Fotodegradação de filmes de polipropileno: efeito da presença de fotoestabilizantes e pigmentos.

Abstract

Polypropylene (PP) is a polymer widely used commercially due to its good properties but it is very vulnerable to degradation. This work had as objective to evaluate the photodegradation of PP films containing two photostabilizers: a UV absorber (Tinuvin 326) and a sterically hindered amine- HALS (Chimassorb 2020), and its combination with a red organic pigment. PP films were produced by extrusion, evaluated by UVvis spectroscopy, infra-red spectroscopy (FTIR), colorimetry, optical microscopy (OM), scanning electron microscopy (SEM) and mechanical properties, then exposed for up to 15 weeks to artificial UV radiation. According to the UV analysis the pigment did not influence the degradation of the material. From FTIR the carbonyl index was determined for each exposure time, showing the progression of chemical degradation with exposure time. Regarding colorimetry, a significant change was observed in the RGB scale with the addition of pigment and photo-stabilizers. The microscopy analyses revealed well distributed particles on the surface and evidence of degradation of the material (cracks) in the films exposed for 15 weeks, except for those compositions containing HALS. The tensile strength of the unexposed films was not altered with the addition of the photostabilizers, however when the pigment was added there was an increase in these values, except for the composition containing HALS. For the elongation a reduction of the values was observed when the pigment was added. In view of the results, it was observed that the compositions containing HALS presented superior performance especially when combined with the pigment, evidencing a favorable combination of effects for periods up to 15 weeks of exposure.