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Review
. 2022 Apr 7;9(4):164.
doi: 10.3390/bioengineering9040164.

Lactide: Production Routes, Properties, and Applications

Bruna L C Cunha  1 , Juliana O Bahú  2 , Letícia F Xavier  1 , Sara Crivellin  2 , Samuel D A de Souza  2 , Leandro Lodi  3 , André L Jardini  2 , Rubens Maciel Filho  2 , Maria I R B Schiavon  2 , Viktor O Cárdenas Concha  1 , Patricia Severino  4   5 , Eliana B Souto  6   7
Affiliations
Review

Lactide: Production Routes, Properties, and Applications

Bruna L C Cunha et al. Bioengineering (Basel). .

Abstract

Lactide dimer is an important monomer produced from lactic acid dehydration, followed by the prepolymer depolymerization process, and subsequent purification. As lactic acid is a chiral molecule, lactide can exist in three isomeric forms: L-, D-, and meso-lactide. Due to its time-consuming synthesis and the need for strict temperature and pressure control, catalyst use, low selectivity, high energy cost, and racemization, the value of a high purity lactide has a high cost in the market; moreover, little is found in scientific articles about the monomer synthesis. Lactide use is mainly for the synthesis of high molar mass poly(lactic acid) (PLA), applied as bio-based material for medical applications (e.g., prostheses and membranes), drug delivery, and hydrogels, or combined with other polymers for applications in packaging. This review elucidates the configurations and conditions of syntheses mapped for lactide production, the main properties of each of the isomeric forms, its industrial production, as well as the main applications in the market.

Keywords: applications; industrial processes; l-lactide; market costs; synthesis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The number of publications about lactide in the last few years in common database research platforms for the search item “lactide”.
Figure 2
Figure 2
Lactide dimer synthesis (reprinted with permission [12], Copyright 1998 Elsevier).
Figure 3
Figure 3
Back-biting reaction of the OH group in the PLA chain (reprinted with permission [15], Copyright 2004 Elsevier).
Figure 4
Figure 4
General lactide coordination-insertion mechanism with Sn(Oct)2 for PLA production (reprinted with permission [18], Copyright 2000 John Wiley & Sons Inc.).
Figure 5
Figure 5
Ester cleavage: (a) carbonyl-oxygen bond, and (b) alkyl-oxygen bond (reprinted with permission [19], Copyright 1997 American Chemical Society); and enolization.
Figure 6
Figure 6
Chemical structure of D-, M-, and L-lactide, respectively (reprinted with permission [12], Copyright 1998 Elsevier).
Figure 7
Figure 7
Conventional two-step lactide synthesis process (reprinted with permission [48], Copyright 2019 American Chemical Society): (1) lactic acid stream, (2) lactic acid + reflux mixed stream, (3) dehydrated lactic acid stream, (4) wastewater, (5) dehydrated lactic acid stream, (6) lactic acid recovery, (7) R-1 liquid phase, (8) catalyst feed stream, (9) lactic acid + catalyst mixed stream, (10) oligomers stream, (11) unreacted oligomers stream, (12) unreacted oligomer recovery, (13) high molar mass oligomers, (14) crude lactide stream, (15) purified lactide stream, (16) unpurified lactide stream, (C-1, C-2) distillation columns, (R-1, R-2) polycondensation and depolymerization reactors, respectively, (F-1, F-2) heating duties.
Figure 8
Figure 8
One-step lactide synthesis process (reprinted with permission [48], Copyright 2019 American Chemical Society): (1) lactic acid feed stream, (2) nitrogen stream, (3) lactic acid + N2 mixed stream, (4) vaporized mixed stream, (5) reactor outlet, (6) crude lactide stream, (7) purified lactide, (8) unpurified stream, (9) vapor outlet of the F-1 flash drum, (10) gas outlet, (11) waste water, (12) N2 gas recycling, (13) N2 purged, (R-1) fixed-bed plug flown reactor filled with SiO2/Al2O3, (H-1, F-1, F-2) heating duties, (C-1) distillation column.
Figure 9
Figure 9
Simplified flow diagram of the life cycle Cargill Dow process for lactide and PLA production (reprinted with permission [72], Copyright 2003 Elsevier).
Figure 10
Figure 10
Industrial plant design of NatureworksTM (Cargill Dow) for the production of lactide and PLA (reprinted with permission [12], Copyright 1998 Elsevier).
Figure 11
Figure 11
Application of PLA in medicine.
See this image and copyright information in PMC

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