Suchergebnisse

Tese de Doutoramento em Engenharia de Materiais. ; Low power portable electronic devices and wireless sensors networks, for application in implantable biomedical sensors and monitoring for agricultural, environmental, building, military and industrial processes are typically powered by batteries, which have a finite supply of energy. The combination of an energy harvesting system with a rechargeable battery is the best way to self-power devices for their entirely lifetime. These harvesters collect energy (in the order of μW to mW) from ambient sources (thermal, mechanical or electromagnetic, among others). Among them, energy harvesting from electromagnetic signals is one of the most challenging and interesting harvesting systems and has been poorly addressed. Magnetoelectric (ME) composite materials are an innovative tool that can convert such electromagnetic singnals into an electrical voltage and can be also be used as novel sensors and actuators. The main objective of this work is to optimize ME laminated composites for sensor, actuators and energy harvesting devices. It is also an objective to find new applications for this ME effect. From the different composite structures, laminated ME composites, comprising bonded piezoelectric and magnetostrictive layers, are the ones with the highest ME response, thus being the most studied materials for their implementation into technological applications. With high ME coupling, easy fabrication, large scale production ability, low-temperature processing into a variety of forms and, in some cases, biocompatibility, polymer based ME materials emerged as an original approach. In this work Vitrovac and Metglas were used as magnetostrictive materials due to their high magnetostriction at low fields, and .poly(vinylidene fluoride) was used as the polymeric piezoelectric material, due to his high piezoelectric constant compared to other polymers. Thus, the effect of the bonding layer type and piezoelectric layer thickness is reported. Vitrovac/poly(vinylidene fluoride) ...

The single screw extrusion optimal design involves the optimization of six criteria that can be efficiently handled by a weighted Tchebycheff scalarization method. The performance of the method has been analyzed for three different methods to generate weight vectors. The experimental results show that the tested strategies provide similar and reasonable solutions and supply a valuable procedure to identify good trade-offs between conflicting objectives. ; European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 734205- H2020-MSCA-RISE-2017. The work has also been supported by FCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020, UIDB/00013/2020 and UIDP/00013/2020 of ...

Waste is commonly, considered an effect separated from the economic processes of production, construction, and consumption. This is seen both in the politics of recycling and in the legal apparatus regarding the reintegration of industrial wastelands, in the aftermath cessation of the exploitation. Consequently, this management represents merely the 'after' attempts that try to minimize the effects of waste negatively affecting our lands and lives. In contrast, this paper addresses the interdependence between production and waste by making visible the 'mounds of marble waste' in Estremoz Anticline (Alentejo, Portugal). These mounds of marble waste allow us to demonstrate that the intervals of 'artificial time', as explained by Cedric Price (1996), that is, that use, reuse, mis-use, dis-use, and refuse, are not only successive but coexistent (Kümmel 1968). ; (undefined) ...

This work reports the development of renewable cellulose nanocrystal (CNC) and ionic liquid (IL) hybrid materials for bending actuator applications. For this purpose, cellulose nanocrystals with different surface charges (neutral, positive and negative) were prepared and increasing amounts of the IL 2-hydroxy-ethyl-trimethylammonium dihydrogen phosphate ([Ch][DHP]) (10 and 25 wt%) were incorporated into the CNC hosting matrix. The morphology of the samples was evaluated, proving that both surface charge and IL incorporation do not affect the characteristic layered structure of the CNC. Atomic force microscopy results reveal a sea-island morphology in the hybrid films, where CNC bundles are surrounded by [Ch][DHP]-rich regions. An increase in the electrical conductivity is observed upon IL incorporation into the CNC matrix, regardless of the CNC surface charge. The highest electrical conductivity values are observed for IL/CNC (+) 25 wt% with an electrical conductivity of 3.18 x 10(-5) +/- 2.75 x 10(-7) S cm(-1) and IL/CNC (-) 10 wt% (1.26 x 10(-5) +/- 5.92 x 10(-6) S cm(-1)). The highest bending displacement of 2.1 mm for an applied voltage of 4.0 Vpp at a frequency of 100 mHz was obtained for the IL/CNC (+) 25 wt% composite, demonstrating the suitability of cellulose to develop soft actuators. ; The authors thank FCT - Fundacao para a Ciencia e Tecnologia - for financial support under the framework of the Strategic Funding UID/FIS/04650/2019 and UID/QUI/50006/2019 and projects PTDC/BTM-MAT/28237/2017, PTDC/EMD-EMD/28159/2017 and PTDC/FIS-MAC/28157/2017. D. M. C., C. M. C. and L. C. F. also acknowledge FCT for the grants SFRH/BPD/121526/2016, SFRH/BPD/112547/2015 and SFRH/BD/145345/2019, respectively. The authors acknowledge funding by the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and from the Basque Government Industry and Education Department under the ELKARTEK and PIBA (PIBA-2018-06) programs, ...

Ultrasound-assisted extraction of hemicellulose and phenolic compounds from bamboo bast fibre powder was investigated. The effect of ultrasonic probe depth and power input parameters on the type and amount of products extracted was assessed. The results of input energy and radical formation correlated with the calculated values for the anti-nodal point (λ/4; 16.85 mm, maximum amplitude) of the ultrasonic wave in aqueous medium. Ultrasonic treatment at optimum probe depth of 15 mm improve 2.6-fold the extraction efficiencies of hemicellulose and phenolic lignin compounds from bamboo bast fibre powder. LC-Ms-Tof (liquid chromatography-mass spectrometry-time of flight) analysis indicated that ultrasound led to the extraction of coniferyl alcohol, sinapyl alcohol, vanillic acid, cellobiose, in contrast to boiling water extraction only. At optimized conditions, ultrasound caused the formation of radicals confirmed by the presence of (+)-pinoresinol which resulted from the radical coupling of coniferyl alcohol. Ultrasounds revealed to be an efficient methodology for the extraction of hemicellulosic and phenolic compounds from woody bamboo without the addition of harmful solvents. ; Financial funding from the OeAD-GmbH and the Austrian Federal Ministry of Science, Research and Economy Scientific and Technological Cooperation Programme under the grant number CN 03/2016. The authors would like to thank to Chinese Foundation Key projects of governmental cooperation in international scientific and technological innovation (No. 2016 YFE0115700), the National Natural Science Foundation of China (Grant No.31470509), and the 111 project (No.B17021). The authors would like also to thank to Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by European Regional Development Fund under the scope of Norte2020—Programa Operacional Regional do Norte ...

In the last decade, there have been significant advances on multifunctional materials development through additive manufacturing techniques, boosted by the Industry 4.0 and the Internet of Things revolution. However, in the particular case of the use of lightweight materials, the performance and multifunctionality is sometimes limited. After a short introduction, this chapter provides a comprehensive assessment of those limitations at the same time as the materials, techniques and challenges on the additive manufacturing of multifunctional materials. In the final paragraphs of this work, the future trends will be presented and discussed. ; FCT- Fundação para a Ciência e Tecnologia- for financial support in the framework of the Strategic Funding UID/FIS/04650/2020 and under project PTDC/BTM-MAT/28237/2017 and PTDC/EMD-EMD/28159/2017. P. Martins (CEECIND/03975/2017- assistant researcher contract Individual Support – 2017 Call) and V. Correia (DL57/2016 junior researcher contract) thank FCT for the contract under the Stimulus of Scientific Employment. The authors acknowledge funding from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively. Funding from the European Union's Horizon 2020 Programme for Research, ICT-02-2018 - Grant agreement no. 824339 – ...

Structural health monitoring (SHM) is a non-destructive process of collecting and analysing data from structures to evaluate their conditions and predict the remaining lifetime. Multifunctional sensors are increasingly used in smart structures to self-sense and monitor the damages through the measurements of electrical resistivity of composites materials. Polymer-based sensors possess exceptional properties for SHM applications, such as low cost and simple processing, durability, flexibility and excellent piezoresistive sensitivity. Thermoplastic, thermoplastic elastomers and elastomer matrices can be combined with conductive nanofillers to develop piezoresistive sensors. Polymer, reinforcement fillers, processing and design have critical influences in the overall properties of the composite sensors. Together with the properties of the functional composites, environmental concerns are being increasingly relevant for applications, involving advances in materials selection and manufacturing technologies, In this scenario, additive manufacturing is playing an increasing role in modern technological solutions. Stretchable multifunctional composites applications include piezoresistive, dielectric elastomers (mainly for actuators), thermoelectric, or magnetorheological materials [1]. In the following, piezoresistive materials and applications will be mainly addressed based on their increasing implementation into applications. ; Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019 and UID/EMS/00151/2019. The authors thank the FCT for financial support under SFRH/BPD/110914/2015 (P. C) and SFRH/BPD/117838/2016 (J. Pereira) grants. Financial support from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA ...

Reprocessing single-use medical devices raises issues of patient safety, ethics, the environment and costs. The aim of this paper is to raise awareness of the problems related to the reprocessing of single-use medical devices in the EU, with a focus on Portugal's position regarding this issue. ; The financial funding from QREN, POFC, Vale Inovação Project Nº 2012/24228 is gratefully acknowledged. ...

Portugal is an important player in the European fashion industry. The Portuguese footwear industry, "low-tech" and traditional industry, dominated by SMEs and located in two main clusters, is a success case in the Portuguese economy. After a long period of decline until 2009, the footwear companies prepared new strategies that made big changes in the image and performance achieved. Since 2009, exports have increased more than 55% and the Portuguese footwear has grown in almost all the most important foreign markets. The competitive strategies followed by the Portuguese footwear companies are different and they can be clearly identified according Porter's three generic competitive strategies: cost leadership, differentiation and focus strategy. This paper had analysed seven Portuguese footwear companies (seven cases, case study strategy) and the results obtained shows how important is to have the right approach to the markets, according the internal and external resources that each firm has available. The footwear clusters in Portugal and the sectorial organizations are also very important in this competitive performance achieved by the companies. Last years the Portuguese government recognize this increasing importance of the fashion industries and prepared several programs to promote these industries in Europe and other continents. ; FCT -Fundação para a Ciência e a Tecnologia(POCI-01-0145-FEDER-007136) ...

In this work, we explore the addition of Ti ribbons on the racetrack of a Zr target to prepare Zr-O-N films including Ti, by reactive magnetron sputtering with a mixture of N2 and O2 as reactive gases. This approach is simple and not invasive, it avoids the modification of the target and minimizes its contamination. These films were compared in terms of chemical composition, density, film growth and crystallographic structure with others prepared in identical conditions without Ti ribbons. In addition, the composition and density of the films were correlated with crystallographic references from literature. The color and electrical properties of the films were evaluated as well. It was observed that poisoning of the Zr target is promoted by the increase of the N2 + O2 flow and the reduction of magnetron current, but it is retarded by the introduction of the Ti ribbons. This effect was particularly remarkable at lower target current, since the sputtering is confined in areas nearer to the racetrack, where the Ti ribbons are located. To account for the poisoning of the target and compare it among the different samples, a 'poisoning parameter' was defined, using a combination of the chemical composition of the films and the deposition rates. The color and electrical properties of the films correlate surprisingly well with their oxygen-to-metal ratio, while the concentration of N does not seem to play any significant role. ; The financial support of Portuguese Foundation of Science and Technology (FCT), under the projects IF/00671/2013, M-ERA-NET2/0012/2016, and Strategic Funding UIDB/04650/2020 are gratefully acknowledged. The financial support from the Basque Government Industry Department under the ELKARTEK program is also ...

This work evaluates the potential of use of mineral dust waste from stone extraction and processing industries to develop composite materials to construction sector. Actually, a high volume of mineral waste was generated, in a stone extraction and processing industries, without any type of recycling and recovery. In this work, this waste was combined with a biopolymeric material, with different mass ratios, namely 70:30 and 50:50 of mineral waste and polymeric material. To accelerate the curing process, a compression moulding process was used. After that, a several characterization tests were performed, in order to compare the main properties of the composite materials obtained with different mass ratios of mineral dust and polymeric material. The physical and mechanical tests were performed to evaluate the density, moisture absorption, flexural strength and flexural modulus. Besides that, the thermal properties were obtained using an Alambeta testing device. The experimental results show a decrease of density of the composite materials from 2.7 g cm-3 to 2.03 g cm-3, compared with virgin slate rock. In terms of mechanical performance, an increase of flexural strength from 17.1 MPa to approximately 80 MPa was verified between Viroc and the composite materials obtained. In addition to this, an HB rating on flammability test guarantees to the composite materials an excellent capacity to fire resistance. These results allow to conclude that the recycling and recovery the slate waste has a big potential of application in several areas, such as construction one. ; project "Fibrenamics Green -Platform for the development of innovative waste -based products", code NORTE-01-0246-FEDER-000008, which is co-financed by the European Union, through the European Regional Development Fund (ERDF) under the NORTE 2020 -North Portugal Regional Operational Program 2014 –2020 ...

Bottom-up fabrication of thermoelectric (TE) materials from colloidal nanocrystal (NC) building blocks can substantially increase their TE efficiency, for example, by reducing lattice thermal conductivity. In this work, 10 nm spherical phase pure oleate-capped PbTe NCs with narrow size distribution were synthesized and employed to fabricate 50 nm thick films on insulating SiO2/Si substrates. The spin-coating, with subsequent ligand exchange procedure, was applied to enhance coupling interactions between the NCs. Using dark conductivity measurements, we confirmed the semiconducting behavior and the Schottky-type electrical field-dependent conductivity mechanism in the resultant thin films. The thermal transport in the thin film was probed by means of a time-domain thermoreflectance method. For this purpose, we used a customized state-of-the-art system based on a picosecond thermoreflectance instrument, which enables area-selective analysis with spatial resolution down to 5 mu m. The results show that the as-fabricated PbTe NC films exhibit ultralow thermal conductivity of 0.9 W m(-1) K-1 at 300 K. The transport property findings suggest potential in the proposed quick and cost-effective spin-coating strategy for bottom-up fabrication of nanostructured TE films from high-quality colloidal NC building blocks. ; M.P. would like to acknowledge INL for post-doctoral fellowship and thank Dr. E. Carbó-Argibay for his fruitful scientific and technical input on electron microscopy. This work was supported by FROnTHERA (NORTE-01-0145-FEDER-000023) project co-financed by European Union Funds, through Portuguese NORTE 2020 programme. ...

The growing demand for weight-saving engineering applications has led to the progress of lightweight composites with functional properties for an increasing number of applications. Lightweight materials with functional properties can be developed using a wide range of host matrices and reinforcement material. These large variety of possible combinations allow the development of new functional materials, structures and devices and that represent the present and the future of different engineering areas. Their novel properties combined with advanced manufacturing processes strongly increases the use of these materials in applications. This chapter presents some relevant challenges and an outlook on the future of this field. ; The authors thank the FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, UID/EEA/04436/2013 and UID/QUI/0686/2016; projects PTDC/EEI-SII/5582/2014 and PTDC/FIS-MAC/28157/2017 and grants s SFRH/BPD/110914/2015 (P.C.) and SFRH/BPD/112547/2015 (C.M.C.) Funding from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, is also ...

A poly(vinylidene fluoride) (PVDF) and its copolymers are polymers that, in specific crystalline phases, show high dielectric and piezoelectric values, excellent mechanical behavior and good thermal and chemical stability, suitable for many applications from the biomedical area to energy devices. This chapter introduces the main properties, processability and polymorphism of PVDF. Further, the recent advances in the applications based on those materials are presented and discussed. Thus, it shown the key role of PVDF and its copolymers as smart and multifunctional material, expanding the limits of polymer-based technologies. ; FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, and UID/QUI/0686/2019 and project PTDC/FIS-MAC/28157/2017, PTDC/BTMMAT/28237/2017, PTDC/EMD-EMD/28159/2017. The author also thanks the FCT for financial support under grant SFRH/BPD/112547/2015 (C.M.C.), SFRH/BPD/98109/2013 (V.F.C.), SFRH/BD/140698/2018 (R.B.P.), SFRH/BPD/96227/2013 (P.M.), SFRH/BPD/121526/2016 (D.M.C.), SFRH/BPD/97739/2013 (V. C.), SFRH/BPD/90870/2012 (C.R.). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA ...

Magnetic materials for magnetoelectric coupling are reported. After an introduction of magnetoelectric effect and materials, an historical on the main developments in this field are presented. Then, the main concepts related to multiferroic and magnetoelectric materials are introduced, together with the description of the main types of magnetoelectric materials and structures. Finally, the magnetic materials used the development of magnetoelectric composites are presented and discussed, highlighting their main physico-chemical characteristics and processing methods. In this way, a complete account on concepts, materials and methods is presented in this strongly evolving research field, with strong application potential in the areas of sensors and actuators, among others. ; FCT- Fundação para a Ciência e Tecnologia- for financial support in the framework of the Strategic Funding UID/FIS/04650/2020 and under projects PTDC/BTM-MAT/28237/2017 and PTDC/EMD-EMD/28159/2017. P.M., A.C.L. and N.P. also support from FCT (for the contract under the Stimulus of Scientific Employment, Individual Support – 2017 Call (CEECIND/03975/2017, for the SFRH/BD/132624/2017 and for the SFRH/BD/131729/2017 grant, respectively). Finally, the authors acknowledge funding by the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) ...