DISINTEGRATION 2023
In 2023, there were some major changes to the ISO 20200 method that will have an effect on future testing. The ISO 16929: 2021 method is the pilot-scale industrial composting process and this method was the preferred method for testing plastic disintegration. The reason it was preferred was that it emulated the industrial scale more accurately than ISO 20200 - a lab scale method. Table 1 shows the differences between ISO 20200 and ISO 16929.
* As compared to a material performing in an industrial compost facility
** The thermo can be two temperatures (58ºC and 45ºC)
ISO 16929: 2021
The ISO 16929 test is conducted in large rotating barrels that can agitate the compost (slowly) and can allow a large volume of compost to be taken through effectively an industrial compost. It relies on the compost self-heating (as it would in industrial composting). The gases in and out of the reactor are measured and controlled - there must be plenty of oxygen going in and the CO2 and ammonia coming out must be kept within the standard’s specified thresholds.
The moisture of the compost within the reactor must be held at 55% to ensure that the microbiology has enough water to continue the fermentation process. If the compost dries out the temperature plummets and an external heat source must be applied - this can often dry the compost out and the scientists are constantly fighting moisture and temperature. The result is that whilst this emulates industry closely, the scientific measurement (and certification) can be impaired by bad luck and “playing catch-up” by the test laboratory. Results sent back from ISO 16929 testing will show that there is a high margin of error on a test that means well, but falls short in being a valuable part of the testing regime. The test could be significantly improved by insisting that the temperature in the reactors be computer monitored and controlled (to ensure a heating pattern that is modelled from current industry practice).
Compost in industrial facilities always follow the following regime:
1) First mesophilic phase (20-40ºC) - limited microbial activity
2) Thermophilic phase (55-75ºC) - intensive decomposition, oxygen limited
3) Cooling phase (40-75ºC) - stabilisation. Compost moves from immature to fresh.
4) Second mesophilic phase (25-45ºC) - maturation. Compost moves from fresh to mature.
ISO 20200
ISO 20200 does not have an initial mesophilic phase as the shoebox sized reactors are placed into incubators (set at 58ºC) and reach that temperature even at the start. The abiotic component of the composting is evident even from the start. The 2015 version of the test then stayed at that high temperature for the full 90 days. Some would argue that this has made the ISO 20200 more intensive, albeit reproducible, because the temperature continuity is stable across the test duration. The ISO 16929 temperature profile fluctuates if not monitored closely making a result from the test laboratory have a high variance.
In 2023, the technical committee reviewing ISO 20200 decided that a constant temperature from the start to finish was not in the best interest of having a disintegration test that accurately simulated industrial processing. The old 90-day method is still available, known as Type 1 method; whilst a new Type 2 method is introduced where a two-stage incubation is used. The two-stage method allows the test to proceed as per Type 1 (58ºC) for 56 days and then the test enters a cooling phase as seen in the regime laid out above - for 84 days in total.
The change, offering a Type 2 mode, means that most test laboratories would go for the shorter (more sustainable) option. Sustainable, in the sense that the test uses less electricity - a definite theme in the improvement of ISO test methods - see if they can be shorter and have less environmental footprint. The difference between Type 1 and Type 2 is not noticeable in the results that laboratories are seeing, justifying the change, and helping lab managers realise how wasteful a Type 1 regime is.
The reproducibility of the ISO 20200 test is unequivocal, the constant temperature that does not rely on temperamental microbiology or natural forces that give rise to heating variance make it the better choice between ISO 16929 and ISO 20200. Compost specifications like EN 13432 and EN 14995 do not permit ISO 20200 as a disintegration choice (there are 4 other criteria beyond disintegration in this specification) - claiming that the lab-scale method does not simulate full-scale processing. The 2023 changes may mean that it will start to be recognised as an equivalent standard. Laboratories that offer modifications to the EN 14995 specifications, allowing leather to be in scope, had always permitted ISO 20200 as an option, recognising that it was a cheaper, more reproducible method. Cheaper, in that ISO 16929 is 6 times more expensive than ISO 20200, usually.
Where to next?
ASTM D6400-23 and ISO 17088: 2021 have permitted the use of ISO 20200 or ISO 16929 for several years now, and it is hoped that EN 13432 and EN 14995 will follow suit in light of the 2023 changes to ISO 20200.
EN 13432 is recognised by European Bioplastics as their composting standard and working with major test laboratories/certifiers, they are forcing all materials to go through this testing regime - regardless of whether the material is destined for packaging or not. Pedants have been beside themselves, pointing out that plastics, leather, and other biomaterials, used in products like shoes, are not within the scope of EN 13432 and the seedling logo (see Figure 2), should not be used on shoe materials if certified against EN 13432.
EN 14995, ASTM D6400, and ISO 17088 are all certification specifications for composting plastics that do not include non-plastic materials within their scope. It is hoped that standards technical committees will be producing identical specifications that have broader scopes that allow laboratories to certify these materials for composting schemes. The first step is getting the acceptance of ISO 20200 in the current compost certifications, and this has begun.
In the next issue: Net zero leather - making leather (and shoes) will emit carbon. But, can the emissions be counteracted by carbon sinking activities in the supply chain? Off-setting and in-setting will be compared and what tanneries and leather supply chains can do to bring in carbon negative inputs to ensure that their overall impact is zero.
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