Toughness and strength improvement of diglycidyl ether of bisphenol-A by low viscosity liquid hyperbranched epoxy resin

This article reports on the use of low viscosity liquid thermosetting hyperbranched poly(trimellitic anhydride-diethylene glycol) ester epoxy resin (HTDE) as an additive to an epoxy amine resin system. Four kinds of variety molecular weight and epoxy equivalent weight HTDE as modifiers in the diglycidyl ether of bisphenol-A (DGEBA) amine systems are discussed in detail. It has been shown that the content and molecular weight of HTDE have important effect on the performance of the cured system, and the performance of the HTDE/DGEBA blends has been maximum with the increase of content and molecular weight or generation of HTDE. The impact strength and fracture toughness of the cured systems with 9 wt % second generation of HTDE are 58.2 kJ/ m(2) and 3.20 MPa m(1/2), which are almost three and two times, respectively, of DGEBA performance. Furthermore, the tensile and flexural strength can be enhanced about 20%. The glass transition temperature and Vicat temperature, however, are found to decrease to some extent. The fracture surfaces are evaluated by using scanning electron microscopy, which showed that the homogeneous phase structure of the HTDE blends facilitates an enhanced interaction with the polymer matrix to achieve excellent toughness and strength enhancement of the cured systems, and the "protonema" phenomenon in SEM has been explained by in situ reinforcing and toughening mechanism and molecular simulation. (c) 2006 Wiley Periodicals, Inc.