Compostability of Biodegradable Plastics

With contributions by H. J. Endres and A, Siebert-Raths, Institute for Bioplastics and Biocomposites, University of Applied Sciences Hannover, Germany [281] 

There are numerous national, European, and international standards defining compostability of biodegradable plastic materials and/or products manufactured using these materials (e.g., packaging). To provide an easier overview, the relevant standards for biopolymers are subdivided into two categories (see Table 2.20)  

Ta b I e 2.20 Overview of Relevant Standards Regarding Compostability of Biodegradable Plastics (for detailed titles of these standards, see Section 2.7.1.6) 

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Biowaste can also be home composted in smaller installations. Biodegradability reqnirements for plastics nnder home composting conditions are defined by Italian standards UNI 11183 [9] and UNI 11355 [10], which regulate the home composting of biodegradable plastic materials and articles. 

UNI 11355, Home Composting of Biodegradable Plastic Items -Requirements and Test Methods, Ente Nazionale Italiano di Unificazione, Italy, 2010. 

The compostability of biodegradable plastics should not encourage irresponsible behaviour leading to litter. Instead, improved awareness and education on proper use and disposal should be promoted. 

These test metho ds, and especially liquid medium tests, are considered as accelerated tests and do not necessarily correlate with the real exposition conditions of biodegradable plastics. Most representative tests are compost tests but they are more difficult to set up (especially when they use labeled material). It is necessary to assess the representativeness of these tests, especially liquid medium ones, in real-life conditions. 

In the waste disposal area, the environmental benefits of biodegradable plastics are limited to waste streams that will be composted, items that are associated with litter problems, and items that are apt to get into sewage treatment systems. If wastes will be disposed by landfill or incineration, biodegradability offers no real advantage. 

Compost worms (Eisenia fetidd) are used for testing the toxicity of biodegradable plastic residues. These worms are very sensitive to metals such as tin, zinc, heavy metals and high acidity. The results are expressed as LC50 (see Table 7.5). 

The performance of biodegradable plastics in composting facilities and under laboratory conditions has been studied by ISR. ISR has determined that plastics need to meet the following three criteria in order to be compostable ... 

Biodegradation is an important feature of biodegradable plastics. Two essential components of the biodegradation process are that the material must be a food source for the bacteria in the disposal environment and that the biodegradation must take place within a short time period, typically 6 months. Therefore, biodegradation can occur in an industrial compost environment for biodegradable plastics if they are used as food source for the bacteria in the compost and that they are... 

Compostability of a plastic article is verified by assessing four characteristics inherent material biodegradability, disintegrability of the article, absence of negative effects on the composting process and the absence of ecotoxic effects of the compost obtained from a feedstock that includes the plastic. 

Nakasaki, K. Degradability of Biodegradable Plastic Under Controlled Composting Conditions, Macromolecular Symposia, 135 (1998), p. 215-221... 

Gillis RJ, Gillis JR (1996) A comparative study of bacterial attachment to high-purity water system surfaces. Ultrapure Water 9 27—36 Gilmore DF, Antoun S, Lenz RW, Goodwin S, Austin R, Fuller RC (1992) The fate of biodegradable plastics in municipal leaf compost. J Indust Microbiol... 

These observations may have some significance for the biological treatment of biodegradable plastics, as anaerobic digestion becomes more and more established beside aerobic composting. It cannot be supposed that synthetic polyesters will be significantly... 

In the first years of the existence of biodegradable plastics, it became clear that the aerobic, aquatic biodegradation tests were not appropriate to evaluate the biodegradation of these polymers in composting. The environmental conditions are of course very different high temperatures up to 60-65 °C in composting as opposed to ambient temperature in water, different moisture content, etc. An important difference is also the activity... 

What about the public administrators, the legislators, the politicians Since public health and food production could be affected by a massive application of biodegradable plastics in compost, the public administrators indubitably prefer any option increasing safety rather than decreasing it. This is particularly true after the recent case of the Mad Cow disease and the presence of dioxins in chickens. Summarizing very low heavy metals content, no ecotoxic effects, no plastic residues, visible or invisible, brought in the field together with compost. 

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