Degradation of Low Density Polyethylene Due To Successive Exposure to Acid Rain and UV Radiation

Abstract

Utilization of polymer products for outdoor applications is continuously increasing. So the stability of polymers against environmental degradation became top of interests for many researchers. The effect of environmental elements on the polymers stability has been studied, but individually. A solution against an environmental element may conflict with a solution against other element. Therefore current study aimed to clarify a sort of these conflicts, by successive exposure of low density polyethylene (LDPE) films to acid rains and ultra violet (UV) radiation for different times. The used LDPE films are selected from the commercial grads which are used for plants greenhouses, in order to use samples fully protected against environmental elements. It is found that acid rains etch PE films, causing removal for some of the UV stabilizer additives, and hence UV radiation could attack PE films seriously causing remarked oxidative degradation. This study includes wide comparisons between effects of acid rain only, UV irradiation only, acid rain followed by UV irradiation and UV irradiation followed by acid rain exposure. Variations in the chemical composition, morphological structures, thermal and mechanical properties are detected by the IRspectroscopy, X-ray diffraction, differential thermal analysis (DTA) and tensile tests. A new view for the differentiation between degradations caused by acid rains and UV radiation is discussed. Lot of experimental data are given in many coloured graphs and tables.. 1. GENERAL VIEW AND OBJECTIVE When sulphur dioxide and nitrogen oxides are emitted into the atmosphere, they come into contact with water where they are chemically converted to acidic compounds of sulphates and nitrates. These strong acids are deposited onto the earth’s surface as rain, snow and fog and through dry deposition; the name “acid rain” is commonly used for describing this painful mechanism. Sulphur is released when fossil fuels are burned, mainly for electricity production and industrial processes. Oxides of nitrogen are released during burning of all fossil fuels too, including gasoline and diesel fuel, where the nitrogen in the fuel and atmosphere reacts with oxygen. Acid rain contaminates drinking water, damages buildings, by corroding cement, accelerates plastics degradation, and causes metals to rust. Of the solar wavelengths, the UV-B component is particularly efficient in bringing about photo-damage in synthetic and naturally occurring materials. This is particularly true of plastics, rubber and wood used in the building and agricultural industries. Solar radiation spectrum ranges over 290-300 nm and it consists of just less than 10% of UV radiation but it has sufficient energies to dissociate C-C or C-H bonds in polymer. The free radicals produced in this way may then react freely with the atmospheric oxygen and contribute to further degradation of the polymer, which is called photo-oxidation. The outdoor service life of common plastic materials is limited by their withstanding solar ultraviolet radiation and other environmental conditions like the acid rain. Many researching efforts have been carried out for evaluating the serious effects of solar UV and acid rains individually, although both environmental elements are acting either simultaneously or successively. As a result, several protection solutions are proposed against each individual element regardless the efficiency of this protection solution in presence of the other element. In the current work, a polymer sample is exposed to acid rain and UV radiation in sequenced manner and the net effects were recorded and analysed. This work aims to present more information to increase the efficiency of polymers protection against all environmental conditions on time. This work tries to show how the UV radiation may restrict the polymer protection against the acid rains attack, and vice versa.