Degradation of Aliphatic-Aromatic Copolyesters

While a number of aliphatic components which alter the biodegradation behaviour of aromatic polyesters have been tested, the aromatic component predominantly used was terephthalic acid. Also the materials which are commercially available on the market contain this aromatic dicarboxylic acid. 

The degradation behaviour of aliphatic-aromatic copolyesters generally depends on the composition of the monomers as well as on the structure of the polymer chains at a given composition. 

Content of terephthalic acid referred to the total amount of acids (mol%) 

Polyester initial molecular weight (g/mol) melting point 

ETA38 62 ETA44 56 PTA39 61 PTA43 57 BTA34 6 BTA42 58 BTA 51 49 

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The first papers published on the biological degradation of aliphatic-aromatic copolyesters came to the conclusion that only at a quite high fraction of aliphatic monomers did the... 

This chapter is mainly focuses on the environmental degradation of aliphatic-aromatic copolyesters. 

Witt U et al. (2001) Biodegradation of aliphatic-aromatic copolyesters evaluation of the final biodegradability and ecotoxicological impact of degradation intermediates. Chemosphere 44 289-299. 

The blends of aliphatic-aromatic copolyesters synthesized from dimethyl succinate, dimethyl terephthalate and butanediol with starch was studied by soil burial [141]. Blends of copofyes-ters with starch posssessed higher degradation rate but lower tensile strength as compared with unfilled copofyesters. 

Since nonbiodegradable aromatic polyesters like PET provide excellent material properties [55], with respect to easily degradable aliphatic polyesters, a number of aliphatic/aromatic copolyesters were studied and developed in order to produce materials which combined good mechanical properties and biodegradability. Major polyester producers in Europe and the USA brought aliphatic/aromatic copolyesters for biodegradable applications to the market. 

Furthermore, novel polyfpropylene terephthalate-co-adipate) random copolymers showed that they can be degraded via hydrolysis, especially in the presence of enzymes (Rhizopus delemar and Pseudomonas cepacia lipases), even for a terephthalate content as high as 66 mol% [38]. In contrast to hydrolysis rates, mechanical properties increased upon increasing the terephthalate content. The main advantage of aliphatic-aromatic copolyesters over pure terephthalates is their biodegradability. 

Kleeberg, L, Hetz, C. et al. Biodegradation of aliphatic-aromatic copolyesters by Thermo-monospora fusca and other thermophilic compost isolates, AppUed Environ. Polymer Degradation, A 64 (1995) 5, p. 1731-1735... 

Witt U, Mtlller R J and Deckwer W D (1996) Studies on sequence distribution of aliphatic/aromatic copolyesters by high-resolution C-13 nuclear magnetic resonsnce spectroscopy for evaluation of bio degradability, Macromol Chem Phys 197 1525-1535. 

Hie ester linkage of aliphatic and aliphatic-aromatic copolyesters can easily be cleaved by hydrolysis under alkaline, acid, or enzymatic catalysis. This feature makes polyesters very attractive for two related, but quite different, applications (i) bioresorbable, bioabsorbable, or bioerodible polymers and (ii) environmentally degradable and recyclable polymers. 

On the other hand, it has been established that aliphatic-aromatic copolyesters are indeed biodegradable and that the biodegradability of these copolyesters is related to the length of the aromatic sequence. Block copolyesters with relatively long aromatic sequences are not rapidly degraded by microorganisms. 

Marten E, Muller R-J, Deckwer W-D (2005) Studies on the enzymatic hydrolysis of polyesters, n. Aliphatic-aromatic copolyesters. Polymer degradation and stability. 88(3) 371-381. 

Kleeberg I, Welzel K, VandenHeuvel J, Muller R-J, Deckwer, W-D (2005) Characterization of a new extracellular hydrolase from Thermobiftda fusca degrading aliphatic-aromatic copolyester. Biomacromolecules 6 262-270... 

Erceg M., Kovacid T, Klaiic L Dynamic thermogravimetric degradation of poly(3-hydroxybu-tyrate)/aliphatic-aromatic copolyester blends, Polym. Deg. Stab. 90 (2005) 86. 

Generally it seemed that many polyesters composed of aliphatic monomers were degradable by lipases, while most aromatic polyesters were characterized as biologically inert [95]. In aliphatic-aromatic copolyesters the tendency was found that biodegradability decreases with the content of aromatic constitnents. For copolyesters composed from adipic acid, terephthalic acid and 1,4-butanediol a maximum content of about 50-60% terephthalic acid in the diacid component was reported to be the hmit for biodegradability. 

Biodegradation of natural and synthetic copofyesters in two different natural environments, i.e. in compost with activated sludge at a sewage farm and in the Baltic Sea, was studied by Rutkowska et al. [142]. The results revealed that the natural aliphatic copolyester 3-hydroxybutyrate-co-3-lydroxyvalerate (PHBV) and its blends with the synthetic aliphatic-aromatic copolyester of 1,4-butanediol with adipic and terephthalic acids degraded faster in compost than in seawater. In both natural environments, blends degraded faster than aliphatic-aromatic copolyester, but at a slower rate than natural component PHBV... 

Erceg, M., Kovacic, T., and Klaric, I. (2005). Dynamic thermogravimetric degradation of poly(3-hydroxybutyrate)/aliphatic-aromatic copolyester blends. Polymer Degradation and Stability 90, 86-94. 

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