Biodegradability of Polyesters

Aliphatic polyesters such as PHAs, and more specifically homopolymers and copolymers of hydroxybutyric acid and hydroxyvaleric acid, have been confirmed to be readily biodegradable. Such polymers are actually synthesized by microbes, with 

Degradability of other polyesters There are two main water-soluble polymer types commercially available polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH). PVOH is a readily biodegradable, water-soluble polymer. The degradation of PVOH is influenced by its crystallinity and molecular weight PVOH does not biodegrade, but simply dissolves in water or can be biodegraded by activated sludge treatment. EVOH is another water-soluble synthetic plastic. 

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Relationship Between Tm and the Biodegradability of Polyester by Lipases. The relationship between Tm and the biodegradability of saturated aliphatic polyester is shown in Figure 6. For the same series polyesters, the biodegradabilities decreased with increasing Tm. 

Figure 6. Relationship between Tm and the biodegradability of polyesters by R> delemar (a) and R> arrhizus (b) lipases, and PEA-degrading enzyme from Penicillium sp. strain ll+-3 (c). PESu polyethylene suberate PEAz polyethylene azelate PESE polyethylene sebacate PEDe polyethylene decamethylate PBS polytetramethyl-ene succinate PBA polytetramethylene adipate PBSE polytetra-methylene sebacate PHSE polyhexamethylene sebacate PPL poly-propiolactone.

Muller, R. J., Kleeberg, I. Deckwer, W. D. (2001). Biodegradation of polyesters containing aromatic constituents. Journal of Biotechnology, 86, 87-95. 

Table I. Biodegradation of polyesters evaluated by the ASTM test and by soil burial [25]...

How does nanoclay in vegetable oil-based polymer nanocomposites act as a catalyst in the biodegradation of polyester/clay nanocomposites ... 

Okada M., Tachikawa K., Aoi K., Biodegradable polymers based on renewable resources. 11. Synthesis and biodegradability of polyesters containing furan rings, J. Poly. Sci. Part A Polym. Chem., 35, 1997, 2729-2737. 

Bikiaris, D.N. (2013) Nanocomposites of aliphatic polyesters an overview of the effect of different nanoparticles on enzymatic hydrolysis and biodegradation of polyesters. Polym. Degrad. Stab., 98, 1908-1928. 

Eqs (15.18) and (15.22) are reaction diffusion equations for biodegradation of polyesters. This type of equation was first proposed by Gillespie (1976) and Grizzi et al. 

Hydrolytic reactions, which are best documented, include saponification of esters, hydrolysis of amides, and hydrolysis of ethers (glycosides). Except for ester saponification, all the other reactions proceed at a measurable rate only by enzymic catalysis. Hydrolytic enzymes are regular constituents of the digestive tract and lysosomes. They are responsible for the biodegradation of polyesters, polyamides (including polypeptides), polysaccharides and, probably, polyurethanes. 

WittU., Muller R.-X, Deckwer W.-D. Biodegradation of polyester copolymers containing aromatic... 

The biodegradation of polyesters is also affected by the chemical structure, hydrophilic/hydrophobic balance within the main chain, MW and crystallinity, which acts as a hindrance to biodegradability. In fact, biodegradation first takes place in the amorphous region of the polymer, where the erosion rate is much higher than in... 

In the biodegradable BTA aliphatic-aromatic polyesters available on the market, the amount of aromatic acid in the polymer chain was always maintained below 49 mol% in view of the significant and sudden decrease of the biodegradation of polyesters above this threshold. This behaviour was attributed to the lower biodegradability of the butyleneterephthalate sequences with length equal or higher than 3 which, above the said threshold, represent more than 10 % of the aromatic fraction of these polyesters [55] (Section 10.3.6). 

Admittedly, the mobility of the polymer chains (the ability of chain segments to temporarily escape to a certain distance from the embedding crystal) is the major and general controlling factor for the biodegradability of polyesters. The concept of chain mobility seems to be a quite universal way to describe and predict the biodegradation rate of synthetic polyesters, independent of their composition or microstructure. 

Witt, U., Muller, R.-J. et al. Synthesis, properties and biodegradability of polyesters based on 1,3-propanediol, Macromol. Chem. Phyp. 195 (1994), p. 793-802... 

R-J. Muller, Mechanistic Studies on the Biodegradation of Polyester, Ed., W. Sand, DECHEMA Monographs Vol. 133, Hamburg, Germany, 1996, 211. 

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