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

• Published in: Journal of applied polymer science 2023-03, Vol.140 (9), p.n/a
• Main Authors: Baruel, Amanda F., Dutra, Rita C. L., Diniz, Milton F., Azevedo, Margarete F. P., Cassu, Silvana N.
• Format: Article
• Language: English
• Subjects: Covalent bonds; Curing; DGEBA; Diffusion; epoxy adhesive; glass transition; Glass transition temperature; liquid‐to‐gel transition; Materials science; Nanocomposites; Oligomers; Polymers; viscoelastic properties
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.53571

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 (Tg). 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 Tg decreasing. EPOXY_SPO nanocomposites show Tg 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. The organoclay catalyzed the epoxy‐amine curing reaction at its beginning. For epoxy nanocomposites with over 3.2 wt% organoclay, a partial cross‐link was observed, mainly due to the formation of H‐bonding between epoxy‐amine oligomers and the polar groups on the organoclay surface. It reduces the amount of free epoxide and amine groups available to reacts, decreasing the degree of crosslinking of the resulting epoxy network. The silylated organoclay bonded covalently to the epoxy network. A Dripping‐free effect was observed for epoxy monomers from 6.2 wt% organoclay addition.