Epoxy Resin Toughened By Hyperbranched Polyesters And Its Toughening Mechanism

The research is focusing on H30. H30 is designed to graft the groups of Benzoyl groups, epoxied groups, etc. Meanwhile, the toughening effect of H30 and its grafted products modified DGEAC/DDM blends were systematically studied, and the effect of different terminal groups on toughening was discussed.Benzoyl chloride and epichlorohydrin were used as modifiers to provide H30 with different terminal groups. The properties of H30 was characterized by GPC, ¹³C NMR, FTIR, DSC, etc. The grafting degree was clearly shown by the ¹³C NMR spectrum, and the degree and Mn were calculated from 13C NMR spectrum.The results of DGEAC/DDM blends modified by H30 demonstrated that H30 can toughen epoxy resin effectively. When the content of H30 was 5hr, the impact toughness of epoxy blend was increased from 21.31±1.77 KJ/m² to 28.60±0.97 KJ/m². The microstructure of the blends showed that H30 in the blends can produce reation-induced separation and be well distributed as particles of 100-200 nm in the expoy matrix. The toughening mechanisms were explained by the cavitation theory and the shear banding theory. The multitude -OH groups create a strong inter-molecule force, which facilitate chemistry-induced separation and form a two-phase structure. This is a key factor of epoxy toughening. Meanwhile, the -OH produced in the process of curing can form strong H bond with H30 particles. Therefore, the there is strong forces between the particles and the martrix, which is another key factor in the epoxy toughening by H30.It was found that the impact toughness of H30 modified DGEAC/DDM blends was decreased rather than being improved. This is because, in one hand, the polarity of H30-Bn were reduced compared with that of H30 as a result of the presence of benzoyl-terminated groups. Therefore, it was not easy to produce the reaction-induced phase separation and the H30-Bn modified DGEAC/DDM blends were homogeneous. In the other hand, the inter-force of benzoyl-terminated groups and epoxy matrix of H30-Bn was too small to toughen the epoxy effectively.