materials of Polyamide 12 incorporating 0.50 wt%, 1.75 wt% and 3.00 wt% of Multi-Walled Carbon Nanotubes were developed aiming to achieve values of surface resistance between 104 - 109 Ω, according to the delivery instructions of Bosch Car Multimedia S.A. Test specimens produced by SLS were dimensionally, mechanically, electrically, thermally and morphologically characterized. Comparing to the neat matrix, the composite materials revealed narrower SLS processing window, reduced mechanical strength, surface resistance in the ESD range and electrical conductivity until 10−6 S/cm. Fundamentals on the sintering process of these functional materials are also provided.This work was co-funded by the European Regional Development Fund through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project No. 47108, “SIFA”; Funding Reference: POCI-01-0247-FEDER-047108] and by the Foundation for Science and Technology (FCT) through the PhD scholarship 2020.04520.BD

The influence of the energy density on dimensional, geometric, mechanical and morphological properties of SLS parts produced with single and multiple exposure types

Selective Laser Sintering (SLS) is a Powder Bed Fusion technology that embraces a large number of variables influencing the properties of the parts produced. The well-known dependence and complex interaction established between the main process parameters demands continuous empirical research for effective SLS monitoring. The assessment of the energy density supplied by the laser beam to the powder bed during the process, that depends on the combination of the laser power, hatch distance, scan speed and layer thickness, is frequently considered for that purpose. Therefore, this research intends to evaluate the influence of the energy density on the dimensional, geometric, mechanical and morphological properties of SLS parts produced with conventional Polyamide 12 material. In this study, we considered different hatching and contour parameters in the energy range between 0.158 J/mm3 and 0.398 J/mm3 through single and multiple exposure types defining individual and combined parameterization sets, respectively. Results from X-ray computed tomography, tensile tests and scanning electron microscopy show that the implementation of a skin/core configuration allows the production of SLS parts with a valuable set of properties, minimizing the trade-off between mechanical strength and overall accuracy.This work was co-funded by the European Regional Development Fund through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project No. 47108, “SIFA”; Funding Reference: POCI-01-0247-FEDER-047108] and by the Foundation for Science and Technology (FCT) through the PhD scholarship 2020.04520.BD

Influence of the local morphology on the surface tension of injection molded polypropylene

Publicado em “Proceedings of PPS-29 : The 29th International Conference of the Polymer Processing Society - Conference Papers. ISBN 978-0-7354-1227-9”In this work, we investigate the development of the morphology of an injection molding polypropylene under the local thermomechanical environment imposed during processing, and its effect on the contact angle and, hence, on the surface tension of the moldings. Melt and mold temperatures were varied in two levels. The local thermomechanical environment was characterized by mold filling computational simulations that allow the calculation of thermomechanical variables (e.g., local temperatures, shear stresses) and indices (related to the local morphology development). In order to investigate the structural hierarchy variations of the moldings in the thickness direction, samples from skin to core were used. The molecular orientation and degree of crystallinity were determined as function of the thickness, as well as the contact angle. The variations of the degree of crystallinity were assessed by differential scanning calorimetry. The level of molecular orientation was evaluated by birefringence measurements. The contact angles were measured in deionized water by sessile drop (needle in) method at room temperature, to determine the wettability of the samples. The contact angles were found to vary along the molding thickness in the skin, transition and core layers. These variations are related to the local morphologies developed. Results suggest that water contact angle increases with the level of molecular orientation and for finer microstructures

A study on shrinkage and warpage of rotational moulded polyethylene

Warpage and poor dimensional stability of rotomoulded products are two of the main obstacles to the use of this technique in the production of engineering parts. The knowledge of the effect of the processing conditions on the shrinkage of rotomoulded parts will allow overcoming some of the restrictions of this process. In the present work the influence of the processing conditions on the development of shrinkage and warpage of rotomoulded parts was studied. The moulding of the parts was performed using a rotational moulding machine build at the University of Minho. The shrinkage and the warpage of the moulded parts were assessed using 3D MMC (3D measuring Machine Control) equipment, and understanding the microstructural development