The role of organoclay in the diffusion of epoxy-amine oligomers and in the cross-linking density of the resulting network

Epoxy nanocomposites are promising for adhesive applications due to their high performance. In this work, an organoclay (PO), prepared by cationic exchanging using a quaternary phosphonium salt or a silylated PO (SPO) was added to an epoxy-amine resin-based adhesive to reduce its dripping. PO and SPO were dispersed in the epoxy network on a nanometric scale, mainly in an intercalated structure. A liquid-to-gel transition occurs at 4-6 wt% PO due to forming a continuous organoclay network throughout the epoxy volume, eliminating its dripping. The PO addition accelerates the curing reaction initially, and cured nanocomposites with over 3 wt% PO show a drastic reduction in the glass transition temperature (T-g). Moreover, a broadening of the secondary relaxation observed by DMA indicates an interaction between the epoxide-amine oligomers with the silicate surface. This interaction, associated with forming a continuous organoclay network at 4-6 wt% PO, reduces the epoxy-amine oligomers diffusion, resulting in their partial curing and consequent T-g decreasing. EPOXY_SPO nanocomposites show T-g values similar to or higher than that observed for the epoxy-amine network attributed to the forming of covalent bonds between the glycidyloxypropyl end groups in the SPO surface and the hardener amine.