Bio-degradability

Green Issues: Bio-degradation, Plastic Waste  & Polymers

From the development of the very first polymeric materials, engineers and other scientists have striven to improve the stability of these materials regarding their versatile environmental influences. The result has been the use of polymeric materials or simply plastics in every section of life as highly durable products containing tailor-made properties.

Nevertheless, over the last ten years, the extensive use of polymeric material together with their huge stability has resulted into serious problems concerning plastic waste particularly in plastic packaging. The waste management strategies such as incineration, landfill and plastic recycling have not been sufficient, are controversial among both the public and scientists.

As a result, a massive campaign has been underway since early 90s, for scientists to create novel plastics that have the same abilities of controversial polymers but are subject to microbial biodegradation.

General definition and mechanism of biodegradation

testing polymers

In general, the term biodegradable plastics refer to a microorganism attack on non-water soluble polymeric materials. Due to the size of polymer molecules, and the lack of water solubility, microorganisms fail to carry the plastics directly to their cells, which is where most of the process of biodegradation takes place.

Instead, the microorganisms must first excrete certain types of enzymes to depolymerize the plastics outside their cells. Consequently, if the polymers’ molar mass is reduced sufficiently to produce water-soluble intermediates, they can be carried to the microorganisms then fed to a suitable metabolic pathway.

The products of this process are water, carbon dioxide, and in the case of anaerobic degradation, methane. Since the extracellular enzymes are too big to deeply penetrate into the plastics, biodegradation normally occurs in the surface only. The main process of biodegradation is the enzyme-catalyzed chain-length reduction of plastics.

Nevertheless, non-biotic physical and chemical processes can as well act on the plastic as a first stage or parallel to the process. Some of the non-biotic effects are thermal polymer degradation, oxidation and chemical hydrolysis.

Testing methods

Testing techniques to determine the biological actions on manufactured materials have existed for many decades as well as for different categories of materials. These days, as a vital element of ecological impact of compounds, evaluation of degradability of chemicals present in the environment particularly in waste water has become crucial in trying to introduce a new product to a marketplace. Due to this fact, scientists have developed various standardized tests for varying environments, and with different analytical techniques.

Long before the development of biodegradable polymers, scientists had established test techniques for the evaluation of microorganism influence on polymers. Even though conventional polymers are resistant to environmental influences, there are instances, where microorganisms will attack the polymers and lead to undesired alterations the properties of the material such as flexibility or color.

Even though a broad range of biodegradation tests are already in place, it was essential to come up with special test techniques when it comes to biodegradable polymers. Scientists based these tests primarily on principles in use for evaluation of low molecular-weight substances.

General testing principles of biodegradable plastics

Bio-degradation

When determining the degradation phenomena of polymers in the environment, a general problem occurs regarding the type of tests scientists should apply and the conclusions to draw. Principally, scientists subdivide the tests into three main classes, which are field tests, laboratory tests and simulation tests.

Filed tests include things such as placing the plastic sample in a lake or river, burying it in the soil and a composting process. Even though this presents the ideal environmental conditions, it has various significant disadvantages. For instance, the conditions in the environment such as pH, temperature and humidity cannot be controlled. Additionally, scientists will be limited in their ability to monitor the degradation process.

Hence, scientists use simulation tests in labs as an alternative to field tests. In this case, the degradation process takes place in soil, compost or water, contained in a control reactor within the lab. Even though the environmental conditions are close to those of the field tests, the scientists can control and adjust the external factors such as temperature, humidity and pH.

Additionally, they have better analytical tools than they would in a field test. In some cases, scientists add nutrients to heighten the microbial activity to accelerate degradation for the purpose of cutting short the period of conducting tests.

Featured images:
  •  License: Creative Commons image source
  •  License: Royalty Free or iStock source: http://pixabay.com/en/earth-globe-recycling-world-60841/
  •  License: Royalty Free or iStock source: http://pixabay.com/en/green-plants-bio-friendly-42609/

Alex Walden, the author of this post, works for ExcelPlas, experts in polymer testing. In his spare time he likes to paint and is passionate about collecting works of arts by Australian artists.

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