Original by Dr. Steve Wong
March 15, 2023
Mechanical recycling is the traditional way of plastic recycling. The process takes the form of sorting/separation, washing, shredding, and hot melt extrusion into raw materials on post-consumer plastic waste or post-industry plastic waste, such as offcuts and floor-sweeps, for manufacturing different products.
Some of the plastic materials are not suitable for thermoplastic recycling due to the unique molecular structures such as PMMA (an example is the material of mahjong), cross-linkable PE (cable jacket), PEX (heat-resistant tube), etc. Besides, some packaging plastic materials also cannot be recycled by mechanical recycling due to the composite materials such as PA/PE (nylon/polyethylene) or PA fishing nets. Therefore, chemical recycling is the most effective way of recycling.
Chemical recycling is breaking down plastic material into its basic monomer and refining it into new materials. It involves pyrolysis: to heat plastic in a non-oxygen environment for hydrocarbon and then refine it for plastic; depolymerization: to break down plastic waste into monomers through chemical reactions and create new materials; solvolysis: to dissolve and decompose plastic waste into monomers.
Chemical recycling is an effective and promising method of recycling plastic. Many petrochemical enterprises are investing in it as it can turn plastic waste into raw materials and gain ESG (Environmental, Social and Governance) achievement. Chemical recycling can complement the shortcomings of mechanical recycling, but its cost is very high, and the quantities are limited. Unlike mechanical recycling, the yearly amount is just a few thousand tons, though the global investments are about hundreds of millions of dollars. Some investors were induced to invest in it by unscrupulous business people and suffered losses when they saw disappointing investment returns. Chemical recycling also needs separation and waste cleaning to achieve a better recycling rate and efficiency.
In a recent meeting of UNEP (United Nations Environment Programme), there was a discussion on chemical recycling. The conclusion was that it still needs to be quantified. Carbon emissions are yet to be assessed, and investment is relatively significant. As it has yet to be popular, we can only evaluate its role in the future.