A model is developed to predict thermal expansion coefficients and elastic moduli of multi-component (hybrid) composites. The model includes the influences of fiber aspect ratio; isotropic and anisotropic fiber materials: planar, threedimensional or arbitrary fiber orientation; hollow and solid spherical reinforcements: and voids. The first step in the procedure is to predict the properties of a n aligned-fiber single-reinforcement composite for each reinforcement type, Various micro-mechanics approaches are used, depending on the type of reinforcement. A simplified version of Lee and Westmann's theory is found to work well for hollow spherical reinforcements. Performing an orientation average accounts for the spatial orientation of each reinforcement, then an aggregate averaging procedure combines the single-reinf orcement properties to model the hybrid. Predictions of the model compare favorably to experimental elastic and thermal properties of short fiber/hollow sphere composites desjgned for very high speed integrated circuit (VHSIC) board applications. 20024.the barrels of PTH.

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Maxwell–Wagner–Silars (MWS) dielectric relaxations have been studied in thermoset composites made with hollow glass microspheres and reinforced with aramid fiber. Over the temperature range reported (140–230 °C) the glass microspheres show a conductivity of 10−10–10−5 (Ω cm)−1 so that MWS loss peaks fall in the 102–105 Hz frequency range. The apparent activation energy for the relaxation is about 20 kcal/mole. The observed MWS relaxation times depend only on temperature and not on volume fraction of microspheres as predicted by MWS theory. Also, the enhancement of activation energy for the relaxation over the activation energy for conduction of the glass seems to be explainable from the standpoint of the frequency and temperature dependence of the glass dielectric constant.

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Films consisting of a rigid-rod polymer and thermoset resin matrixes were prepared. Poly{(benzo [1,2-d : 5,4-d]bis(oxazole-2,6-diyl))-1,4-phenylene} (PBO) in polyphosphoric acid (PPA) was blended with 2,6-bis(4-benzocyclobutene) benzo[1,2-d : 5,4-d]bis(oxazole) ( 1), and films were extruded from these solutions. The coagulated films were soluble in methanesulfonic acid (MSA). After heat treatment at 300ЊC, the films became insoluble in MSA. Crosslinked films were homogeneous and did not show phase segregation between the two components. These were composite films at the molecular level. Transmission electron microscopy (TEM) showed enhanced interlayer integrity and reduced microfibril separation for the molecular composite films as compared to normal PBO film. These films had significantly better torsion and tension delamination resistance. The incorporation of a second component did not sacrifice the tensile properties of PBO film. Thermal stability of these composite films was only slightly lower than that of normal PBO film.