HALS stabilization of LDPE films used in agricultural applications

The mechanism of stabilization of low density polyethylene (LDPE) films use d in agricultural applications with hindered amine light stabilizer (HALS) has been studied under the influence of natural weather for 750d. The struc tural modifications in the exposed films were monitored by Fourier transfor m infrared spectroscopy (FTIR), while the examination of the surface behavi or was performed by scanning electron microscopy (SEM). Finally, the stabil ity of the material was evaluated by measuring the percent elongation at br eak. The performance of HALS in the films was analyzed through a comparativ e study carried out on unstabilized LDPE samples exposed to the same weathe ring conditions for 170 d. The FTIR results have shown that HALS reduces si gnificantly the rate of formation of ketone groups in the exposed films due to deactivation of the excited ketonic carbonyls. This indicates the role of HALS to prevent the occurrence of Norrish I and II reactions. On the oth er hand, the development of vinyl groups at 909 cm(-1) in the film and the photooxidation of the polymer. The decrease observed in the ester band sugg ests the loss of the stabilizer. For the unstabilized LDPE film, the result s have revealed a fast increase in both ketonic and vinyl groups attributed mainly to Norrish II reactions. This resulted in chain scission responsibl e for both the rapid drop in elongation at break and the considerable deter ioration of the surface of the exposed film. On the contrary, the presence of HALS in the film resulted in a large retention of the elongation at brea k. Moreover, SEM analysis reveals the role of HALS to prevent the surface d amage by reducing the number and size of microcracks.