Influence of surface crystallinity on light barrier properties of polypropylene Films

R. A FUENTES; Y. ALONSO; L. CASTILLO; S. BARBOSA

Buenos Aires

Congreso; 11th WORLD CONGRESS OF CHEMICAL ENGINEERING - WCCE11; 2023

The development of light barrier films for food packaging has gained more interest in industry to protect products fromdeterioration and quality loss while it is exposed to light during transportation, storage and sales conditions [1]. Toanalyze the influence of surface crystallinity of polypropylene (PP) films on light barrier properties, PP films with differentthicknesses prepared by compression molding with cooling under pressure were studied. In this sense, light barriercapacity of PP films with thicknesses ranging from 50 to 200 μm was determined from measurements of transmittanceby UV-vis spectroscopy at 300 and 600 nm [2]. For the analysis of this optical property, transmittance values werenormalized considering the film thickness. Crystalline phases and possible changes in surface and bulk crystallinitywere analyzed by X-ray diffraction (XRD) and differential scanning calorimetric (DSC).In Figure 1, the normalized transmittance at 300 and 600 nm of PP films is presented as a function of thickness. Theseresults showed a notable decrease in transmittance values with film thickness regardless of wavelength, which couldbe related to variations in surface crystallinity since bulk crystallinity was similar for all films. From XRD results, it waspossible to observe an increment of surface crystallinity with the thickness, although all samples presented the samecrystalline phases. This behavior could be associated with the differential cooling rate induced by film thickness, givinga useful tool to increase light barrier in thick films, changing their surface crystallinity.