James P. Wightman

Surface characterization and adhesive bonding of toughened bismaleimide composites

Abstract The use of composite materials in structural applications requires that they be joined or fastened in some manner. The objective of this research was to obtain an improved understanding of the factors which contribute to bond strength and durability in adhesively bonded bismaleimide matrix composites. Composite surface pretreatments included solvent wipe, grit, blast, peel, ply and gas plasma treatment. The results of lap shear and wedge testing in ambient, hot/dry, hot/wet and chemically aggressive environments were correlated to the surface composition after pretreatment as measured by X-ray photoelectron spectroscopy, ion scattering spectroscopy and contact angle analysis. The topography of the pretreated composite surfaces was analysed by scanning electron microscopy and profilometry. Solvent wiping was not effective in removing processing contamination and resulted in poor bond strengths. Peel ply and oxygen plasma pretreatments provided good initial bond strength as well as superior hot/wet durability; however, grit blasting was detrimental to both strength and moisture resistance.

The Influence of Surface Properties on Carbon Fiber/Epoxy Matrix Interfacial Adhesion

Abstract The mechanical performance of composite materials depends not only on the matrix and the reinforcing fiber, but also to a great extent on the fiber/matrix interfacial adhesion. The focus of this work was to study carbon fiber surface chemical and physical properties and their effects on fiber/matrix adhesion. Untreated, commercially-surface-treated, and oxygen-plasma-treated PAN-based carbon fibers were used. SEM was used to examine the fiber surface topography. XPS was used to determine fiber surface chemistry. A two-liquid tensiometric method was conducted to determine fiber surface energy and its dispersive and polar components. Carbon fibers with varying surface properties were incorporated into epoxy matrices. Single fiber fragmentation tests were carried out to evaluate the strength as well as the temperature and humidity effects on interfacial adhesion. Commercially-treated carbon fibers having a higher surface oxygen content and a higher surface energy clearly produced superior interfacia...

Interphases developed from fiber sizings and their chemical-structural relationship to composite compressive performance

The relationship between interphase microstructure produced from fiber surface chemistry and the resulting composite structural properties is not well understood. This relationship is, however, key to predicting composite performance and to the understanding of how to assemble the constituents properly for best use of the unique properties of the fibers. In this study, a significant difference in laminate compressive performance is observed for both static and dynamic loading. Two different fiber sizings, an unreacted bisphenol-A-based epoxy and the thermoplastic, polyvinylpyrrolidone (PVP), are identified as the source of these observations. The fiber, matrix and processing remained the same in both systems. However, morphological differences in the interphase region were observed. The resulting mechanical properties indicated that the PVP sizing improved static compressive strength by 51% and increased the fatigue life of notched cross ply laminates (cycled at R=-1) by at least two orders of magnitude over the bisphenol-A-sized composites. The mechanism by which PVP brought about these changes is unclear and requires further study. However, these results also indicate that the selection of interphase characteristics requires additional information about the fiber-matrix bond than merely strength

Wetting of powdered coals by alkanol-water solutions and other liquids

Abstract The wetting rates of powdered coals by alkanol-water solutions have been measured. A critical concentration of each alkanol is needed before any wetting occurs and this critical wetting concentration is lower for alcohols with longer carbon chains. A critical surface tension of 0.033 J m−2 for Pocahontas No. 3 coal is estimated from the measured wetting concentrations. Studies with a Calvet microcalorimeter show that the heats of immersion of powdered coal in water-methanol mixtures vary smoothly with changing concentration, reaching a maximum value of 16 J g−1 at 30 mol % methanol. Both for alkanols and other liquids, the heat of immersion of coal dust is released over long periods of up to nine hours.

In Vitro Cell Attachment to Characterized cp Titanium Surfaces

Abstract An in vitro assay was developed to study cell attachment to modified cp titanium surfaces. Titanium surfaces were polished to different roughnesses and were modified by rinsing in either deionized water, pH 7 or pH 11 buffers or NaOH solution following acid passivation with nitric acid. Smooth acid passivated surfaces rinsed in deionized water resulted in a surface having minimal contamination which promoted optimum cell attachment. Surface characterization, including SEM (Scanning electron microscopy) and XPS (X-ray photoelectron spectroscopy) indicated that most rinses resulted in deposition of particles whose morphology and composition were dependent upon the nature of the rinse solution. Cell attachment was dramatically affected by the surfaces with altered chemistry. These results indicated that cellular attachment is dependent, in large part, on the chemistry of the implant surfaces. A better understanding of the role of implant surface chemistry on cell attachment and other biological proc...

Sodium Hydroxide Anodization of Ti-6AI-4V Adherends

Abstract The durability of adhesively bonded titanium structures is a topic of concern in a variety of fields today. There appears to be a definite connection between durability and surface pretreatment of the adherend. A variety of pretreatments are reported for Ti-6-41-3. For example, the chromic acid anodization (CAA) pretreatment has received a lot of attention in creating surfaces resulting in improved durability of adhesive bonds.

Analysis of mid-tropospheric space shuttle exhausted aluminum oxide particles

Abstract Aluminum oxide (Al2O3) particles from the exhaust of the space shuttle were collected from the shuttle column cloud immediately after the launch of STS-61A on 30 October 1985. The participates were collected on Teflon filters during a tight descending aircraft spiral maneuver over the altitude interval of 7.6-4.6 km. Scanning electron microscope (SEM) examination of the particles revealed that they were virtually all spherical and ranged in diameter from about 0.1 μm to 10 μm. Particles of

Actions of wetting agents on coal dust

Abstract The rate of wetting of coal dust by aqueous solutions of surface active agents (surfactants) has been studied. It has been shown that surfactant is adsorbed onto the coal surface during the wetting process. Rates of wetting by solutions of the widely used sodium salt of di(2-ethylhexyl)sulphosuccinic acid (Aerosol OT) are strongly influenced by low concentrations (1–2 mg/l) of dipositive metal ions. After wetting, electron spectroscopy for chemical analysis (ESCA) has been used to show the presence of these metal ions and the surfactant on the surface of the particles of coal dust.

Phase inversion sulfonated polysulfone membranes

Abstract The use of two nonsolvents serving as a cosolvent system, replacing the traditional volatile solvent plus less volatile nonsolvent system, in the formation of asymmetric phase inversion membranes was investigated. Specifically, asymmetric membranes of sulfonated polysulfone were cast from a cosolvent system consisting of tetrahydrofuran and formamide. The nonsolvents and the proportions in which they are mixed to produce the cosolvent system, as well as the gelation medium isopropyl alcohol, were selected based on the three-component solubility parameter concept of Hansen. The structure of each membrane was evaluated using scanning electron microscopy; the performance was evaluated for use in pressure-driven membrane separation processes. The membranes were found to be dependent on the composition of the original casting solution and the composition of the nascent membrane at the instant of gelation. These ideas are clearly represented through the use of a triangular polymer solubility diagram.

Surface Characterization of Plasma Treated Carbon Fibers and Adhesion to a Thermoplastic Polymer

Abstract The surface chemistry of IM7 carbon fibers was characterized by x-ray photoelectron spectroscopy (XPS). The fiber surface energetics were determined from a two-liquid tensiometric method. The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) was measured by the microbond pull-out test. The surface characterization techniques showed that the effect of any plasma treatment is attained within less than 15 seconds. It was found that both argon and air plasmas increased the oxidation state of the fiber surface and that they reduced the dispersive component (γs d) of the fiber surface free energy considerably. The ammonia plasma treatment resulted in a cleaning of the surface. This plasma treatment was also effective in improving the fiber/matrix adhesion of quenched samples. A similar adhesion enhancement between as-received fibers and PES is obtained by annealing the samples above the Tg of the polymer. The air plasma treatment did not have any significant effec...