Different Crystalline Populations for Biopolyesters within Graphene-Based Nanopapers

The control and design of the semicrystalline structure of polymer binders within nanopapers based on graphene-related materials (GRM) may have a significant impact on the nanopapers' physical properties, including thermomechanical resistance and thermal conductivity. In this article, biopolyesters differing in methylene chain length between ester groups were studied, specifically using poly-(ε-caprolactone) (PCL) and poly-4-hydroxybutyrate (P4HB), with additional comparisons to polyglycolide (PGA). The crystallization behavior and crystalline structure of the polymers embedded in GRM nanopapers were studied by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). In particular, high melting point crystals originating from strong nucleation and strong molecular interactions with the GRM were observed with thermal stability dependent on the chemical structure of the polymer. The crystals having the highest melting temperatures, well above the equilibrium melting points of PCL and P4HB, are of particular interest. Besides their high thermal stability, these crystals cannot be fractionated through successive self-nucleation and annealing. At the same time, WAXS revealed distinct crystal diffraction reflections and relatively broad rings, suggesting the formation of crystals stabilized up to high temperatures by their interfacial adsorption onto GRM. These findings offer new insights into the mechanism of polymer crystallization at the interface with nanoparticles and may have implications for the development and application of hybrid organic/inorganic flexible nanopapers in electronic devices.