Lactic Acid-based Degradable Polymers

Although some microbial enzymes can degrade lactic acid-based polymers and stereocopolymers in vitro [18], biodegradation in vivo was soon excluded because humans do not possess enzymes capable of degrading high molar mass lactic acid polymers [19]. 

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Hiltunen, K., Sepp, J. V., It, M., Mika, H. The Biodegradation of Lactic Acid-Based Poly (ester-Urethanes)./. Environ. Polym. Degrad., 1997, 5,167-173. 

Tsuneizumi et al. [13] studied the chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts, clay catalysts, and enzymes. Poly(L-lactic acid) (PLLA)-based polymer blends (e.g., PLLA/polyethylene [PE] and PLLA/poly(butylenes succinate) [PBS]) were degraded into repolymerizable oligomer. 

Hiltunen K, Seppala JV, Itavaara M, Harkonen M (1997) The biodegradation of lactic acid-based poly(ester-urethanes). J Environ Polym Degrad 5 167-173 Hossein AK, Seyed HJ, Ahmad A (2008) A review on homopolymer, blends, and nanocomposites of poly(trimethylene terephthalate) as a new addition to the aromatic polyesters class. Iran Polym J 17 19-38... 

Basically, lactic acid-based polymers can be degraded chemically or enzymatically. Although some exotic enzymes can degrade lactic acid stereocopolymers in vitro [54] and occasionally some microorganisms in the environment [55, 56], these aliphatic polyester chains are primarily degraded by the hydrolytic action of absorbed water molecules, carboxylic chain ends and any acid or base additive or impurity acting as an occasional catalyst [26]. In the case of chain end catalysis, one talks of autocatalysis, a well-known phenomenon in organic chemistry that has particularly complex consequences in the case of polymers [15]. 

To summarise, any phenomena or characteristics that can affect the rate of hydrolysis, the rate of ester bond cleavage and/or the solubility of degradation by-products will affect the macroscopic degradation. Therefore, it is essential that careful identification of investigated lactic acid-based polymers be included in any investigation of degradation characteristics of a specific compound. 

Petinakis, E., Liu, X., Yu, L., Way, C., Sangwan, P., Dean, K., et al., 2010. Biodegradation and thermal decomposition of poly (lactic acid)-based materials reinforced by hydrophilic fillers. Polym. Degrad. Stabil. 95, 1704-1707. 

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