Adipic acid, biodegradation

Some 50 years later, in the 1990s Bayer produced their BAK polyesteramides by co-reacting either hexamethylene diamine or e-caprolactam with adipic acid and butane glycol. These materials do have sufficient regularity to be crystallisable and are of interest as biodegradable plastics and are discussed further in Chapter 31. 

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. 

Biodegradability improves with higher content of adipic acid in the copolymer however, the melting point decreases and the crystallization is worse. 

Scow et al. 1986, 1989 Zaidi et al. 1988, 1989). The products of biodegradation have also been studied with pure cultures of microorganisms. Catechol, beta-keto adipic acid, and nitrite have been identified as products of aerobic biodegradation of 2-nitrophenol (Zeyer and Kearney 1984) and 4-nitrocatechol, hydroquinone, gamma-hydroxymuconic semialehyde, and nitrite from 4-nitrophenol (Raymond and Alexander 1971 Spain et al. 1979). On the other hand, 2-aminophenol and 4-aminophenol have been isolated from anaerobic biodegradation of 2-nitrophenol and 4-nitrophenol, respectively (Adhya et al. 1981 Villanueva 1961). 

The solution is a combination of aliphatic polyesters and aromatic polyesters. This involves modifying the crystalline structure of PBT by incorporating aliphatic monomer (adipic acid) in the polymer chain in such a way that the material properties of the polymer would remain acceptable (e.g., melting point of the crystalline range still around 100 °C), but the polymer would also be readily compostable/biodegradable. In this way it was possible to combine the degradability of aliphatic polyesters with the outstanding properties of aromatic polyesters. 

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

Blends of poly(3-hydroxyalkanoic acid)s (PHAs) with various natural and synthetic polymers have been reported as reviewed in Refs. [21,22]. By blending with synthetic polymers it is expected to control the biodegradability, to improve several properties, and to reduce the production cost of bacterially synthesized PHAs. The polymers investigated as the blending partners of PHAs include poly(ethylene oxide) [92, 93], poly(vinyl acetate) [94], poly(vinylidene fluoride) [95], ethylene propylene rubber [94, 96], po-ly(epichlorohydrin) [97, 98], poly(e-caprolactone) [99], aliphatic copolyesters of adipic acid/ethylene glycole/lactic acid [100] and of e-caprolactone/lactide... 

Arvanitoyannis, I., Nikolaou, E., and Yamamoto, N., 1994, Novel biodegradable copolyamides based on adipic acid, bis(p-aminocyclohexyl) methane and several alpha-amino acids - Synthesis, characterization and study of their degradability for food packaging applications - 4. Polymer 35 4678-4689. 

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. 

Ahn BD, Kim SH, Kim YH, Yang JS (2001) Synthesis and characterization of the biodegradable copolymers from succinic acid and adipic acid with 1,4-butanediol. J Appl Polym Sci 82 2808-2826... 

Figure 4.3 Biodegradability of Copolyesters from Butanediol (B), Succinic acid (S), and Adipic acid (A) (30) Numbers refer to the monomer content in mol-%.

To produce a terephtalate adipate copolyester, dimethyl terephthalate, adipic acid, 1,4-butanediol, and glycerol are mixed together with tetrabutyl orthotitanate as a catalyst (44). The reaction mixture is then heated to a temperature of 180°C for 6 h and at 240°C. The excess dihydroxy compound can be removed by distillation in vacuo. Then hexamethylene diisocyanate is slowly added to the mixture. The diisocyanate act as chain extenders. From this material, a biodegradable polyester film can be produced. In addition, the s mtheses of related copolyesters have been described in detail (45). It has been found that the addition of chalk can achieve an additional improvement in the biodegradability. 

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. 

The master batches were then blended with a variety of biodegradable materials. As usual, the biodegradable materials are chosen from commercial available brands of PLA, PCL or other suitable polyesters made from adipic acid, succinic acid, butanediol and a small amoimt of terephthalic acid (17). 

Poly(butylene succinate-co-adipate)/PLA Blends Poly(butylene succinate adipate), poly(butylene succinate-co-adipate), or poly(butylene succinate-co-butyl-ene adipate) (PBSA) is a random aliphatic copolyester comprised of 1,4-butanediol, succinic acid, and adipic acid [157]. PBSA has lower thermal properties (Tg of —45°C, Tc of 50-53°C, I m of 93-95°C, crystallinity of 20-35%, and HDT at 0.45 MPa of 69°C), more flexibility (tensile strength of 34 7 MPa, tensile elongation of 400-900%, and flexural modulus of 323-340 MPa), and a faster biodegradation rate than PBS [142, 157]. PBSA/PLA blends are immiscible, and a complicated cocontinuous phase (domains of the other polymers dispersed in each continuous phase) was observed... 

Etylene glycol/adipic acid and 1,4-butanediol/succinic acid were copolymerized in the presence of 1,2-butanediol and 1,2-decanediol to produce etl rl and n-octyl branched poly(ethylene adipate) (PEA) and poly(butylene succinate) (PBS), respectivefy [77]. The modified Strum test showed that the two polymers were assimilated to CO2 at a similar rate. As the degree of chain branching increased, the biodegradation rate of PEA increased to a greater extent than that of PBS due to the faster reduction in the crystallinity of PEA compared to the crystallinity of PBS. 

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