Characterization of mixture epoxy syntactic foams highly loaded with thermoplastic and glass microballoons

Syntactic foams comprising glass or thermoplastic microballoons have gained considerable attention in recent years due to mechanical and thermal properties that are advantageous for naval and aerospace applications. This work reports a method for producing syntactic foams with unusually high-volume fraction microballoon loadings (>0.74) and its utilization for the creation of “hybrid” epoxy resin-based syntactic foams comprising various mixtures of glass and thermoplastic microballoons. Microstructural analyses using X-ray micro-computed tomography provided non-destructive quantitative characterization of microballoon packing, confirming the high loading levels suggested by density measurements. By systematically varying the glass/thermoplastic microballoon ratio, it was shown that a range of mechanical properties can be engineered into these lightweight materials. The peak impact force of these syntactic foams can be significantly reduced (∼30% reduction) through combining glass and thermoplastic microballoons in a ratio where the thermoplastic microballoons are the dominant fraction but not the sole microballoon component.