Biodegradation and Recycling of Polyethylene into Composite Building Materials
This work presents the results of experimental and theoretical studies of the biodegradation of polyethylene, recycling of polyethylene into strong and tough earth-based composite building materials and the statistical distribution and particle size analysis of the polyethylene composites. Serratia marcescens subsp. marcescens and its supernatants are able to biodegrade linear low density polyethylene (LLDPE). The results show that the cell-free extracts degrade LLDPE faster than the bacterium. The mechanisms of degradation are also elucidated using Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and Fourier Transform Infra-Red Spectroscopy (FTIR). These methods show that the bacterium and its supernatant both degrade LLDPE. There was also an increase in the concentrations of the carbonyl groups (new peaks) after the microbial degradation of LLDPE. Waste PE can be recycled and used as reinforcement in laterite bricks for sustainable building materials. The bricks are produced with different volume percentages (0-30 volume percent) of PE. The flexural/compressive strengths and fracture toughness values of the composite blocks were compared with those of mortar (produced from river sand and cement). The composite containing 20 vol. % of PE had the best combination of flexural/compressive strength and fracture toughness. The flexural/compressive strengths and fracture toughness values then decreased, respectively, to minimum values for 30 vol. % of PE. The trends in the measured strengths and fracture toughness values are explained using composites and crack bridging models. Different particle sizes of the PE composites were shown to have statistical variations in flexural/compressive strengths and fracture toughness. The statistical variations in the flexural/compressive strengths and fracture toughness are shown to be well characterized by the Weibull distributions.