Conducting polymer composites: Polypyrrole and poly (vinyl chloride-vinyl acetate) copolymer

Composites of a polypyrrole (PPy) and poly (vinyl chloride-vinyl acetate) copolymer (PVC-PVA) were prepared both chemically and electrochemically. An insulating polymer was retained in the blend and the thermal stability of the polymer was enhanced by polymerizing pyrrole into the host matrix in both cases. The composites prepared electrochemically gave the best results in terms of conductivity and air stability. © 1997 John Wiley * Sons, Inc

Pinning of a solid--liquid--vapour interface by stripes of obstacles

We use a macroscopic Hamiltonian approach to study the pinning of a solid--liquid--vapour contact line on an array of equidistant stripes of obstacles perpendicular to the liquid. We propose an estimate of the density of pinning stripes for which collective pinning of the contact line happens. This estimate is shown to be in good agreement with Langevin equation simulation of the macroscopic Hamiltonian. Finally we introduce a 2--dimensional mean field theory which for small strength of the pinning stripes and for small capillary length gives an excellent description of the averaged height of the contact line.Comment: Plain tex, 12 pages, 3 figures available upon reques

Theoretical and Experimental Analysis of the Equilibrium Contours of Liquid Bridges of Arbitrary Shape

The equilibrium shape of the liquid bridge interface is analyzed theoretically and experimentally.Both axisymmetric and nonaxisymmetric perturbations are considered. The axisymmetric deviationsare those related to volume effects, the difference between the radii of the disks, and the axial forcesacting on the liquid bridge. The nonaxisymmetric deviations are those due to the eccentricity of thedisk and the action of lateral forces. The theoretical study is performed using three differenttechniques: ~i! an analytical expansion around the cylindrical solution, ~ii! a finite differencescheme, and ~iii! an approximate numerical approach valid only for slight nonaxisymmetricdeviations. The results of the three methods are compared systematically. There is a very goodagreement between the analytical and the numerical approaches for contours which are close tocylindrical, and the agreement extends to configurations with only moderate deviations fromcylindrical. Experiments are performed using the so-called neutral buoyancy or plateau technique.Theoretical and experimental contours are compared considering a wide range of values for theparameters characterizing the perturbations. In general, the finite difference method providesreasonably accurate predictions even for large deviations of the liquid bridge contour fromcylindrical

EXPERIMENTAL INVESTIGATION OF THE AXIAL IMPREGNATION OF ORIENTED FIBER-BUNDLES BY CAPILLARY FORCES

Capillary impregnation of a viscous liquid into carbon fiber bundles is investigated experimentally. Axial impregnation is examined in which flow occurs primarily parallel to the fibers' axes. For silicone oils, as well as for a curing epoxy system, the kinetics of axial impregnation follow closely h-alpha-t1/2, where h is the average displacement of the advancing front and t is the time of impregnation. The impregnation rates are higher than those predicted by theoretical models based upon simple geometries. The rates are strongly influenced by the pore size distribution in the fiber bundles. At a given overall average porosity, higher rates of impregnation are observed for samples having a higher pore heterogeneity than those with a narrow distribution of pore sizes. An analysis of the experimental data is presented which allows the effective pore size distribution to be calculated

Short glass fiber reinforced ABS and ABS/PA6 composites: Processing and characterization

In this study acrylonitrile-butadiene-styrene (ABS) terpolymer was reinforced with 3-aminopropyltrimethoxysilane (APS)-treated short glass fibers (SGFs). The effects of SGF concentration and extrusion process conditions, such as the screw speed and barrel temperature profile, on the mechanical properties of the composites were examined. Increasing the SGF concentration in the ABS matrix from 10 wt% to 30 wt% resulted in improved tensile strength, tensile modulus and flexural modulus, but drastically lowered the strain-at-break and the impact strength. The average fiber length decreased when the concentration of glass fibers increased. The increase in screw speed decreased the average fiber length, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength were affected negatively and the strain-at-break was affected positively. The increase in extrusion temperature decreased the fiber length degradation, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength increased. At higher temperatures the ABS matrix degraded and the mechanical strength of the composites decreased. To obtain a strong interaction at the interface, polyamide-6 (PA6) at varying concentrations was introduced into the ABS/30 wt% SGF composite. The incorporation and increasing amount of PA6 in the composites broadened the fiber length distribution (FLD) owing to the low melt viscosity of PA6. Tensile strength, tensile modulus, flexural modulus, and impact strength values increased with an increase in the PA6 content of the ABS/PA6/SGF systems due to the improved adhesion at the interface, which was confirmed by the ratio of tensile strength to flexural strength as an adhesion parameter. These results were also supported by scanning electron micrographs of the ABS/PA6/SGF composites, which exhibited an improved adhesion between the SGFs and the ABS/PA6 matrix

Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: an interfacial approach

The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, gamma-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid-base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix

Powder metal development for electrical motor applications

In this paper, first the development process of a soft magnetic composite material for use in motor applications is described. Various mixtures are prepared to identify an optimum mix. It is found that highest packing is achieved for a mixing ratio of 45 % of 170 mesh particle size with 55 % 325 mesh particle size. The coating of the particles is obtained by using the "wetting method". The mechanical properties of the samples; such as stress versus strain, Strain% versus composition%, etc. are given, also surface characterization is carried out by XPS. This is followed by a series of tests to determine the magnetic properties of the material produced. It is shown that the results obtained are as successful as the best commercial samples available in the market

Mechanical properties of HTPB-IPDI-based elastomers

A polyurethane elastomer having mechanical and adhesive properties suitable for liner applications in solid rocket propellants was developed using HTPB as the prepolymer and IPDI as the curing agent. The effects of the NCO/OH ratio (R value) and the triol/diol ratio on the mechanical properties of the polyurethane matrix were investigated. The reaction of HTPB and IPDI is followed by monitoring the changes in the IR absorption bands of the NCO stretching at 2255 cm(-1) and the CO stretching at 1730 cm(-1). It was found that the rate of the polyurethane formation obeys an overall second-order kinetics. At an R value of 1.15, the elastomer shows the maximum tensile strength and 200% elongation at break. The hardness, elongation, and the tensile strength reach a steady value around the same R value. The elastomers having a triol/diol ratio less than 0.03 show a decrease in the tensile strength and modulus with a concomitant increase in elongation. At a triol/diol ratio greater than 0.05, the tensile strength increases to about the same value for the liner composition without any triol component. The elongation reaches a steady level at a triol/diol ratio of 0.10 and one observes a steady increase in hardness up to about 0.5. The modulus for the compositions having a triol/diol ratio greater than 0.1 is about 50% higher than that for the composition without triol. (C) 1997 John Wiley & Sons, Inc

Investigations on the electrochemical surface treatment of carbon fibers

Desized polyacrylonitrile (PAN) based carbon fibers (CF) were chemically and electrochemically oxidized and reduced. CF surfaces were activated via cyclic voltammetry studies with anodic and cathodic scans. The changes in CF surfaces were studied by contact angle measurements. Lifshitz-van der Waals and acid-base components of single fibers were determined. In general, oxidation resulted in the formation of an acidic surface energy component and reduction gave rise to no change in the number of basic functionalities at the CF surface

Adhesion of an HTPB-IPDI-based liner elastomer to composite matrix and metal case

Adhesional characteristics of an elastomeric liner composition toward a highly filled composite matrix and metal case were investigated. The system is composed of an excess isocyanate functionality in the elastomer compared to an excess hydroxyl functionality in the composite matrix. Both phases essentially contain the same binder (HTPB) and curing agent (IPDI). A bifunctional aziridine (MAPO) is used as a bond (adhesion) promoter. The effects of the R value, triol/diol ratio, and MAPO concentration on the adhesive nature of the metal-elastomer-matrix system were investigated by tensile and peel test methods. Maximum T-peel values were obtained for the NCO/OH ratio of R = 1.15 and for the triol/diol ratio of 0.054. The optimum MAPO concentration was found to be around 1-2% for the elastomer. As a result of this investigation, three candidate compositions were selected to be employed as an elastomeric material. On these compositions, metal-elastomer-composite (MEC) tensile, MEC-shear, lap-shear, elastomer-composite (EC) peel, and T-peel tests were applied. These compositions reflect acceptable combinations of strength and elasticity as well as good adhesive values required for a liner material. In particular, one of the compositions tested seems to be a good candidate when all the required characteristics of an elastomeric liner material are considered. It has a large enough elasticity with the required modulus to withstand the compressive and shearing forces in applications together with good adhesive properties toward the composite matrix and the metal. (C) 1997 John Wiley & Sons, Inc