Mechanical properties of thermoplastic elastomers based on silicone rubber and an ethylene–octene copolymer by dynamic vulcanization

Thermoplastic vulcanizates (TPVs) are a special class of thermoplastic elastomers that are generally produced by the simultaneous mixing and crosslinking of a rubber with a thermoplastic polymer at an elevated temperature. Novel peroxide‐cured TPVs based on blends of silicone rubber and the thermoplastic Engage (an ethylene–octene copolymer) have been developed. These TPVs exhibit very good overall mechanical and electrical properties. With an increasing concentration of dicumyl peroxide, the tensile strength, modulus, and hardness of the TPVs increase, whereas the elongation at break decreases. Significant correlations have been obtained from oscillating disc rheometer torque values with various physical properties, such as the modulus and tension set of the TPVs. The aging characteristics and recyclability of the silicone‐based TPVs are also excellent. Scanning electron microscopy photomicrographs of the TPVs have confirmed a dispersed phase morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of electron beam radiation on structural changes of trimethylol propane trimethacrylate,ethylene vinyl acetate,and their blends

The effect of electron beam irradiation at different radiation doses (2, 5, 10, 15, and 20 Mrad) on trimethylol propane trimethacrylol propane trimethacrylate (TMPTMA), ethylene vinyl acetate (EVA, 12% vinyl acetate content), and their blends (0.5, 1, 1.5, 2, 2.5, 3, and 5 parts/100 parts EVA) was investigated. An IR study showed some residual unsaturations retained in irradiated pure TMPTMA, while in blends all unsaturations were used up at a very early stage of irradiation. The concentration of the carbonyl group due to air oxidation increased in pure EVA and blends, but it reached a maximum at the 1.5-part TMPTMA level and 5-Mrad dose. some ether linkages were formed during irradiation in pure EVA and the blends, although in pure EVA the concentration of ether linkages reached a maximum at the 2-Mrad dose and then decreased and in the blends it increased with an increase in radiation dose. Gel content showed an increasing trend with an increase in radiation dose, but it increased marginally with TMPTMA level. A blend of EVA with 1 part TMPTMA produced more gel than pure EVA at the same irradiation dose. © 1996 John Wiley & Sons, Inc.     

Compatibility study of chlorinated polyethylene/ethylene methacrylate copolymer blends using thermal,mechanical, and chemical analysis

Blends of chlorinated polyethylene (CPE) elastomer and ethylene methacrylate copolymer (EMA) in various compositions were studied for their compatibility using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) spectroscopy techniques. Irrespective of measurement techniques used, all blends showed a single glass transition temperature (T_g) lying in between the T_g of control polymers in both DSC and DMA. Glass transition temperatures of blends obtained from DSC were in consistency with Couchman–Karasz equation. Also, the T_g obtained from both DSC and DMA are above the “rule of mixing” line of the two control polymers. These results from thermal analysis clearly indicate some compatibility between the two polymers. Furthermore, compatibility of CPE/EMA blends were also been investigated by FTIR spectroscopy and scanning electron microscopic analysis. A shifting of characteristic C? Cl stretching peak of CPE and C?O stretching peak of EMA toward lower wave number indicate the presence of specific interaction between the two polymers. Mechanical properties like tensile strength, modulus at 100% elongation, elongation at break, and hardness were observed above the line of additivity drawn between the two control polymers, which corroborate compatibility between CPE and EMA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40316.     

Verifiability in Systems and Data Engineering: Preface by the Special Issue Editors

Innovations in Systems and Software Engineering -     

NBR Powder Modified Phenolic Resin Composite: Influence of Graphite on Tribological and Thermal Properties

The incorporation of graphite as a solid lubricant in the formulation of brake friction material is well-recognized practice. However, achieving the desired level of performances using graphite is still a significant challenge, due to difficulty in dispersion and loading of graphite in composite materials. The present investigation was aimed at identifying the effect of graphite loading on the tribological and thermal properties of a composite made from phenolic resin modified with powdered acrylonitrile butadiene rubber (NBR). Five composites were prepared with different proportions of graphite (0–40 phr) to the phenolic resin. Thermogravimetric analysis (TGA) and thermal conductivity measurements were carried out to demonstrate the thermal stability and thermal conductivity behaviors. Both the thermal stability and thermal conductivity were found to increase with an increase in graphite content. On the other hand, the tribological properties were found to be optimum at a definite loading of graphite (30 phr). The change in surface morphology of these composites was studied before and after the friction test and correlated with the tribological properties. This investigation provides guidelines for achieving a high-performance composite using graphite for brake friction materials.     

Tuning of optical,thermal and antimicrobial capabilities of CdS nanoparticles with incorporated Mn prepared by chemical method

Cadmium sulfide (CdS) nanoparticles with different amounts of incorporated Manganese (Mn: 10, 15 and 20 mol%) has been prepared by chemical method. In optical properties the UV–Vis–NIR absorption spectra of all samples showed blue shift compared with the bulk CdS and decrease in band gap with Mn concentration. The presence of functional groups was identified by fourier transform infrared spectroscopy. It confirmed presence of metal sulfur bonding and weak interaction between anions (S^2?) and cations (Mn²⁺). The Photoluminescence spectra showed two emission peaks at 397 and 541 nm corresponding to the electron-hole recombination of CdS and surface trap induced emission respectively. In thermal properties thermogravimetric curve indicated increase in weight loss with Mn incorporation suggesting that pure CdS nanoparticles are thermally more stable than Mn incorporated CdS nanoparticles. The antimicrobial activities of Mn incorporated CdS were studied against Gram-positive and Gram-negative bacteria as test microorganisms using agar plating-spot inoculation method.     

Polyaniline/ethylene vinyl acetate composites as dielectric sensor

The compressive stress (pressure) sensitivity of dielectric properties has been studied on ethylene vinyl acetate (EVA)/polyaniline (Pani) composites prepared through In‐situ synthesis of polyaniline in the solution of insulating EVA matrix. It is observed that the dielectric constant and loss increase with the increase in applied pressure, that is some piezoelectric effect is observed for these composites. The dielectric properties are also found to increase with respect to time when subjected under constant pressure. It is seen that changes in dielectric constant and loss follow some exponential relationships with respect to applied pressure and time duration under constant stress, and the relaxation time for the composites can be calculated. The relaxation time decreases with the increase in concentration of Pani in a composite. However, a composite with lower Pani content exhibits relatively higher change in dielectric properties against applied pressure and time duration under compression compared to one with higher loading. Granular crew type morphology of Pani is observed through scanning electron microscopic (SEM) study. This study reveals that these EVA‐Pani composites can be used as dielectric sensor. POLYM. ENG. SCI., 54:1632–1639, 2014. © 2013 Society of Plastics Engineers     

Densification and strengthening of silver-reinforced hydroxyapatite-matrix composite prepared by sintering

Ductile-phase reinforcement of hydroxyapatite (HA) was achieved by addition of silver particulates (5–30 vol %) in HA powder and subsequent sintering of HA–Ag powder compacts. A composite made by sintering 10 vol % Ag and the balance HA at 1200 °C for 1 h in air had flexural strength of 75±7 MPa, which was almost double that of pure HA sintered under an identical condition. The density of HA-10 vol % Ag composite was 90±2% of the theoretical density (as calculated from the rule of mixture) and was lower than that (98.7±0.4%) of pure HA sintered at a similar condition. The X-ray diffraction pattern of the composite did not indicate any decomposition of HA or any reaction between HA and Ag. Ag in the composite melted during sintering, but, due to poor wetting, did not spread in between HA particles. The addition of Ag reduced densification and grain growth during sintering of HA–Ag composites. Indentation cracks in the composites went around Ag inclusions and often stopped at Ag inclusions. The increase in the flexural strength of the composites was thought to be due to crack-bridging and crack-arrest by silver particles.     

Effect of surface modification of high-density polyethylene by direct current and radio frequency glow discharge on wetting and adhesion characteristics

The present investigation aims to optimize the process parameters of Direct Current (DC) and Radio Frequency (RF) glow discharge treatment through air in terms of discharge power and time of exposure for the surface modification of high-density polyethylene (HDPE) sheet, for attaining best adhesive joint of the polymer to mild steel. In order to estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to glow discharge have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that at a given power level of DC glow discharge, surface energy and its polar component increase with increasing exposure time, attaining a maximum and then decreasing. In the case of RF glow discharge, surface energy and its polar component increase with increasing exposure time and then saturate. Surface modification by DC glow discharge increases the surface energy of HDPE relatively more at a lower power compared to that observed for RF glow discharge. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by electron spectroscopy for chemical analysis (ESCA) and energy-dispersive spectra (EDS). A significant oxygen peak is observed for surface-modified polymer as detected by ESCA and EDS. Lap shear tensile test of an adhesive (Araldite AY 105) joint of HDPE with mild steel has been carried out in optimizing the parameters of DC and RF glow discharge for maximum joint strength. When HDPE is exposed to DC glow discharge, improvement of adhesive joint strength of HDPE to mild steel is found to be by a factor more than 7. On the other hand, when HDPE is exposed to RF glow discharge, results in improvement of adhesive joint strength of HDPE to mild steel by a factor nearer to 7 are found. Thus, DC glow discharge is more capable for increasing wetting and adhesion characteristics of the polymer.     

Electrical conductivity of carbon black and carbon fibre filled silicone rubber composites

Electrically conductive silicone rubber composites have been prepared through incorporation of conductive acetylene black and short carbon fibre (SCF). The percolation limit for the attainment of high conductivity is found to be relatively less for silicone rubber based composites compared to EPDM or NBR based composites reported earlier. Percolation limit is found to be lower for SCF-filled systems (7.5 phr) compared to black-filled ones (14 phr). Both black- and SCF-filled systems exhibit an increase in resistivity with the increase in temperature (PCT effect). This PCT effect may be explained in terms of differences in the thermal expansion between the rubber matrix and the conductive filler. However, resistivity-versus-temperature plots are not identical during the heating-cooling cycle, leading to some hysteresis and electrical set. The current-voltage relationship is linear (Ohmic in nature) at room temperature but becomes non-linear (non-Ohmic) at elevated temperatures. The resistivity of these composites is measured under different conditions such as on applying pressure and being subjected to different mechanical stress and strain over the specimens. An effort has been made to correlate the effect of different parameters on electrical resistivity with the change in the conductive network structure under different conditions.