NATURAL AGEING OF STABILIZED AND UNUSTABILIZED LDPE FILMS USED AS GREENHOUSES COVERING MATERRIALS: ATR-FTIR AND SEM ANALYSIS

Abstract

This article focuses on the study of both stabilized and unstabilized low-density polyethylene films aged under natural weathering in the middle of Morocco (Sidi Kacem city). The study was undertaken on three samples for each LDPE films: a new sample taken as reference; another exposed to outdoor weathering for one year; and a sample exposed for two years. The outdoor exposure effects were followed by analysis of the total reflection Fourier transform infrared spectroscopy (ATRFTIR). This technique provides information on the main chemical functions and evaluates the internal causes of natural ageing of our samples. The infrared spectra show the formation of hydroperoxides -O-OH, carbonyls >C=O, aliphatic esters R-(CO)-O-R, ether R-O-R, vinyl C=C, vinylidene >C=CH2 and trans-vinylene RHC=CRH in the amorphous regions. These compounds lead to initiate the mechanism of photo-oxidation of the unstabilized LDPE samples. Therefore, the increase in the formation of oxidation products into the aged samples (LDPEUS) indicates an accelerated degradation of these latter on climatic factors (UV, O2, humidity, rain ...). The UV stabilizer (free radicals scavengers) added to the formulation of LDPE films can delay the attack of the amorphous phase and prevent the formation of compounds that can cause and accelerate photo-oxidation. The results obtained by the infrared have been confirmed by observing the morphology of the samples with scanning electron microscopy technology (SEM).