Effect of combinations of nanofillers on rheology-structure relations in biodegradable poly(ε-caprolactone) nanocomposites

In this work, binary and ternary nanocomposites based on biodegradable polycaprolactone (PCL) reinforced with organo-modified montmorillonites (OMt), epoxy-functionalized graphene (Gr) and their mixtures (OMt/Gr) were prepared using the melt blending process. Two kinds of organoclays having different surfactants were introduced within the matrix, Cloisite (R) 15A (non-polar) and Cloisite (R) 30B (polar). In order to study the effect of nanofillers on the matrix properties, rheological tests, morphological, barrier and thermal characterizations were carried out on the hybrid materials. The viscoelastic behavior of PCL based materials was studied using time sweep, amplitude sweep, and frequency sweep tests. The storage modulus of the matrix was improved by adding OMt, and it was further enhanced when OMt is coupled with graphene, especially in the case of the C15A/Gr pair. All the rheological parameters showed that ternary OMt/Gr-PCL mixtures exhibited more pseudo-solid like behavior than binary nanocomposites, reflecting the formation of three-dimensional networks and better distribution of OMt/Gr pairs in the PCL matrix. TEM micrographs confirmed the formation of nanocomposite materials in the case of OMt-PCL and OMt/Gr-PCL. The incorporation of fillers into the biodegradable PCL matrix was significantly improved its permeability toward water vapors. This property is substantially related to the dispersion where a high barrier effect is recorded for ternary OMt/Gr-PCL nanocomposites. The thermal stability of the PCL matrix is affected in the presence of organoclays and/or epoxy-functionalized graphene, giving rise to more thermally stable materials. All the results confirmed that the combination of two nanofillers leads to interesting materials for some applications such as packaging.