Biodegradable Aliphatic-Aromatic Copolyesters

Since aromatic polyesters turned out to be quite resistant to hydrolytic degradation under physiological conditions, a number of attempts were made to implant structures open to biological attack in such polyesters. These attempts have predominately been effectuated by introducing aliphatic acid components into the aromatic polyester chains [52]. 

Tensile strength (MPa) 32 (ISO 527) 24 (ASTM D638) 54 (ASTM D412-87) 

Tradename Bionolle 1001 series Bionolle 3000 series Ingeo 4043D 

Aromatic polymer Aliphatic component Mode of degradation References 

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C. Bastioli, T. Milizia, G. Eloridi, A.S. Lallaro, G. Celia, and M. Tosin, Biodegradable aliphatic-aromatic copolyester, US Patent 8193300, assigned to Novamont S.p.A. (Novara, IT), June 5, 2012. 

Compositions have been developed that include a biodegradable aliphatic-aromatic copolyester, i.e., poly(tetramethylene adi-pate-co-terephthalate) and a plasticizer. The composition exhibits a moisture vapor transmission rate of at least 400 (1). 

Zhang E, Huang E, Wang B. Characterization of biodegradable aliphatic/aromatic copolyesters and their starch blends, Polym.-Plast Technol Eng. 41 (2002) 273. 

Novamont patented a series of biodegradable aliphatic/aromatic copolyesters which are prepared by the copolymerisation of diol components with aromatic diacids and long chain aliphatic diacids of natural origin, such as azelaic, sebacic and brassylic acids [64-67]. 

Table 10.2 History of the development of biodegradable aliphatic-aromatic copolyesters ...

The main characteristics of biodegradable aliphatic-aromatic copolyesters are detailed in Section 10.3.1 and Table 10.3. Data has been taken from the technical bulletins available from the producers. 

In contrast to most aliphatic polyesters, aromatic polyesters like PET provide excellent material properties [50]. To combine good material properties with biodegradability, aliphatic/aromatic copolyesters have been developed. Several major polyester producers in Europe and the United States have recently begun marketing aliphatic/aromatic copolyesters for biodegradable applications. BASF markets a product, Ecoflex , which is a copolyester of butanediol, adipic acid, and dimethyl terephthalate. Eastman s Eastar Bio Copolyester 14766 is a similar aliphatic/aromatic copolyester. DuPont markets a modified PET known as Biomax . 

The basic general requirements for biodegradable plastics and also biodegradable aliphatic-aromatic copolyesters can be summarised as follows ... 

Starch-based materials represent the largest class of biodegradable polymer with 44,800 tonnes (including loose-fill foam packaging) consumed in 2005. Excluding loose-fill, starch-based materials amounted to 21,700 tonnes in 2005. Polylactic acid (PLA) is the second largest material class with 35,800 tonnes in 2005, followed by synthetic aliphatic-aromatic copolyesters with 14,000 tonnes. The embryonic PHA category amounts to around 250 tonnes. 

Figure 21.9 The biodegradable polyester family poly(hydroxyalkanoates) (PHA), poly(hydroxybulyrate) (PHB), poly(hydro3qdiexanoate) (PHH), poly(hydrox3rvalerate] (PHV), polyflactic acid) (PLA), poly(caprolactone) fPCL), poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), aliphatic-aromatic copolyesters (AAC), poly(ethylene terephthalate) (PET), poly(butylene adipate/terephthalate) (PBAT), poly(methylene adipate/terephthalate) (PTMAT). Adapted from [103].

With the attempt to combine good material properties of aromatic polyesters and biodegradability of aliphatic polyesters, aliphatic aromatic copolyesters have been developed during the last years to be used as technical biodegradable plastics The BASF AG / Germany is now producing a biodegradable material based on a copolyester of 1,4-butanediol, adipic acid and terephthalic acid (BTA-copolyester) tmder the trade name Ecoflex in a several thousand tons per year scale. 

However, questions have been raised with regard to the complete biodegradability of aliphatic-aromatic copolyesters because aromatic copolyesters such as poly(ethylene terephthalate) (PET)... 

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. 

Instead of the conventional binder pol5miers described above, biodegradable polymers may be used advantageously, such as aliphatic-aromatic copolyesters. A preferred aliphatic dicarboxylic acid is adipic acid and as aromatic dicarboxylic acid terephthalic acid can be used. As a glycol component 1,4-butanediol has been suggested. The natural cellulose fibers are selected from hemp, sisal, flax, kenaf, cotton, jute, or coconut (32). Commercial natural cellulose containing fibers are summarized in Table 5.10. 

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. 

While the biological susceptibility of maity aliphatic polyesters has been known for maiy years, aromatic polyesters such as polyetltylene terephthalate (PET) or polybutylene tereph-thalate are regarded as non-biodegradable [39]. To improve the use properties of aliphatic polyesters, an attempt was made to combine the biodegradability of aliphatic polyesters with the good material performance of aromatic polyesters in novel aliphatic-aromatic copolyesters. 

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... 

Kleeberg I., Hetz C., Kroppenstedt R.M., Muller R.-X, Deckwer W-D. Biodegradation of aliphatic-aromatic copolyesters by Thermonospora fusca and other thermophilic compost isolates, Appl Environ. Microbiol. 64 (1998) 1731. 

Poly (butylene adipate-co-terephthalate) (PBAT) is an interesting polymer [116,117] and has attracted more attention. PBAT is also a biodegradable poljmier, which has proper viscosity and elasticity. Moreover, the balance of biodegradability (e.g., life time) and its physical properties (e.g., thermal and mechanical properties) can be adjusted by controlling the molar ratio of comonomers in the copolymer [118,119]. It has been reported that the aliphatic/aromatic copolyester with aromatic units within the range of 35 - 55 mol% offers an optimal compromise of its biodegradability and physical properties. 

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