Application of Bismuth Catalysts for the Methanolysis of End‐of‐Life Poly(lactide)

Abstract

The chemical recycling of poly(lactide) (PLA) was investigated especially the depolymerization for generating useful monomers/polymer precursors. In more detail, applying catalytic amounts of bismuth compounds PLA was converted to methyl lactate using methanol as depolymerization reagent. An excellent performance was observed for bismuth subsalicylate with turnover frequencies of up to 13,800 h À 1 using microwave heating. Moreover, the usefulness of the bismuth subsalicylate catalyst was demonstrated in the depolymerization of various PLA goods. Interestingly, the bismuth subsalicylate was easily recovered after the reaction and was sent again to depolymerization revealing recyclability of the catalyst.

The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities

“…For both bismuth subsalicylate and Zn(OAc) 2 , high Me‐LA yield (>99 %) was retained irrespective of PLA source. [ 138 , 139 ] Conversely, Me‐LA yield was found to vary more significantly for the alkali halide and Sn(Oct) 2 systems, observing moderate to high yields (43–128 %). Note yields greater than 100 % were observed in instances when the starting material was assumed to be 100 % PLA but contained a substantial number of additives by mass (e. g., black sushi box).…”

“…This is particularly impressive given catalyst recovery is often a limiting industrial feature of homogeneous catalysis. Recently, Enthaler and co‐workers[ 136 , 137 , 138 , 139 ] have extensively reported the use of simple metal salts for PLA alcoholysis under microwave irradiation. Commercially available alkali halide salts of the general formula MX, such as KF, LiCl and KBr, were found to be potent catalysts for PLA ( M n =43600–150400 g mol −1 ) methanolysis between 140–160 °C.…”

“…To address toxicity concerns associated with Sn(Oct) 2 , Enthaler and co‐workers explored the use of environmentally benign alternatives, including bismuth‐ and zinc‐based salts. [ 138 , 139 ] Promisingly, TOFs up to 13800 and 45000 h −1 were observed for bismuth subsalicylate and Zn(OAc) 2 , respectively, at 180 °C using 0.1 mol % catalyst. However, in both instances a large excess of MeOH (67.5 equiv.)…”

Sterically rigid bismuth pincer complexes; observation of the growing polymer chain in polar monomer polymerisation

“…18 Furthermore, Enthaler and coworkers have recently utilised F for the depolymerisation and chemical recycling of end of life PLA materials. 19 However, the Bi initiator is insoluble and the nature of the active species is not known but is likely to be a polynuclear species based on crystallographic studies of the parent subsalicylate; importantly, the insolubility renders catalytic activity dependent on particle size. 20 Bi{N(SiMe 3 ) 2 } 3 has been investigated by Visseaux and coworkers as a simple, soluble initiator (Fig.…”

High molecular weight poly(l‐lactide) via ring‐opening polymerization with bismuth subsalicylate–The role of cocatalysts

“…Finally, it should be mentioned that quite recently a study about methanolytic degradation (and recycling) of used polylactide articles catalyzed by various Bi(III) salts was published 33 . There, it was found that BiSub was the most effective transesterification catalyst of all Bi(III) salts used in that study.…”