Mecanismos de degradación de polímeros oxo-degradables

Abstract

La reciente aparición en el mercado argentino de aditivos oxo-degradables ha motivado el estudio del efecto de los factores abióticos [temperatura y radiación ultravioleta] y bióticos [biodegradación aeróbica] sobre la estructura y el comportamiento mecánico de películas de polietileno, PE, y de polietileno oxo-degradables [PE+AD]. Tanto el estudio de la deformación a rotura, como el índice de carbonilo dan cuenta de que ambos materiales se degradan al ser sometidos a radiación UV y que el aditivo ejerce un rol benéfico en la degradación y consecuente decaimiento del peso molecular. Se observó que para una misma dosis, el material más deteriorado es el expuesto a menor irradiancia, destacando la importancia del tiempo de degradación UV. Se determinó para cada material un tiempo característico que, a una dada irradiancia, da cuenta de la dosis crítica, DC, para la cual se produce un decaimiento abrupto de la deformación a rotura. Además se observa que esta DC disminuye apreciablemente al aumentar la temperatura del ensayo de foto-degradación. En la degradación térmica el PE sin aditivo es más susceptible a la degradación que el PE+AD, que se degrada en forma apreciable sólo para la condición más severa. Los ensayos de biodegradación mostraron inicialmente una mayor producción de CO2 para el PE+AD, tanto del previamente degradado como del sin tratar. Así mismo se destaca que 2 muestras de PE+AD con claras diferencias en su nivel de degradación abiótica alcanzaran el mismo nivel de biodegradación del 20 por ciento. Se observa que si bien el aditivo favoreció la degradación abiótica, esta disminución del peso molecular no es suficiente para alcanzar el máximo nivel de biodegradación del polímero en compost según normas internacionales.|The recent introduction of oxo-degradable additive in the Argentinean market has motivated the study of the effect of abiotic [temperature and UV radiation] and biotic [aerobic biodegradation] factors on the structure and mechanical behavior of films of polyethylene [PE] and oxo-degradable polyethylene [PE + AD]. The strain to failure and the carbonyl index of degraded PE and PE+AD samples depends on the UV irradiation dose. Furthermore, the additive plays a beneficial role in the degradation and subsequent decay in molecular weight. It was observed that, for the same dose, the most deteriorated material was the one exposed to the lowest irradiance, emphasizing the importance of time exposure on UV radation. A characteristic time, determined for each material, is a proportional factor between the irradiance and the critical dose, Dc, associated to a sharp decay on the failure strain. Dc decreases significantly to the increasing the temperature of photo-degradation assay. PE is more susceptible to thermal degradation than PEA+AD; the latter only degrades under thermal aging at the highest temperature. Initially biotic degradation in compost showed an increasing production of CO2 for both previously degraded and untreated PEA+AD. It is also remarkable that two samples of PE+AD with distinct differences in their abiotic degradation level, reached the same final biotic degradation level [20 per cent]. It was observed that although the additive increase the abiotic degradation, the molecular weight reduction in compost was not enough to reach the maximum biotic degradation level according to international biodegradation standards.

Tesis para optar al título de Magister en Ciencia y Tecnología de Materiales

The recent introduction of oxo-degradable additive in the Argentinean market has motivated the study of the effect of abiotic [temperature and UV radiation] and biotic [aerobic biodegradation] factors on the structure and mechanical behavior of films of polyethylene [PE] and oxo-degradable polyethylene [PE + AD]. The strain to failure and the carbonyl index of degraded PE and PE+AD samples depends on the UV irradiation dose. Furthermore, the additive plays a beneficial role in the degradation and subsequent decay in molecular weight. It was observed that, for the same dose, the most deteriorated material was the one exposed to the lowest irradiance, emphasizing the importance of time exposure on UV radation. A characteristic time, determined for each material, is a proportional factor between the irradiance and the critical dose, Dc, associated to a sharp decay on the failure strain. Dc decreases significantly to the increasing the temperature of photo-degradation assay. PE is more susceptible to thermal degradation than PEA+AD; the latter only degrades under thermal aging at the highest temperature. Initially biotic degradation in compost showed an increasing production of CO2 for both previously degraded and untreated PEA+AD. It is also remarkable that two samples of PE+AD with distinct differences in their abiotic degradation level, reached the same final biotic degradation level [20 per cent]. It was observed that although the additive increase the abiotic degradation, the molecular weight reduction in compost was not enough to reach the maximum biotic degradation level according to international biodegradation standards.