Study On Microwave-curing Controlling Phase Separation And Toughening Polyethersulfone/epoxy Resin System

Thermally resistant thermosetting resins have been key and base materials for many cutting-edge industries such as aerospace,electronic information,automotive and new energy field.However,thermosetting resins have low toughness and poor impact performance reducing application value due to their highly crosslinking structure.When epoxy resin is prepared by traditional heat curing,there are problems such as long curing cycle and temperature gradient.Toughness of thermoplastic polymer/thermosetting resin system is an important toughened thermosetting resin system extremely dependent on the final phase structure which is closely related to the curing process.Therefore,how to quickly prepare high-toughness thermosetting resin is a crucial issue.In this paper,polyethersulfone(PES)/epoxy resin(EP)was used as the research object to study on microwave-curing controlling phase separation and toughness.Four parameters(flame type,heating time,interval time and curing time)which affect microwave curing process and final sample surface conditions were investigated by orthogonal experiments.Temperature changes of PES/EP system with different PES content under microwave-curing conditions was characterized.It was found that the PES content does not affect temperature under microwave-curing.Microwave-curing process with high fire flame,10s heating time,10s interval time and 10 min curing time was finally determined.The phase separation process of PES/EP system under thermal curing and microwave-curing conditions was studied separately,and differences of phase separation mechanism was discussed.The results show that both microwave-curing and thermal curing follow spinodal decomposition mechanism(SD)near the critical point of the PES content;however,when the PES content is far away from the critical point,the thermal curing still follows SD mechanism.PES/EP system under microwave-curing follows nucleation and growth mechanism(NG).Microwave-curing results in a much faster phase separation rate which is much greater than the thermal curing and ultimately leads to a difference in phase separation mechanism.The relationship between static mechanical properties(impact strength,fracture toughness and flexural strength)and dynamic mechanical properties and phase structure was systematically investigated.Microwave-curing can result in a higher degree of phase separation than thermal curing due to its rapid temperature rise.When the PES content is 8wt%,the phase structure formed by the two curing conditions is sea-island structure,and the toughening mechanism is crack bridging,crack deflection and crack termination.When the PES content is 13 wt%and 18 wt%,two curing conditions are capable of forming a continuous phase of PES.The toughening mechanism is plastic deformation caused by the PES continuous phase.The properties of resins prepared under microwave-curing are better than those prepared under thermal curing.Therefore,microwave-curing can effectively control phase structures of PES/EP system and improve comprehensive performance of resins.