The microstructures of chemically polymerized polypyrrole 100 to 800 Å films were studied by transmission electron microscopy (TEM). The fibers are embedded in an amorphous matrix which forms a self-reinforced composite. The shape of the fibers ranged from thin rods to ellipsoids depending on the preparation conditions. The density and size of the fibers were affected by the polymerization time and the concentration ratio of pyrrole and oxidants. Polypyrrole fibers were aligned along the thin film plane and were randomly oriented in the plane. The two-dimensional orientation of the crystalline fibers produced strongly anisotropic electrical properties in the thin films. It has been found that by properly adjusting the polymerization condition, it is possible to obtain the polypyrrole conducting ultra thin films with improved mechanic and electric properties.

Present work reports the results of a study of characterization of dielectric, piezoelectric and pyroelectric properties of calcium modified lead titanate ceramic/poly (vinylidene-trifluorethylene) composites with zero-three connectivity. The paper also presents a theoretical model to optimize such properties with respect to particle size, dielectric constant and composition.

Polyimide-based composites offer one of the best opportunities to bring the advantages of high modulus-to-density ratio materials to higher temperature applications, such as jet engines. In the present work, thin films (1000 - 2000Å) of aluminum oxide have been deposited by plasma-enhanced chemical vapor deposition from aluminum triisopropoxide precursor on polyimide composite substrates. The films were characterized for stoichiometry, thickness uniformity, and adhesion, and their effectiveness in the prevention of thermo-oxidative degradation of the composite at temperatures up to 371 °C has been examined and compared to that provided by other thin film materials. These preliminary results indicate that Al2O3 is not as successful as SiO2 at preventing oxidative degradation, although significant variability in the quality of the polyimide composite substrate makes precise comparison difficult.

A detailed investigation has been performed to relate the environmental stress cracking (ESC) behaviour of thermoplastic toughened phenolic materials to their morphology. Within the range of added thermoplastic studied (0 to 35%), two scales of morphology were seen to occur. In addition to a small scale interpenetrating network, there exists a larger scale morphology formed from “seas” of excess and immiscible thermoplastic. The large scale morphology was studied by performing interference contrast optical microscopy on samples etched with permanganate. A good correlation was obtained between the amount of thermoplastic in the immiscible regions and the overall fraction of thermoplastic in the sample.

Etched samples were subject to ESC via bend tests in methanol and the effects of the morphology on the crack behaviour were observed microscopically while samples were still in the bent condition. It was evident that the large scale morphology was responsible for deflecting microcracks so that they preferentially grew along the interface between the immiscible thermoplastic and well mixed regions.

The environmental stress cracking (ESC) behaviour of thermoplastic toughened phenolics has been studied. As these materials have applications for ‘under the bonnet’ automotive components, testing took place in several ‘in - service’ environments and in some of the constituent chemicals as well as in air.

Initial screening of the materials using three point bend testing highlighted the most hostile environments for further study. More detailed creep tests were then performed with methanol and air. ESC effects led to an increase in creep rate which relates to crack initiation. Crack initiation is lowest at intermediate levels of thermoplastic with an optimum content of about 12%. It was found that there was a significant decrease in the creep rupture lifetimes as the fraction of thermoplastic toughening agent increased. With low thermoplastic content, crack blunting becomes an important factor.

The effects of physical ageing and prior immersion time on the ESC behaviour of polycarbonate in ethanol were studied. Constant strain rate tensile tests were performed at a range of strain rates for samples with ageing times varying from 100 hours to 3000 hours and for prior immersion times of between 1 hour and 500 hours. Comparison of tests performed in ethanol and in air gave a good indication of the point of craze initiation. The results showed that there was a reduction in strain to crazing as the strain rate decreased, apart from with the lowest strain rate used. A longer prior immersion time also promoted craze formation. Both of these results are attributable to diffusion effects. Physical ageing had little effect on the ESC behaviour, due to the large amounts of deformation encountered in this system.

Polyimide resins are used as matrix materials in fiber reinforced composites. Such composites are lightweight, have relatively high strength, and can be used at temperatures above 300°C. Postcured PMR-15 produces room temperature electron paramagnetic resonance (epr) spectra from stable free radical species formed during the postcuring stages. The variable temperature EPR spectral intensities indicate the presence of at least two free radical species. The thermo-oxidative degradation involves free radicals generated during the postcuring process in the presence of oxygen gas. These and other recent results including ENDOR and HYSCORE work are discussed.

An intelligent, closed-loop expert system has been developed for the widely used high performance polyimide PMR-15. This expert system has been used for intelligent, automated sensor/model control of the fabrication of flat panels in both the autoclave and the thermal press. Panels have been made, ranging in thickness from less than 1/8 inch to 1/4 inch, using PMR-15 prepreg. Various prepreg samples have been used, ranging in age from fresh to one year old under freezer storage conditions. These materials exhibit significantly different processing properties as a result of the aging process. This expert system uses in-situ Frequency Dependent Electromagnetic Sensing (FDEMS), the Loos processing model for PMR-15, and the Qualitative Processing Automation Language (QPAL) software shell developed by Frances Abrams in conjunction with the Universal Technology Corporation for the United States Air Force.

Infiltration of preforms used to manufacture high-performance, advanced polymer composites can lead to void formation due to inhomogeneities within the preforms. Void formation occurs at three distinct length scales: the fiber, tow and part scales. Flow visualization experiments were used to characterize void formation at the tow and fiber scales. Effects of tow-scale inhomogeneities were studied by varying the warp angle of a woven fabric. Effects of fiber-scale inhomogeneities were studied using scale models of typical tows. The experiments indicate that minimization of void content requires a trade-off between fiberscale and tow-scale void formation.

High performance polymers require new processing technologies to achieve their full potential properties. The strength, stiffness, coefficient of thermal expansion, and barrier properties of LCPs and blends are strongly dependent on processing. The use of biaxial shear flow during extrusion, elongational strain after extrusion, electromagnetic field effects, and thermal treatment will be discussed with respect to LCP film processing. The effect of these conditions on the properties of films will be reviewed and applications for high barrier containers, electronic substrates and lightweight structures will be described.