Poly(lactic acid) Degradation into Methyl Lactate Catalyzed by a Well-Defined Zn(II) Complex

Román‐Ramírez, Luis A.; McKeown, Paul; Jones, Matthew D.; Wood, Joseph

doi:10.1021/acscatal.8b04863

Cited by 115 publications

(162 citation statements)

References 51 publications

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“…For Zn( D ) 2 , the reduced activity may suggest the presence of the pendant amine groups to be important, perhaps assisting in the degradation mechanism through hydrogen‐bonding interactions as suggested for the polymerization studies. In comparison, commercially available ZnCl 2 was found to be inactive for degradation under these conditions, and we have previously shown Zn(OAc) 2 to be much less active than Zn( A ethyl ) 2 …”

Section: Methodsmentioning

confidence: 88%

“…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 …”

Section: Methodsmentioning

confidence: 99%

“…The use of metal complexes for this purpose is rare despite the amount of complexes reported for LA polymerization . Recently, we have reported the use of a discrete homoleptic Zn II complex [Zn( A ethyl ) 2 ] (ethyl denotes the length of the N−N backbone with the same substituents as in Scheme ) for PLA degradation to Me‐La . To demonstrate the versatile nature of the process, a range of PLA grades were degraded in a controlled manner; experimental design and kinetic modelling were used to further elucidate key experimental factors and reaction mechanism …”

Section: Methodsmentioning

confidence: 99%

“…This technique quantified the relative concentrations of methine groups, which are defined as internal (Int), chain end (CE) and alkyl lactate (A‐La). We have previously shown the production of Me‐La is a two‐step process with the intermediate formation of CE groups (see the Supporting Information) . For comparison, internal methine conversion ( X Int ), alkyl lactate selectivity ( S A‐La ) and alkyl lactate yield ( Y A‐La ) are provided for each catalyst.…”

Section: Methodsmentioning

confidence: 99%

“…The calculated X Int , S A‐La , Y A‐La and rate coefficient for the degradation step ( k 1 , Table ) are in good agreement with the values obtained in the small‐scale studies (Table ), demonstrating the scale‐up potential of the process. Rate coefficients k 2 and k ‐2 correspond to the reversible reaction for A‐La formation from CE groups (Figures S31 and S39 in the Supporting Information), calculated from the kinetic model presented in .…”

Section: Methodsmentioning

confidence: 99%

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

et al. 2019

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As eries of Zn II complexes, based on propylenediamineS chiff bases, have been prepared and fully characterized. X-ray crystallography and NMR spectroscopy identified significant differences in the solid and solution state for the Zn II species. All complexes have been applied to the ring-opening polymerization of l-lactidew ith emphasis on industrial conditions. High conversion and good molecularw eight control were generally achievablef or Zn(A-D) 2 ,a nd high-molecular-weight poly(lactic acid) (PLA) was prepared in 1min at a1 0000:1:33 [lactide]/ [Zn]/[BnOH] loading. The more active Zn II catalysts were also appliedt oP LA degradation to alkyl lactateu nder mild conditions. Zn(A-B) 2 demonstrated high activity and selectivity in this process with PLA being consumed within 1h at 50 8C. Zn(C-D) 2 were shown to be less active, and these observations can be relatedt ot he catalysts' structure and the degradation mechanism. Initialr esultsf or the degradation of poly(ethylene terephthalate) and mixed feeds are also presented, highlighting the broader applicability of the systems presented.Owing to the inevitable depletion of fossil fuel resources, and inherentc arbon emissions, alternatives to petrochemical plastics are desperately needed. [1] Poly(lactic acid) (PLA) is apotential replacement for fossil-fuel-derived plastics used for packaging applications. [2,3] PLA has the added advantageo f being biocompatible and therefore suitable for biomedical applications. [4,5] Because it is derived from annually harvested crops, PLA is biorenewable and has promising green credentials in terms of CO 2 emissions and life-cycle assessment. [6,7] High-molecular-weight PLA is preferentially prepared from the cyclic dimer of lactic acid, lactide (LA), through ring-opening polymerization (ROP). [8] CurrentP LA research seeks to reduce energy/material input of LA monomer synthesis, [9][10][11][12] demonstrate ande lucidate stereoselective initiation [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and prepare robust initiators to compete with Sn(Oct) 2 under industrial conditions. [30][31][32][33][34] Plastic waste andp ollution are af urther 21 st century challenge forboth academia and industry.Although PLA is biodegradable under high-temperature industrial conditions, it will not readily degrade in the natural environmenta nd therefore will contribute to the millions of tonnes of waste in landfill and in oceans. [35][36][37] End-of-life plastic waste managementi s key to tackling this issue, andi ti si mperative this is addressed for all aspiring materials such as PLA. For PLA, chemical recycling is ap articularly attractive route because it can produce value-added products such as alkyl lactates, lactic acid and acrylic acid. [38,39] These can be usefuli nt heir own right or used to reform LA, and therefore PLA, to facilitate ac ircular-economy approach. Lactic acid, for example, is regarded as ap latform chemical, and alkyl lactates are considered green solvents. [40][41][42][43][44] The conversion of PLA ...

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Section: Methodsmentioning

confidence: 88%