Depolymerisation

Depolymerisation, or depolymerization, is the chemical process by which a polymer chain is cleaved into its constituent monomers or shorter oligomers. It is the reverse of polymerisation and can be driven by heat, chemical reagents, or biological catalysts. In industry and research, depolymerisation is pursued for chemical recycling, material recovery, and end-of-life management, with the aim of producing feedstock for new polymers or enabling closed-loop recycling.

Mechanisms and methods include thermal, catalytic, and chemical approaches. Thermal depolymerisation uses elevated temperatures to break covalent bonds in the polymer backbone. Catalytic depolymerisation employs acids, bases, or solid catalysts, sometimes at lower temperatures, to lower activation energy and improve selectivity. Chemical depolymerisation encompasses hydrolysis, alcoholysis, glycolysis, and aminolysis, in which water, alcohols, glycols, or amines react with polymer chains to yield monomers or useful oligomers.

Common examples are seen in polymer recycling. Hydrolytic depolymerisation of polyesters and polyamides can yield diacids and diamines; glycolysis of PET produces bis(2-hydroxyethyl) terephthalate; methanolysis of PET yields dimethyl terephthalate and ethylene glycol. Enzymatic depolymerisation uses enzymes such as hydrolases (for example PETase) to break down certain polymers under mild conditions, offering a more selective and potentially energy-efficient route. Natural polymers, such as polysaccharides, can also undergo depolymerisation to simple sugars.

Applications and significance include chemical recycling of plastics, recovery of monomers for high-purity reuse, and contribution to a circular economy. Challenges involve energy requirements, material purity, process efficiency, and economic viability across diverse polymer types.