Polyolefin based antibacterial membranes derived from PE/PEO blends compatibilized with amine terminated graphene oxide and maleated PE

In this study, various strategies like amine terminated GO (GO-NH2), in situ formed polyethylene grafted GO (PE-g-GO) and their combinations with maleated PE (maleic anhydride grafted PE) were adopted to reactively compatibilize blends of low density polyethylene (LDPE) and polyethylene oxide (PEO). These blends were further explored to design porous, antibacterial membranes for separation technology and the flux and the resistance across the membranes were studied systematically. It was observed that GO-NH2 led to uniform dispersion of PEO in a PE matrix and further resulted in a significant improvement in the mechanical properties of the blends when combined with maleated PE. The efficiency of various compatibilizers was further studied by monitoring the evolution of morphology as a function of the annealing time. It was observed that besides rendering uniform dispersion of PEO in PE and improving the mechanical properties, GO-NH2 further suppresses the coalescence in the blends. As the melt viscosities of the phases differ significantly, there is a gradient in the morphology as also manifested from scanning acoustic microscopy. Hence, the membranes were designed by systematically reducing the thickness of the as-pressed samples to expose the core as the active area for flux calculations. Selected membranes were also tested for their antibacterial properties by inoculating E. coli culture with the membranes and imaging at different time scales. This study opens new avenues to develop PE based cost effective anti-microbial membranes for water purification.

Polyolefin based antibacterial membranes derived from PE/PEO blends compatibilized with amine terminated graphene oxide and maleated PE

In this study, various strategies like amine terminated GO (GO-NH2), in situ formed polyethylene grafted GO (PE-g-GO) and their combinations with maleated PE (maleic anhydride grafted PE) were adopted to reactively compatibilize blends of low density polyethylene (LDPE) and polyethylene oxide (PEO). These blends were further explored to design porous, antibacterial membranes for separation technology and the flux and the resistance across the membranes were studied systematically. It was observed that GO-NH2 led to uniform dispersion of PEO in a PE matrix and further resulted in a significant improvement in the mechanical properties of the blends when combined with maleated PE. The efficiency of various compatibilizers was further studied by monitoring the evolution of morphology as a function of the annealing time. It was observed that besides rendering uniform dispersion of PEO in PE and improving the mechanical properties, GO-NH2 further suppresses the coalescence in the blends. As the melt viscosities of the phases differ significantly, there is a gradient in the morphology as also manifested from scanning acoustic microscopy. Hence, the membranes were designed by systematically reducing the thickness of the as-pressed samples to expose the core as the active area for flux calculations. Selected membranes were also tested for their antibacterial properties by inoculating E. coli culture with the membranes and imaging at different time scales. This study opens new avenues to develop PE based cost effective anti-microbial membranes for water purification.

Large deformation dynamic finite element analysis of delaminated composite plates using contact-impact conditions

A new C-0 composite plate finite element based on Reddy's third order theory is used for large deformation dynamic analysis of delaminated composite plates. The inter-laminar contact is modeled with an augmented Lagrangian approach. Numerical results show that the widely used ``unconditionally stable'' beta-Newmark method presents instability problems in the transient simulation of delaminated composite plate structures with large deformation. To overcome this instability issue, an energy and momentum conserving composite implicit time integration scheme presented by Bathe and Baig is used. It is found that a proper selection of the penalty parameter is very crucial in the contact simulation. (C) 2014 Elsevier Ltd. All rights reserved.

High Value of Proton Relaxivity Achieved by Graphene Oxide-Cobalt Ferrite Nanoparticle Composite: A Potential Contrast Agent in Magnetic Resonance Imaging

This work investigates the potential of graphene oxide-cobalt ferrite nanoparticle (GO-CoFe2O4) composite as image contrast enhancing material in Magnetic Resonance Imaging (MRI). In the preset work, GO-CoFe2O4 composites were produced by a two-step synthesis process. In the first step, graphene oxide (GO) was synthesized, and in the second step CoFe2O4 nanoparticles were synthesized in a reaction mixture containing GO to yield graphene GO-CoFe2O4 composite. Proton relaxivity value obtained from the composite was 361 mM(-1)s(-1). This value of proton relaxivity is higher than a majority of reported relaxivity values obtained using several ferrite based contrast agents.

Matrix Crack Detection in Composite Plate with Spatially Random Material Properties using Fractal Dimension

Fractal dimension based damage detection method is investigated for a composite plate with random material properties. Composite material shows spatially varying random material properties because of complex manufacturing processes. Matrix cracks are considered as damage in the composite plate. Such cracks are often seen as the initial damage mechanism in composites under fatigue loading and also occur due to low velocity impact. Static deflection of the cantilevered composite plate with uniform loading is calculated using the finite element method. Damage detection is carried out based on sliding window fractal dimension operator using the static deflection. Two dimensional homogeneous Gaussian random field is generated using Karhunen-Loeve (KL) expansion to represent the spatial variation of composite material property. The robustness of fractal dimension based damage detection method is demonstrated considering the composite material properties as a two dimensional random field.

Probabilistic stress variation studies on composite single lap joint using Monte Carlo simulation

The work presented in this paper involves the stochastic finite element analysis of composite-epoxy adhesive lap joints using Monte Carlo simulation. A set of composite adhesive lap joints were prepared and loaded till failure to obtain their strength. The peel and shear strain in the bond line region at different levels of load were obtained using digital image correlation (DIC). The corresponding stresses were computed assuming a plane strain condition. The finite element model was verified by comparing the numerical and experimental stresses. The stresses exhibited a similar behavior and a good correlation was obtained. Further, the finite element model was used to perform the stochastic analysis using Monte Carlo simulation. The parameters influencing stress distribution were provided as a random input variable and the resulting probabilistic variation of maximum peel and shear stresses were studied. It was found that the adhesive modulus and bond line thickness had significant influence on the maximum stress variation. While the adherend thickness had a major influence, the effect of variation in longitudinal and shear modulus on the stresses was found to be little. (C) 2014 Elsevier Ltd. All rights reserved.

Properties of the chalcogenide-carbon nano tubes and graphene composite materials

Composite can deliver more than the individual elemental property of the material. Specifically chalcogenide- multi walled carbon nano tubes and chalcogenide- bilayer graphene composite materials could be interesting for the investigation, which have been less covered by the investigators. We describe micro structural properties of Se55Te25Ge20, Se55Te25Ge20 + 0.025% multi walled carbon nano tubes and Se55Te25Ge20 + 0.025% bilayer graphene materials. This gives realization of the alloying constituents inclusion/or diffusion inside the multi walled carbon nano tubes and bilayer graphene under the homogeneous parent alloy configuration. Raman spectroscopy, X-ray photoelectron spectroscopy, UV/Visible spectroscopy and Fourier transmission infrared spectroscopy have also been carried out under the discussion. A considerable core energy levels peak shifts have been noticed for the composite materials by the X-ray photoelectron spectroscopy. The optical energy band gaps are measured to be varied in between 1.2 and 1.3 eV. In comparison to parent (Se55Te25Ge20) alloy a higher infrared transmission has been observed for the composite materials. Subsequently, variation in physical properties has been explained on the basis of bond formation in solids. (C) 2014 Elsevier B. V. All rights reserved.

Wave propagation analysis in adhesively bonded composite joints using the wavelet spectral finite element method

A wavelet spectral finite element (WSFE) model is developed for studying transient dynamics and wave propagation in adhesively bonded composite joints. The adherands are formulated as shear deformable beams using the first order shear deformation theory (FSDT) to obtain accurate results for high frequency wave propagation. Equations of motion governing wave motion in the bonded beams are derived using Hamilton's principle. The adhesive layer is modeled as a line of continuously distributed tension/compression and shear springs. Daubechies compactly supported wavelet scaling functions are used to transform the governing partial differential equations from time domain to frequency domain. The dynamic stiffness matrix is derived under the spectral finite element framework relating the nodal forces and displacements in the transformed frequency domain. Time domain results for wave propagation in a lap joint are validated with conventional finite element simulations using Abaqus. Frequency domain spectrum and dispersion relation results are presented and discussed. The developed WSFE model yields efficient and accurate analysis of wave propagation in adhesively-bonded composite joints. (C) 2014 Elsevier Ltd. All rights reserved.

Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

In the present work, effect of pouring temperature (650 degrees C, 655 degrees C, and 660 degrees C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg2Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg2Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg2Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg2Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650 degrees C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg2Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.

Effect of extrusion ratio on the microstructure, texture and mechanical properties of (Mg/AZ91)(m)-SiCp composite

Cast Mg/SiCp and AZ91/SiCp composites were successfully hot extruded vis-a-vis cast and unreinforced Mg and AZ91 alloy up to low (R=15:1) and high (R=54:1) extrusion ratios at 350 degrees C. Significant matrix grain refinement was noticed after extrusion due to dynamic recrystallization; the degree of refinement being relatively higher for the two composites. The AZ91 based materials (AZ91 and AZ91/SiCp) exhibited comparatively finer grain size both in cast condition and after extrusion due to strong pinning effect from alloying elements as well as Mg17Al12 intermetallic phase. Compositional analyses eliminated the possibility of any interfacial reaction between matrix (Mg/AZ91) and second phase reinforcement (SiCp) in case of the composites. Texture evolution shows the formation of < 10 (1) over bar0 >parallel to ED texture fibre for all the materials after extrusion irrespective of SiCp addition or alloying which is primarily due to the deformation of the matrix phase. Micro-hardness did not significantly increased on extrusion in comparison to the respective cast materials for both composites and unreinforced alloys. Dynamic mechanical analysis, however, confirmed that the damping properties were affected by the extrusion ratio and to a lesser extent, due to the presence of second phase at room temperature as well as at higher temperature (300 degrees C). (C) 2014 Elsevier B.V. All rights reserved.

Matrix crack detection in spatially random composite structures using fractal dimension

Fractal dimension based damage detection method is studied for a composite structure with random material properties. A composite plate with localized matrix crack is considered. Matrix cracks are often seen as the initial damage mechanism in composites. Fractal dimension based method is applied to the static deformation curve of the structure to detect localized damage. Static deflection of a cantilevered composite plate under uniform loading is calculated using the finite element method. Composite material shows spatially varying random material properties because of complex manufacturing processes. Spatial variation of material property is represented as a two dimensional homogeneous Gaussian random field. Karhunen-Loeve (KL) expansion is used to generate a random field. The robustness of fractal dimension based damage detection methods is studied considering the composite plate with spatial variation in material properties.

Effect of solvent; enhancing the wettability and engineering the porous structure of a calcium phosphate/agarose composite for drug delivery

Tissue engineering deals with the regeneration of tissues for bone repair, wound healing, drug delivery, etc., and a highly porous 3D artificial scaffold is required to accommodate the cells and direct their growth. We prepared 3D porous calcium phosphate ((hydroxyapatite/beta-tricalcium phosphate)/agarose, (HAp/beta-TCP)/agarose) composite scaffolds by sol-gel technique with water (WBS) and ethanol (EBS) as solvents. The crystalline phases of HAp and beta-TCP in the scaffolds were confirmed by X-ray diffraction (XRD) analysis. The EBS had reduced crystallinity and crystallite size compared to WBS. WBS and EBS revealed interconnected pores of 1 mu m and 100 nm, respectively. The swelling ratio was higher for EBS in water and phosphate buffered saline (PBS). An in vitro drug loading/release experiment was carried out on the scaffolds using gentamicin sulphate (GS) and amoxicillin (AMX). We observed initial burst release followed by sustained release from WBS and EBS. In addition, GS showed more extended release than AMX from both the scaffolds. GS and AMX loaded scaffolds showed greater efficacy against Pseudomonas than Bacillus species. WBS exhibited enhanced mechanical properties, wettability, drug loading and haemocompatibility compared to EBS. In vitro cell studies showed that over the scaffolds, MC3T3 cells attached and proliferated and there was a significant increase in live MC3T3 cells. Both scaffolds supported MC3T3 proliferation and mineralization in the absence of osteogenic differentiation supplements in media which proves the scaffolds are osteoconducive. Microporous scaffolds (WBS) could assist the bone in-growth, whereas the presence of nanopores (EBS) could enhance the degradation process. Hence, WBS and EBS could be used as scaffolds for tissue engineering and drug delivery. This is a cost effective technique to produce scaffolds of degradable 3D ceramic-polymer composites.

Unique nanoporous antibacterial membranes derived through crystallization induced phase separation in PVDF/PMMA blends

In this study, a unique method was adopted to design porous membranes through crystallization induced phase separation in PVDF/PMMA (poly(vinylidene fluoride)/poly(methyl methacrylate)) blends. By etching out PMMA, which segregates either in the interlamellar and/or in the interspherulitic regions of the blends, nanoporous hierarchical structures can be derived. Different nanoparticles like titanium dioxide (TiO2), silver nanoparticle (Ag) decorated carbon nanotubes (Ag-CNTs), TiO2 decorated CNTs (TiO2-CNTs), Ag decorated TiO2 (Ag-TiO2) and Ag-TiO2 decorated CNTs (Ag@TiO2-CNTs) were synthesized and melt mixed with 80/20 PVDF/PMMA blends to render antibacterial activity to the membranes. Scanning electron microscopy (SEM) was used to study the crystalline morphology of the membranes. A significant improvement in the trans-membrane flux was obtained in the blends with Ag@TiO2 decorated CNTs as compared to the membranes derived from the neat blends, which can be attributed to the interconnected pores in these membranes. Both qualitative and quantitative studies of antifouling and antibacterial activity (using E. coli as a model bacterium) were performed using the standard plate count method. SEM micrographs clearly showed that the antifouling activity of the membranes was improved with addition of Ag@TiO2-CNTs. In the quantitative standard plate count method, the bacterial colony significantly decreased with the addition of Ag@TiO2-CNTs as against neat blends. This study opens a new avenue in the fabrication of polymer blend based membranes for water filtration.

Post-failure Analysis and Fractography of In-plane Tension-Tested Tufted Carbon Fabric-Reinforced Epoxy Composite Laminates

Tufted and plain unidirectional carbon fabric-reinforced epoxy composite laminates were fabricated by vacuum-enhanced resin infusion technology and subjected to in-plane tensile tests with a view to study the changes in mechanical properties and failure responses. Owing to the presence of tufts in the laminates, both the tensile strength and modulus decrease by similar to 38 and similar to 20%, respectively, vis-A -vis the values recorded for plain composites. The fracture features point to the fact that though both the composites fail in brittle manner, they, however, exhibit differing fiber pull out lengths. Further, it was noticed that for the tufted ones, crack originates in the vicinity of tuft thread, spreads through the composite in a brittle manner, and results in a display of shorter fiber pull out lengths. These observations and other results are discussed in this paper.

Electrochemical behavior of Zn-graphene composite coatings

A Zn-graphene composite coating was electrodeposited on mild steel. The graphene was synthesized by electrochemical exfoliation of graphite. Electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction techniques were used to characterize the coatings. Compared to a pure Zn coating, the Zn-graphene coating exhibited reduced grain size, reduced surface defects, hillock structures over the coating surface and an altered texture. The corrosion behavior of the coatings was examined by Tafel polarization and electrochemical impedance spectroscopic methods. A significant improvement in the corrosion resistance in terms of reduction in corrosion current and corrosion rate and increase in polarization resistance was noted in the case of the Zn coating containing graphene.