Effect of high power ultrasound on physical-chemical properties of polypropylene films aimed for food packaging: structure and surface features

Biaxially oriented polypropylene (BOPP) coated with acrylic/polyvinylidene chloride (BOPPAcPVDC) and biaxially oriented coextruded polypropylene (BOPPcoex) films have been treated with high power ultrasound (HPUS) while submerged in water. Polymer structure and the surface morphology changes were noticed, and obtained results were correlated with the physical properties of tested materials. In anticipation of sonochemically enhanced reactions, physical-chemical profile of film samples was determined using thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, UV spectrophotometry and environmental scanning electron microscopy. HPUS-treated samples showed better thermal stability than untreated ones. BOPPAcPVDC samples sonicated for a period of 2 and 6min and amplitudes 50 and 100% showed higher thermal stability as compared to the untreated one. BOPPcoex film surface change occurred after ultrasonic treatment of 6 min and 100% amplitude which was also attributed to the phenomenon of formation of crystalline cluster on the film surface. The implications of the results are used as possibility of HPUS treatment of packaged food.