The suppression of strain induced crystallization in PET through sub micron TiO2 particle incorporation

The effects of TiO₂ particles on the crystallization and uniaxial stress-strain behavior of poly(ethyleneterephthalate) (PET) films from amorphous precursors were investigated. The addition of small fraction of sub micron sized TiO₂ particles were found to suppress the mechanical relaxation processes associated with high temperature side of the β relaxation while enhancing the low temperature relaxation. When crystallized from unoriented precursors, TiO₂ particles act as a nucleation agent and enhance the thermally induced crystallization of the PET chains. However, when stretched from the amorphous precursors in rubbery temperature range (T_g<T_p<T_cc), the TiO₂ concentration levels as low as 0.35 wt% was found to reduce the overall stress and retard strain hardening and accompanying stress induced crystallization. As a result, under the same stretching conditions, the films containing TiO₂ were found to possess lower crystallinity and orientation levels. This was attributed to suppression of stress induced crystallization as these particles act to disrupt the formation of crystalline lattice by their physical presence. This may be as a result of the reduction of chain entanglements in the presence of these sub micron sized TiO₂ particles in the structure of the polymers that retard the formation of physical network whose nodes are made up of entanglements and small crystalline domains. The development of this long range ‘connected’ network is primarily responsible for the rapid upturn in the stresses at the onset of strain hardening observed in stress strain curves.This method represent a unique way to apply ‘anti-nucleating agent’ effect to control the development of stress induced crystallization that will help control the film and fiber forming processes.