Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer Blends

This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non‐Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix.     

Modelling of the Nonlinear Behavior of Compatibilized Polyethylene/Polyamide Blends in Shear and Extensional Flows

We have studied the effect of the amount Φ_c of a reactive compatibilizer on the rheological properties of a polyethylene/polyamide blend, under steady shear and transient extensional flows. Here, we propose to describe the viscosity η(γ) and the first normal stress coefficient γ₁(γ) using a Carreau‐type power‐law model, which is a three‐parameter model. A single model is sufficient to express the behavior of γ₁(γ) On the other hand, the complete η(γ) curve is described by the superposition of two Carreau models, in relation to the presence of two relaxation mechanisms. Moreover, the extentional viscosity η_E(?), estimated using the end pressure drop observed in capillary flow experiments, is expressed by a two‐parameter power‐law model.     

Interpolymer associations between poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) in aqueous dilute solution

This article studied the compatibility of poly(vinyl alcohol) (PVA) with poly(diallyldimethylammonium chloride) (PDADMACl) in a dilute aqueous solution. At a total mixture concentration and a constant molecular weight of PDADMACl, it was found that interpolymer associations increase with the molecular weight and decrease with the degree of hydrolysis of the PVA sample (87–89 and 98–99%). From these results, it can be deduced that the compatibility of PVA and PDADMACl is due to specific intermolecular interactions that could be assigned mainly to electrostatic interactions between hydroxyl groups within PVA chains and ion atoms within PDADMACl. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 433–435, 2002     

Effect of dynamic vulcanization on the microstructure and performance of polyethylene terephthalate/elastomer blends

Blends of polyethylene terephthalate (PET) and ethylene‐ethyl acrylate‐maleic anhydride terpolymer (E‐EA‐MAH) were dynamically crosslinked in a one‐step extrusion process. An amine‐terminated glycol reacting with MAH moieties was used as the crosslinking agent. The effect of blend composition and dynamic crosslinking on the microstructure and mechanical properties were investigated. Blend ratios ranging from 80:20 to 20:80 PET/E‐EA‐MAH were studied. The region of phase inversion was located for uncrosslinked and dynamically crosslinked blends. The rheological characterization was also carried out for these blends in comparison with the neat materials. After dynamic crosslinking, the phase inversion is shifted from the 30–40% range to the 70–80% range of elastomer content. This shift is induced by the increase of viscosity and elasticity of the network formed. Dynamically crosslinked blends show significant improvements in impact strength but also exhibit a decrease in elongation at break.     

PP/EMA TPV: Dynamic cross‐linking through an alcoholysis reaction

Dynamically cross‐linked polypropylene/ethylene‐methyl acrylate copolymer (PP/EMA) blends were prepared by reactive extrusion in a twin‐screw extruder. A transesterification reaction catalyzed by an organotin compound and involving the acrylic moieties of EMA with the hydroxyl functions of pentanediol was used to cross‐link the elastomeric EMA. The extent of cross‐linking was estimated through the insoluble content of the blend. The alcohol‐to‐acrylic ratio and the dibutyltin oxide content were both found to increase the extent of EMA cross‐linking. Processing conditions such as screw rotation rate and extrusion temperature profile also had large effects on the reaction extent. Conditions leading to improved pentanediol dispersion were found to generate larger insoluble fraction. Gel contents of EMA phase as high as 75% to 85% were obtained. Interestingly, the stress‐strain curves of the cross‐linked PP/EMA TPV are very well represented by a single master curve. Dynamically cross‐linked blends show systematically better tensile properties than the non‐reactive system. Blends with higher insoluble content show strain at break in the 650%–750% range. Material processability was maintained, even for the systems with high insoluble content.     

Nickel Nanoparticles Supported on Silica of Low Surface Area. Hydrogen Chemisorption and TPD and Catalytic Properties

Nickel metal nanoparticles supported on silica of low surface area (15 m² g^-1) were prepared by reduction of nickel acetate by hydrazine in aqueous medium. Their gas-phase stability and surface properties depended on thermal pre-treatment under H₂ or air atmosphere. Small nickel particles (<10 nm), in oxidized or reduced state, are strongly resistant to reductive or oxidative treatment respectively. For H₂-treated catalysts, H₂ chemisorption and TPD results suggested the occurrence of spillover hydrogen between the metal nickel phase and silica. For air then H₂ treated catalysts, hydrogen spillover seemed to involve the NiO phase. The activity of the catalysts in gas-phase benzene hydrogenation also depended on the thermal pre-treatment. Pre-calcined then reduced catalysts exhibited higher TOFs than non pre-calcined catalysts, suggesting that the presence of NiO phase may have influenced the hydrogenation process.     

Effects of CF4/O2 gas plasma power/exposure time on dielectric properties and breakdown voltages of PVDF films

Dielectric properties and electrical breakdown strengths were measured on 12-μm-thick poly(vinylidene fluoride) films before and after exposure to various power levels and exposure times in a 96% CF₄/4% O₂ gas plasma. Significant changes in dielectric constant, dielectric losses, and breakdown voltages were observed. Breakdown voltages for PVDF films as a function of exposure time and plasma power appear to go through a maximum. © 1992 John Wiley & Sons, Inc.     

Multiphase coatings from complex radiation curable polyurethane dispersions

The waterborne nature of radiation curable polyurethane dispersions largely respond to the current environmental concerns and do not require any additional coalescent since the film formation (drying) and hardening (photo-curing) take place in distinct steps. It is possible to design aqueous dispersions with distinct polymer particle populations resulting in micro-structured coatings with optimized properties over a wide range of curing conditions. Mixed dispersions based on hard and soft acrylated polyurethane particles were used as model systems for the present study. The minimum film formation temperature has been investigated as a function of the hard:soft polymer ratio. The elastic modulus of the dry coatings shows a reinforcing effect consistent with the inclusion of hard domains in a soft continuous matrix. However, the level of reinforcement is not properly predicted by the usual mechanical models and it is qualitatively accounted for by assuming a composition gradient (interphase) between the hard domains and the matrix. The multiple-phase structure was clearly established by Atomic Force Microscopy in agreement with thermal analysis data. Furthermore the local nanoscale mechanical properties were mapped using a new imaging mode based on real-time force–distance curve analysis. Finally, the coatings prepared using this multiple-phase pattern present a clear benefit over conventional homogeneous coatings by offering an improved balance of chemical and mechanical resistance in pigmented systems applied on melamine-coated MDF panels.     

Pheromone Response Inhibitors of the Corn Stalk Borer Sesamia nonagrioides. Biological Evaluation and Toxicology

The behavioral activity of some trifluoromethyl ketones (TFMKs) as inhibitors of the pheromone activity of the corn stalk borer Sesamia nonagrioides (Lef.) (Lepidoptera: Noctuidae) is reported. The most closely-related analogue to the pheromone tested, (Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:TFMK), elicited a significant decrease in the number of male catches in traps baited with mixtures with the pheromone in 1:1 and 10:1 ratios in comparison to the pheromone alone. The E isomer of the analogue as well as two highly hydrated ketones, 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) and 1,1-difluoropentadecyl trifluoromethyl ketone, were inactive. Conversely, the saturated TFMKs n-dodecyl trifluoromethyl ketone and, particularly, n-hexadecyl trifluoromethyl ketone induced a synergistic effect when mixed with the synthetic pheromone in 10:1 ratio. However, in a wind tunnel these chemicals did not elicit any differential effect on flying moths attracted to a source containing a 10:1 blend of the analogue and the pheromone. In a dual choice bioassay with two dispensers, containing the pheromone alone, and mixtures of Z11-16:TFMK and the pheromone and separated 5 cm apart, males showed no particular preference for either dispenser. The ketone mixture, however, induced moths to execute erratic flights with frequent crosswind counter-turns and intersections with plume boundaries. The total number of contacts with the source were reduced when a control dispenser was paired with a dispenser containing Z11-16:TFMK and pheromone. Z11-16:TFMK and OTFP showed little toxicity on mice with a LD₅₀ of 1 g/kg after the 6th day of treatment. For comparitive purposes, the major component of the pheromone, Z11-16:Ac, displayed a LD₅₀ of 5 g/kg 6 days after application. Our results provide additional information about the activity of the TFMKs, which might be useful for the utilization of these chemicals in future pest control studies.