Low-Density Phenolic Syntactic Foams: Processing and Properties

Low-density phenolic syntactic foams with different volume percentages of microballoons were processed and their mechanical performance has been evaluated in terms of tensile, flexural, compressive and the corresponding specific properties. Tensile and flexural strength increased with volume fraction of microballoon and optimized at 72–74 percentage by volume of microballoon. Both the properties decreased with further addition of microballoon. The corresponding specific properties also manifested a similar order. Compressive and specific compressive strength decreased with increase in microballoon volume percentage. The flexural and compressive modulus values followed the same trend as the strength values. The properties of phenolic syntactic foams were compared with syntactic foams based on an addition cure phenolic resin, Propargyl Ether Novolac resin (PN). The mechanical properties of the latter were inferior to those of phenolic syntactic foams. The morphology of the failed samples as examined by SEM showed that failure occurred by a combination of matrix and microballoon failure at low microballoon loading whereas it occurred by microballoon cracking and resin to microballoon debonding at high concentration of filler. The dynamic mechanical analysis of phenolic and PN resin syntactic foams showed a higher use temperature for PN system in comparison to phenolic.