Rigid Amorphous Fraction and Thermal Diffusivity in Nanocomposites Based on Poly(l-lactic acid) Filled with Carbon Nanotubes and Graphene Oxide

The fraction of the polymer located at the nanoparticle–polymer interface in polymer nanocomposites (PNCs) [interfacial rigid amorphous fraction (RAF filler )] is under extensive investigation as it is generally considered responsible for the modified properties of PNCs as compared to the neat polymers. In semicrystalline PNCs, an additional interfacial polymer exists in the vicinity of crystals, that is, the RAF crystal, with the properties of the latter (structure and dynamics) being also under investigation. While the presence of nanoparticles and/or crystals themselves can be directly correlated with the modified PNC properties (e.g., mechanical performance), the respective direct effects of the RAFs have been rarely demonstrated. In a recent work, we studied RAF in PNCs based on two different polymers, amorphous stryrene butadiene rubber, wherein RAF = RAF filler, and semicrystalline low-density polyethylene wherein RAF ≈ RAF crystal, filled with carbon nanotubes (CNTs), and we revealed quite systematic dependences of thermal diffusivity α on the amount of RAF at each matrix. Strikingly, the α(RAF) trends were diverse for the two matrices, namely, RAF crystal, which facilitates heat transport, and RAF filler, which hinders heat transport. In the present work, we checked the latter α(RAF) trends in different PNCs based however on the same polylactide matrix at the amorphous and semicrystalline states, filled with small amounts of thermally conductive CNTs and graphene oxide platelets. Results for α(RAF) here were interestingly found similar with those in the previous study. These findings supply additional evidence for the different structural characteristics exhibited by the two types of RAF, a still open debate in the literature; namely, polymer chains exhibit higher level of ordering in RAF crystal as compared to RAF filler . Finally, we propose that RAF filler can be used as a measure of the phonon’s scattering in PNCs, whereas RAF crystal in conjunction with bulk crystallites forms additional thermal diffusion paths.