Effect of dynamic cross-linking on mixing torque behavior and tensile yield behavior of isotactic polypropylene (iPP) / ethylene-propylene diene rubber (EPDM) /nitrile rubber (NBR) elastomeric blends

The mixing torque behavior of ter blends of isotactic-polypropylene (iPP) with ethylene-propylene diene rubber (EPDM)/Nitrile rubber (NBR) was studied with the help of Rheometer using resole type phenolic resin as a cross-linking agents. Systematic changes with varying blend composition were observed in stress-strain behavior in the yield region viz., width of yield peak, work of yield, yield stress and yield strain. Analysis of yield stress data was made on the basis of various mathematical expressions of first power and two-thirds power laws of blend composition dependence and the porosity model. It led to consistent result from the expressions about the variation of stress concentration effect in both uncross-linked and cross-linked blend systems. With the aid of scanning electron microscopy (SEM) shapes and sizes of dispersed elastomer phase (EPDM / NBR) domains at varying blend compositions were studied.     

Manganese stearate initiated photo‐oxidative and thermo‐oxidative degradation of LDPE,LLDPE and their blends

This study is an attempt to investigate the effect of a representative pro‐oxidant (manganese stearate) on the degradation behavior of 70 ± 5 μ thickness films of LDPE, LLDPE and their blends. Films were prepared by film blowing technique in the presence of varying quantities of manganese stearate (0.5–1% w/w) and subsequently subjected to accelerated degradative tests: xenon arc exposure and air‐oven exposure (at 70°C). The physico–chemical changes induced as a result of aging were followed by monitoring the mechanical properties (Tensile strength and Elongation at break), carbonyl index (CI), morphology (SEM), melt flow index (MFI), oxygen content (Elemental analysis), and DSC crystallinity. The results indicate that the degradative effect of pro‐oxidant is more pronounced in LDPE than LLDPE and blends, due to the presence of larger number of weak branches in the former. The degradation was also found to be proportional to the concentration of the pro‐oxidant. Flynn‐Wall‐Ozawa iso‐conversion technique was used to determine the kinetic parameters of degradation, which were used to determine the effect of the pro‐oxidant on the theoretical lifetime of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Photovoltaic performance of dye-sensitized solar cells fabricated with polyvinylidene fluoride–polyacrylonitrile–silicondioxide hybrid composite membrane

Electrospun fibrous membranes of hybrid composites of polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN) and silicon dioxide (SiO₂) (PVdF–PAN–SiO₂) are prepared with different proportions of SiO₂ (3, 5 and 7% w/w). The field emission scanning electron microscopy (FE-SEM) reveals that these membranes have three-dimensional, fully interconnected network structures, which are combined with micropores of fine SiO₂ distribution. The surface roughness of the membranes increases with increasing the SiO₂ content. It is found that 7 wt% SiO₂/PVdF–PAN electrolyte membrane has the highest ionic conductivity (6.96 × 10⁻² S cm⁻¹) due to the large liquid electrolyte uptake (about 570%). As the concentration of SiO₂ nanoparticles increase, the contact angle value also increases, ranging from 135.70° to 140.60° which indicates that the membrane has higher hydrophobicity. The dye sensitized solar cells (DSSCs) are fabricated using the hybrid composite membrane with PVdF–PAN with 7 wt % SiO₂. Its photovoltaic performance exhibits an open circuit voltage (V_oc) of 0.79 V and a short circuit current 11.6 mA cm⁻² at an incident light intensity of 100 mW cm⁻², producing an efficiency of 5.61%. DSSC, using the hybrid composite electrospun membrane which shows more stable photovoltaic performance than other assembled DSSCs.     

Dielectric relaxation in Ba(Y1/2Nb1/2)O3–BaTiO3 ceramics

Lead-free (1 ? x)Ba(Y_1/2Nb_1/2)O₃–xBaTiO₃; (0 ≤ x ≤ 1) ceramics have been synthesized using solid-state reaction method and characterized by X-ray diffraction, scanning electron microscopy, dielectric and impedance studies. The crystal-structure of the compounds is found to be cubic with the space group Pm3m(221) except for BaTiO₃ for which it is tetragonal (P4/mmm). Complex impedance spectroscopy analysis indicated the presence of non-Debye type dielectric relaxation in Ba(Y_1/2Nb_1/2)O₃–BaTiO₃ system. Compound 0.25Ba(Y_1/2Nb_1/2)O₃–0.75BaTiO₃ exhibited a low value of temperature coefficient of capacitance (<±8 %) in the working temperature range (up to +100 °C), room temperature dielectric constant equal to 295 and low loss tangent (0.039) which meets the specifications for “Z5F” of Class I dielectrics of Electronic Industries Association. Hence, this composition might be a suitable candidate for capacitor applications. Ac conductivity and electric modulus studies supported the hopping type of conduction in the system and frequency dependent ac conductivity data obeyed Jonscher’s power law.     

Enhancement of electrical properties and blue emission due to nanostructuring of BaZr0.05Ti0.95O3 ferroelectric ceramics

Nano-structuring of various ferroic materials has tailored the existing properties in their bulk counterpart. Keeping this fact in view, nano-crystalline barium zirconate titanate (BaZr_0.05Ti_0.95O₃) ferroelectric ceramics were prepared by mechanical activation process using high-energy planetary ball milling followed by the sintering process. In the present work, effect of milling duration (15, 30 and 45 h) on structural and microstructural properties has been observed with the help of X-ray diffraction, scanning electron microscopy and transmission electron microscopy (for optimized milling duration). The crystallite size of the milled specimen decreases to 14.17 nm on increasing the milling duration from 15 to 45 h. A comparison with its bulk counterpart showed significant enhancement in di-, ferro-, piezo- and pyro-electric properties with strong blue emission in UV light (265 nm). The blue emission in UV light makes it a potential candidate for LEDs and optical devices.     

Enhancement in Strain Hardening on Boron Addition in As-Cast Ti–6Al–4V Alloy

It has been previously reported that the addition of boron to Ti–6Al–4V results in significant refinement of the as-cast microstructure and enhancement in the strain hardening. However, the mechanism for the latter effect has not been adequately studied. The aim of this study was to understand the reasons for the enhancement in room temperature strain hardening on addition of boron to as cast Ti–6Al–4V alloy. A study was conducted on slip transmission using SEM, TEM, optical profilometry and four point probe resistivity measurements on un-deformed and deformed samples of Ti–6Al–4V–xB with five levels of boron. Optical profilometry was used to quantify the magnitude of offsets on slip traces which in turn provided information about the extent of planar or multiple slip. Studies on deformed samples reveal that while lath boundaries appear to easily permit dislocation slip transmission, colony boundaries are potent barriers to slip. From TEM studies it was also observed that while alloys containing lower boron underwent planar slip, deformation was more homogeneous in higher boron alloys due to multiple slip resulting from large number of colony boundaries. Multiple slip is also proposed to be the prime cause of the enhanced strain hardening.     

A new method of determination of series and shunt resistances of silicon solar cells

A new method of measurement of series resistance R_s and shunt resistance R_sh of a silicon solar cell is presented. The method is based on the single exponential model and utilizes the steady state illuminated I–V characteristics in third and fourth quadrants and the V_oc–I_sc characteristics of the cell. It enables determination of values of R_sh and R_s with the intensity of illumination. For determination of R_s it does not require R_sh to be assumed infinite and realistic values of R_sh can be used. The method is very convenient to use and in the present study it has been applied to silicon solar cells having finite values of R_sh. We have found that R_sh is independent of intensity but the R_s decreases with both the intensity of illumination and the junction voltage.     

Comprehensive studies on polyethylenimine filled polypropylene and its potential application in carbon dioxide sequestration

Polypropylene (PP) was blended with branched polyethylenimine (PEI) with the aim to prepare blends having CO₂ adsorption property. The CO₂ adsorption properties will be conferred due to the presence of variety of amine functionality in PEI. PEI contains primary, secondary as well as tertiary amine groups. Before testing CO₂ adsorption, PP–PEI blends were characterized using variety of techniques, for example, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, scanning electron microscopy, and polarized light optical microscopy. In this work, we have studied in detail both compatibilized as well as noncompatibilized blends of PP and PEI. The compatibilization was achieved via addition of maleic anhydride grafted PP. Finally, all the compatibilized as well as noncompatibilized blends were studied for CO₂ adsorption. The compatibilized blends showed better thermal, mechanical as well as CO₂ adsorption properties as compared to the noncompatibilized blends. POLYM. ENG. SCI., 59:2092–2102, 2019. © 2019 Society of Plastics Engineers     

The tale of proteolysis targeting chimeras (PROTACs) for Leucine-Rich Repeat Kinase 2 (LRRK2)

Here we present the rational design and synthetic methodologies towards proteolysis-targeting chimeras (PROTACs) for the recently-emerged target leucine-rich repeat kinase 2 (LRRK2). Two highly potent, selective, brain-penetrating kinase inhibitors were selected, and their structure was appropriately modified to assemble a cereblon-targeting PROTAC. Biological data show strong kinase inhibition and the ability of the synthesized compounds to enter the cells. However, data regarding the degradation of the target protein are inconclusive. The reasons for the inefficient degradation of the target are further discussed.