Nanoparticle effects during pressure-induced crystallization of polypropylene

We describe here phase and morphological changes that are induced when polypropylene containing dispersion of nanoclay is isothermally crystallized in the pressure range of 0.1-200 MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat polypropylene and polypropylene containing dispersion of nanoclay under similar experimental conditions. The significant finding is that nanoparticles of clay interact with the host polypropylene in a manner such that they alter the structural morphology of α- and γ-crystals of polypropylene presumably via nanoparticle interface driven evolution. Interestingly, nanoclay promotes the formation of γ-phase at low pressure, which is expected to have significant bearing on physico-chemical and mechanical properties. The equilibrium melting point measurements point to thermodynamic interaction between nanoclay and polypropylene, which is supported by the change in glass transition temperature and modification of absorption bands of polypropylene between 995 and 973 cm−1 corresponding to tertiary methyl skeletal in Fourier transform infrared spectrum.