Novel bio-based epoxidized cardanol/cenosphere syntactic foams

Cenosphere-filled epoxidized cardanol syntactic foams were fabricated using stir-casting technique: 10–40 wt% of cenosphere was mixed gradually in several steps in order to avoid any damage of the cenosphere. The syntactic foams were cured at room temperature for a day followed by postcure for 3 h at 100°C. Completion of the cure reaction was ascertained using differential scanning calorimetry of the fresh sample and postcured sample. Homogeneous distribution of cenosphere was confirmed with the scanning electron microscopic (SEM) images. The fracture mechanism was also analysed using SEM image of the compression failed sample. Thermal, hygrothermal and compressive properties of the syntactic foams were studied. Epoxidized cardanol-based syntactic foams were found to have lower density, good thermal stability and higher char residue as revealed from the thermogravimetric analysis result. The yield strength decreased with the increase in cenosphere. The specific modulus was optimum for 30% loading of cenosphere and it increased by 42% in comparison to the neat sample. Hygrothermal studies conducted using deionized water and sea water at room and high temperature conditions revealed stability and lower water absorption. The bio-based syntactic foams derived from cardanol promised sustainable path for the preparation of light-weight foam core materials.