Abstract
The demand for new methods of diverting materials from waste streams has grown as sustainability and landfill reduction goals continue to be set. Municipal solid waste combustion and waste-to-energy (WTE) facilities reduce landfill waste accumulation but ash material by-products are commonly sent to landfills. In this work, we evaluate the potential for fly ash to be used as an inert filler in post-consumer recycled polyethylene to maximize landfill diversion of high-volume materials. Using fly ash from solid waste combustion as a filler increases landfill diversion, reduces associated costs, and offsets the cost of the recycling for post-consumer plastics by blending with a low cost filler. Characterization of the fly ash revealed high variability in ash particle composition and size, which was expected due to the municipal solid waste source. A series of composites were compounded incorporating fly ash into recycled linear low-density polyethylene utilizing various compatibilizers. The composites were characterized for molecular interactions, thermal properties, mechanical properties and changes in melt processing via infrared spectroscopy, differential scanning calorimetry, electromechanical testing, and oscillatory melt rheology, respectively. Mechanical testing of the fly ash composites indicated that the fly ash did not significantly change the Young’s modulus or yield stress and the addition of various compatibilizer additives increased impact strength. The impact strength of the neat polymer decreased drastically from ∼55 kJ/m2 to ∼20 kJ/m2 at 5 wt. % fly ash. However, the addition of PGME compatibilizer at 0.75 wt. % increased the composite’s impact strength to roughly the same value as the neat polymer. Thus, the addition of a compatibilizer could be used to alter the fly ash filler composite’s resistance to flexural shock. These results indicate that fly ash can be added to recycled linear low-density polyethylene up to 10% while maintaining physical properties.
Highlights
With the increasing need to improve waste processing and develop materials and products capable of a circular economy, the focus on recycling and other landfill diversion strategies has intensified over the last few decades
The coarse mode (a) has a much higher geometric mean of nearly 1,500 μm. This suggests either 1) particles comprise agglomerates, causing particles to appear larger in the measurement, or 2) there is a group of particles with a larger average size compared to the rest of the distribution (Mora et al, 1998; Lloyd, 2003; Cepuritis et al, 2017)
If the ash could be used as a component in widely used products such as plastic consumer goods, it would result in further landfill diversion
Summary
With the increasing need to improve waste processing and develop materials and products capable of a circular economy, the focus on recycling and other landfill diversion strategies has intensified over the last few decades. One approach for reducing landfill waste volume includes municipal solid waste (MSW) waste-to-energy (WTE) facilities. These facilities combust non-hazardous waste under confined and controlled conditions, leaving fly ash and bottom ash as solid material by-products. The fly ash and bottom ash are collected, treated, mixed, and transported to a landfill, which costs up to $60 per ton in tipping charges depending on the landfill location. These WTE facilities recover energy from the combustion process to generate electricity. Sweden, and Norway all incinerate over 50% of waste (Seltenrich, 2013), which is represented by the number of WTE facilities in each country: 79 in Germany, 127 in France, and 234 in Japan (Lu et al, 2017)
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