Fabrication and characterization of poly(methyl methacrylate)/CaCu3Ti4O12 composites

Composites comprising Poly(Methyl Methacrylate) (PMMA) and CaCu3Ti4O12 (CCTO) via melt mixing followed by hot pressing were fabricated. These were characterized using X-ray diffraction, thermo gravimetric, scanning electron microscopy, and Impedance analyzer for their structural, morphology, and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. The composite, with 38 Vol % of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low frequency relaxation is attributed to the space charge polarization/MWS effect. Theoretical models were employed to rationalize the dielectric behavior of these composites. At higher temperatures, the relaxation peak shifts to higher frequencies, due to the merging of both beta and alpha relaxations into a single dielectric dispersion peak. The AC conductivity in the high frequency region was attributed to the electronic polarization. POLYM. ENG. SCI., 54:551-558, 2014. (c) 2013 Society of Plastics Engineers

Aminosilane Functionalized Cenosphere in Poly(vinyl butyral) Composite Films: Moisture Resistant Encapsulated Schottky Devices

Functionalized cenosphere in PVB composite films were fabricated by melt processing. The composites show higher tensile strength with lower failure strain with increased filler ratio in the matrix. Fractographic images of the samples and DMA studies indicate brittle failure of the matrix. Moisture permeation and water contact angle studies reveal improved hydrophobicity of the matrix, while the factor of surface roughness increases the wettability at higher filler content. Schottky-structured devices encapsulated with functionalized cenosphere indicate enhanced resistance to moisture and increased life time for the devices.

Effect of silane functionalized alumina on poly(vinyl butyral) nanocomposite films: Thermal, mechanical, and moisture barrier studies

In this work, a hybrid-polymer nanocomposite film, based on polyvinyl butyral/amino-silane functionalized nano alumina, was fabricated by melt processing. The calcium degradation measurements suggest the functionalized nanocomposite films exhibit higher resistance towards moisture penetration as compared to the neat alumina loaded films. Thermal stability, mechanical strength, and contact angle studies of the composites were also conducted to evaluate the performance of the functionalized alumina loaded films. These nanocomposite films were encapsulated over Al/P3HT/ITO Schottky structured device. The changes observed in the current density of the devices to the applied voltage before and after accelerated aging conditions are presented. The nanocomposite with functionalized alumina films exhibits 50% change in current density, which is superior to that attained with neat and non-functionalized films. POLYM. COMPOS., 35:1426-1435, 2014. (c) 2013 Society of Plastics Engineers

Conducting polymer-carbon black nanocomposite sensor for volatile organic compounds and correlating sensor response by molecular dynamics

Volatile organic compounds (VOCs) are present in our every day used products such as plastics, cosmetics, air fresheners, paint, etc. The determination of amount of VOC present in atmosphere can be carried out via various sensors. In this work a nanocomposite of a novel thiophene based conducting polymer and carbon black is used as a volatile organic compound sensor. The fabricated 2 lead chemiresistor sensor was tested for vapours of toluene, acetone, cylcohexane, and carbon tetrachloride. The sensor responds to all the vapours, however, exhibit maximum response to toluene vapours. The sensor was evaluated for various concentrations of toluene. The lower limit of detection of the sensor is 15 +/- 10 ppm. The study of the effect of humidity on senor response to toluene showed that the response decreases at higher humidity conditions. The surface morphology of the nanocomposite was characterized by scanning electron microscopy. Diffuse reflectance spectroscopy was used to investigate the absorption of vapours by the nanocomposite film. Contact angle measurements were used to present the effect of water vapour on the toluene response of nanocomposite film. Solubility parameter of the conducting polymer is predicted by molecular dynamics. The sensing behaviour of the conducting polymer is correlated with solubility parameter of the polymer. Dispersion interaction of conducting polymer with toluene is believed to be the reason for the selective response towards toluene. (C) 2014 Elsevier B.V. All rights reserved.

Dielectric Impedance Studies of Poly(vinyl butyral)-Cenosphere Composite Films

In the current study, amino silane functionalized cenosphere particles was used as a reinforcing filler in poly(vinyl butyral) matrix and were made by melt blending. The changes observed in the dielectric performance of the composite films with varying weight percentage of cenosphere particle in the matrix were investigated. The dielectric property and impedance spectroscopy were evaluated as a function of applied frequency in the range of 50 Hz to 5 MHz. It is observed that, because of orientation polarization of the PVB polymer, the permittivity and impedance decrease, whereas conductivity increases. Tangent loss graph indicates that the property of the matrix is associated with geometrical fill factor and the lowest quality factor. Therefore, above 10 kHz, these composites can be considered as dielectric loss-less material. (C) 2013 Society of Plastics Engineers

Cross-linked Chitosan/Thermoplastic Starch Reinforced with Multiwalled Carbon Nanotubes Using Maleate Esters as Coupling Agent: Mechanical, Tribological and Thermal Characteristics

Bio-nanocomposites have been developed using cross-linked chitosan and cross-linked thermoplastic starch along with acid functionalized multiwalled carbon nanotubes (f-MWCNT). The nanocomposites developed were characterized for mechanical, wear, and thermal properties. The results revealed that the nanocomposites exhibited enhanced mechanical properties. The composites containing 3% f-MWCNT showed maximum compression strength. Tribological studies revealed that, with the addition of small amount of f-MWCNTs the slide wear loss reduced up to 25%. SEM analysis of the nanocomposites showed predominantly brittle fractured surface. Thermal analysis showed that the incorporation of f-MWCNTs has improved the thermal stability for the nanocomposites.

Investigations on pressure and thickness profiles in carbon fiber-reinforced polymers during vacuum assisted resin transfer molding

Systematic experiments have been carried out by monitoring the in-situ pressure and thickness profiles for three different configurations, viz., flat plate, flat plate with a central circular hole, and an L-section using vacuum assisted resin transfer molding (VARTM) process. The effect of anisotropy on resin flow has been quantified by considering uni-directional carbon fiber preforms with 0 degrees and 90 degrees orientation to the flow direction for each configuration. A quasi-isotropic 45 degrees/0 degrees/-45 degrees/90 degrees](S) layup has also been included for flat plate case. Additionally, the study has been extended to understand the effect of using high permeability medium for each configuration. Fluid pressure profiles and thickness variation profiles have been obtained using an array of pressure sensors and linear variable differential transformers for each configuration. Experimental data reveal that anisotropy (due to changing fiber orientations), configuration, and gravity significantly change fluid pressure and displacement fields obtained during VARTM.

Compressive and Flexural Properties of Functionally Graded Fly Ash Cenosphere-Epoxy Resin Syntactic Foams

The present study focuses on developing functionally graded syntactic foams (FGSFs) based on a layered co-curing technique. The FGSFs were characterized for compressive and flexural properties and compared with plain syntactic foams. The results showed that the specific compressive modulus was 3-67% higher in FGSFs compared to plain syntactic foams. FGSF exhibited 5-34% and 34-87% higher specific modulus and strength, respectively in flexural mode. The microscopic examinations of comparative responses of the filler and matrix to deformation suggest that the failure is dominated by the matrix. The gradient in the composition of syntactic foams helps in effectively distributing the stress throughout the microstructure and results in improved mechanical performance of syntactic foams. From the microscopy studies, it is evident that, the failure mechanism in the FGSF under flexural loading is governed by a crack that initiated on the tensile side of the specimen and propagated through the thickness to cause complete fracture. The microscopic observations further clearly demonstrate the existence of seamless interfaces between the layers and a clear difference in the cenosphere concentration across the interface, affirming the gradation in the prepared samples. The results show that appropriate compositions of FGSFs can be selected to develop materials with improved mechanical performance. POLYM. COMPOS., 36:685-693, 2015. (c) 2014 Society of Plastics Engineers

Mechanical properties of CNT-Bisphenol E cyanate ester-based CFRP nanocomposite developed through VARTM process

This paper reports on the effect of multiwall carbon nanotubes (CNTs) without and with chemical functionalization on the mechanical properties of Bisphenol E cyanate ester resin (BECy) based carbon fibre reinforced plastic (CFRP) laminated composites. BECy with its low viscosity, low moisture uptake and superior mechanical properties is selected for its application in CFRP laminates through the cost-effective Vacuum Assisted Resin Transfer Moulding (VARTM) process. However, unlike CNT-epoxy-CFRP composites, processing and performance issues such as dispersion of CNTs, chemical bonding with resin, functionalization effects, effects on mechanical properties, etc. for BECy-CNT-CFRP composite system are not well reported. The objective of this study is to improve the mechanical properties of BECy resin with small additions of CNTs and functionalized CNTs in CFRP laminates. CNTs and fCNTs are infused into BECy using ultrasonication and standard mixing methods. Improvements in Young's modulus and strength in tension, compression, shear, flexure and interlaminar shear strength are analysed. It is observed that addition of 0.5wt% CNTs effected for maximum mechanical properties of the resin and 1wt% CNTs for the mechanical properties of CNT-CFRP nanocomposite. Further, improvements obtained with fCNTs are marginal. Dispersion behaviour and effect of CNTs/fCNTs in load transfer corroborated with SEM pictures are presented. The enhanced mechanical properties realized in VARTM processing of BECy-CFRP laminate indicate clear advantage of CNT based modification of the process.

AN INVESTIGATION OF CUTTING MECHANISMS AND STRAIN FIELDS DURING ORTHOGONAL CUTTING IN CFRPs

Fiber-reinforced plastics (FRPs) are typically difficult to machine due to their highly heterogeneous and anisotropic nature and the presence of two phases (fiber and matrix) with vastly different strengths and stiffnesses. Typical machining damage mechanisms in FRPs include series of brittle fractures (especially for thermosets) due to shearing and cracking of matrix material, fiber pull-outs, burring, fuzzing, fiber-matrix debonding, etc. With the aim of understanding the influence of the pronounced heterogeneity and anisotropy observed in FRPs, ``Idealized'' Carbon FRP (I-CFRP) plates were prepared using epoxy resin with embedded equispaced tows of carbon fibers. Orthogonal cutting of these I-CFRPs was carried out, and the chip formation characteristics, cutting force signals and strain distributions obtained during machining were analyzed using the Digital Image Correlation (DIC) technique. In addition, the same procedure was repeated on Uni-Directional CFRPs (UD-CFRPs). Chip formation mechanisms in FRPs were found to depend on the depth of cut and fiber orientation with pure epoxy showing a pronounced ``size effect.'' Experimental results indicate that in-situ full field strain measurements from DIC coupled with force measurements using dynamometry provide an adequate measure of anisotropy and heterogeneity during orthogonal cutting.

Low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Vertically aligned carbon nanotubes were grown at temperatures as low as 120degreesC by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2-1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices. (C) 2003 American Institute of Physics.

Films de polietileno oxo-degradados mediante envejecimiento acelerado por radiación UV y calor

Resumen: Los materiales plásticos utilizados en la industria del embalaje y transporte de mercaderías familiares e industriales, presentan numerosas ventajas que los han puesto en su lugar durante los últimos 50 años. En la actualidad, son miles de millones de toneladas anuales de bolsas o embalajes de polietileno, las que diariamente se producen, se usan, se recuperan (en muy pequeña parte) y son finalmente dispuestas, quemadas o literalmente arrojadas al medio ambiente. La alta estabilidad química o la muy baja tasa de degradación, hace que estos residuos perduren en el medio - en la mayoría de los casos por más de 100 años- dependiendo las condiciones ambientales locales. Hace pocos años, se adaptaron conocimientos científicos a esta problemática, y de ello nacieron dos formas de atacar la eliminación del plástico como desecho (más allá del reciclado y uso racional): por un lado, la utilización de bioplásticos con propiedades biodegradables; y por otro, el agregado de aditivos pro-degradantes a plásticos convencionales. El presente trabajo, tiene por objeto tomar a esta última herramienta, sobre la cual se han comenzado a estudiar los mecanismos químicos por los cuales cumplen su función, evaluándolos en distintas condiciones aceleradas de laboratorio. De esta manera, se caracterizaron velocidades de degradación abiótica mediante envejecimientos acelerados con radiación ultravioleta y térmica, para films de polietileno aditivados con un compuesto oxodegradante comercial. Se estudiaron distintas concentraciones de aditivo en el polímero, en función del tiempo de envejecimiento. Las caracterizaciones incluyeron análisis mecánico, análisis térmico diferencial, espectroscopía de absorción infrarroja y de Absorción Atómica.

Recuperar plásticos desechables a los fines de conformar elementos constructivos de una vivienda económica como respuesta social, analizada como un problema de ingeniería industrial

Resumen: El hecho de seleccionar a los plásticos dentro de nuestro proyecto es porque son en particular, partes abundantes y visibles en la composición de los residuos generados en nuestra sede UCA Campus Rosario. Razonamos que son varias las áreas que los producen en forma cotidiana o de modo transitorio (como es el caso de eventos), a las que podemos sumar un accionar ambientalmente responsable. Ello nos impone la responsabilidad de proponer algún modo de re-utilizarlos en el diseño de ciertos elemento que los integre como materia prima, material de aporte, insumo o material auxiliar, con un amplio campo de posibilidades como es en la construcción, a partir de una mirada desde la ingeniería ambiental. La metodología de trabajo que desarrollamos implica inspeccionar la materia prima con la cual se va a trabajar, a los fines de conocerla fehacientemente, así como internalizar la posible combinación entre los distintos tipos de plásticos de acuerdo a su composición y su respuesta en la integración con otros materiales de uso tradicional, de acuerdo a experiencias reconocidas Desde una mirada lineal la educación sola no alcanza, como tampoco la tecnología ni las medidas parciales son suficientes para aliviar este tremendo desequilibrio que venimos heredando. Ante estos hechos es perentorio comprender la complejidad, actuar desde allí descubriendo la conexión invisible entre el ser humano y el medio, y los seres humanos entre sí. Debido a ello entendemos que para restaurar el medio ambiente en principio hay que comenzar por restaurar los vínculos y los ciclos que los contienen, esto implica re-ciclar.

Vibration analysis of laminated shells using a refined shear deformation theory

A previously published refined shear deformation theory is used to analyse free vibration of laminated shells. The theory includes the assumption that the transverse shear strains across any two layers are linearly dependent on each other. The theory has the same dependent variables as first-order shear deformation theory, hut the set of governing differential equations is of twelfth order. No shear correction factors are required. Free vibration of symmetric cross-ply laminated cylindrical shells, symmetric and antisymmetric cross-ply cylindrical panels is calculated. The numerical results are in good agreement with those from three-dimensional elasticity theory.

On the influence zone and the prediction of tensile strength of particulate polymeric composites

An intended numerical investigation is carried out. The results indicate that, even if a perfect adhesive bond is preserved between the particles and matrix materials, the two-phase element cell model is unable to predict the strength increment of the particulate polymeric composites (PPC). To explore the main reinforcing mechanism, additional microscopic experiment is performed. An ''influence zone'' was observed around each particle which is measured about 2 to 10 micrometers in thickness for a glass-polyethylene mixture. Then, an improved computational model is presented to include the ''influence zone'' effect and several mechanical behaviors of PPC are well simulated through this new model.