Análisis Teórico- Experimental de la foto-termodegradación acelerada del poliestireno expandido empleando concentración solar.

Abstract

Expanded polystyrene (EPS) is used in containers like dishes and glasses which are converted into great amounts of solid waste that need reprocessed. One possibility to degrade this material is by the combination of photo and thermal degradation provided by sunlight radiation. In this work the effect of concentrated solar radiation, ultraviolet and thermal treatments is studied on the chemical structure of EPS through X-ray photoelectron (XPS) and infrared (IR-ATR) spectroscopies to obtain a quantitative measure of its degradation at 4 different depths from the surface. The mechanisms of carbonization, oxidation and hydrogenation were compared between the individual effects of photodegradation in the region from 295 to 365 nm and thermodegradation at 120 °C and with their combination under concentrated solar radiation in similar conditions. The main objective of the work is the EPS degradation increase in a solar collector to decrease its time of environmental reintegration when it is discarded in landfills. The results showed that in general terms, there are three degradation processes, oxidation, dehydrogenation and carbonization. Thermal treatment promotes dehydrogenation and carbonization of the material increasing chemical states with double and triple C-C bonds, fragmenting the polymeric chains and forming chemical configurations with consecutive double bonds =C=, with a gradual loss of expanded conditions with the heating time. The main change was carbonization, which increased up to 6.6% extending to the inner part of the polymer, therefore it was considered as a representation of the percentage degradation of EPS. Irradiation treatment indicated formation of C=O and C-O-C chemical groups, leading to yellowing and reduction in the sample volume as a function of the irradiation time, which may be oxidation products of the material indicating its degradation. Oxidation was the main change, increasing up to 9.7%, therefore it was considered that the oxidation percentage could represent the percentage degradation. The results of concentrated solar radiation indicated the formation of the same chemical groups found in the thermal process and the ones formed as a product of the irradiation after 9 weeks of solar exposure, indicating a combined effect of the degradation. The main change was carbonization, which increased up to 18.4%, greater in EPS samples exposed to the solar collector than for those exposed to thermal and photo treatments individually. Therefore it was considered as a representation of percentage degradation. Percentage degradation under different experimental conditions: longer heating time and material depth from the surface, was estimated based on Artificial Neural Networks using thermodegradation database divided in two parts. The results showed that carbonization as a function of heating time from 0 to 17h increased in 11.19%, 19.95% and 14.28%, at 0, 30 and 90 nm, respectively. Respect to the depth levels, it reduced in 3.8% and 5% at 120 and 150 nm. The correlation coefficient obtained over the data approximation was 0.98 and 0.97 iv for the percentage of carbonization estimated at different heating time and depth levels, indicating a strong positive correlation in the estimation, and it also shows that the network has potential to estimate the degradation in longer periods if training data is increased.