Thermal molecular motion at surface of atactic polypropylene films

Surface molecular motion in atactic polypropylene (aPP) films was studied by scanning force microscopy. Glass transition temperature at the surface, Tgs, was determined to be 251±1 K on the basis of temperature dependence of lateral force, whereas its bulk glass transition temperature, Tgb, by dynamic viscoelastic and differential scanning calorimetric measurements was 262 K. In general, polyolefin is easily oxidized, and thus, many kinds of additives are mixed in it for practical use. Hence, effects of oxidation and additives on surface properties of the aPP surface were examined as well. To achieve oxidation, the aPP films were annealed at 428 K for 100 min under the ambient atmosphere. After this treatment, Tgs decreased by approximately 15 K in comparison with the intact film due to degradation of surface chains. On the contrary, in the case of the aPP containing 10 wt% antioxidant, Tgs was almost the same as that of the intact film before and even after the oxidation treatment.