Rubbery and Glassy Epoxy-Clay Nanocomposites

摘要

The reinforcing effect of organoclays on the mechanical properties of thermoplastics has been well documented; however, it has not been clear what mechanism governs the reinforcing effect of organoclay in thermoset epoxy resins, whose characteristics can vary over a broad range from rubbery to highly glassy. This paper attempts to contribute to some extent to reduce this lack of comprehension. The two chosen epoxy matrices, one rubbery and one glassy, were chosen to have very similar chemistry in order to minimize its impact on the comparison of properties. The epoxy resin was Shell EPON 828 and the two hardeners were based on amine-terminated polyoxypropylene diols having different average molecular weights (Mw) of 2000 and 230 g/mol, namely Huntsman Jeffamine D-2000 (D2000) and Jeffamine D-230 (D230), respectively. As a result of the difference in molecular weight of the hardener, after curing at 120°C the epoxy matrix prepared with D2000 is a rubbery material with a glass transition temperature T_g = -46.3°C, whereas the one prepared with D230 is a glassy solid with a high T_g= 86.8°C. The nanocomposites were prepared with the organoclay Cloisite 30B (C30B) from Southern Clay Products. The quality of dispersion and intercalation/exfoliation were analyzed by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM) and transmission electron microscopy (TEM) The T_g of the materials was also determined by differential scanning calorimetry (DSC) at a heating rate of 20°C min~(-1). Tensile properties and hardness of epoxy and epoxy nanocomposites were measured according to ASTM standards D638-02 and D2240-00, respectively. Fracture surfaces were also analyzed by FEGSEM. The results indicate that the presence of C30B does not significantly affect the T_g of either the rubbery or the glassy epoxy; however, the fracture surface and mechanical properties were found to be influenced by the presence of nanoclay. It is also found that the quality of clay dispersion and clay intercalation/exfoliation, and the mechanical behavior of the glassy and rubbery epoxy nanocomposites are quite distinct. Finally, several different reinforcing mechanisms are proposed and discussed for the rubbery and glassy epoxy nanocomposites.