Abstract: Epoxy resin had been widely used in light industry, construction, machinery, aerospace, etc. But after curing, there were some disadvantages such as high crosslink density, excessive internal stress, crisp, poor fatigue resistance and impact resistance. Those shortcomings limite its application in a number of high-tech fields. In this paper, polyether sulfone (PES) was used to toughen epoxy resin. Different proportions of PES/E51 system were prepared by hot melt. Hot stage microscope, SEM and mechanical tests were applied to investigate morphologies and structures of E51 modified by PES, and also to evaluate fracture surface, phase separation, strength and toughness of castings. The results show that PES can dissolve in the E51 by hot melt in the absence of solvent. At PES content of 15wt%, the tensile strength and impact strength of castings increased by 130% and 200%. Phase separation occurred when the castings were cured. PES formed a semi-continuous or continuous phase structure in the E51. When PES was 15wt%, bicontinuous structure appeared in the castings.

Key words: PES, epoxy resin, mechanical properties, phase separation