ASTM GUIDANCE ON COMPOSTABILTY OF PLASTICS  
  IN 1991, 15 industry organizations involved in the manufacture and use of environmentally degradable polymers formed and funded the Degradable Polymeric Materials Program as part of the American Society for Testing and Materials' (ASTM) Institute for Standards Research. A primary objective of the program was "to determine the behavior of degradable polymeric materials in real disposal systems, and how those results correlate with laboratory results, in order to assure that such materials are safe for disposal and effectively degraded." After five years of testing, the Standard Guide to Assess the Compostability of Environmentally Degradable Plastics was is sued in October, 1996, along with a final report, a compilation of compost test reports and a compost biblio graphic database with more than 6,500 abstracts and references.

The guide (known as D 6002) advocates a three tiered strategy that cornbines rapid screening tests (Tier 1) with laboratory and pilot-scale composting assessments (Tier 2) and a field/fullscale assessment (Tier 3). The objective was to progress from a lower cost, rapid screening of polymeric materials and other organic components to relatively long term, more complex and higher cost evaluations.

For example, after screening (Tier 1) with one of several suggested procedures to "determine whether biodegradation of polymeric materials and other organic components in the plastic product can occur," Tier 2 methods are designed to establish a degradation rate for the material under lab scale thermophilic composting conditions and evaluate the resulting compost for environmental safety. Steps that should be taken to provide confirmation of compostablility in a full scale operation or in the backyard (Tier 3) follow.

"Comparing the results obtained for the same material at each tier shows that for all materials compared, without exception, the degradation results obtained in a higher-level test equaled or exceeded those obtained in a lower level test," reports ASTM. "This observation has important ramifications with regard to environmental claims based upon laboratory and pilot tests. In order to provide valid and useful information, a full-scale test must be very well planned and executed, while the logistics of conducting a test at that scale can be extremely difficult. Furthermore,the full scale information cannot stand alone, but must be supported by Tier 2 results. On the other hand, the fullscale test might not provide any further knowledge on the performance of a material than the laboratory and pilot tests together developed. The fullscale tests can, however, provide verification of results obtained at Tier 2."

Other conclusions drawn from the ASTM/ISR work include the "overriding observation" that temperature and duration are of primary importance to testing. Additionally, the report concludes that "the three major parameters of compostability‹mineralization, weight loss and disintegration‹ are not identical and the results sometimes diverge. Care must be taken in comparing these, and in establishing compostability." Details of test methodologies for all three tier levels are provided in the guide, including objectives and a summary which presents potential test methods, method principles, test duration, implication of results and suggested priority. The reports and database are available from ASTM/ISR, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. (610) 832-9585. Email: amoklind@astm.org.