Degradation under Composting Conditions

In 1998, BASF AG (Ludwigshafen, Germany) presented a respirometric measurement of the copolyester Ecoflex (approximately 45 mol% of terephthalic acid in the acid component), showing that this material was more than 90% metabolised in compost within three months [91]. 

Two of the most active strains were identified and belong both to the genus Thermobifida and are consistent with the Thermobifida fusca taxon. 

A copolyester depolymerising extracellular enzyme was isolated and characterised from the strain Thermobifida fusca DSM 43793. The enzyme exhibits a homology of 65% with a triacylglycerol-lipase from Streptomyces sp. (strain Mil) [94], has a molar mass of approximately 27,000 D and an optimal temperature for hydrolysing BTA-copolyesters of about 60 °C. The identification of the enzyme having a lipaselike structure is in accordance with the observation that many lipases are able to attack polyesters [2, 86, 95] and are probably also predominantly responsible for the microbial induced depolymerisation of synthetic polyesters in nature. 

With this thermophilic actinomycete strain it was possible to investigate the degradation behaviour of BTA-copolyesters very accurately over a timescale of a few weeks [66], and using the enzyme, the hydrolysis of BTA-copolyesters could be measured within less than 24 h [93]. 

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The biodegradation of Ecoflex film was tested under composting conditions. After 100 days in a composting environment more than 90% of the carbon in the polymer was converted to carbon dioxide. Tests also showed no toxic effects of degradation intermediates. 

Degradation of Eastar Bio was tested under composting conditions after 210 days of composting about 80% of the polymer carbon was released as carbon dioxide. 

DuPont s Biomax product is a standard PET with the addition of three aliphatic monomers to allow degradation to take place. Comparable to PLA, the degradation mechanism is described as an initial attack of water to the special monomers, which are sensitive to hydrolysis. Although it appears that Biomax sufficiently disintegrates under composting conditions, the process of decomposition of the material was too slow to meet accepted standards. 

Benoit and Barriuso (1997) carried out experiments to study the transformation of C-ring-labeled 2,4-D, 4-chlorophenol (4-CP) and 2,4-dichlorophenol (4-DCP) during straw composting under controlled laboratory conditions. Incubation under sterile and nonsterile conditions was done to evaluate the relative importance of the biotic and abiotic processes. Precomposted straw was treated with three chemicals and the availability of the different chemicals was monitored during incubations as well as their degradation. Under nonsterile conditions, Benoit and Barriuso (1997) observed that the mineralization of both chlorophenols reached 20% of the applied... 

Kim Y, Kim S. Effect of chemical structure on the biodegradation of polyurethanes under composting conditions. Polym Degrad Stab 1998 62 343-52. 

PLA Poly(lactic acid) commercial bottles and deh containers Composting under real conditions (compost pile temp. 65°C moisture 63%, pH 8.5) visual inspection molecular weight changes (GPC method) glass transition and melting temperature (DSC method) decomposition temperature (TGA method). Degradation of PLA containers <30 days under composting conditions [26]... 

However, although it seems that Biomax sufficiently disintegrates under composting conditions [100], the final metabolisation of the material in a reasonable time scale is still under discussion. The producer itself admits that Biomax in the current formulation (June 2000) does not degrade fast enough to meet the accepted standards and thus, will improve the material with regard to its biodegradability [101]. 

A t5 ical degradation of PLA under composting conditions is shown in Fig. 10.11 (Baiardo et al, 2003). For a product of at least 1mm thickness, degradation is faster inside than at the surface because of diffusion-reaction... 

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