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Elastomeric bio-based epoxy/clay nanocomposites

Abstract:

The emphasis of this research was to develop a fully bio-based elastomeric epoxy and its clay nanocomposites. Blends of sorbitol glycidyl ether (SGE) and epoxidized castor oil (ECO) were cross-linked with a dimer diamine (DDA) as curing agent in a solvent-free procedure. Blends of SGE and ECO (0/100, 30/70, 50/50, 70/30 and 90/10, w/w) were cured with stoichiometric amounts of DDA alone or following the addition of 5 wt% of one of two organically modified montmorillonite (OMMT) nanoclays, Cloisite 20A and 30B. Pure SGE was immiscible with DDA at room temperature, but SGE/ECO blends were compatible with DDA. All networks were cured at 60°C for 6 hours, with crosslinking kinetics monitored via near-infrared (NIR) spectroscopy. Epoxy conversion increased with increasing ECO content due to improved compatibility with DDA. The greatest concentration of unreacted primary and secondary amine groups was observed in the 90/10 SGE/ECO blend. Nanoclay dispersion and affinity for the matrix was assessed via x-ray diffraction (XRD), and an intercalated structure was confirmed regardless of nanoclay type or epoxy formulation. Mechanical properties were also investigated. A broad range of Young's Moduli (~0.7-4.8 MPa) and hardness values (30-81 Shore A) were obtained, with the highest stiffness and hardness observed in the 90/10 SGE/ECO / 5 wt% Cloisite 30B nanocomposite. Indeed, these results support the existence of a synergistic effect on mechanical properties due to nanoclay addition, thanks both to increased chemical crosslink density and nanofiller reinforcement. Based on these studies, SGE/ECO/DDA clay nanocomposites show promise as versatile elastomeric networks whose hydrophobicity and mechanical properties may be adjusted for a range of industrial applications.