Melting behavior of the nonisothermally crystallized polypropylene/organosilica nanocomposite

Melting behavior of nonisothermally crystallized samples of the neat isotactic polypropylene homopolymer (PP-0) and the nanocomposite containing 4.68 wt% of organosilica (PP-4.68) was studied in the temperature-modulated differential scanning calorimetry (DSC) mode at three underlying heating rates and five modulation frequencies. It was established that the patterns of melting endotherms in both the neat PP sample and the PP-organosilica nanocomposite could be semiquantitatively characterized by a simple Debye model with a single, temperature- and underlying heating rate-dependent characteristic time. The mechanisms of structural rearrangements in the melting intervals of the neat PP sample and the PP-organosilica nanocomposite were basically similar; however, the spatial scale of such rearrangements in the latter sample was significantly reduced due to severe steric constraints on the PP chain mobility in the melt state from the infinite cluster of nanoparticles.