Morphology and viscoelastic properties of isotropic and oriented polypropylene films

The physical structure of semicrystalline polymers influences many of their properties. It has been shown that thermal treatment (rate of cooling and annealing) as well as the action of mechanical forces (drawing) of isotactic polypropylene (PP) resulted in materials with different mechanical properties. In the case of isotropic films the crystallization temperature or annealing temperature from the glass and consequently morphological structure which has been formed, determine the values of modulae, yield stress and viscoelastic properties. Reoptical behaviour has been found to be sensitive to structural differences too. The structure and mechanical properties of highly oriented PP samples which have been obtained by drawing through a flat die have been found to be dependent on parameters characterizing this process (drawing rate, apex angle of die and elongation ratio).