Thermal and viscoelastic property of epoxy-clay and hybrid inorganic-organic epoxy nanocomposites

The properties of nanostructured plastics are determined by complex relatio nships between the type and size of the nanoreinforcement, the interface an d chemical interaction between the nanoreinforcement and the polymeric chai n, along with macroscopic processing and microstructural effects. In this a rticle, we investigated the thermal and viscoelastic property enhancement o n crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS ) macromers. Glass transitions of these nanocomposites were studied using d ifferential scanning calorimetry (DSC). Small-strain stress relaxation unde r uniaxial deformation was examined to provide insights into the time-depen dent viscoelastic behavior of these nanocomposites. Since the size of the P OSS macromer is comparable to the distance between molecular junctions, as we increase the amount of POSS macromers, the glass transition temperature T-g as observed by DSC, increases. However, for an epoxy network reinforced with clay, we did not observe any effect on the T-g due to the presence of clay reinforcements. In small-strain stress relaxation experiments, both t ypes of reinforcement provided some enhancement in creep resistance, namely , the characteristic relaxation time, as determined using a stretched expon ential relaxation function increased with the addition of reinforcements. H owever, due to different reinforcement mechanisms, enhancement in the insta ntaneous modulus was observed for clay-reinforced epoxies, while the instan taneous modulus was not effected in POSS-epoxy nanocomposites. (C) 1999 Joh n Wiley & Sons, Inc.