Degradability tests unique

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During the past 15 years, plastic has evolved into the preferred product choice for many packaging applications. During the same time it has also attracted increased scrutiny from consumers and marketers interested in environmentally responsible approaches to plastic packaging applications.

In response to these concerns, manufacturers have developed and employed technologies that evaluate and help reduce the environmental impact of plastic packaging. But within that process, multiple objective testing standards have emerged. So while the goal of confirming improved environmental performance is welcomed by all, unfortunately sorting out the results can become confusing.

Most confusion stems from cross-technology comparisons, in which a set of standards, meant to analyze performance of products developed for one marketplace, are incorrectly applied to plastic products developed for very different applications and from different technologies.

Essentially, environmentally conscience plastics technologies can be categorized into three different approaches: oxidatively biodegradable plastics, hydrolyzed-bio­degradable plastics, and bioplastics.

Recently, there has been a lot of confusion about testing standards and which standard can encompass all plastic bioproducts. Each of these technologies is unique, and comes with its own benefits and preferred applications in the global plastics packaging marketplace. For this reason, there is no one standard that can fully test each type. Depending on the technology being used, certain standards have been developed with specific technologies in mind.

The multiple testing stan-

dards and the technology they test for can be separated as follows:

Oxo-bio standards

* ASTM D-6954 is a standard guide for exposing and testing plastics that degrade in the environment by a combination of oxidation and biodegradation. It follows an oxo-biodegradable plastics' life cycle from creation through degradation, biodegradation and reclamation into the environment. Information obtained from this testing can provide the plastic packaging manufacturer with data to measure the logistical usable life cycle of the finished product, and proof of feasibility for making environmental claims. It also provides a method for choosing the biodegradation test that best matches the desired disposal environment.

* BS-8472 refers to methods for assessing oxo-biodegradation of plastics and of the phytotoxicity of the residues in controlled laboratory conditions.

Hydro-bio standards

* ASTM D-6400 is a standard specification specific to labeling of plastics designed to be aerobically composted in municipal or industrial facilities.

* EN13432 is also an industrial composting specification, but one which tracks requirements for packaging that is recoverable through composting and biodegradation.

Both EN13432 and ASTM D-6400 test methods determine the amount of "new carbon" that is found within the polymer, though since the tests were originally developed, scientists have had to issue a correction factor for carbon isotope analysis as a result of decades of nuclear testing.

Thus, anything that contains surface carbon such as plant byproducts, animal byproducts, and microbial byproducts will exhibit a post-1950 carbon isotope signature. Fossil-fuel carbon, however, will display a pre-1950 carbon isotope signature. And in neither case will the test show if the new carbon is biodegradable; it will only determine the age of the carbon.

Finally, due to requirements that accompany industrial composting conditions, a specific pass/fail limit is imposed on products being tested, even though the wording in EN13432 clearly specifies that: "It is important to recognize that it is not necessary that biodegradation of packaging material or packaging be fully completed by the end of biological treatment in technical plants, but that it can subsequently be completed during the use of the compost produced."

This statement has been the source of some of the confusion surrounding plastic packaging environmental testing results, due to an apparent contradiction to EN13432's pass/fail criteria. These standards also specifically exclude oxo-biodegradable plastics due to the thermal aging testing, or natural aging, which is critical to determining reliable usable life-cycle results.

c ISO17088 contains specifications meant for application only to compostable plastics.

c Standard 4736 is the Australian standard for measuring and rating biodegradable plastics.

Bioplastic standards

ASTM D-6866 contains the standard test methods for determining the bio-based content of solid, liquid, and gaseous samples using radiocarbon analysis.

No 'one standard'

Reliable and appropriate testing methods exist for measuring the environmental impact of plastic packaging, whether utilizing oxo-bio, bioplastic or hydro-bio plastic technologies. There has been widespread confusion that still exists regarding the correct test to measure oxo-bio effectiveness.

This confusion has been exacerbated by the fact that oxo-bio testing standards claim a biodegradation efficiency rate of 60 percent, but without offering a corresponding time frame to achieve that level of degradation.

Within the oxo-bio community, however, this omission is widely understood, because other naturally occurring biodegradable materials — such as leaves, straw and other lignocellulose materials — have been assigned no such timetable either. In fact, though widely revered in scientific circles, if any of these natural biodegradable materials were mistakenly measured against industrial rather than natural composting criteria, they would fail based on industrial-generated pass/fail scoring.

In the end, when applied correctly all testing methods outlined in this article can deliver valuable results in determining whether an end-use product can be biodegradable after joining a microbially rich environment. But it is worth remembering that in the case of industrial composting disposal methods, time is a more critical component. In the case of oxo-bio plastic, similar efficiencies can be achieved within natural, more user-friendly life cycles.

Brandon Atwood is R&D and technical sales director, and Ray Loflin is lab manager for Willow Ridge Plastics Inc. in Erlanger, Ky.