Viscoelastic effects on the phase separation in thermoplastics-modified epoxy resin

The phase separation of the diglycidyl ether of bisphenol A (DGEBA)/methyltetrabydrophthalic anhydride (MTHPA) blends modified with polyetherimide (PEI) in the presence of various amounts of accelerator benzyldimethylamine (BDMA) was investigated by scanning electron microscopy (SEM) and time-resolved light scattering (TRLS). The morphologies of the blends with the accelerator are of the co-continuous type, exhibiting irregular shapes. They are quite different from that without accelerator, in which the morphology is spherical. The TRLS results display clearly that the phase separation takes place according to a spinodal decomposition mechanism and the evolution of scattering vector q(m) corresponding to epoxy droplets follows a Maxwell-type relaxation equation. The temperature-dependent relaxation time tau obtained for these blends can be described by the Williams-Landel-Ferry equation. It demonstrates experimentally that the coarsening processes of epoxy droplets and the final morphologies obtained in these thermoplastic-epoxy systems are affected by viscoelastic behavior.