Enzymatic poly and co-polymerisation of lactic acid

V.L.LASSALLE; M.L.FERREIRA

Oviedo, España

Simposio; 8th International Symposium on Biocatalysis and Biotransformations; 2007

Enzymatic poly and co-polymerisation of lactic acid V.L. Lassalle and M.L Ferreira PLAPIQUI-UNS-CONICET-Cmno La Carrindanga Km 7, CC 717, 8000 B. Bca. Argentina e-mail: mlferreira@plapiqui.edu.armlferreira@plapiqui.edu.ar Because of its biocompatibility and degradability to non-toxic products, polylactic acid (PLA) based polymers and copolymers have been employed in novel specific functions, such as absorbable bone plates, artificial skin, and carriers of drugs for controlled release systems. In recent years, the benefits of enzymes, especially with regard to selectivity and high stereoespecificity in polymer synthesis, have been investigated [1]. This work presents a systematic study on the polymerisation of lactic acid (LA) using three different lipases with the aim to determine the most efficient biocatalyst. Candida Antarctica lipase (Nov.435), Pseudomonas cepacia (PC) and páncreas porcine lipase (PPL) were tested. The reactions were conducted in 10ml vials in solution or in bulk, at 60ºC during 96hs. The conversion of LA to PLA was estimated by titration and the polymer’s molecular weight was determined by the end group method [2]. FTIR spectroscopy was used to verify the complete elimination of the enzyme from the obtained polymer. The influence of experimental parameters, such as concentration of lipase, addition of water, kind of reaction-solvent-free or with solvent-, kind of solvent and time, on the conversion and on the recovered polymer, was also explored. The Table 1 contains the conversion percentage of LA and PLA’s Mn as a function of the concentration of each lipase. According to these results the most effective biocatalyst is Nov.435 since leads to satisfactory LA conversion as well as almost 50% of the theoretical complete polymer recuperation as solid. Candida Antarctica lipase (Nov.435), Pseudomonas cepacia (PC) and páncreas porcine lipase (PPL) were tested. The reactions were conducted in 10ml vials in solution or in bulk, at 60ºC during 96hs. The conversion of LA to PLA was estimated by titration and the polymer’s molecular weight was determined by the end group method [2]. FTIR spectroscopy was used to verify the complete elimination of the enzyme from the obtained polymer. The influence of experimental parameters, such as concentration of lipase, addition of water, kind of reaction-solvent-free or with solvent-, kind of solvent and time, on the conversion and on the recovered polymer, was also explored. The Table 1 contains the conversion percentage of LA and PLA’s Mn as a function of the concentration of each lipase. According to these results the most effective biocatalyst is Nov.435 since leads to satisfactory LA conversion as well as almost 50% of the theoretical complete polymer recuperation as solid. Table 1 Enzyme Conc.of enzyme (mg/mmol LA) % Conversion % Solid recovered PLA Mn 9 24 6 - 18 27 44 2461 Novozyme 435 36 47 45 925 54 58 55 446 1.7 22 - Not recovered 3.3 56 - Not recovered PC 6.7 75 3 Not recovered 10 88 12 400 9 92 - Not recovered PPL 18 92 - Not recovered 36 91 - Not recovered 54 96 10 768 In reference to the percentage of recovered solid PLA, the soluble lipases are not effective, however higher conversion levels than in the case of Nov435 were achieved. This high LA conversion can be assigned to the formation of LA volatile oligomers. Some strategies such as heat treatments are actually in development with the aim to increase molecular weight of PLA. Besides homopolymers, copolymers (PLGA) were also synthesized, using glycolic acid as co-monomer, and were characterized by DSC, GPC and NMR C13when possible . References: [1]a) S. Kobayashi, J. of Pol. Sci. Part A: Pol. Chem. 1999,37, 3041; b) I.Varma, A. Albertsson, R.Ritimonti, R. Srivastava, Prog. Pol. Sci. 2005, 30, 949.c) K. Distel, K. Zhu, G.Wang, Bioresource Technology. 2005, 96, 617 [2] P. Allen, "Techniques of polymer characterization", Butterworths, London 1959, p.20. , J. of Pol. Sci. Part A: Pol. Chem. 1999,37, 3041; b) I.Varma, A. Albertsson, R.Ritimonti, R. Srivastava, Prog. Pol. Sci. 2005, 30, 949.c) K. Distel, K. Zhu, G.Wang, Bioresource Technology. 2005, 96, 617 [2] P. Allen, "Techniques of polymer characterization", Butterworths, London 1959, p.20. Techniques of polymer characterization", Butterworths, London 1959, p.20. References: [1]a) S. Kobayashi, J. of Pol. Sci. Part A: Pol. Chem. 1999,37, 3041; b) I.Varma, A. Albertsson, R.Ritimonti, R. Srivastava, Prog. Pol. Sci. 2005, 30, 949.c) K. Distel, K. Zhu, G.Wang, Bioresource Technology. 2005, 96, 617 [2] P. Allen, "Techniques of polymer characterization", Butterworths, London 1959, p.20. , J. of Pol. Sci. Part A: Pol. Chem. 1999,37, 3041; b) I.Varma, A. Albertsson, R.Ritimonti, R. Srivastava, Prog. Pol. Sci. 2005, 30, 949.c) K. Distel, K. Zhu, G.Wang, Bioresource Technology. 2005, 96, 617 [2] P. Allen, "Techniques of polymer characterization", Butterworths, London 1959, p.20. Techniques of polymer characterization", Butterworths, London 1959, p.20.