Plastic deformation behaviour of thermoplastic/clay nanocomposites

Polymer/clay nanocomposites are materials that display rather unique properties, even at low clay content, by comparison to more conventional mineral-filled polymers. Two systems are considered in the present study: the first one consists of nylon 6/clay hybrids in which in situ polymerisation is aimed at obtaining a nylon matrix strongly bonded to the delaminated clay platelets. The second one is prepared by melt dispersion of organophilic clay in polypropylene, which should in principle result in a reduced degree of polymer–clay interaction. Dynamic viscoelastic analysis is indeed indicative of a noticeable difference when referring to the molecular dynamics of the glass transition. Plasticity results, in which volume strain is recorded by video-extensometry, show extensive cavitational behaviour while retaining a fairly large strain at break, as long as deformation is performed above the glass transition temperature of the matrix. In the particular case of PA6, it is clear that the usual shear banding plastic deformation mode is altered at least in its initiation step. Localised interfacial damage promotes extensive polymer matrix fibrillation and fracture occurs predominantly in areas where delamination of the clay platelets was not fully achieved.