An Investigation into Catalytic Photobiodegradation of Polythene Films

Abstract

Polyethylene (PE), in common with other plastics has a low tendency to degrade in the environment naturally and has the potential to harm the environment in a variety of ways. The polymer backbone in plastics is mainly composed of carbon and is utilized by microbes as an energy source, thus, bacterial degradation of plastic does occur in nature, albeit very slowly. There have been some developments in this field but the so-called heir mark. Plastic degradation in the environment also takes place through interaction with sunlight and the process can be accelerated by the addition of a photocatalytic agent such as titanium dioxide TiO2 n of titania nanoparticles (TNPs) in polyethylene has proved to be very effective and when the titania nanoparticles used are doped with suitable metals, the photocatalytic degradation occurs very fast even in the sunlight. It was hypothesized, therefore, that the titania embedded polyethylene films, upon light exposure, would break into smaller fragments, which could be easily degraded by the indigenous bacteria at an accelerated rate. The aim of this research was to develop polyethylene films that would photocatalytic efficiency of the tiatania nanoparticles, these were modified with composites of visible light active photocatalyst (e.g. Ag3PO4). A thorough study of the effect of titania concentration on the photocatalytic behavior of polyethylene films was undertaken with the films doped up to 20% (w/w), the maximum that the polymer could hold, exhibiting a UV half-life of 63 days. As expected degradation under visible light was two-and-a-half times slower but with a half-life of 139 days means that the material could be effectively used to develop environment friendly photodegradable items like shopping bags. For practical purposes a 5% (w/w) concentration of titania nanoparticles in polyethylene is recommended.

structures were also dye sensitized with food colorants resulting in enhanced photocatalytic activity. Dye sensitization using food grade dyes was considered effective as the dye would not be toxic towards the bacteria, to be involved later in the polyethylene degradation itself. In this context, the red color (betacyanin) extracted from beet root was investigated. Dye sensitization of titania nanoparticles, using food grade colorants, enhanced the photocatalytic activity of the particles. Photodegradation of polyethylene films containing dye sensitized titania nanoparticles showed much better degradation characteristics than the films containing normal titania nanoparticles. For biodegradation of the PE films, soiled polyethylene samples were collected from an abandoned solid waste dump site and indigenous bacterial strains were isolated and identified. These strains were tested for their ability to survive in titania containing environment and to utilize polyethylene as a sole carbon source. The best strains were selected on the basis of their growth and biofilm forming abilities and analyzed through gene sequencing. Laccase a plastic degrading enzyme producing genes were also confirmed in the selected bacterial strains. Out of the 18 microbial strains, capable of growth using polyethylene as the sole carbon source, the three best ones were selected based on their biofilm formation ability, protein content, and BATH san SAT analyses. Among these selected microbes, Stenotrophomonas pavanii (CC18) had the highest potential for degradation of polyethylene, the strain also exhibiting the highest laccase activity with the gene responsible for this behavior being duly identified in the bacterium. Polyethylene films, initially photodegraded to some extent, when exposed to Stenotrophomonas pavanii culture, containing additives (starch and/or glucose), showed much improved degradation than non-photodegraded polyethylene films. This was caused by the availability of the carbonyl groups on the polymer surface, made available through the photodegradation process. As a result the polythene became more hydrophilic making it more amenable to biofilm formation and consequent biological degradation. This suggests that polyethylene containing dye sensitized titania nanoparticles can lead to the development of a polyethylene consumer product that may be photo-biodegradable in its true sense. ene films were developed by incorporating additives like starch, and glucose etc., in addition to the photocatalytic material, with very positive results. Such results could be extended to the development of commercial products, with desired half-lives, and which would be very environmental friendly. Interestingly, such partially photodegraded polyethylene films possessed a very high photocatalytic activity for breaking down the molecules of the Drimarene Brilliant Red (DBR) used as model pollutant. The degrading polyethylene films could thus serve the additional purpose of degrading other organic pollutants, in air and water, through photo catalysis for general environmental improvement. It was, thus, very effectively demonstrated that the photo-biodegradable polyethylene developed above, while going through the degradation process, also serves as a substrate for photocatalytic degradation of obnoxious pollutants. The semi degraded polyethylene surface could thus help in improving the local environment by, for example, providing odor control to some extent. of obnoxious pollutants. The semi degraded polyethylene surface could thus help in improving the local environment by, for example, providing odor control to some extent.