Transforming polylactide into value‐added materials

Abstract

The production of chemical building blocks and polymer precursors from biorenewable and sustainable resources is an attractive method to bypass traditional fossil fuel derived materials. Accordingly, we report the organocatalytic recycling of postconsumer polylactide (PLA) into value-added small molecules. This strategy, using the highly active transesterification catalyst triazabicyclodecene, is shown to completely depolymerize PLA in the presence of various alcohols into valuable lactate esters. Using previously used PLA packaging material, the depolymerization is complete in minutes at room temperature and fully retains the stereochemistry of the lactate species. Further, the modularity and utility of this methodology with respect to polyester substrate is detailed by using a variety of functional alcohols to depolymerize both PLA and polyglycolide, with the corresponding ester smallmolecules being used to make new polymeric materials. The opportunities to transform waste streams into value-added chemicals and new materials through simple and versatile chemistry hold significant potential to extend the lifecycle of renewable chemical feedstocks. KEYWORDS: biodegradable; depolymerization; glycolate ester; lactate ester; organic catalysis; polyesters; polyglycolide; polylactide; recycling; transesterification INTRODUCTION As society increasingly deals with inherently limited natural resources, the utilization of 7% of fossil fuels for the production of plastics is a significant drain on petrochemical feedstocks.1 With the demand for polymeric materials increasing, it is imperative to develop building blocks based on renewable and sustainable resources.2 The conversion of biomass to value-added small molecules and polymer precursors is an attractive method to bypass traditional fossil fuel-based chemical production.3-5 For example, polylactide (PLA) has emerged as one of the most promising biorenewable and biodegradable polymers due to its utility in packaging, textile, and biomedical applications. [6][7][8][9] The recent addition of Natureworks TM LLC facility in the US has put annual production capacity of PLA at over 150,000 tons, making it a high-volume commodity material. [10][11][12] This largescale production and the predicted annual growth rate of 19% for bioplastics 13 assures that many new PLA derived products will enter the marketplace in the coming decades.

Zinc Complexes for PLA Formation and Chemical Recycling: Towards a Circular Economy

“…Compared to other waste management strategies such as incineration and biodegradation, chemical recycling offers the greatest value with potential to reduce the cost of PLA and increase market uptake . Previous examples of PLA recycling processes include hydrolysis, alcoholysis, hydrogenation and hydrosilylation …”

“…Sobota and co‐workers have also shown the use of metallic precursors at relatively high temperatures, demonstrating a range of alcohols for transesterification . There are also examples of organocatalyzed degradation with triazabicyclodecene (TBD) and 4‐dimethylaminopyridine (DMAP) . The use of metal complexes for this purpose is rare despite the amount of complexes reported for LA polymerization .…”

Mechanical recycling of polylactide, upgrading trends and combination of valorization techniques

“…The organocatalytic recycling of post-consumer polylactide (PLA) into added-value small molecules has been also reported [140] by the use of active transesterification catalyst triazabicyclodecene, which was shown to completely depolymerize PLA in the presence of various alcohols into lactate esters. The opportunities to transform waste streams into added-value feedstock and new materials through simple and versatile chemistry hold significant potential to extend the lifecycle of renewable chemical feedstocks.…”

Mono- and dimeric zinc(ii) complexes for PLA production and degradation into methyl lactate – a chemical recycling method

“…[27][28][29] A number of different PLA transesterification methods have been reported in the literature. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] DuPont possess a patent for PLA degradation in the presence of H 2 SO 4 , achieving high conversion (69-87%) to various lactate esters (R = Me, Et and n Bu) within 2 h between 150-190°C. 30 Coszach et al 17 demonstrated the hydrolysis of PLA to lactic acid, observing enhanced PLA dissolution and polymer separation with lactate esters as the solvent of choice.…”