| Epoxy resin adhesives are widely used in many fields due to their excellent properties such as high adhesion,high hardness and high strength.However,due to the inherent brittleness of the epoxy resin material,its tensile properties,impact strength and other flexibility are poor which can't meet the practical application requirements of high-performance structural adhesives.Therefore,the epoxy resin needs to be toughened and modified to make it a "hard and tough" high performance structural adhesive.In this dissertation,the toughness of the polyether segments in polyurethane prepolymers and the high reactivity of isocyanate-terminated isomers are used to study the toughening of epoxy materials.The high toughness and high elasticity of polyurethane materials are combined with the high bondability,high hardness,and high strength of epoxy resins through the construction of chemical bonds and polymer-space interpenetrating networks(IPNs),The polyurethane modified epoxy resin structural adhesive with good thermal stability,high adhesive strength,large tensile strength,high elongation at break,corrosion resistance and aging resistance is prepared.The main work is as follows:1.Preparation of polyurethane prepolymers.Polyether polyols N210,N220 and N330 are used as raw materials to prepare polyurethane prepolymer by condensation addition reaction respectively with diphenylmethane diisocyanate(MDI)and polyphenyl polymethylene polyisocyanate(PAPI).The prepared polyurethane prepolymers are N210-MDI,N220-MDI,N330-MDI,N210-PAPI,N220-PAPI and N330-PAPI.The structure of the polyurethane prepolymer is analyzed and characterized by infrared spectroscopy.The content of isocyanate in the prepolymer is determined according to GB12009.4-89.2.Preparation and characterization of modified epoxy resin structural adhesives.The modified epoxy resin structure glue is A,B two-component system.Among them,the A component is the main body of the structural adhesive,which is obtained by fully mixing the epoxy resin(E44 or E51),polyurethane prepolymer and the diluent(660A).The B component is a curing agent,mainly including benzene.Dimethylamine and T31,A,B components are mixed according to the measurement ratio and cast into a PTFE mold coated with a mold release agent.The adhesive is completely cured for 24 hours and then 120 hours maintainance to obtain a solid product.The viscosity of the structural adhesive glue is measured with a rotational viscometer.The tensile and tensile shear strengths of the structural rubber solids are measured with a microcomputer-controlled electronic universal testing machine.Scanning electron microscopy is used to observe the morphology of the tensile fracture surface of the solids.Thermal analysis is used to characterize the thermal stability of the structure.Refer to GB/T 13477.5-2002 to explore the impact of the epoxy resin structural adhesive curing rate.In accordance with the standard GB/T 2567-2008 made dumbbell-like spline,measure the corrosion resistance of the fully cured material.Finally refer to the national standard GJB159.9-86 test conditions determine the aging resistance of structural adhesives.3.Study on performance of epoxy resin structural adhesives modified by polyurethane prepolymer based on MDI.Epoxy structural adhesives are mainly used for the bonding of structural parts.It is best to cure at room temperature during construction.The viscosity of the adhesive should be ? 20000 mPa·s.In the curing time,the gel time ? 30 minutes,and the dry time ? 3 hours.The mechanical properties of tensile strength ? 30 MPa,tensile shear strength ? 10 MPa.Through the selection and optimization of the composition and proportion of component A,curing agents,accelerators,and reactive diluents.the results show that:(1)The type of polyurethane prepolymer,the content of isocyanate in the polyurethane prepolymer and the addition amount of the polyurethane prepolymer all have an influence on the mechanical properties of the structural adhensive.When the prepolymer N220-MDI is used to toughen epoxy resin,the mechanical properties of the structural adhensve are the best.The tensile strength is 36.27 MPa and the tensile shear strength is 20.34 MPa when the addition amount is 15% and the-NCO content is about 3%.(2)The results of thermal stability test shows that the temperature of the fastest weight loss rate of modified epoxy resin structure adhesive is 15.94 °C higher than that of unmodified structural glue.(3)The results of determination of the corrosion resistance and aging resistance of the structural adhesive show that the tensile strength loss of the structural adhesive after acid and alkali resistance test and water resistance test are 2.04% and 5.03%,respectively.The tensile strength loss after accelerated aging is 4.13%.(4)The phenolic amine T31 curing agent,accelerator(DMP-30)and reactive diluent propylene oxide butyl ether(660A)will accelerate the curing speed of the structural adhesive.When the addition amount of accelerator is 5 PHR(100 PHR of structural glue,by mass),the curing time is the most shortened.The gel time is shortened by 49 minutes and the dry time is shortened by 42 minutes.4.Study on properties of PAPI-based prepolymer toughened epoxy resin structural adhesives.Polyurethane prepolymers N210-PAPI,N220-PAPI and N330-PAPI are used to toughen epoxy resin structural adhesives.The results of the study are as follows:(1)The N220-PAPI prepolymer toughened epoxy resin structural adhesive with the-NCO content of about 3% and the addition amount of 15% has the best mechanical properties.The tensile strength is 42.64 MPa and the tensile shear strength is 21.04 MPa.The tensile strength of prepolymer N220-PAPI modified structural adhesive is higher by 20.90% than that of the same component modified by prepolymer N220-MDI,and the shear strength increases by 3.14%.(2)In the thermal stability test of the modified structural adhesive,the fastest weight loss rate of the epoxy resin structural adhesive modified by prepolymer N220-PAPI is 28.82°C higher than that of the unmodified toughened structural adhesive and rises by 12.88°C than the structural glue modified by prepolymer N220-MDI.The heat resistance is better.(3)The tensile strength loss of the modified epoxy resin structure after acid and alkali resistance test and water resistance test are 2.02% and 2.62%,respectively.The tensile strength loss of the structural adhesive after accelerated aging for 8 hours is 1.83%.In summary,through the composite toughening modification of polyurethane prepolymers,the epoxy resin structural adhesives with high bonding strength,high strength,high toughness,and good heat resistance has been obtained. |
PDF Full Text Request