“Like Recycles Like” : Selective Ring-Closing Depolymerization of Poly(L-Lactic Acid) to L-Lactide

• Chemical recycling of poly(L-lactic acid) to the cyclic monomer L-lactide is hampered by low selectivity and by epimerization and elimination reactions, impeding its use on a large scale. The high number of side reactions originates from the high ceiling temperature (Tc) of L-lactide, which necessitates high temperatures or multistep reactions to achieve recycling to L-lactide. To circumvent this issue, we utilized the impact of solvent interactions on the monomer–polymer equilibrium to decrease the Tc of L-lactide. Analyzing the observed Tc in different solvents in relation to their Hildebrand solubility parameter revealed a “like recycles like” relationship. The decreased Tc, obtained by selecting solvents that interact strongly with the monomer (dimethyl formamide or the green solvent γ-valerolactone), allowed chemical recycling of high-molecular-weight poly(L-lactic acid) directly to L-lactide, within 1–4 h at 140 °C, with >95 % conversion and 98–99 % selectivity. Recycled L-lactide was isolated and repolymerized with high control over molecular weight and dispersity, closing the polymer loop. 

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Polymerteknologi (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Polymer Technologies (hsv//eng)

Nyckelord

Chemical Recycling

L-Lactide

Ring-Opening Polymerization

Solvent Effects

Thermodynamics

Amides

Lactic acid

Molecular weight

Monomers

Recycling

Ring opening polymerization

Solvents

Cyclic monomers

Elimination reaction

Epimerization

Large-scales

Poly-l-lactic acids

Ring-closing depolymerization

Side reactions

dilactide

dioxane derivative

polyester

polylactide

polymer

solvent

Dioxanes

Polyesters

Polymers

Publikations- och innehållstyp

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