Nanoparticle effects on the crystallization of polyethylene at elevated pressures

We describe here phase and morphological changes that are induced when polyethylene-containing dispersion of nanoclay is isothermally crystallized in the pressure range of 0.1-150 MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat polyethylene and polyethylene containing dispersion of nanoclay under similar experimental conditions. X-ray diffraction studies support the evidence of monoclinic phase at high crystallization pressure in addition to commonly observed orthorhombic phase of polyethylene. The nucleation of monoclinic phase is encouraged by nanoclay even at low crystallization pressures. Furthermore, orientation effects were observed in the nanocomposite system. The equilibrium melting point is insignificantly influenced on the addition of nanoclay and weakly refines the structure, such that the crystallization pressure has no obvious effect. The weak thermodynamic interaction between nanoclay and polyethylene compared to polypropylene-nanoclay system is supported by the small shift in glass transition temperature and no changes in the modification of absorption bands of polyethylene in Fourier transform infrared spectrum. (c) 2008 Elsevier B.V. All rights reserved.