Thermal, nanoindentation and dielectric study of nanocomposites based on poly(propylene furanoate) and various inclusions

Abstract

In this work, we investigate polymer nanocomposites (PNCs) based on a poly(propylene furanoate) (PPF), a relatively new biobased polymer, envisaged for various application, e.g. exploiting its exceptional gas barrier properties. PPF exhibits extremely slow crystallization and subsequently poor mechanical performance, therefore, targeting at improving its properties, PPF is filled here with five fillers of different geometries, i.e. Carbon Nanotubes (CNT), Halloysite nanotubes, Graphene nanoplatelets, and two Montomorillonite (MMT) clays. Crystallization, glass transition and mechanical performance are investigated employing differential scanning calorimetry (DSC) and mechanical nanoindentation tests supplemented by X-ray diffraction (XRD), on both amorphous and semicrystallized samples. Moreover, we attempt to investigate the structure (filler morphology, semicrystalline morphology) / properties relationship also in combination with recording molecular dynamics via broadband dielectric spectroscopy (BDS). For the fixed filler content of 1 wt%, the majority of the inclusions were found to increase the rate of PPF crystallization at the relatively mild temperature of 100 °C, which is desirable in industrial polymer processing. However the impact of the fillers on the degree of crystallinity is quite low, the latter being expected to correlate with semicrystalline morphology alternations in the composites as compared to the unfilled PPF. The nanoindentation tests showed clear beneficial effects of the various inclusions on the elastic modulus and indentation hardness, being, as expected, more profound in the case of semicrystallized PPF matrix. Additionally, the full-temperature dielectric-calorimetric map was constructed, showing that the effects on local and segmental polymer dynamics (β and α relaxations, respectively) by the PNC composition are insignificant whereas those by crystallization are dominant. Finally, an additional filler-related process (αf relaxation) was recorded in two cases of PNCs, showing non cooperative character and independency from crystallization, the origins of this process being still under investigation.