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Epoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non-uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non-uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power-law dependence with respect to the relative density.

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Glass fiber reinforced hollow epoxy macrospheres (GFR-HEMS) and hollow glass microspheres (HGMS) were used to prepare a three phase epoxy syntactic foam (ESF) in this study. An innovative "rolling ball method" was implemented in the preparation of GFR-HEMS where expanded polystyrene (EPS) beads were used as an initiation template. The EPS beads were coated with the epoxy resin and glass fiber using the "rolling ball method", and these coated EPS beads were later cured and post-cured at high temperature which caused the EPS beads to shrink thus producing a hollow macrosphere structure. The effects of the volume fraction of the GFR-HMES, the wall thickness of the GFR-HEMS and the volume fraction of the HGMS on the compressive properties were discussed to find a comprehensive understanding of the structure-property relationship between the epoxy matrix and sphere fillers.Scanning electron microscopy (SEM) shows that the "rolling ball method" can make glass fibers form a fiber spherical x-y network throughout the macrosphere wall, which can make the GFR-HEMS and three phase ESF have great compressive strength. The ESF (570 kg m À3 , 27.3 MPa) can withstand 2730 meters water pressure and provide 430 kg m À3 buoyancy, which can give some advice to the preparation of buoyancy material used in deepwater oil exploration.