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Inspeção termográfica de danos por impacto em laminados compósitos sólidos de matriz polimérica reforçada com fibras de carbono.; Thermographic inspection of impact damage in solid fiber-reinforced polymer matrix composite laminates.

Almeida, Euripedes Guilherme Raphael de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/04/2010 PT
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Laminados compósitos com matrizes poliméricas, respectivamente termorrígida e termoplástica, reforçadas com fibras contínuas de carbono foram submetidos a impacto único transversal com diferentes níveis de energia. Os danos imprimidos aos materiais estruturais foram avaliados por termografia ativa infravermelha na modalidade transmissão. Em geral, os termogramas do laminado termoplástico apresentaram indicações mais claras e bem definidas dos danos causados por impacto, se comparados aos do compósito termorrígido. O aquecimento convectivo das amostras por fluxo controlado de ar se mostrou mais eficaz que o realizado por irradiação, empregando-se lâmpadas incadecentes. Observou-se também que tempos mais longos de aquecimento favoreceram a visualização dos danos. O posicionamento da face impactada do espécime, relativamente à câmera infravermelha e à fonte de calor, não afetou a qualidade dos termogramas no caso do laminado termorrígido, enquanto que influenciou significativamente os termogramas do compósito termoplástico. Os resultados permitiram concluir que a termografia infravermelha é um método de ensaio não-destrutivo simples, robusto e confiável para a detecção de danos por impacto inferior à 5 Joules em laminados compósitos poliméricos reforçados com fibras de carbono.; Continuous carbon fiber-reinforced thermosetting and thermoplastic composite laminates were exposed to single transversal impact with different energy levels. The damages marked to the structural materials were evaluated by active infrared thermography in transmission mode. In general...

Implantação iônica de baixa energia em polímero para desenvolvimento de camadas compósitas nanoestruturadas condutoras litografáveis.; Low energy ion implantation into polymers to develop conductive composite layers for lithography.

Teixeira, Fernanda de Sá
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/06/2010 PT
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46.3%
Eletrônica utilizando polímero em substituição ao silício é uma área de pesquisa recente com perspectivas econômicas promissoras. Compósitos de polímeros com partículas metálicas apresentam interessantes propriedades elétricas, magnéticas e ópticas e têm sido produzidos por uma grande variedade de técnicas. Implantação iônica de metais utilizando plasma é um dos métodos utilizados para obtenção desses compósitos condutores. Neste trabalho é realizada implantação de íons de ouro de baixa energia em PMMA utilizando plasma. O PMMA tem grande importância tecnológica sendo largamente utilizado como resiste em litografias por feixe de elétrons, raios-X, íons e deep-UV. Como resultado da implantação iônica de baixa energia em PMMA há formação de uma camada nanométrica de material condutor. Esse novo material, denominado compósito isolante-condutor, permite criar micro e nanodispositivos através de técnicas largamente utilizadas em microeletrônica. Medidas elétricas são realizadas in situ em função da dose de íons metálicos implantada, o que permite um estudo das propriedades de transporte desses novos materiais, que podem ser modeladas pela teoria da percolação. Simulações utilizando o programa TRIDYN permitem obter a profundidade e o perfil da implantação dos íons. São mostradas caracterizações importantes tais como Microscopia Eletrônica de Transmissão...

New trends in concrete-polymer composite materials and systems

Czarnecki, Lech; Garbacz, Andrzej; Knapen, Elke; Aguiar, J. L. Barroso de; Ferreira, Rui Miguel; Gemert, D. van
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2009 ENG
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56.27%
Appropriate combination of polymers and classical construction materials provides opportunities for innovative applications and systems, for improved performance and for increased durability. Particularly in restoration and retrofitting, polymer based materials highly contribute to sustainable construction activity. This paper highlights the innovations, new approaches and durability assessments, presented at the International Symposium on Polymers in Concrete in Guimarães, Portugal, 2006. Emphasis is put on microstructure formation, modification by means of hardener free epoxy resin by polymers in solution or by recycled particles, bond assessment and improvement, durability of bond under moisture and temperature effects, concrete protection by means of coatings.

Using a glass-fibre reinforced polymer composite in the production of sustainable water storage vessels

Simões, Carla L.; Nunes, J. P.; Bernardo, C. A.; Vasconcelos, M.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2014 ENG
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56.3%
The quest for sustainability by rethinking materials, products and production strategies is an enormous challenge currently laid upon the economic sector. Materials selection plays a critical role in this challenge. The present work describes a technological, environmental and economic study of the production of a water storage glass-fibre reinforced composite vessel. The vessel was evaluated via a Life Cycle Assessment/Life Cycle Costing (LCA/LCC) integrated model. The most significant life cycle phase was found to be the raw materials production, in which the Fossil fuels, Respiratory inorganics and Climate change were the relevant impact categories. The vessel environmental and economic performances could be improved if an end of life (EoL) option different from landfill had been chosen. The present work describes a new integrated way of analysing the environmental and economic performances of a structural product full life cycle. It also highlights the role and importance of fibre reinforced polymer composites in the quest for sustainable products.; FCT projeto SFRH/BD/60852/2009 e IPC projeto UID/CTM/50025/2013

Aligned Protein–Polymer Composite Fibers Enhance Nerve Regeneration: A Potential Tissue-Engineering Platform**

Chew, Sing Yian; Mi, Ruifa; Hoke, Ahmet; Leong, Kam W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
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46.3%
Sustained release of proteins from aligned polymeric fibers holds great potential in tissue-engineering applications. These protein–polymer composite fibers possess high surface-area-to-volume ratios for cell attachment, and can provide biochemical and topographic cues to enhance tissue regeneration. Aligned biodegradable polymeric fibers that encapsulate human glial cell-derived neurotrophic factor (GDNF, 0.13 wt%) were fabricated via electrospinning a copolymer of caprolactone and ethyl ethylene phosphate (PCLEEP) with GDNF. The protein was randomly dispersed throughout the polymer matrix in aggregate form, and released in a sustained manner for up to two months. The efficacy of these composite fibers was tested in a rat model for peripheral nerve-injury treatment. Rats were divided into four groups, receiving either empty PCLEEP tubes (control); tubes with plain PCLEEP electrospun fibers aligned longitudinally (EF-L) or circumferentially (EF-C); or tubes with aligned GDNF-PCLEEP fibers (EF-L-GDNF). After three months, bridging of a 15 mm critical defect gap by the regenerated nerve was observed in all the rats that received nerve conduits with electrospun fibers, as opposed to 50% in the control group. Electrophysiological recovery was seen in 20%...

Modeling Carbon-Black/Polymer Composite Sensors

Lei, Hua; Pitt, William G.; McGrath, Lucas K.; Ho, Clifford K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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46.35%
Conductive polymer composite sensors have shown great potential in identifying gaseous analytes. To more thoroughly understand the physical and chemical mechanisms of this type of sensor, a mathematical model was developed by combining two sub-models: a conductivity model and a thermodynamic model, which gives a relationship between the vapor concentration of analyte(s) and the change of the sensor signals. In this work, 64 chemiresistors representing eight different carbon concentrations (8–60 vol% carbon) were constructed by depositing thin films of a carbon-black/polyisobutylene composite onto concentric spiral platinum electrodes on a silicon chip. The responses of the sensors were measured in dry air and at various vapor pressures of toluene and trichloroethylene. Three parameters in the conductivity model were determined by fitting the experimental data. It was shown that by applying this model, the sensor responses can be adequately predicted for given vapor pressures; furthermore the analyte vapor concentrations can be estimated based on the sensor responses. This model will guide the improvement of the design and fabrication of conductive polymer composite sensors for detecting and identifying mixtures of organic vapors.

Effects of mechanical properties of polymer on ceramic-polymer composite thick films fabricated by aerosol deposition

Kwon, Oh-Yun; Na, Hyun-Jun; Kim, Hyung-Jun; Lee, Dong-Won; Nam, Song-Min
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 22/05/2012 EN
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Two types of ceramic-polymer composite thick films were deposited on Cu substrates by an aerosol deposition process, and their properties were investigated to fabricate optimized ceramic-based polymer composite thick films for application onto integrated substrates with the advantage of plasticity. When polymers with different mechanical properties, such as polyimide (PI) and poly(methyl methacrylate) (PMMA), are used as starting powders together with α-Al2O3 powder, two types of composite films are formed with different characteristics - surface morphologies, deposition rates, and crystallite size of α-Al2O3. Through the results of micro-Vickers hardness testing, it was confirmed that the mechanical properties of the polymer itself are associated with the performances of the ceramic-polymer composite films. To support and explain these results, the microstructures of the two types of polymer powders were observed after planetary milling and an additional modeling test was carried out. As a result, we could conclude that the PMMA powder is distorted by the impact of the Al2O3 powder, so that the resulting Al2O3-PMMA composite film had a very small amount of PMMA and a low deposition rate. In contrast, when using PI powder, the Al2O3-PI composite film had a high deposition rate due to the cracking of PI particles. Consequently...

Fabrication of an Electrically-Resistive, Varistor-Polymer Composite

Ahmad, Mansor Bin; Fatehi, Asma; Zakaria, Azmi; Mahmud, Shahrom; Mohammadi, Sanaz A.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 23/11/2012 EN
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This study focuses on the fabrication and electrical characterization of a polymer composite based on nano-sized varistor powder. The polymer composite was fabricated by the melt-blending method. The developed nano-composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FeSEM), and energy-dispersive X-ray spectroscopy (EDAX). The XRD pattern revealed the crystallinity of the composite. The XRD study also showed the presence of secondary phases due to the substitution of zinc by other cations, such as bismuth and manganese. The TEM picture of the sample revealed the distribution of the spherical, nano-sized, filler particles throughout the matrix, which were in the 10–50 nm range with an average of approximately 11 nm. The presence of a bismuth-rich phase and a ZnO matrix phase in the ZnO-based varistor powder was confirmed by FeSEM images and EDX spectra. From the current-voltage curves, the non-linear coefficient of the varistor polymer composite with 70 wt% of nano filler was 3.57, and its electrical resistivity after the onset point was 861 KΩ. The non-linear coefficient was 1.11 in the sample with 100 wt% polymer content. Thus, it was concluded that the composites established a better electrical non-linearity at higher filler amounts due to the nano-metric structure and closer particle linkages.

Research Summary: Object Oriented Finite Element Analysis for Materials Science*: A Tool for Viscoelastic Polymer Composite Deformation Analysis

Raghavan, Rajesh; Carter, W. Craig
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 527116 bytes; application/pdf
EN
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A public domain code "Object Oriented Finite element analysis for materials science" (OOF) has been extended to include tools for analysis of viscoelastic materials. Utility of these tools has been discussed along with possible applications in this publication. Added features in OOF include means to quantitatively analyze the spatiotemporal response of a composite polymeric material in dynamic as well as in static deformation conditions. These coupled with the existing features of OOF, in particular, the complete analysis of mechanical characteristics of materials provide a comprehensive tool for the studies of time dependent behavior of variety of materials including polymeric solid composites, polymer nanocomposites, polymer blends, block copolymers, and so on. The viscoelastic module draws its strength from the underlying OOF architecture to provide a macroscopic evaluation of mechanical properties using microstructural details. An application of this module for deformation analysis is the characterization of mechanical behavior a polymer nanocomposites. The deformation behaviour of polymer composite depends on the combined characteristic relaxation times of its constituents as well as its microstructural details. Results of analysis are expected to provide better insight into the role of microstructure as well as the role of interphase on the average mechanical; Singapore-MIT Alliance (SMA)

Apatite-Polymer Composite Particles for Controlled Delivery of BMP-2

Yong, Tseh-Hwan; Hager, Elizabeth A.; Ying, Jackie Y.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 337522 bytes; application/pdf
EN_US
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46.44%
We have developed a versatile delivery platform comprising a novel composite of two biomaterials with proven track records: apatite and poly(lactic-co-glycolic acid) (PLGA). These composites have been tested in the delivery of a model protein, bovine serum albumin (BSA), as well as a growth factor, bone morphogenetic protein-2 (BMP-2), which is a potent inducer of bone formation. The controlled release strategy is based on the use of a polymer with acidic degradation products to control the dissolution of a basic inorganic component, resulting in protein release. The release profile can be modified systematically by changing variables that affect polymer degradation and/or apatite dissolution, such as polymer molecular weight, polymer composition, apatite loading, and apatite particle size. We have found that an increase in polymer molecular weight and polymer hydrophobicity led to slower polymer degradation, and in turn, slower apatite dissolution and protein release. Protein release was enhanced by reducing apatite particle size and by lowering the apatite content in the composites. We anticipate that this delivery platform can be extended to the controlled release of other therapeutic proteins and chemicals.; Singapore-MIT Alliance (SMA)

Apatite-Polymer Composite Particles for Controlled Delivery of BMP-2: In Vitro Release and Cellular Response

Yong, Tseh-Hwan; Ying, Jackie Y.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 151443 bytes; application/pdf
EN
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46.4%
Bone morphogenetic protein-2 (BMP-2) has the ability to induce osteoblast differentiation of undifferentiated cells, resulting in the healing of skeletal defects when delivered with a suitable carrier. We have applied a versatile delivery platform comprising a novel composite of two biomaterials with proven track records – apatite and poly(lactic-co-glycolic acid) (PLGA) – to the delivery of BMP-2. Sustained release of this growth factor was tuned with variables that affect polymer degradation and/or apatite dissolution, such as polymer molecular weight, polymer composition, apatite loading, and apatite particle size. The effect of released BMP-2 on C3H10T1/2 murine pluripotent mesenchymal cells was assessed by tracking the expression of osteoblastic makers, alkaline phosphatase (ALP) and osteocalcin. Release media collected over 100 days induced elevated ALP activity in C3H10T1/2 cells. The expression of osteocalcin was also upregulated significantly. These results demonstrated the potential of apatite-PLGA composite particles for releasing protein in bioactive form over extended periods of time.; Singapore-MIT Alliance (SMA)

Use of fiber reinforced polymer composite in bridge structures; Use of FRP in bridge structures

Tuakta, Chakrapan, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 50 leaves; 2551286 bytes; 2555317 bytes; application/pdf; application/pdf
ENG
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46.36%
Fiber reinforced polymer composite (FRP) is a new construction material, gradually gaining acceptance from civil engineers. Bridge engineering is among the fields in civil engineering benefiting from the introduction of FRP composite. Its advantages over traditional construction materials are its high tensile strength to weight ratio, ability to be molded into various shapes, and potential resistance to environmental conditions, resulting in potentially low maintenance cost. These properties make FRP composite a good alternative for innovative construction. In the past 10 years, experiments have been conducted to investigate the applicability of FRP composite in bridge structures, including the applications of FRP composite girder and bridge deck, column and beam strengthening, etc. This document will first present the basic information of FRP composite, including its mechanical behaviors and manufacturing processes relevant to civil engineering applications. Then the application of FRP composite in bridge engineering will be investigated, through three case studies. Four main issues contributing to the slow acceptance of the material into construction industry as a whole, despite its success in aerospace and automobile industries...

Envelhecimento ambiental acelerado em PRF a base de tecidos híbridos kevlar/vidro: propriedades e instabilidade estrutural

Felipe, Renata Carla Tavares Santos
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências
Tipo: Tese de Doutorado Formato: application/pdf
POR
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There are a number of damaging mechanisms that various materials can suffer in service. However, when working with polymer composite materials, this is something that requires analysis, especially when exposed to adverse environmental conditions. Thus, the objective of the present thesis is the study of the direct influence of environmental aging and the form of hybridization of the reinforcement woven on the structural stability, surfacedegradation and fracture process of polymer composites laminates. For this, the development of two polymer composite laminates was necessary, where one of them was reinforced with a bi-directional woven with hybrid strandsofkevlar-49/glass-Efibers, and the other also with a bi-directionalwoven, however with weft and warpformed of alternating strandsof Kevlar-49 fibers and glass-E fiber The reinforcementwoven are industrially manufactured. Both laminates use a polyester resin as a matrixand are made up of four layers each. All laminates were industrially prepared by the hand lay-up method of manufacturing. To do this, test specimens were manufactured of the respective laminates and submitted to environmental aging accelerated through the aging chamber. They were exposed to alternating cycles of UV radiation and moisture (heated steam) for a standard defined period. At the end of the exposure period the specimens were subjected to mechanical tests of uniaxial tensile and bending in three points and to the characterizationsof the fracture and surface deterioration. In addition...

The chemical modification of tropical wood polymer composites

Islam, M.S.; Hamdan, S.; Hassan, A.; Talib, Z.A.; Sobuz, M.D.H.R.
Fonte: Sage Publicador: Sage
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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56.33%
Wood polymer composites were manufactured from several types of tropical wood species by impregnating the woods with acrylonitrile monomer solution. The physical and mechanical properties of wood polymer composites were then investigated in this study. The vacuum-pressure method was employed to impregnate wood samples with monomer and in situ polymerization. Acrylonitrile reacted and incorporated with wood, which was confirmed through Fourier transform infrared spectroscopy and scanning electron microscopy test analysis. The mechanical properties of wood samples in terms of modulus of elasticity and compressive modulus were found to be improved on acrylonitrile treatment. Besides, the fabricated wood polymer composite samples had lower water absorption and higher surface hardness (Shore D) value as compared to their corresponding raw one. For wood polymer composites, a significant improvement was found in physical and mechanical properties compared to the raw woods.; Md. Saiful Islam, Sinin Hamdan, Azman Hassan, Zainal Abidin Talib, and HR Sobuz

Carbon Nanotubes Filled Polymer Composites: A Comprehensive Study on Improving Dispersion, Network Formation and Electrical Conductivity

Chakravarthi, Divya Kannan
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
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46.36%
In this dissertation, we determine how the dispersion, network formation and alignment of carbon nanotubes in polymer nanocomposites affect the electrical properties of two different polymer composite systems: high temperature bismaleimide (BMI) and polyethylene. The knowledge gained from this study will facilitate optimization of the above mentioned parameters, which would further enhance the electrical properties of polymer nanocomposites. BMI carbon fiber composites filled with nickel-coated single walled carbon nanotubes (Ni-SWNTs) were processed using high temperature vacuum assisted resin transfer molding (VARTM) to study the effect of lightning strike mitigation. Coating the SWNTs with nickel resulted in enhanced dispersions confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS). An improved interface between the carbon fiber and Ni-SWNTs resulted in better surface coverage on the carbon plies. These hybrid composites were tested for Zone 2A lightning strike mitigation. The electrical resistivity of the composite system was reduced by ten orders of magnitude with the addition of 4 weight percent Ni-SWNTs (calculated with respect to the weight of a single carbon ply). The Ni-SWNTs - filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts indicated by the minimal carbon fiber pull out. Methods to reduce the electrical resistivity of 10 weight percent SWNTs -- medium density polyethylene (MDPE) composites were studied. The composites processed by hot coagulation method were subjected to low DC electric fields (10 V) at polymer melt temperatures to study the effect of viscosity...

An engineering model on penetration of eroding rods into ceramic/polymer composite

Zaera, Ramón; Arias Hernández, Ángel; Navarro Ugena, Carlos
Fonte: EDP Sciences Publicador: EDP Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em /09/2003 ENG
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A new material composed of a polymer matrix loaded with ceramic partiales, at low cost and of higher ballistic efficiency than that of the metallic materials used for armouring applications, is proposed as an alternative to the ceramic tiles traditionally adopted for mixed panels. An engineering model was developed to simulate normal impacts of projectiles against this particulate composite backed by a metallic plate. The equation governing the erosion of projectile and ceramic is that proposed by Tate and Alekseevskii, modifie to consider a moving target. For the volume of particulate composite between the projectile and the metallic plate, an equation was derived to include a momentum balance. For the metallic plate, an energy balance equation was used. When the projectile has eliminated the ceramic/polymer composite and meets the plate, the model of Awerbuch & Bodner is adopted, again modifie to consider a moving target. ln this way, the impact process is described by a set of non-linear differential equations, to be integrated in time. The model was validated with experimental results and with full numerical simulations and showed agreement with both of them.; The authors are indebted to the Comunidad Autónoma de Madrid (Project 07N/0004/1998) for the financial support of this work.; 6 pages...

A case study undertaken recycling & reuse of glass fiber reinforced thermoset polumer wastes of composite materials industry

Ribeiro, M.C.; Meira Castro, A.C.; Silva, F.J.; Meixedo, J.P.; Dinis, M. L.; Fiúza, António
Fonte: eSYMBIOSIS Publicador: eSYMBIOSIS
Tipo: Conferência ou Objeto de Conferência
Publicado em //2014 ENG
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46.43%
Glass fibre-reinforced plastics (GFRP) have been considered inherently difficult to recycle due to both: crosslinked nature of thermoset resins, which cannot be remoulded, and complex composition of the composite itself. Presently, most of the GFRP waste is landfilled leading to negative environmental impacts and supplementary added costs. With an increasing awareness of environmental matters and the subsequent desire to save resources, recycling would convert an expensive waste disposal into a profitable reusable material. In this study, efforts were made in order to recycle grinded GFRP waste, proceeding from pultrusion production scrap, into new and sustainable composite materials. For this purpose, GFRP waste recyclates, were incorporated into polyester based mortars as fine aggregate and filler replacements at different load contents and particle size distributions. Potential recycling solution was assessed by mechanical behaviour of resultant GFRP waste modified polymer mortars. Results revealed that GFRP waste filled polymer mortars present improved flexural and compressive behaviour over unmodified polyester based mortars, thus indicating the feasibility of the GFRP industrial waste reuse into concrete-polymer composite materials.

Addition of magnetic markers for non-destructive evaluation of polymer composites

Fulco,Ana Paula Pereira; Melo,José Daniel Diniz; Paskocimas,Carlos Alberto; Medeiros,Suzana Nóbrega de; Machado,Fernando Luis de Araujo; Rodrigues,Alexandre Ricalde
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 EN
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46.49%
Polymer composite pipes are an appealing option as a substitute for conventional steel pipes, particularly due to their inherent corrosion resistance. However, the composite pipes currently used do not allow non-destructive evaluation (NDE) using instrumented devices which operate with magnetic sensors. The present work aims at the development of polymer composites with the addition magnetic markers to allow the application non-destructive evaluation techniques which use magnetic sensors. Glass-polyester composite flat, circular plates were fabricated with the addition of ferrite particles (barium ferrite and strontium ferrite) and four types of notches were introduced on the plates' surfaces. The influence of these notches on the measured magnetic properties of each material was measured. X-ray diffraction (XRD), X-ray fluorescence (XRF) and Brunauer, Emmett, and Teller (BET) nitrogen adsorption were used for the characterization of the ferrite particles. Particle dispersion in the polymer matrix was analyzed by scanning electron microscopy (SEM). According to the results, a particular variation in magnetic field was detected over the region surrounding each type of notch. The results suggest that the proposed technique has great potential for damage detection in polymer composites using magnetic sensors and thus constitute a valuable contribution which may ultimately lead to the development of non-destructive evaluation techniques for assessing the structural integrity polymer composite pipes.

Near-infrared photoresponse in single walled carbon nanotube/polymer composite films

Sarker, Biddut K.; Arif, M.; Khondaker, Saiful I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We present a near-infrared photoresponse study of single-walled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (SWCNT/P3HT-b-PS) composite films for different loading ratios of SWCNT in the polymer matrix. Compared to the pure SWCNT film, the photoresponse [(light current - dark current)/dark current] is much larger in the SWCNT/polymer composite films. The photoresponse is up to 157% when SWCNTs are embedded in P3HT-b-PS while for a pure SWCNT film it is only 40%. We also show that the photocurrent strongly depends on the position of the laser spot with maximum photocurrent occurring at the metal-film interface. We explain the photoresponse due to exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode - SWCNT interface; Comment: CARBON (in press)

Electrospun Reinforced Polymer-Polymer Composite Membranes for Applications in PEM Fuel Cells

Wilson, David
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
EN_US
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46.35%
Erik Thostenson; Polymer electrolyte membrane (PEM) ffuel cells are seen as the next generation of clean energy, sought to replace the likes of batteries. However, PEM fuel cells are limited by a mechanically unstable Nafion membrane that limits its lifespan. To combat this dilemma, it has been suggested that such membranes can be mechanically reinforced in a variety of ways, specifically through the consolidation of electrospun nanofiber mats. Previous research in the development of electro-active composites successfully derived the procedure for producing such hierarchically consolidated nanofiber composite films, called the ??VARTM method. Application of this technique towards the PEM fuel cell membrane dilemma, thus, could result in the next huge step in PEM fuel cell lifespans. Therefore, as a proof-of-concept, polystyrene and polyvinylidene fluoride were chosen and dissolved in dimethyl formamide to be electrospun for the creation of the reinforcements for this study. Afterwards, degradation testing provided that the reinforcements should be consolidated within a Nafion solution dissolved in methanol and deionized water at a 4:1 ratio. Dimethyl acetamide was also a tested solvent to compare against Methanol, however, was shown to destroy the reinforcements. In consequence...