Fade resistance of propylene-ethylene copolymer. Effect of low concentration of organophilic montmorillonite

Abstract

Propylene-ethylene copolymer (PEC) is an important material used in the production of a large diversity of plastic goods. However, its low polarity and lack of functional groups make PEC challenging for dye coloring. A method to obtain colored PEC using the cationic dye Rhodamine 6G (RA) was investigated. It involves modification with very low concentrations of organophilic montmorillonite (o-Mt) and a propylene copolymer grafted with maleic anhydride by producing nanocomposites having very thin clay tactoids. Mixing was performed in molten state in a batch mixer considering 0.1 wt% of dye and up to 3 wt% of clay. FT-IR, XRD, SEM and rheology were used to analyze the effect of clay and dye on composite morphology while fade resistance to solvent and UV-radiation was analyzed by UV–visible spectroscopy and colorimetry. Neither structure nor properties of polymeric systems are affected by addition of RA. In fact, the degree of oxidation reached by the polymeric material after UV irradiation as well as its fade resistance is determined by clay concentration. The addition of just 1 wt% of o-Mt reduces in about one eighth the exposure time at which the polymer reaches a given value of total color difference, ∆E*.