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Degradation of polymers and microplastics

Biologically degradable materials are increasingly used in areas where the durability of products is undesirable after their use phase. Examples are mulch films or vegetable pots in agriculture and forestry or the "litter"-problem of packaging residues or cigarette butts in the environment. Furthermore biologically degradable materials can be recycled under certain conditions by composting them aerobically or by digesting them aerobically together with bio-waste. For this, the harmlessness of the ingredients and the biodegradability of material within he common duration of treatment has to be proven.

In the current discussion about the entry of microplastics into the environment, the degradation of polymers has gained additional importance. In January 2019, the ECHA initiated a restriction on intentional uses of microplastics in products in order to reduce their release to the environment. According to the (draft) ANNEX XV “Restriction Report on Intentionally Added Microplastics” an exemption has been included for microplastic which proved to be biodegradable in ready type tests (OECD 301 series, OECD 310) within 28 days or in enhanced ready type tests within 60 days. Further on, microplastic particles, which achieve 90% of the biodegradation extent relative to a reference material such as microcrystalline cellulose within one of several ISO tests described below, are considered as biodegradable. The ECHA restriction report also refers to higher tier tests under relevant environmental conditions such as OECD 307, OECD 308 or OECD 309 which are considerably more cost intensive.

The requirements for packaging recoverable through composting and plastics are described in the following standards:

DIN EN 13432 (2000-12): Requirements for packaging recoverable through composting and biodegradation. Test scheme and evaluation criteria for the final acceptance of packaging

DIN EN 14045 (2003-06): Evaluation of the disintegration of packaging materials in practical oriented tests under defined composting conditions

DIN EN 14046 (2003-07): Evaluation of the ultimate aerobic biodegradability and disintegration of packaging materials under controlled composting conditions - Method by analysis of released carbon dioxide

DIN EN 14995 (2007-03): Plastics - Evaluation of compostability - Test scheme and specifications.

DIN EN ISO 14851 (2019-07): Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium -- Method by measuring the oxygen demand in a closed respirometer

DIN EN ISO 14852 (2018-12): Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium -- Method by analysis of evolved carbon dioxide

EN ISO 14855-1 (2013-04): Determination of the ultimate aerobic biodegradability and disintegration of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide

DIN EN ISO 19679 (2019-10, draft): Plastics - Determination of aerobic biodegradation of non-floating plastic materials in a seawater/sediment interface - Method by analysis of evolved carbon dioxide

DIN EN ISO 16929 (2020-02): Kunststoffe - Bestimmung des Zersetzungsgrades von Kunststoffmaterialien unter festgelegten Bedingungen der Kompostierung mittels einer Technikumsmaßstab-Prüfung

Hydrotox has been engaged since 1992 on the problem of the degradability of polymers and performs several standardised tests for determining the aerobic and anaerobic degradation in aquatic compartments according to the methods above mentioned. Studies under simulated composting conditions are carried out by co-operation laboratories.

The Hydrotox testing strategy on microplastics consists in applying the ISO 14852 or ISO 18451, which are mainly identical to OECD 301B and OECD 301F, with optional extension of the test duration up to 60 days and the use of microcrystalline cellulose as a reference material and polyethylene as negative material.