Viscoelastic Effects On The Phase Separation In Thermoplastics Modified Epoxy Resin

The phase separation of diglycidyl ether of bisphenol A(DGEBA)/methyltetrahydrophthalic anhydride (MTHPA) blends modified withpolyetherimide (PEI) in the presence of various amount of acceleratorbenzyldimethylamine (BDMA) was investigated by optical microscopy (OM),scanning electron microscopy (SEM) and time resolved light scattering (TRLS). Optical microscopy was employed to monitor the phase separation process. Theresults indicated that the morphology evolved from co-continuous, phase inversion toirregular PEI-rich dispersion phase. The morphologies of the blends observed by SEMwere different with amount of accelerator, PEI composition and molecular weight ofPEI: Droplet PEI-rich dispersion phase, or co-continuous type irregular PEI-richdispersion phase or even phase inversion structures with Epoxy-rich phase asdispersion phase. The TRLS results display clearly that the phase separation take place according tospinodal decomposition mechanism and the evolution of scattering vector qmcorresponding to epoxy droplets follows Maxwell-type relaxation - 3 -3- 复旦大学 高分子科学系 英文摘要 博士学位论文equation qm(t) = q0 + A0 exp(?t /τ) . The temperature-dependent relaxation time τwas thus obtained. It should be the time for escape of the epoxy-anhydride n-mersfrom the so called 'cage'of PEI-rich phase by their relaxation movement. Meanwhile,according to the modified Cahn-Hilliard equation, the plot of lnI(q,t) versus time tyield relaxation rate or amplification factor R(q), then apparent diffusion coefficientDapp and mobility coefficient 2Mk values could be obtain from the intercept and slopeof the plot of R(q)/q2 versus q2 . The values of relaxation time τ , apparent diffusion coefficient Dapp and mobilitycoefficient 2Mk at different temperatures had been fitted with Williams-Landel-Ferryequation separately. It was found that all the above values fitted the equation verywell and the reference temperature Ts obtained from the fitting, about 50K higherabove Tg of epoxy-anhydride blend, consisted with each other. It demonstratesexperimentally that the coarsening processes of epoxy droplets and the finalmorphologies obtained in these thermoplastic-epoxy systems are affected byviscoelastic behavior and the viscoelastic behavior could be attributed to the escapemovement of epoxy-anhydride n-mers from the PEI-rich phase. The kinetics of phase separation was studied and it was found that the the phaseseparation induced by curing reaction of epoxy resin was different with the typicalthermal induced phase separation and could not be described by the scaling law.Otherwise, the activation energy for relaxation movement of epoxy-anhydride n-merswere calculated from the temperature-dependent relaxation timeτ . Meanwhile theactivation energy for diffusion movement could be obtained by the apparent diffusioncoefficient Dappunder different temperatures.