Biodegradable aromatic copolyesters

At the end of the 1990s, BASF commercialized Ecoflex F, a completely biodegradable statistical copolyester based on the fossil monomers 1,4-butanediol (BDO), adipic acid and terephthalic acid (see Fig. 3). Ecoflex F combines the good biodegradability known from aliphatic polyesters with the good mechanical properties of aromatic polyesters. 

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. 

Adipic acid aromatic copolyesters Biodegradable polyester used in degradable plastic... 

A large number of biodegradable polyesters are based on petroleum resources, obtained chemically from synthetic monomers [Okada, 2002 Albertsson and Varma, 2002 Vert et al., 1995 Sinclair, 1996 Lunt, 1998 Steinbuchel, 2003 Bigg, 1996]. According to the chemical structures, we can distinguish polycaprolactone, aliphatic copolyesters, and aromatic copolyesters. All these polyesters are soft at room temperature [Averous and Pollet, 2012]. 

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. 

With the twin driving forces of usefulness and eventual biodegradation, many studies have been made on the biodegradation of copolyesters containing aromatic and aliphatic segments to develop greener materials [58-79]. 

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. 

The introduction of a sulfonate functionality into some polyesters has been foimd to enhance the biodegradation rate of the materials. Shaped articles produced from sulfonated aromatic copolyesters containing hydroxyalkanoic acid residues have improved thermal properties (62). 

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. 

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. 

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). 

Compared to totally aliphatic copolyesters, aromatic copolyesters are often based on terephthalic acid. Figure 17.2 and Table 17.2 show, the chemical structure and the properties of such products, respectively, (e.g., Eastar Bio from Eastman). Besides, BASF and DuPont commercialize aromatic copolyesters under Ecoflex (Steinbuchel and Doi 2002) and Biomax trademarks, respectively. Biomax shows a high terephthalic acid content that modifies some properties such as the melting temperature (200°C). But, according to Muller et al. (1998), an increase of terephthalic acid content tends to decrease the degradation rate. Ecoflex biodegradation has been analyzed by Witt et al. (2001). They concluded that there is no... 

The matrix is a biodegradable and aromatic copolyester (polybutylene adipate-co-terephthalate, PBAT), from Eastman (EASTAR BIO Ultra Copolyester 14766). Copolyester chemical structure is given in Table 17.2. This copolyester is soluble at room temperature in different solvents such as THF, CH2CI2, or CHCI3. Determined by HNMR, PBAT composition is 43% of butylene terephthalate and 57% of butylene adipate. Determined by size exclusion chromatography (SEC), molecular weight (Mw) and polydispersity index (IP) are 48,000 and 2.4, respectively. Melt flow index (MFI) is 13 g/10 min at 190°C/2.16 Kg. PBAT density is 1.27 g/cm at 23°C. 

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. 

Poly(butylene adipate-co-succinate)/poly(butylene terephthalate) copolyesters prepared by the transesterification reaction of PBAS and PBT were characterized [93]. The biodegradability of copolyesters depended on the terephthalate unit in the composition and average block length of the aromatic unit. 

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