Characterization of the Binder Phase in a Three-Phase Carbon Microballoon Syntactic Foam

In three-phase syntactic foams, the (often polymeric) binder phase plays the vital role of holding the compressive load bearing microballoon components in place. When characterizing three-phase syntactic foams, it is important to characterize this binder phase. To obtain thermal and mechanical properties, we have performed differential scanning calorimetry and nanoindentation on samples of the binder in a three-phase carbon microballoon syntactic foam system. The binder is a specific variety of bismaleamide, APO-BMI, differing from the prototypical bismaleamide by an extra methyl group and two sulfur atoms between the central benzene rings. Through differential scanning calorimetry, we determined that the melting temperature of neat APO-BMI is 120 °C and that curing begins at 230 °C. The presence of carbon microballoons was seen to affect the curing reaction of APO-BMI, reducing the onset of curing temperature. The Young's modulus of cured APO-BMI was determined by nanoindentation to be 6.6 GPa.