Browsing by Author "Malça, C."
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- An Additive Manufacturing Solution to Produce Big Green Parts from Tires and Recycled PlasticsPublication . Domingues, J.; Marques, T.; Mateus, A.; Carreira, P.; Malça, C.Recycling is crucial for the conservation and improvement of the environment. The reduction of natural resource exploration and recovery of waste are examples of actions to contribute to a sustainable development. Waste from end-of-life tires and undifferentiated plastics represents an environmental problem due to the very high number of tons of used tires and plastics produced, but with a high economic potential because their incorporation into high value-added products is an issue of utmost importance. The manufacturing technologies oriented to the increase in quality levels, functional advantages, structural and financial gains of the produced products are currently a hot topic in industry. Similarly, the use of additive manufacturing technologies, instead of conventional techniques, e.g. moulding to process materials obtained from waste recovery, is a great industrial challenge. In order to promote greater environmental responsibility and to present innovative solutions for the management and sustainable destination of used waste recovery from tires and undifferentiated plastics, a composite made from the blend of 60% of tire waste granulate and 40% of polypropylene (PP) recycled was tested with the final purpose of generating components with added value. Both waste recovery materials were used in the micronized state. The thermal and mechanical behaviours of the synthesized composite were studied through DSC/TGA analysis and tensile testing. The implementation of additive manufacturing methodologies to process the blends between used tires granulated with a high incorporation of wastes from undifferentiated plastics was also explored in this work in order to produce big green parts without mould needed, such as urban furniture.
- Application of a Hybrid Additive Manufacturing Methodology to Produce a Metal/Polymer Customized Dental ImplantPublication . Silva, M.; Felismina, R.; Mateus, A.; Parreira, P.; Malça, C.In this paper an integrated methodology for implants personalized manufacturing is presented. This methodology materializes the hybrid material implants manufacturing through the integration of two or more advanced Additive Manufacturing (AM) technologies. Furthermore, high strength biomechanical implants with optimized geometry and mass can be manufactured by biomimetic concepts application. The combination of polymers and ceramics or polymers and metal materials (or metal alloys) allows a significant leap in the development and production of a great diversity of components and applications. The combination of advanced additive manufacturing processes, e.g. the Selective Laser Melting (SLM) or Selective Laser Sintering (SLS) and the StereoLithography (SL), make possible the production of parts with almost unlimited geometric freedom and custom multimaterial. The manufacturing flexibility and the processing capacity of the different combinations of materials - metal/polymer - obtained from hybrid additive manufacturing systems - SLM/SL - are demonstrated here by the manufacture of a dental bridge implant.
- Cooperação entre a comunidade e o ensino superiorPublication . Abreu, Madalena; Bigotte De Almeida, Maria Emília; Brites, Claudia; Araújo, Inês; Capitão, Silvino; Chang, Nelson; Carvalho, Vera; Carreiro, João; Costa, Lúcia Simões; Castro, Luis; Dias, Susana; Dinis, I.; Ferraz, Helena; Ferreira, Pedro; Ferreira, Rui; Gaspar, José; Gomes, David; Malça, C.
- Cork Plastic Composite Optimization for 3D Printing ApplicationsPublication . Brites, F.; Malça, C.; Gaspar, F.; Horta, J. F.; Franco, M. C.; Biscaia, S.; Mateus, A.Among natural fillers, cork has been acknowledged as a suitable alternative of other cellular materials that are widely employed in engineering applications due to their low conductivity to heat, noise and vibration, high abrasion resistance and flexibility, high compressibility ratio, among other characteristics [1]. The eco-friendly features of natural fillers based composites make them a very promising and sustainable solution to large markets mainly if additive manufacturing technologies, such as 3D printing, are used [2]. Through 3D printers, engineers, designers and architects can create design and decor products with a free complexity of geometry. In this research work, plastic matrices of HDPE – obtained from conventional suppliers – were reinforced with different ratios of cork waste and natural cork powders – obtained from cork transformation industries – to find the optimum mixture for 3D printing. The effects of cork powders content in the plastic on the morphological, physical and mechanical properties of the composites were investigated through the density, optical microscopy, wettability, thermal analysis and tensile testing. Cork-based composites were processed by an extrusion system, and the mixture of polymer, adhesive and fillers is discussed. The results show that the addition of pure cork and cork waste can be processed with polymers such as HDPE, having adequate physical and mechanical properties.
- Cyclic plastic behaviour of 7075 aluminium alloyPublication . Nogueira, F.; Cunha, J.; Mateus, A.; Malça, C.; Costa, J. D.; Branco, R.This paper aims at studying the cyclic plastic behaviour of the 7075-T651 aluminium alloy under fully-reversed strain-controlled conditions. Tests are conducted under strain-control mode, at room temperature, in a conventional servo-hydraulic machine, from smooth samples, using the single step method, with strain amplitudes (∆ε/2) in the range ±0.5 to ±2.75%. This material has exhibited a mixed behaviour, i.e. cyclic strain-hardens at higher strain amplitudes (∆ε/2/>1.1%) and cyclic strain-softens at lower strain amplitudes (∆ε/2<1.1%). A linear relationship between the degree of cyclic strain-hardening and the strain amplitude has been established for higher strain amplitudes. Fatigue-ductility and fatigue-strength properties agree with those found in the open literature for the same loading conditions.
- Development of an Additive Manufacturing System for the Deposition of Thermoplastics Impregnated with Carbon FibersPublication . Reis Silva, Miguel; Pereira, António M.; Alves, Nuno; Mateus, Gonçalo; Mateus, Artur; Malça, C.This work presents an innovative system that allows the oriented deposition of continuous fibers or long fibers, pre-impregnated or not, in a thermoplastic matrix. This system is used in an integrated way with the filamentary fusion additive manufacturing technology and allows a localized and oriented reinforcement of polymer components for advanced engineering applications at a low cost. To demonstrate the capabilities of the developed system, composite components of thermoplastic matrix (polyamide) reinforced with pre-impregnated long carbon fiber (carbon + polyamide), 1 K and 3 K, were processed and their tensile and flexural strength evaluated. It was demonstrated that the tensile strength value depends on the density of carbon fibers present in the composite, and that with the passage of 2 to 4 layers of fibers, an increase in breaking strength was obtained of about 366% and 325% for the 3 K and 1 K yarns, respectively. The increase of the fiber yarn diameter leads to higher values of tensile strength of the composite. The obtained standard deviation reveals that the deposition process gives rise to components with anisotropic mechanical properties and the need to optimize the processing parameters, especially those that lead to an increase in adhesion between deposited layers.
- A Hybrid Processing Approach to the Manufacturing of Polyamide Reinforced Parts with Carbon FibersPublication . Silva, M; Pereira, A. M.; Alves, N.; Mateus, A.; Malça, C.The use of thermoplastic composites reinforced with long or continuous fibers underwent an amazing increase due to advantages such as good mechanical performance, high temperature resistance, recyclable and chemical stability when compared with simple thermosetting matrices. These advantages allowed for the replacement of thermosetting systems by composites that led to the discovery of new applications. However, the processing procedure of thermoplastics reinforced with prepregs yarns entails some technological and scientific challenges mainly due to its high viscosity that results in difficulty and complexity in impregnating the reinforcements. Concerning engineering components market requirements, the polyamide thermoplastic matrices reinforced with carbon fibers have a huge demand due to the versatility of the applications where they can be used. This work presents, therefore, the development of a low-cost device that combines the Fused Filament Fabrication (FFF) additive manufacturing technique together with the processing and consolidation of thermoplastic prepregs yarns for manufacturing parts made of polyamide reinforced with carbon fibers without need of post-processing operations. To evaluate the mechanical properties of the polyamide reinforced with carbon fibers, samples were manufactured and three point bending and tensile tests were done. From results it was demonstrated the very high structural strength to both bending and tensile loads of tested material.
- Numerical study on injection parameters optimization of thin wall and biodegradable polymers partsPublication . Santos, Cyril; Mendes, A; Carreira, P.; Mateus, Artur; Malça, C.Nowadays, the molds industry searches new markets, with diversified and added value products. The concept associated to the production of thin walled and biodegradable parts mostly manufactured by injection process has assumed a relevant importance due to environmental and economic factors. The growth of a global consciousness about the harmful effects of the conventional polymers in our life quality associated with the legislation imposed, become key factors for the choice of a particular product by the consumer. The target of this work is to provide an integrated solution for the injection of parts with thin walls and manufactured using biodegradable materials. This integrated solution includes the design and manufacture processes of the mold as well as to find the optimum values for the injection parameters in order to become the process effective and competitive. For this, the Moldflow software was used. It was demonstrated that this computational tool provides an effective responsiveness and it can constitute an important tool in supporting the injection molding of thin-walled and biodegradable parts.
- Optimization of a Wood Plastic Composite for Architectural ApplicationsPublication . Martins, G.; Antunes, F.; Mateus, A.; Malça, C.The actual demand for sustainable construction has fostered the research of alternative products made of new materials, such as composites based on renewable resources obtained directly from nature or, most importantly in this context, from the wastes of industries thus encouraging the implementation of recycling processes. This study reports the optimization of wood plastic composites (WPC) made of industrial residues of pine sawdust, high density polyethylene (HDPE) and maleic anhydride-grafted-polyethylene (PE-g-MA) as coupling agent. These composites were specifically designed for the production of an innovative shading system to apply in the forefront of buildings, thus requiring an adequate combination of material properties concerning resistance to weather conditions, with mechanical and functional performance of the final products. The composites were optimized to enable their production and the fabrication of the shutter units through sequential extrusion processing. The optimization of the composites started with a thorough characterization of the raw materials and the mixtures were prepared after analysing the effect of the concentration of pine sawdust in the polymeric matrix, with variable amounts of the coupling agent. Torque rheometry was used to determine the most adequate viscosities for extrusion processing. The composites with optimized contents of pine sawdust and additives were characterized using SEM, FTIR, DSC-TGA, tensile testing, measurements of water contact angle and water absorption capacity. This allowed determining the respective microstructure, chemical interactions, thermal stability, mechanical properties, surface wettability and swelling capacity.
- Recovery and evaluation of cellulose from agroindustrial residues of corn, grape, pomegranate, strawberry-tree fruit and favaPublication . Vallejo, Mariana; Cordeiro, Rachel; Dias, Paulo A. N.; Moura, Carla; Henriques, Maria; Seabra, Inês J.; Malça, C.; Morouço, PedroConsidering the expected increasing demand for cellulose fbers in the near future and that its major source is wood pulp, alternative sources such as vegetable wastes from agricultural activities and agro-food industries are currently being sought to prevent deforestation. In the present study, cellulose was successfully isolated from six agroindustrial residues: corncob, corn husk, grape stalk, pomegranate peel, marc of strawberry-tree fruit and fava pod. Cellulose fb ers were characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, stereomicroscopy and scanning electron microscopy (SEM). Despite the evident morphological diferences among the extracted celluloses, results revealed similar compositional and thermal properties with the wood-derived commercial microcrystalline cellulose used as a control. Trace amounts of lignin or hemicellulose were detected in all cellulose samples, with the exception of corncob cellulose, that exhibited the greatest extraction yield (26%) and morphological similarities to wood-derived microcrystalline cellulose, visible through SEM. Furthermore, corncob cellulose was found to have ther mal properties (TOnset of 307.17 °C, TD of 330.31 °C, and ΔH of 306.04 kJ/kg) suitable for biomedical applications