Multiscale morphology and thermo-mechanical history of poly(vinyl chloride) (PVC)

The multiscale morphology of rigid poly(vinyl chloride) (PVC) formulations (in the nanometre to the micrometre range) was investigated by high resolution scanning electron microscopy, ultra-small-, small- and wide-angle X-ray scattering, as a function of thermo-mechanical history. It has been shown that the hierarchical structure of PVC grains, when in the dry blend, disappeared during gelation that combines mechanical stress (ie shear stress and hydrostatic pressure) and heating. Nevertheless, the memory of the presence of the smallest particles (domains with diameters of about 80 nm) containing dense amorphous PVC and nanoscaled crystallites, has been highlighted by the study of the change of the microstructure when PVC was reprocessed with high mechanical deformation at a lower temperature than the previous gelation temperature. As a result, the main phenomena occurring during gelation were, in a first step, the disappearance of the hierarchical structure of the grains and, in a second step, the inter-diffusion of the chains across the frontiers of the primary particles (mechanically reversible), but maintaining the domain structure. The crystalline microstructure was affected by thermo-mechanical history, but the gelation level should not be estimated strictly in relation to the crystalline morphology. (C) 2004 Society of Chemical Industry.