Influence of silica and electron beam radiation on the properties of a high vinyl styrene-butadiene-styrene block copolymer

Radiation crosslinking of polymers has gained importance over conventional crosslinking because the system is fast, pollution free and relatively simple. In high energy electron beam curing, which is one of the radiation curing methods, the material to be cured is bombarded with electrons of specified energy to produce free radials. These radicals unite to give rise to chemical crosslinks. In the process, some unwanted chain scission may also occur. The mechanical properties of such electron beam crosslinked systems can further be improved by the incorporation of nanosilica. In this work, a high vinyl (~50%) S-B-S block copolymer incorporated with varying doses of specific hydrophilic nanosilica was irradiated with electron beam at 25 and 50 kGy. Mechanical properties were studied and compared with that of the unirradiated system. The influence of a silane coupling agent was also investigated. Morphological studies were done to understand the dispersion of nanosilica in the polymer matrix. Relatively moderate amounts of nanosilica along with an optimum dose of the coupling agent were found to be effective in improving the properties. Rheological properties were also studied in details to understand the possibility of recycling the polymer.     

Corrosion and Fire Protective Behavior of Advanced Phosphatic Geopolymeric Coating on Mild Steel Substrate

The research objectives of this study were to investigate and compare corrosion and fire protective properties of conventional and advanced phosphatic geopolymeric coating on mild steel substrate using spray coating technique For these studies two composition were developed using conventional geopolymerisation route by adding alkali activator solution to fly ash and six compositions were developed using advanced geopolymerisation process in which water was added to solid precursor powder obtained by together co-ginding of raw materials for a period of 8 h. Coated plates were tested for adhesion strength, water resistance, fire protection and corrosion resistance. Results indicated that coating developed from two passes with thickness 100 ± 15 μm showed better adhesion as compared to single pass and also proved to be promising corrosion protective coating material for mild steel substrate under sea water conditions. The developed material is able to withstand flame for more than 45 min and also no cracks were observed in coating by direct heating on liquefied petroleum gas flame. Thus developed phosphatic geopolymeric material is well suited for protecting the mild steel structures from fire and corrosion.     

Salt Effect on the Solution Properties of Cationic Gemini/Conventional Surfactants in the Presence of the Nonionic Polymer Hydroxypropylmethyl Cellulose

In this article, we report the salt effect on interaction of a water-soluble polymer hydroxypropylmethyl cellulose (HPMC) with the cationic Gemini surfactant (ethane-1, 2-diyl bis(N,N-dimethyl-N-hexadecylammoniumacetoxy) dichloride, 16-E2-16), and also its monomeric counterpart cetyltrimethylammonium chloride (CTAC) using the tensiometric method. Surface tension of the amphiphiles diminished in the presence of the polymer as well as salts; eventually, the polymer gets saturated with the surfactant and there is no further change of surface tension of the solution. Interaction between the polymer and surfactant starts at the critical aggregation concentration (CAC) that is stronger for 16-E2-16 than CTAC. CAC and critical micelle concentration (CMC) values of the surfactant-polymer binary mixtures at various concentrations of the polymer were determined. CAC as well as CMC of 16-E2-16 are considerably lower than CTAC. The inorganic salts (KCl and KBr) have a considerable influence on the polymer–surfactant interaction.     

Optimization of ozone bleaching conditions for improving wheat straw pulp quality using response surface methodology

Ozone bleaching conditions for wheat straw soda pulp were optimized using response surface methodology with central composite design. Effect of pH, consistency, and ozone dose on kappa number, brightness, and viscosity was investigated. Optimized process conditions to get minimum kappa number, maximum viscosity, and brightness were obtained as follows: pH 2.08–2.25, pulp consistency 27.4–30.0%, and ozone dose 0.4%. Validation of the model predicted values and experimental values obtained for optimum conditions has the difference of 0.5–2.0%, which shows that the developed model for ozone bleaching of wheat straw pulp is satisfactory.     

Evidences of solvent‐induced miscibility in polychloroprene‐co‐ethylene‐propene diene terpolymer blends

Solvent dependent changes in the compatibility behavior of Polychloroprene/Ethylene–propylene–diene terpolymer blends (CR/EPDM) have been investigated using dilute solution viscometry and solvent permeability analysis. To predict the compatibility of rubber blends of different compositions in solvents of different cohesive energy densities, Huggins interaction parameter (ΔB), hydrodynamic interaction (Δη) and Sun's parameter (α) were evaluated from the analysis of the specific and reduced viscosity data of two and three‐component polymer solutions. Miscibility criteria were not satisfied for CR/EPDM blends over the entire composition range in toluene, xylene, and carbon tetrachloride (CCl₄), however, a narrow miscibility domain was observed in chloroform (CHCl₃) for CR/EPDM/CHCl₃ system. These results were further corroborated with the analysis of heat of mixing (ΔH_m) and polymer–polymer interaction parameter (χ₁₂), for all rubber blend compositions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Size selection of dispersed,exfoliated graphene flakes by controlled centrifugation

Liquid exfoliation of graphene generally results in flakes with lateral size of one micron or less on average, too small for many applications. In this paper we describe a method to separate an existing dispersion with mean flake length of ～1 μm into fractions, each with different mean flake size. The initial dispersion is centrifuged at a high centrifugation rate, separating small flakes in the supernatant from large flakes in the sediment. Redispersion of the sediment, followed by successive centrifugation, separation and redispersion cycles can be used to separate the flakes by size so long as the centrifugation rate is decreased with each cycle. This procedure results in a range of dispersions with mean flake length varying from 1 μm for the highest final centrifugation rate to 3.5 μm for the sample whose final centrifugation rate was 500 rpm.     

Selective interfacial localization in conducting polycaprolactam/ethylene vinyl acetate/carbon black composites

Unusual electrical conductivity was demonstrated by ethylene vinyl acetate/polycaprolactam/carbon black (CB) composites. The critical exponent value was 1.2 ± 0.2 for ternary composites and was greater than 2.0 for the binary composites, indicating two‐dimensional electrical conduction in ternary composites. The ternary composites also showed inverted U‐shaped conductivity curves when CB weight fraction was greater than 10 wt%. However, at 10 wt% CB, a discontinuous conductivity curve showing conductivity only when polycaprolactam content was greater than 50% was observed, suggesting substantial variation in the interfacial characteristics with the change in the blend composition. Small‐angle X‐ray scattering studies pointed out that ternary composites can be viewed as a two‐phase system with sharp boundaries, and that interface layer in the composites does not exist. Differential scanning calorimetry studies suggested composition dependent variation in the crystallinity of polycaprolactam phase, partially contributing to the increase in the composites' conductivity at higher polycaprolactam fractions. POLYM. COMPOS., 34:912–919, 2013. © 2013 Society of Plastics Engineers     

Polychloroprene rubber/ethylene-propylene diene monomer/multiple walled carbon nanotube nanocomposites: synergistic effects of radiation crosslinking and MWNT addition

Synergistic effect of MWNT induced reinforcement and high energy radiation induced crosslinking on the physico-mechanical and thermal characteristics of polychloroprene rubber (PCR)/ethylene-propylene diene rubber (EPDM)/MWNT elastomeric nanocomposites was investigated. The extent of reinforcement, as assessed using the Kraus equation suggested high reinforcement of the blend on MWNT addition; though, the thermal stability and glass transition of the PCR and EPDM components were not significantly affected by MWNTs. The elastic modulus increased with the radiation dose as well as with the increase in MWNT content. The reinforcing mechanism of the nano-composites was studied by various micromechanics models all of which predicted higher moduli than the experimentally observed results, indicating agglomeration in the nano-composites. Nevertheless, in all the composites synergistic effect of radiation crosslinking and MWNT induced reinforcement were seen, suggesting radiation induced crosslinking between polymer and MWNT interface.     

Aspirin analogues as dual cyclooxygenase-2/5-lipoxygenase inhibitors: synthesis, nitric oxide release, molecular modeling, and biological evaluation as anti-inflammatory agents

Analogues of aspirin were synthesized through an efficient one-step reaction in which the carboxyl group was replaced by an ethyl ester, and/or the acetoxy group was replaced by an N-substituted sulfonamide (SO(2)NHOR(2):R(2) =H, Me, CH(2)Ph) pharmacophore. These analogues were designed for evaluation as dual cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitors. In vitro COX-1/COX-2 isozyme inhibition studies identified compounds 11 (CO(2) H, SO(2)NHOH), 12 (CO(2)H, SO(2)NHOCH(2)Ph), and 16 (CO(2)Et, SO(2)NHOH) as highly potent and selective COX-2 inhibitors (IC(50) range: 0.07-0.7 μM), which exhibited appreciable in vivo anti-inflammatory activity (ED(50) range: 23.1-31.4 mg kg(-1)). Moreover, compounds 11 (IC(50) =0.2 μM) and 16 (IC(50) =0.3 μM), with a sulfohydroxamic acid (SO(2)NHOH) moiety showed potent 5-LOX inhibitory activity. Furthermore, the SO(2)NHOH moiety present in compounds 11 and 16 was found to be a good nitric oxide (NO) donor upon incubation in phosphate buffer at pH 7.4. Molecular docking studies in the active binding site of COX-2 and 5-LOX provided complementary theoretical support for the experimental biological structure-activity data acquired.