The effects of temperature, pressure and flow on relaxation times, nucleation density, spherulitic growth rate, as well as the interrelation among these quantities and the distributions of deformation rate and cooling time during the process, determine the morphology distribution in the final polymeric part. Each of the effects mentioned above was experimentally analyzed and described by a model for the iPP grade considered in this work. The combination of all these specific models becomes a model for the morphology evolution during polymer processing and its application to the injection molding process was numerically developed into the UNISA code.
Injection molded samples were obtained with a fast evolution of cavity surface temperatures technique allowing to keep, for assigned time intervals, the cavity surface temperature at intermediate values between injection and cooling channels temperatures. A modulation of the level of the cavity surface temperature and of the time, it was kept active, allowed to control the final sample morphology all the way from the complexity of a standard injection molded part down to a completely (skin and shear layers free) spherulitic structure.
The fibrillar layer morphology was related to the achievement of critical values of both the molecular stretch and the mechanical work, the latter being performed after the achievement of the critical molecular stretch. The dependence of the morphological layers (skin, shear, spherulitic layers, the latter including the transition from the shear zone) thicknesses upon the heating conditions was satisfactorily described by the models adopted.