| Epoxy resin(EP)for its outstanding advantages on high thermal stability, excellent electric properties and technique as advanced resin matrix has been widely used in high science and technique fields,such as aviation,spaceflight and national defence,etc.However,epoxy resin is generally rather bittle,because of its highly crosslinked structure.Improving the toughness of this resin is very important for epoxy technology,a successful attempt is flexible crosslinking agent toughening or flexible crosslinldng in main-chain of epoxy.However,the presence of flexible chain may greatly decrease the thermal stability,the strength and the modulus of the material.Whilst for adhesive applications such decreases in modulus and temperature resistance are usually of no significance,in matrices for fiber-composites such effects can lead to unacceptable decreases in the properties of the firer-composite.In this thesis,the methods of toughening EP were reviewed and the toughening mechanism was summarized,and the aliphatic side chains were presented.Using 1-aminododecane and epoxy resin as reagent,epoxy resin were synthesized by the reaction of amidocynogen and epoxy group.The structural changes are studied using IR spectroscopy(FTIR)and chemical analysis(epoxy value determination).The studies determined that the epoxy groups were decreased during the modification process.The mechanical properties of epoxy modified with flexible side chain are studied.The mechanical properties of the cured blends show that the toughness of epoxy modified with flexible side chain is increasing markedly while the modulus of the cured epoxy resin drop a bit.The pure epoxy polymer is typical of a brittle thermosetting epoxy polymer and the impact toughness is 13 KJ·m-2.There is a steady increase in toughness with increasing content of side chains,when the content increased to 4.7%,the impact toughness achieved 25.8KJ·m-2.At that time,the flexural strength decreased by only 1.7%,the flexural modulus decrease by only 6.8%.Dynamic mechanical thermal analysis(DMA)show that the cured blends clearly display only one maxima on the tand curves and scanning electron microscopy(SEM)of the fracture surfaces shows that the cured blends doesn't undergo phase-separation upon curing the blends and there are not cavities in blends.The studies had fully demonstrated that cross-linked is homogenous network,no phase separation.It is the toughening mechanism for the flexible side chain modified epoxy.Besides,the side chains were wrapped in the three-dimensional network of the epoxy.The impact energy could be held back or delayed due to the existence of the flexible chain.In this case, the dissipation(or absorption)of relatively large part of the impact energy may be attributed to crack bifurcation and crack path alternation.
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