Studies on the Chemical recycling of Poly(lactic acid) via Alcoholysis

Lamberti, Fabio (2023). Studies on the Chemical recycling of Poly(lactic acid) via Alcoholysis. University of Birmingham. Ph.D.

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Abstract

Continual reduction of landfill space, rising CO2 levels, and plastic pollution are global issues that will only grow in time if not correctly addressed. The opportunity exists to replace petroleum-derived plastics with bioplastics. This, in conjunction with mechanical and chemical recycling, is a potential remedy that enables a circular economy. PLA is a leading bioplastic; its growing production capacity means its end-of-life treatment is becoming increasingly important. One beneficial disposal route for PLA is its chemical recycling via alcoholysis. The alcoholysis of PLA leads to the generation of value-added products alkyl lactates; this route also has potential for a circular economy. In this work, the alcoholysis of PLA was studied in a autoclave reactor. A range of alcohols were used as reactants to generate various alkyl lactates. Discrete synthesised catalysts and commercially available catalysts were investigated, as well as dual catalysis systems. Three kinetic models were applied to the experimental data: a simple first order model that only considers the initial degradation of PLA, a two-step consecutive model with irreversible second step, and a two-step consecutive model with the second step in equilibrium. This work concluded that increasing the nucleophilic alcohol chain length decreases alcoholysis reaction rate; the increased steric hinderance of a larger alcohol inhibits coordination to the catalyst and PLA ester groups. This work also concluded that dual catalyst synergy is only present if there is a great enough difference in pKa for each catalyst in addition to having both acid and base character. Further research is needed to fully explore synergistic Lewis acidsbase pairs; an understanding of their coordination and mechanism is required in order to fully exploit dual-catalysts systems for enhanced chemical recycling. The chemical recycling of PLA via alcoholysis is a promising end-of-life solution, adding value to the PLA supply chain through the generation of value-added ALs.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):