Compost degradation tests

In Europe, there is currently no standard test method [41 -43 ]. The technical committee 261, which has been operating since 1991, is setting up the standardization of bio degradability testing methods in the field of packaging and the environment. The European Committee of Normalization (ECN) has written a draft about the evaluation of the ultimate bio degradability under controlled composting conditions (Table 2). Other tests are in preparation in different environmental conditions aerobic and anaerobic environment, freshwater, etc. 

In this context, numerous hydrolytic degradation tests have been performed on PLA to simulate its degradation process in the human body (T 37 and in natural media as soil or compost (25 °C < T< 58 °C) , all reporting that PLA can be hydrolyzed to give low-molecular-weight water-soluble oligomers. 

While the reduced enzymatic susceptibility of the aromatic ester bonds is caused by the interaction of the long chains in the polymer, the chain length itself has no direct influence on the biodegradability above a minimum molar mass. Tests with copolyesters from terephthalic acid, adipic acid and 1,4-butanediol, which were chain extended with hexamethylene-diisocyanate, did not result in a decrease in the biological degradation rate (in a compost simulation test), although the molar mass of the prepolyesters of about 48,000 D was increased to 232,000 D by the chain extension [85]. 

Degradation results obtained in a compost environment at elevated temperatures or in soil differ significantly from those determined in a liquid system. In liquid media the degradation rate is usually much slower for the copolyesters. Besides the lower temperature, which is in most cases at ambient temperature, a different microbial population may be responsible for the differences. In degradation tests in liquid environment, the inoculum to provide microbial activity is often taken from sewage sludge. Although in some cases eluates from soil or compost are used to inoculate the media, a liquid environment is not optimal to... 

Starch mixed with polyethene is also known as biobased (hydrodegradable) material and reaches the American Standards for Testing Materials as well as the European norms for compostability degrading in 60% under 180 days. 

The maximum material gauge of a plastic is determined by its compostability in standard practice composting operations. AU tests must be passed. Success in individual tests will not be sufficient The EN standard test methods are based on the scientific definitions of the ISO standards 14851 [26], 14852 [24] (aerobic degradability in water), 14853 [27] (anaerobic degradability in water), and 14855 [5] (aerobic composting). The tests must be conducted by recognized test laboratories. 

Table 1 Fragments of Ecoflex after degradation with isolated pure strain (Tests 1-3) and with pure and mixed cultures from compost...

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. 

---