Research On Polyurethane Modified Epoxy Resi

Epoxy resin is widely used in adhesives and other fields because of its good bonding property and low curing shrinkage.The toughness of cured epoxy resin is inadequate,necessitating toughening and modification to enhance its comprehensive application performance.Polyurethane is a material that can effectively enhance and modify the properties of epoxy resin.It has attracted many researchers,because of its strong designability of molecular structure,outstanding interface bonding performance,and good compatibility with epoxy resin.Conventional polyurethanes are toughened by chemical reactions to modify epoxy resins that contain hydroxyl groups in their structure.Most of the epoxy resins without hydroxyl group were toughened by polyurethane by physical mixing,but the toughening effect was not ideal.But polyurethane is introduced into the curing agent,which needs to be done at low temperatures.This part of the preparation process is relatively harsh,not suitable for mass production.In this paper,carboxy-terminated polyurethane（PUIC）and series of non-isocyanate polyurethane modified hardener（NIPU）were designed and prepared.Multifunctional epoxy resin 4,4’-methylene bis（N,N-dicyclopropoxyaniline）（TGDDM）was toughened and modified by PUIC.Two modified resin systems TGDDM-PUIC-1and TGDDM-PUIC-2 were formed by adjusting the proportion of pre-reaction.The precursor cyclocarbonate PPE-C₁was prepared by reacting polypropylene glycol diglycidyl ether（PPE）with CO₂.By comparing the appearance,viscosity and bonding properties of PPE-C₁,the preparation process of PPE-C₁was optimized.Eight kinds of cyclic carbonate compounds were designed and synthesized,and eight kinds of NIPU modified hardeners were formed correspondingly.By changing the PUIC content,the blended resins TGDDM/TGDDM-PUIC-1 and TGDDM/TGDDM-PUIC-2 were prepared.The viscosity of a series of modified mixed resins was investigated by rheometer.The bonding properties of the curing system were investigated in detail.When the PUIC content of TGDDM/TGDDM-PUIC-2 blends is40%,the shear strength at 25℃and the peel strength at 90°are increased by 163%and378%.Mechanical properties are improved to a certain extent.The thermal and thermal mechanical properties of the curing system were studied by DSC,DMA and TGA.The results show that TGDDM is toughened by PUIC and its thermal properties remain relatively stable.The microstructure fracture morphology of solidified samples was detected by SEM.With the addition of PUIC,the fracture surface changes from brittle to ductile and significantly enhances toughness.Modified curing agent NIPU was mixed with epoxy resin E-51 for curing.The bonding performance of modified curing agent NIPU-6 prepared by resorcinol diglycidyl ether cyclic carbonate（RDGE-C）is comparatively good.Modified curing agent NIPU-6 was prepared by adjusting the ratio of RDGE-C to D-230.The curing kinetics of modified curing agent NIPU-6 mixed with E-51 was investigated by DSC.The E_a,A,reaction order and curing kinetics equation of the curing system were determined.The bonding and mechanical properties of the blend system of modified curing agent NIPU-6 were studied.At 25℃,modified curing agent NIPU-6-3 with a molar ratio of 1:1.75 exhibits shear strength and 90°peel strength of 36.98 MPa and6.08 k N/m respectively,which are significantly higher than those of pure D-230 curing system by 127%and 251%.The toughening effect is remarkable.The mechanical properties are relatively stable.The thermo-mechanical and thermal properties of the blending system were studied by DSC,DMA and TGA.The results show that NIPU-6modified curing agent is helpful to stabilize the thermal performance of curing system.SEM was used to detect the fracture morphology of the cured system,and the whole system showed ductile fracture.