Preparation Of Flexible Structure And Modification Of Epoxy Resin

Epoxy resins are widely employed as the basis for adhesive compositions and as the matrix material for composites because of it's excellent mechanical properties and processability.When cured,epoxy resins are highly crosslinked,amorphous thermoset polymers and this structure results in many useful properties,such as high modulus,high strength and low creep.However,it also means that the unmodified epoxy resin are relatively brittle polymers with poor resistance to crack growth and low impact strength.Several methods have been proposed to increase the toughness of epoxies and one of the most successful involves the addition of a suitable rubber to the uncured epoxy resin and then controlling the polymerization reactions in order to induce phase separation during the curing of the epoxy due to their incompatibility.Our work builds two systems around this idea.The main research contents and results are as follows:First,using isophorone diisocyanate(IPDI)as a coupling agent between the epoxy resin and hydroxyl-terminated polyethers with different molecular weight by controlling the reaction temperature and ratio.The EP with long polyethers side chains are synthesized and the molecular weight of poly propylene glycol are 400,1000,2000 respectively.In the following we call it PPG400,PPG 1000,PPG2000.The progress of the reaction and the changes during the synthesis are studied using FTIR and chemical analysis(epoxy and isocyanate value determination).The studies support the method that IPDI act as a coupling agent forming PPG grafted epoxy resin(PPG-g-EP).We selected amino-terminated polyoxypropylene(D230)as curing agent and the mechanical properties was tested by universal testing machine and impact testing machine.Epoxy resins with different length side chains and different graft degree have different mechanical properties.The PPG400-g-EP system has an impact strength of 21.44 KJ/m2 at a graft degree of 30%,an elongation at break of 11.4%,and an increase of 78.37%and 28.09%with respect to the pure epoxy resin,respectively.In PPG1000-g-EP system,the impact strength of epoxy resin is more obvious,the grafting rate is 30%,the impact strength is up to 30.85KJ/m2,which is 2.5 times of pure epoxy resin,and the elongation at break is 15.8%,an increase of 77.53%.The introduction of the large molecular weight PPG2000 has a poor effect on the improvement of the impact strength,and the tensile strength and modulus are greatly reduced.The second part of the work is the preparation of core-shell rubber nanoparticles(CSR)by emulsion polymerization and then physically blend the core-shell particle and epoxy resin.PSi/PMMA and PSi/P(MMA-GMA)core-shell particles were prepared by adding PSi as seed emulsion,adding methyl methacrylate(MMA)and functional monomer glycidyl methacrylate(GMA).FTIR and TEM confirmed that the method successfully prepared core-shell rubber(CSR)with silicone rubber as core structure.Then blend the core-shell particles and epoxy resin,and the dispersion of the particles was observed by SEM.We selected amino-terminated polyoxypropylene(D230)as curing agent and the mechanical properties was tested by universal testing machine and impact testing machine.The results show that when the core shell particles are added below 15phr,the glass transition temperature is comparable to that of pure epoxy resin.The impact strength of PSi/PMMA modified epoxy resin is 23.09KJ/m2,which is twice as high as that of pure epoxy resin.The impact strength of PSi/P(MMA-GMA)modified epoxy resin is 30.92KJ/m2,which is 3 times that of pure epoxy resin.The elongation at break reaches a maximum at 15phr,which is greatly improved compared to the unmodified system,and both the tensile strength and the tensile modulus decrease as the amount of addition increases.