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Standard Guide for Exposing and Testing Plastics that Degrade in the Environment by a Combination
The American Society for Testing and Materials (ASTM International) acknowledges the oxo-biodegradable technology in ASTM D 6954 C04. This is a standard guide specifically developed for plastics that degrade initially by an oxidative process and subsequently biodegrade. D 6954 prescribes the tests to be done in order to rate these materials in terms of their ability to degrade, biodegrade and to assess their eco-toxicity impact to the environment of disposal.
The ASTM6954 guide provides a framework or a road map to compare and rank the controlled laboratory rate and degree of physical property losses of polymers by thermal and photo oxidation processes and biodegradation, and ecological impacts after degradation in defined applications and disposal environments. Disposal environments range from exposure in soil, landfill, and compost where thermal oxidation may occur, and to land cover and agricultural use where photo-oxidation may also occur.
This standard guide uses established ASTM standards in three tiers
Tier1: for accelerating and measuring the loss in properties and molecular weight by both thermal and photo-oxidation processes, and other abiotic processes;
Tier2: for measuring biodegradation;
Tier3: to assess ecological impact of the products from these processes;
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The Tier 1 conditions selected for thermal oxidation accelerate the degradation likely to occur in a chosen application and disposal environment. The conditions should include a range of humidity or water concentrations based on the application and disposal environment in mind. The measured rate of degradation at typical oxidation temperatures is required in order to compare and rank the polymers being evaluated in that chosen application to reach a molecular weight that constitutes a demonstrable. By way of example, accelerated oxidation data must be obtained at temperatures and humidity ranges typical in that chosen application and disposal environment, e.g. in soil (20C to 30C), landfill, 20C to 35C) and composting facilities (30C to 65C). For applications in soils, local temperatures and humidity ranges must be considered as they vary widely with geography. At least one temperature must be reasonably close to the end use temperature, but under no circumstances should this be more than 20C. It must, also, be established that the polymer does not undergo a phase change, such as glass transition temperature (Tg). The residues resulting from the oxidations are then exposed to appropriate disposal or use environments in standard biometric test methods to measure the rate and degree of biodegradation (Tier 2). The data generated under Tier 1 evaluation and the determined time for the biodegradation in the chosen environment (Tier 2) allows ranking relative to other polymers evaluated under similar environmental conditions with this guide. The degree and time for biodegradation should be consistent with ASTM methods and any residues from the intermediate oxidation stage and from biodegradation must be shown to be environmentally benign and not persistent (Tier 3).
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