Thermomechanical Behavior of Vinyl Ester Oligomer-Toughened Epoxy-Clay Hybrid Nanocomposites

Abstract

Interpenetrating networks of varying percentages of vinyl ester oligomer (VEO) toughened epoxy-clay hybrid nanocomposites were developed. VEO was prepared by reacting commercially available epoxy resin LY556 and acrylic acid and was used as a toughening agent for DGEBA epoxy resin. DGEBA was toughened with 5, 10 and 15% (by wt) of VEO using 4, 4′-diaminodiphenylmethane (DDM) as a curative. The formation of VEO (nucleophilic addition) and its chemical reaction with epoxy resin (via Michael addition) was confirmed by FT-IR spectra. Epoxy and VEO toughened epoxy systems were further modified with 1, 3 and 5% (by wt) of organophilic montmorillonite (MMT) clay. Organoclay-filled hybrid VEO epoxy matrices, developed in the form of castings, were characterized for their thermal and mechanical properties. Thermal behavior of the matrices was characterized by DSC, TGA and DMA analysis. Mechanical properties were studied as per ASTM standards. Data from mechanical and thermal studies indicate that the introduction of VEO into epoxy resin improved the thermal stability and impact strength to an appreciable extent. The introduction of 10% VEO into 5% organoclay-filled epoxy resin improves the impact strength (from 103.3 MPa to 141.3 MPa) by 36.7% compared to that of unmodified epoxy resin system. XRD analysis confirmed the exfoliated nanocomposites, which exhibit higher dynamic modulus (from 3012 MPa to 3710 MPa) than unmodified epoxy resin. Further SEM analysis ascertained the homogeneous morphologies of the hybrid nanocomposites.