| The key to toughening epoxy resins is to improve the toughness while maintaining high elastic modulus and glass transition temperature.In this thesis,based on the unique chemical composition of biosynthetic eucommia ulmoides gum(EUG)and the duality of rubber and plastic,liquid epoxidized eucommia ulmoides gum(LEEUG)was prepared by indirect oxidation,that is,the epoxidized eucommia ulmoides gum(EEUG)was first prepared by the emulsion process and then oxidative degradation of EEUG under low temperature to prepare LEEUG with the number average molecular weight of 8000-10000,which terminated by ketone group or aldehyde group.Furthermore,the LEEUG was used as toughening agent to modify epoxy resin adhesive.GPC,IR,13C-NMR,1H-NMR and DSC were used to analyze the molecular structure and crystallization ability of LEEUG,and the effect of molecular weight and molecular weight distribution on its rheological behavior was studied using a rotary rheometer;The influence of LEEUG on the toughening effect and thermomechanical properties of epoxy adhesive was studied by lap shear,impact strength and DMA.The micro morphology and phase separation behavior of impact fracture surface were observed by scanning electron microscopy(SEM)and small angle X-ray diffraction(SAXD).The research results of the preparation of LEEUG show that degradation reaction conditions such as epoxy degree,reaction time and the amount of periodic acid have significant effects on the molecular weight and molecular weight distribution of LEEUG.When nH5IO6:nC=C=0.03,oxidative degradation at 30 ? for 6h,the molecular weight range of LEEUG is 8000-10000.The epoxy degree has little effect on the molecular weight of LEEUG.Compared with EUG,the content of carbon-carbon double bonds in LEEUG did not decrease,and the content of epoxy groups decreased,indicating thatperiodate attacked epoxy bonds rather than carbon-carbon double bonds during oxidative degradation.The higher the degree of epoxidation,epoxidation and oxidative degradation destroy the order and symmetry of the molecular chain of EUG,and increase the rigidity of the molecular chain,resulting in the destruction of the crystallization ability of LEEUG.However,due to the significant reduction in molecular size,the LEEUG has increased mobility and improved crystallization ability.The thermal stability analysis shows that the thermal stability of EEUG is equivalent to that of EUG,but the thermal degradation temperature of LEEUG is increased by 56 ?.The molecular weight and molecular weight distribution of LEEUG have a significant effect on its rheological behavior.The higher the number average molecular weight,the narrower the molecular weight distribution,the greater the complex viscosity of LEEUG.The study of LEEUG toughening epoxy resin adhesive shows that the LEEUG and epoxy resin can be co-cured,and the gel content of cured products is more than 99%.The co-cured product has a two-phase structure.LEEUG as the second phase was dispersed in the epoxy resin E-51 matrix with micron-sized spherical particles.At the same time,the mesoscale of LEEUG in the second phase was ordered and presents a microcrystalline structure.The effect of chemical bond between E-51 and LEEUG not only affects the size and distribution of rubber particles,but also affects the degree of phase separation,thus affecting the toughening effect.The addition of LEEUG can significantly improve the E-51 notch impact strength and shear strength.When the content of LEEUG is 10 phr,the toughening effect is the best,the shear strength is increased by 26%,and the notched impact strength is increased by 34.7%.At the same time,the storage modulus of the co-cured product did not decrease,but increased;the Tg of the epoxy resin did not decrease significantly.When the amount of LEEUG was 10 phr,the Tg decreased only by 3.6?.These are all manifestations of of the crystallite structure of LEEUG in the crosslinked network structure.TG-DTG results showed that the thermal stability of E-51/LEEUG blends was improved. |
PDF Full Text Request