Cooperative Rearranging Regions in Polylactide based nanocomposites

In the last decade, calorimetric methods situate among the widely used techniques assisting the investigation of the molecular dynamic changes occurring in the amorphous phase during the polymer ?-relaxation process1,2. In spite of its complexity, the glass transition is collectively characterized by its dynamical heterogeneity and its cooperative nature. Adam and Gibbs3 first defined the Cooperative Rearranging Region (CRR) as the smallest subsystem which, upon a sufficient thermal fluctuation, can undergo a conformational change independently of its environment. To investigate the cooperativity length from calorimetric measurements, the Donth's approach4 is the most appropriated since it allows obtaining the resulting fluctuation of the dynamic glass transition temperature. Particular attention has been paid recently to the effects of interfaces and geometrical confinement on the molecular dynamics of polymers5,6. Previous works have highlighted that interfacial interactions between amorphous polymer and exfoliated clays lead to a cooperativity length increase while confinement of polymer chains in the galleries of clays (intercalated nanocomposite) produces a strong reduction of cooperativity7. In this work we propose to investigate the nature of the polymer/clay interactions thanks to the cooperativity length determination in Polylactide-based nanocomposites with the presence of polybutyrate adipate terephthalate (PBAT) compatibilizer. Polylactide (PLA) is a semi-crystalline polymer which thermal crystallization can easily be tailored due to its slow kinetic, and can induce different crystalline forms (? and ?) depending on the crystallization temperature8, leading to strongly ordered or defective crystals. So this study aims at picturing the dissociated or cumulated impact of compatibilization and crystallization on the cooperativity in exfoliated and intercalated morphologies