Photo-stabilisation mechanism under natural weathering and accelerated photo-oxidative conditions of LDPE films for agricultural applications

Abstract

Spectroscopic methods, ultraviolet (UV) and Fourier transform infrared (FTIR) were used to determine the concentrations of the two components of hindered amine light stabilisers (HALS) in low density polyethylene (LDPE) films exposed to natural weathering up to 650 days. The used HALS is a Ciba-Geigy commercial mixture of Chimassorb 944 and Tinuvin 622 with same percentage in weight (50/50% (wt/wt)). The spectroscopic measurements were carried out on the LDPE films having some different HALS contents of 0.1, 0.2, 0.4, and 0.6% (wt/wt). The Chimassorb 944 concentration was determined by means of the absorption band area centred at 225 nm in UV spectra for the absorption of 1,3,5-triazine group, while Tinuvin 622 concentration was measured by the absorption band area at 1734 cm −1 in FTIR spectra corresponding to the ester group absorption. The plots describing the loss of the concentration of each component versus time exhibited similar profiles. The results suggest that the two HALS components are involved at the same time in the polymer stabilisation processes. The effect of the HALS concentration on LDPE stabilisation was interpreted applying the well-known operative mechanisms involving piperidinoxyl radicals for natural and accelerated photo-oxidative conditions. Finally electron spin resonance spectroscopy performed on 0.6 and 0.2% under natural exposure formulations are in good agreement with the spectroscopic determination of the HALS contents in the different formulations.