Study On The Effect Of Cure Conditions On The Structure And Properties Of Modified Epoxy Systems

Epoxy resin is a thermoset polymer with high strength,high modulus,good adhesion,stability,low shrinkage,good processability,electrical insulation.It has become essential material in industrial application.But the brittleness and poor crack resistance of cured resin limits its application.The toughening of epoxy resin has been extensively studied.There are many ways to toughen epoxy resin,and the factors that affect the toughening effect are also great.This thesis has studied the effect of curing condition on the morphology and mechanical properties of rubber toughened polyamine cured epoxy system.Epoxy resin was modified with varying content(0,5,10,15,20 parts per hundred,phr)of hydroxyl terminated polybutadiene(HTPB)and cured with polyamine D-230.Differential scanning calorimetry(DSC)has been studied to analysis the heat involved during the cure.60 °C,80 °C,and 100 °C have been chosen as cure or pre-cure temperature.Peak temperature 120 °C has been chosen as post-cure temperature.Gel times of neat and modified epoxy system have been studied and have been used as pre-cure time.Fourier transform infrared(FTIR)analysis and gel permeation chromatography(GPC)have been used to monitor the reaction between the epoxy resin and rubber.Tensile,flexural and impact properties of all epoxies have been tested through universal testing machine and impact testing machine.The results show the tensile strength,flexural strength and flexural modulus reduced with increasing rubber content.Those without post-cure have higher tensile and flexural properties.The impact strength reaches to peak when rubber content is 10 phr,the impact strength of isothermal cured modified epoxies successively lost the toughenability when rubber content excess 15 phr and 20 phr for the systems cured at 60 °C and 80 °C.But for the systems with post-cure the toughenability remain.Those with post-cure exhibit higher impact strength.The morphology has been examined by scanning electron microscopy(SEM).The results show the surface of neat epoxy resin is smooth indicating a brittle fracture.But for the modified epoxy,the surface has a large number of deformation lines indicating a ductile fracture.The domain size of precipitated rubber particles decreased with increasing the temperature.The particle size distribution is unimodal.Post-cured samples exhibit smaller particle size.Dynamic mechanical analysis(DMA)has been performed to study the dynamic mechanical properties of cured resin.The results show the glass transition temperature(Tg)increased with elevating the cure temperature.The glass transition temperature has been suppressed by the addition of rubber.