Curing epoxy resin with anhydride in the presence of halloysite nanotubes: the contradictory effects of filler concentration

Epoxy resins can be cured with a wide variety of curing agents such as amines and anhydrides, but anhydride curing would be more favorable for research purpose because of epoxy-anhydride curing taking place slowly at room temperature. Incorporation of natural nanosized minerals into epoxy is of environmental importance. Halloysite nanotubes (HNTs) display chemical properties similar to those of silica and alumina, and hydroxyl groups positioned somewhere in between or at the edge of HNTs layers give them potential to participate in epoxy ring-opening. Curing epoxy/anhydride systems containing HNTs at various concentrations (0.5, 1 and 2 wt.% based on 100 parts by weight of epoxy) via nonisothermal differential scanning calorimetry at three heating rates (5, 10 and 15 degrees C.min(-1)) is discussed here to study the effect of HNTs concentration on epoxy anhydride curing reactions. The extent of crosslinking reaction was promoted at 03 and 1 wt.% of HNTs as a result of participation of hydroxyl groups of HNTs in epoxide ring-opening, while at 2 wt.% of HNTs a hindered curing was the case, which has been speculated on account of probable deactivation of anhydride curing agent by the internal surface of HNTs pursued by anhydride molecules diffusion into the lumen of HNTs.