Degradation of Conventional and Oxodegradable High Density Polyethylene in Tropical Aqueous and Outdoor Environments

Abstract

Polyethylene is widely used in packaging due to its chemical stability, lightness, impermeability and low cost. However, these properties become questionable when it is discarded. Oxodegradable plastics, which degrade by an abiotic-biotic process, have been promoted as a solution to the pollution caused by plastics. This research assesses the degradability of conventional and oxodegradable high density polyethylene in marine, freshwater, and outdoor tropical environments. Samples of these plastics, with and without previous abiotic degradation, were exposed to direct weathering in the Caribbean Sea and the Magdalena River, in Colombia. Their degradation was evaluated during six months by the formation of carbonyl groups, a decrease in elongation at break and visual evidence of deterioration. We found faster degradation for outdoor, followed by marine and freshwater conditions, evidencing that UV and temperature are the most relevant promoters of degradation, especially for oxodegradable plastics, as evidenced by the increase in carbonyl index. In aqueous environments, all specimens showed the formation of biofilm and in some cases cracks and fragmentation, especially in oxidized oxodegradable high density polyethylene specimens in the marine environment. Even if oxodegradables plastics, and in a lesser degree conventional ones, began their degradation process, they did not achieve complete disintegration or mineralization, due to lack of environmental conditions that can only be guaranteed in carefully monitored waste management systems.Palabras clave: contaminación por plásticos, microplásticos, ambientes acuáticos, fotooxidación RESUMENEl polietileno se utiliza ampliamente en el envasado debido a su estabilidad química, ligereza, impermeabilidad y bajo costo. Sin embargo, estas propiedades son cuestionables cuando se desecha. Los plásticos oxodegradables, que se degradan por un proceso abiótico-biótico, se han promovido como solución. Esta investigación evalúa la capacidad de descomposición del polietileno convencional de alta densidad y el oxodegradable en ambientes tropicales marinos, de agua dulce y a la intemperie. Las C.A. Arias-Villamizar and A. Vázquez-Morillas 138 muestras de polietileno convencional y oxodegradable, con y sin degradación abiótica previa, se expusieron en directo a la intemperie, en el mar Caribe y en el río Magdalena, en Colombia. Se evaluó su degradación durante seis meses por la formación de grupos carbonilo, la disminución del porcentaje de elongación a la ruptura y mediante evidencias visuales de deterioro. Se encontró degradación más rápida para las condiciones al aire libre, lo que demuestra que la radiación UV y el perfil de temperatura son los promotores más pertinentes de la degradación, especialmente en plásticos oxodegradables, como se evidencia por el aumento en el índice de carbonilo. En sistemas acuosos, todas las probetas exhibieron biopelícula, en algunos casos se encontraron grietas y se observó fragmentación. Especialmente se encontró este comportamiento en l...

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