Morphologies and Mechanical Properties of High-Density Polyethylene Induced by the Addition of Small Amounts of Both Low- and High-Molecular-Weight Polyolefin under Shear Stress Applied by Dynamic Packing Injection Molding

This paper focuses on the mechanical properties and crystal morphology of a self-reinforced high-density polyethylene 5000S (HDPE 5000S) by simultaneously blending with 9 wt% high-molecular-weight polyethylene (HMWPE) and 9 wt% low-molecular-weight polyethylene (LMWPE) (A9) under the shear stress field which was engendered by a self-made dynamic packing injection molding (DPIM) machine. The results of mechanical properties, differential scanning calorimetry, and scanning electron microscopy characterization were as follows: (1) The tensile strength of the dynamic samples increased to 112.1 MPa, 4.85 times as much as that of static packing injection molding (SPIM) samples (23.1 MPa), as a result of realizing polyethylene's self-enhancement; (2) Shish-kebab structure was found in the dynamic samples; (3) The crystallinity of the DPIM A9 sample reached 68.6%, on increase by 18.7% compared with that of the SPIM sample. The formation of the shish-kebab structure and enhancement of mechanical properties are explained.     

A new method for preparing powders for transmission electron microscopy examination

In this paper we describe a novel method to prepare powder specimens for transmission electron microscopy examination. The powder samples are embedded in a metallic matrix by a route based on the plastic flow of a soft metal, using a small laboratory type hand driven hydraulic press. The resulting composites are processed with the conventional procedure based on grinding polishing and ion beam milling. The resulting TEM specimens have a self-supporting structure, good thermal and electrical conductivity while showing a well-polished surface resulting from the ion milling process. The method can be applied to a large variety of samples with sufficiently strong mechanical properties; a few examples are reported. The limits, mainly due to the mechanical toughness of the powder, are discussed.     

Effects of Viscosity Ratio on Morphological,Rheological and Mechanical Properties of PP/PBT Melt Spun Alloy Fibers

Phase morphology formation plays an important role in the mechanical properties of polymer alloy fibers. The development of the blend morphology depends not only on the intrinsic properties of the component polymers but also on extrinsic factors such as viscosity ratio, λ, in the melt spinning process. The effects of blend component viscosity ratio on the morphological, rheological, and mechanical properties of polypropylene/poly(butylene terephthalate) (PP/PBT) melt spun alloy fibers were investigated. Accordingly, two kinds of PP as matrix phase and two kinds of PBT as dispersed phase, with various melt viscosity, were physically mixed and then blended during the extrusion step of melt spinning. SEM micrographs and rheological and mechanical properties evaluations showed that the morphology of PP/PBT alloy fibers strongly depend on the viscosity ratio, λ. Finer diameter PBT fibrils were observed for Viscosity ratios less than 1 (λ < 1) compared to samples with λ > 1. The best mechanical properties in alloy fiber samples were obtained for the viscosity ratio closest to unity (sample with λ = 0.9). The lowest differences among measured complex viscosities at various shear rates (0.1, 10, and 100 s^?1) were also observed in samples with λ = 0.9. The results showed that the mechanical properties of alloy fiber samples are affected not only by morphological properties observed at different viscosity ratios but also by the properties of the individual polymer components.     

Raman spectroscopy: a tool for biomechanical characterization of Stratum Corneum

The mechanical properties of the Stratum Corneum (SC) have been studied by different authors at the macroscopic level, but the modification of its ultra structure during mechanical extension remains unknown. Moreover, little is described about the effect of the mechanical stress on SC barrier function. In this study, we have examined the SC structure changes, at the molecular level, during uniaxial tensile experiments. This was performed on isolated SC samples using Raman spectroscopy. We could identify the strain status of the analyzed samples by using combination of Raman spectra and Partial Least Squares processing. In addition, this approach provided information about lipids and proteins behavior during the sample extension. The structure of the intercellular lipids bilayer became less organized up to ~9% deformation. For higher strains, a plateau corresponding to the minimum organization is observed till the complete failure of the sample. In the same time, protein structures including desmosomes, were characterized by monotonic secondary structure modifications for deformations up to ~9% followed by a plateau. These observations are relevantly demonstrating the effect of extension on the skin barrier state. Such an approach could be objectively used for clinical applications to evaluate skin discomfort degree and skin elastic behavior. This could therefore help with proof of efficacy for cosmetic and dermatologic products. Copyright © 2013 John Wiley & Sons, Ltd.     

Ultrashort high repetition rate exposure of dielectric materials: laser bonding of glasses analyzed by micro-Raman spectroscopy

We report on the joining of different glass types with dissimilar optical, thermal and mechanical properties by ultrashort laser welding at high repetition rates. Femtosecond laser pulses were focused at the interface of two optically contacted transparent samples. Using nonlinear absorption processes and heat accumulation of successive pulses, we achieved strong bonds between the samples. We used a three-point bending test to determine the breaking strength. With this technique, we achieved for instance for a borosilicate glass a breaking strength of up to 95 % of the bulk material. In addition, we even welded different material combinations. Although the welded glasses exhibit different thermal and mechanical properties, we obtained breaking strengths which are comparable to the utilized bulk materials. Using Raman spectroscopy we mapped the laser-processed material along the welded interface. Thereby, we determined that the welds consist of a mixture of both species, which is formed during the laser induced melting of the materials.     

Mössbauer comparative study of Fe–Si (3.5 wt%) alloys produced by melting and by mechanical alloying

Mössbauer spectroscopy and X-ray diffraction measurements were done on Fe–Si (3.5 wt%) alloys produced by melting and by mechanical alloying during 15, 30, 50 and 75 milling hours from over 99% purity powders. The Mössbauer spectra were fitted using hyperfine field distribution and it was obtained for all the samples in three ferromagnetic sites with fields of 27, 30 and 33 T for the mechanical alloyed samples and 26.8, 30.13 and 32.83 T for the commercial sample. These three sites are attributed to the pure Fe, Fe with one Si in the next near neighbor (nnn) and Fe with two Si in the nnn. As the milling time increases, the mean field increases too. X-ray diffraction measurement shows that all the samples are BCC, with a lattice parameter that increases with the milling time. These lattice parameters are bigger than that of the commercial alloy.     

Correlation between interfacial interactions and mechanical properties of PA-6 doped with surface-capped nano-silica

The polyamide-6 pellets were mixed with nano-SiO₂ particles surface-capped by 3-aminopropyltriethoxysilane (APS) via a melt blending route. PA-6 composites doped with surface-capped nano-SiO₂ (designated as PAMNS, where AMNS refers to APS surface-capped nano-SiO₂). AMNS and the silica samples (designated as EAMNS) extracted by acid etching from various PAMNS samples containing different concentration of amino functional groups on surface-capped nano-silica surfaces were characterized by means of Fourier transformation infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). This aims at revealing the interfacial interaction between AMNS and PA-6 matrix and its effect on the mechanical properties of the filled PA-6 composites. The chemical features and microstructures of the PAMNS composites were analyzed by means of FTIR and transmission electron microscopy (TEM), respectively, while their mechanical properties were evaluated using standardized test rigs. Results demonstrate that the surface-modified nano-SiO₂ particles were uniformly dispersed in PA-6 matrix. The residue silica extracted from various PAMNS samples showed characteristic FTIR absorbance peak of PA-6 and had larger weight losses than AMNS, implying that the polymeric matrix was chemically bonded with the nanofiller particles. The interfacial interactions are closely related to the concentration of functional groups in AMNS, and there might exist a critical concentration at which the strongest interfacial interactions could be reached. Beyond the critical concentration of the functional groups in AMNS, the mechanical properties of the filled PA-6 composites tended to decrease to some extent.     

Magnetic and structural properties of magnetoresistive FexAu100−x alloys produced by mechanical alloying

Fe_xAu_100−x alloys have been produced for the first time by mechanical alloying. X-ray diffractograms show FCC peaks. From the X-ray diffracion peak-widths we estimate the final grain size, which vary with x from 112 nm (for x=15) to 32 nm (for x=30). Lattice parameter decreases with concentration (minimum 0.401 nm at x=30), but above Vegard's law values. Susceptibility measurements show cluster-glass behaviour. Critical temperatures are consistently lower than similar alloys produced by arc melting followed by fast quenching. A magnetic phase diagram is presented. Giant magnetoresistance is present in all samples, with a maximum at x=25. This effect is caused by the dispersion of small iron clusters produced by the mechanical work.     

Nanoporous gold: 3D structural analyses of representative volumes and their implications on scaling relations of mechanical behaviour

We present a quantitative study of the salient structural parameters identified from so-called ‘representative volumes’ of the bicontinuous nanoporous gold (NPG) network, and examine the validity of self-similarity in describing its evolution. The approach is based on 3D-focused ion beam tomography applied to as-dealloyed and isothermally annealed NPG samples. After identifying sufficiently large representative volumes, we show that the ligament width distributions coarsen in a sufficiently self-similar, time-invariant manner, while the scaled connectivity density shows a self-similar ligament network topology. Using these critical parameters, namely mean ligament diameter and connectivity density, the Gibson–Ashby scaling laws for the mechanical response of cellular materials are revisited. The inappropriateness of directly applying the Gibson–Ashby model to NPG is demonstrated by comparing finite element method compression simulations of both the NPG reconstruction and that of the Gibson–Ashby solid model; rather than the solid volume fraction, we show that an effective load-bearing ring structure governs mechanical behaviour.     

Characterization of aluminum-carbon composites obtained via mechanical activation of aluminum and carbon nanotubes

The relaxation of structural defects of aluminum-multiwall carbon nanotubes (MWCNT) composite materials obtained via mechanical activation is studied in situ by X-ray diffraction using synchrotron radiation. Mechanically activated Al-MWCNT mixtures are annealed at temperatures of up to 600°C in an inert gas flow and X-ray diffraction patterns are simultaneously registered with a position-sensitive X-ray detector. It is demonstrated that mechanically activated samples of pure Al and composites with large-diameter MWCNTs (～20 nm) begin to experience the relaxation of defects accumulated during mechanical activation at temperatures as low as 100–150°C, while samples with small-diameter MWCNTs (～10 nm) exhibit thermal stability of structural defects up to 500°C.     

Study of Metallocene-Catalyzed Linear Low-Density Polyethylene Solid-State Extrusion: Processing and Mechanical Properties

The effect of extrusion temperature and extrusion drawing ratio (EDR) on the die swell ratio (DSR) and mechanical properties of metallocene-catalyzed linear low-density polyethylene (m-LLDPE) was examined with the application of solid-state extrusion (SSE). Scanning electron microscopy (SEM) was employed to characterize the microstructure and morphology of the extrudates. Extruded from a convergence-divergence die, compared with samples obtained by melt-state extrusion (MSE), the DSR decreases for SSE samples prepared at low extrusion temperature and high EDR. Mechanically strong SSE samples were also obtained at low extrusion temperatures and high EDR. Mechanically strong SSE samples were also obtained at low extrusion temperatures and high EDR. SEM indicates that the microstructures of the MSE samples consist primarily of ring-banded spherulites; the microstructure of the SSE samples was microfibers oriented along the direction of extrusion. The highly oriented microfibers contribute to the improved mechanical strength of the SSE samples.     

Deposition of tungsten nitride thin films by plasma focus device at different axial and angular positions

Tungsten nitride thin films were deposited on stainless steel-304 substrates by using a low energy (2 kJ) Mather type plasma focus device. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and microhardness are used to study the surface of treated samples. The XRD analysis shows that the degree of crystallinity of deposited thin films strongly depends on axial and angular positions of samples. The SEM micrographs of the deposited films at different angular positions (0°, 10° and 30°) and axial position of 8 cm show that the content of WN sub-micro crystalline structures on the surface of deposited films decreased with increasing the angle with respect to anode axis. From AFM results we observe that for the sample deposited at 8 cm and 0° axial and angular positions, respectively, the most uniform surface and the most homogenous distribution of grains are obtained. Also the hardness results show that the highest mechanical hardness is obtained when the film is deposited at 8 cm and 0° axial and angular positions, respectively.     

Mössbauer Studies of Thermal Power Plant Coal and Fly Ash

Iron-57 Mössbauer spectroscopic studies were carried out at room temperature on samples of coal, slag (bottom ash) and mechanical ash collected from Bhatinda (India) thermal power plant. Hyperfine parameters such as isomer shift, quadrupole splitting and total internal magnetic field of ⁵⁷Fe nuclei were used to characterize various iron-bearing minerals. The observed parameters indicate the presence of pyrite, siderite and ankerite in coal sample while magnetic fractions of mechanical ash and slag samples show the formation of hematite and Al-substituted magnesio-ferrite. The non-magnetic fraction of slag ash shows the dominance of Fe²⁺ phases while that of mechanical ash demonstrates the formation of both Fe²⁺ and Fe³⁺ phases. These findings are compared with Mössbauer and magnetic susceptibility studies on fly ash samples of Panipat (India) thermal power plant reported earlier.     

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.     

Study on Properties and Structure of Near Melt Point Extruded High‐Density Polyethylene

The effect of extrusion temperature on the mechanical properties of high‐density polyethylene (HDPE) was examined using solid‐state extrusion (SSE) and melt‐state extrusion (MSE) techniques. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) investigations were employed to provide evidence for explaining the relationship between mechanical properties and morphology of extrusion moldings. Extruded from a convergence‐divergence die, compared with samples obtained by MSE, the yield strength of samples obtained by SSE was enhanced in both longitudinal and transverse directions with a ductile failure. The yield strength decreased sharply with increasing extrusion temperature. The maximum longitudinal yield strength of samples extruded at 112°C was 181 MPa with an 87% elongation at break; the corresponding values were 28 MPa and 800% for samples extruded at 140°C (MSE); in the transverse direction the yield strength was 27 MPa with a 101% elongation at break for samples extruded at 140°C, while the maximum yield strength was 51 MPa with a 45% of elongation at break for samples extruded at 116°C. Compared with sheets extruded at 140°C, DSC data shows a 5.3°C increase in melting point, a 9.5°C decrease in melt point width, and a 7.1% decrease in crystallinity for sheets extruded at 112°C. SEM indicates that spherulites predominate in MSE samples, while a preferred orientation of the lamellae along the extrusion direction were mainly produced by SSE.     

Modifying a cylindrical surface irradiated with a radial beam of argon ions with energies of up to 5 keV

Aspects of the ion modification of the outer surfaces of tubular samples of E110 (Zr–1% Nb) alloy is studied. The samples are irradiated with a radial beam of argon ions (0.5–5.0 keV, (5–10) × 10¹⁸ ion/cm²) on the ILUR-03 setup. It is found that such ion bombardment smooths the relief formed by mechanical abrasive treatment. It is demonstrated that the effect of ion polishing is most pronounced for surface irregularities of a certain size.     

Tribological changes on SS304 stainless steel induced by nitrogen plasma immersion ion implantation with and without auxiliary heating

In order to achieve quite thick treated layers with reasonable thickness uniformity in SS304 steel, the plasma immersion ion implantation (PIII) process was run in high-temperature, up to 350 °C, to induce high thermal diffusion but avoid the white layer formation. In these experiments, we heated the sample-holder with a shielded resistive wire properly wound around it and subjected the SS samples to nitrogen glow discharge PIII with relatively low voltages (10 kV) in different temperatures. We also treated the SS samples by the traditional PIII method, slowly increasing the high voltage pulse intensities, until 14 kV at the end of processing, reaching temperatures of up to 350 °C. These modes of treatments were compared with respect to nitrogen implantation profiles, X-ray diffraction, tribology and mechanical properties. X-ray diffraction results indicated a much higher efficiency of auxiliary heated PIII mode compared to the ordinary PIII. Very prominent γ_N peaks were observed for the first mode, indicating large concentration of nitrogen in thick layers, confirmed by the nitrogen profiles measured by GDOS and AES. Improved mechanical and tribological properties were obtained for SS304 samples treated by the PIII with auxiliary heating, more than for ordinary PIII. Hardness was enhanced by up to 2.77 times, as seen by nanoindentation tests.     

Radiation effects on poly(vinylidene fluoride)

Melt-crystallized poly(vinylidene fluoride)s (PVF₂) with different crystallization histories were irradiated with γ-rays within the range of irradiation doses 0–83 Mrad. The effects on the crystalline structure and mechanical properties have been measured, compared, and discussed. The degree of crystallinity of the samples was found to increase with radiation dose. The differential scanning calorimeter scans of the quenched samples indicate that there are two melting peaks, and that the area of the lower temperature peak increases while the area of higher temperature peak decreases with increasing dose. Yield stress and breaking stress for all samples are not significantly affected by irradiation but elongation at break is.     

Practical scale modification of oleogels by ultrasonic standing waves

Lipid-based materials, such as substitutes for saturated fats (oleogels) structurally modified with ultrasonic standing waves (USW), have been developed by our group. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed. Here, we report scale-up of our procedure of structurally modifying oleogels via the use of USW by a factor of 200 compared to our previous microfluidic chamber. To this end, we compared three different USW chamber prototypes through finite element simulations (FEM) and experimental work. Imaging of the internal structure of USW-treated oleogels was used as feedback for successful development of chambers, i.e., the formation of band-like structures was the guiding factor in chamber development. We then studied the bulk mechanical properties by a uniaxial compression test of the sonicated oleogels obtained with the most promising USW chamber, and sampled local mechanical properties using scanning acoustic microscopy. The results were interpreted using a hyperelastic foam model. The stability of the sonicated oleogels was compared to control samples using automated image analysis oil-release tests. This work enabled the effective mechanical-structural manipulation of oleogels in volumes of 10–100 mL, thus paving the way for USW treatments of large-scale lipid-based materials.     

Laser remelting of Al-1.5 wt%Fe alloy surfaces: Numerical and experimental analyses

A 3D heat transfer mathematical model based on the finite element method is applied to the laser surface remelting (LSR) process with a view to simulating temperature fields and melt pool dimensions. The theoretical predictions furnished by the model are validated against LSR experimental results from tests carried out in the present study with Al-1.5 wt%Fe alloy samples. The work also encompasses an analysis of microstructural and microhardness variations throughout the resulting treated and untreated zones. A remarkable effect of the LSR treatment on the mechanical and corrosion resistance of the treated samples is shown.