Polyester aliphatic-aromatic copolyester

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. 

In this chapter, information on the different types of aliphatic polyesters, aliphatic-aromatic copolyesters and their biodegradable mechanisms will be disclosed. 

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. 

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].

The sulfonated aliphatic-aromatic copolyesters exhibit improved thermal properties, in particular, a desirable balance of high temperature properties and improved compostabUity Sulfonated polyesters can be prepared as follows (60) ... 

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. 

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. 

Indeed, a large number of biodegradable polyesters are based on petrolenm resources, obtained chemically from synthetic monomers and polycaprolactone, poly-esteramide, or aliphatic/aromatic copolyesters can be distinguished. Generally, these petroleum-based polyesters are soft at room temperature since their glass transition temperatures are lower. 

The great majority of industrial biodegradable polymers and plastics developed in recent decades are polyesters. Not all polyesters are biodegradable the biodegradation rate is influenced by the percentage and distribution of aromatic monomers in the polymer chain [23]. For this reason aliphatic-aromatic copolyesters, that combine biodegradability with enhanced mechanical properties, have been developed. 

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. 

In order to try to combine both the excellent material properties of aromatic polyesters and the potential biodegradability of aliphatic polyesters, several aliphatic-aromatic copolyesters have been developed over the last 20 years and are now, together with the aliphatic polyester polylactic acid (PEA), one of the most common biodegradable resins on the market with a production of several thousand tonnes per year. The... 

In recent years, Novamont developed a family of aliphatic-aromatic copolyesters with its aliphatic dicarboxylic acid component predominantly based on long chain dicarboxylic acids of natural origin (sebacic acid, azelaic acid and brassylic acid) [56-58]. Compared with aliphatic-aromatic polyesters where the aliphatic dicarboxylic component is a shorter carbon chain length, such as BTA polyesters, these copolyesters do not show the sudden decrease of biodegradation properties above... 

As opposed to aliphatic polyesters, which can be easily classified on the different repetitive unit, aliphatic-aromatic copolyesters are, nowadays, constituted of terephthalic acid, adipic acid (or a long dicarboxylic acid) and 1,4-butanediol. For this reason, their classification is by brand name or producers. 

Samsung Fine Chemicals has slightly changed the brand name into S-EnPol which now comprises both aliphatic polyesters based on succinic acid (G4000 series - Section 10.2.2) and aliphatic-aromatic copolyesters based on a composition of terephthalic acid, adipic acid and 1,4-butanediol (PBG7000 series) which is changed with respect to the previous G8000 series. 

This phenomenon is attributed to the melting point of the material - a correlation already demonstrated by Tokiwa and co-workers for different aliphatic polyesters [79]. In aliphatic-aromatic copolyesters, the melting behaviour is mainly determined by the length of the aromatic sequences in the polymer chains, which depends both on the composition and structure [86, 87]. For many aliphatic polyesters, a correlation of the degradability with the melting point was observed [2]. Marten [86] interpreted it as a decrease in the mobility of the polyester chains at lower temperatures in this situation the polymer chains are highly fixed in the polymer crystals and cannot adjust easily into the active sites of the extracellular enzymes. A random insertion of some aromatic monomers in aliphatic polymer chains disturbs the formation of crystals. 

So far, wholly renewable biodegradable polyesters belong only to the aliphatic family, but efforts are being made to obtain aromatic dicarboxylic acids from renewable resources in order to fill this gap, as demonstrated by the research achievements involving aliphatic-aromatic copolyesters based on furandicarboxylic acid [59-61]. 

BASF has introduced their aliphatic-aromatic copolyesters (AAC) product under the name Ecoflex . This material is widely used to produce compostable packaging and films. According to the BASF s corporate website, annual production of Ecoflex has risen to 60,000 MT to keep up with the demand for biodegradable plastics, which is growing at a rate of 20% per year. At the same time, BASF also produces a blend of polyester and PLA — a product called Ecovio . This high-melt-strength polyester—PLA can be directly processed on conventionally blown film lines without the incorporation of additives. Moreover, Ecovio has extraordinary puncture-and tear-resistance and weldability. Another company, Eastman, has also produced AAC, with the tradename Eastar Bio . Eastar Bio has a highly linear structure, while Ecoflex contains... 

FIGURE 19 Representative composting time (in months) of biopolymers (TPS - Thermoplastic starch, PC - Polycaprolactone, mc-PHA - medium chain length PHA, Al-co-PEs -Ahphatic co-polyester, PEA - Polyester amides, Ah/arocoPEs - Aliphatic/aromatic copolyester, and CDAc - Cellulose diacetate). 

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