The exploration of spectroscopic and physical sorting techniques to sort plastic recycling

Plastic consumption has skyrocketed in recent decades, but the development of disposal and recycling of these products has not kept pace. The biggest challenge to recycling plastic products is the inability to efficiently sort them. Six different types of plastics are commonly recycled and since they are mostly incompatible with one another they need to be accurately sorted. In recent years, researchers have begun to explore the use of spectroscopic instruments to sort these plastics. Fourier transform infrared spectroscopy and Raman spectroscopy were used to see how well a variety of household plastic waste could be sorted. Parameters such as colours, labelling, instrument resolution, and spectral region were considered. Raman was only able to identify some of the plastic types but could identify through the label, whereas FTIR was able to identify all the plastic types but was unable to identify plastics through the label. A physical sorting technique was also explored. The sink-float tank was able to sort plastics into two categories based on their densities and the density of the sorting medium. Polyethylene terephthalate and polyvinyl chloride always sank, high- and low-density polyethylene and polypropylene always floated and polystyrene sank or floated depending on the density of the medium used.