Compostability Norms

Because of the complex nature of many biodegradable materials such as plastics or packaging and also because of several aspects related to the composting process and to 

1) Biodegradation the complete breakdown to mineral endproducts (carbon dioxide, water) and biomass. This can be situated at the chemical, molecular level of a given test material and is therefore an inherent material characteristic. The physical form of the test material is irrelevant. 

2) Disintegration the degradation on a visual, physical level. The test item must physically fall apart and disintegrate into invisible particles. The physical form of the test item is essential and typically materials will be approved until a certain thickness (plastics) or a certain weight per surface (paper materials). 

3) Compost quality may not be negatively influenced by the addition of a biodegradable material. 

Several compostability norms have been developed in different standardisation committees but in all norms these three basic requirements can be found back as the principal rationale. In some standards a fourth requirement has been added, saying that the addition of a compostable product may not hinder the normal operation of the composting process. Yet, a precise method or procedure to evaluate and approve this is missing. 

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Most norms and standards are dealing with a testing procedure, e.g., measurement of biodegradation by following a certain parameter in a given environment. In such cases, the main purpose of the norm is to harmonise test conditions, e.g., temperature, nutrients, pH, concentration of test substance, concentration of inoculum, etc. Some norms however are related to required properties for a certain characteristic and the necessary criteria and pass levels. Typical examples are the compostability norms, which comprise several aspects for which each specific criteria and pass levels are defined. 

There are a certain number of norms in existence, such as the American norm ASTM D-5488-94d, or the European harmoiuzed standard EN 13432, giving defiiutions for terms such as biodegradable, compostable and others which are widely used - and sometimes incorrectly - as an argument in favor of the use of so-called enviromnentally friendly materials. 

While the incubation medium is no longer soil, but compost, the teehnique is similar to that which we have just described, with some differences (Figure 14.13). The method recommended in the norm is in fact only an adaptation of the open-circuit Sturm test. Just like the Stiinn test, this system can be entirely automated (Figure 14.14). In this case, the costs are much greater. (It costs at least 60,000 for a battery with 12 units allowing the testing of 2 samples at the same time = 3 controls + 3 cellnloses + 3 samples 1+3 samples 2). 

The terms compostable and compostability are not defined in many dictionaries, but can be found in technical norms, particularly in Europe (NF EN 13432). This world recognized European standard defines the conditions that must be satisfied for a packaging (according to the European directive 94/62/CE) to be declared compostable under industrial conditions. 

No, we must always specify the compostability conditions, i.e. by saying my product is compostable according to norm NF EN 13432 or even my product complies with norm NF EN 13432 and can be declared biodegradable by composting imder industrial conditions or even by consulting a known mark of conformity that refers to the same norms ad hoc. 

In composting, 12-week tests proposed by the norms do not sahsfy many composting industrialists working with methods that can obtain compost after only four weeks. Current studies are also trying to hmit the dtrrahon of the tests. 

DIN 54900,1998, Testing of the compostability of polymeric materials. Entwurf Deutsche Norm DIN 54900. Deutsches Institut fur Normung e.V. (DIN), Berlin, Gomany. 

The noncompliance of these products with the international norms of biodegradability and compostability, however, prevented significant market growth in Western countries. 

According to these standard norms, a compostable plastic demonstrates a satisfactory rate of biodegradation when achieving 90% of the organic carbon in the whole item or for each organic constituent, which is present in the material at a concentration of more than 1 wt% (by diy mass), and is converted to carbon dioxide by the end of the test period when compared to a positive control. 

The temperature had to be kept below 230°C to prevent decomposition of the starch, and exposure of the master batch to air had to be minimized to avoid water absorption. Direct addition of starch and autoxidant withont the master batch step can also be used as this requires some specific equipment, it is only practical for large volumes (42). It was claimed that under appropriate conditions, the disintegration time of a buried carrier bag, containing an Ecostar additive to reach 6% starch, will be reduced from himdreds of years to 3-6 years (38). However there is no evidence of a compliance of such materials with the norms of biodegradability and compostability already in place at the international level. Moreover, the destabilization of polyethylene indneed by the pro-oxidants may significantly affect its in-use performance as a function of time. 

In Europe, compostable plastics are being used in several applications. Compostable plastics must comply with the International Norm... 

The development of national and international norms on biodegradability proved not to be an easy task as it necessitated the bringing together of biological processes (e.g., composting) in all their complexity, on the one hand, and polymer chemistry on the other. Yet, over the last 20 years significant progress has been made and several standards and norms have been developed and will be further elaborated. 

By the end of the 1990s, when standards and criteria were in place, the first certification systems for compostahility were also started (e.g., OK Compost, seedling logo). Throngh these systems, a third party polices the correct use of the above norms, which shonld facilitate the market introduction of biodegradable materials even further. 

Principle The test item is placed into an aqueous mineral medimn, spiked with inoculum and incubated under batch conditions (this is a single, one-shot feeding). The inoculum can be either activated sewage sludge, compost eluate, soil eluate or a combination of 2 or 3 of these. The duration of the test is not really specified. The test should be run until a plateau in activity is reached. In practice, a minimum duration is typically 4 weeks. The maximum duration, in contrast, is defined precisely in the norm and is 6 months. 

Besides norms for tests in which the biodegradation is measured directly by quantifying CO2 production or O2 consumption, some exposure tests have also been standardised, e.g., ASTM D5509-96 and ASTM D5512-96. In these tests, plastic test items are exposed to composting conditions which are precisely defined. After a certain period of incubation a loss of property is measured, such as weight, MW, tensile strength, tear resistance and so on. It may be clear that these parameters are only secondary... 

For biodegradable polymers (industrial), composting was the first environmental process for which specifications were developed. In the nineties, two parallel developments took place in Europe, resulting in the publication of DIN V 54900 in 1998 and EN 13432 in 2000. In spite of some minor differences, both norms were largely similar. After a few years, the DIN norm was made redundant as several international norms (EN and ISO) dealt with the same issue. In addition, in North America a norm was published in 1999 on specifications for (industrial) compostability ASTM D6400. On a global level, ISO 17088 in the field of plastics was published in 2008, while a similar norm for packaging is close to publication and now available under the form of a Draft International Standard (DIS), ISO DIS 18606. 

An overview of the different standards on specifications for industrial compostability is given in Table 5.2. Overall, there is a large similarity between these various norms. Differences are relatively small and mostly limited to minor details. 

The norms of compostability specifications can be considered as umbrella norms in which various necessary characteristics are summarised, along with the test methods on how to check these and the necessary pass levels to be met. An overview of the main characteristics is given in Figure 5.7. Two main characteristics are related to environmental safety, which in the case of composting falls back to compost quality chemical analyses and ecotoxicity. Two other characteristics are related to degradation biodegradation and disintegration. 

OK Compost is based on EN 13432 and also uses an additional certification scheme for further interpretation and use of the norm. The procedure for application is similar to that of the seedling logo. Testing must be performed at recognised laboratories. Approved products can carry the OK Compost logo (Figure 5.9), with a mmiber. 

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