Biodegradable additives

Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain itself.

Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene, polypropylene, polystyrene or polyethylene terephthalate.

Testing methods of biodegradable additives

ASTM D5511-12 testing is for the "Anerobic Biodegradation of Plastic Materials in a High Solids Environment Under High-Solids Anaerobic-Digestion Conditions"[1]

ASTM D5526-12 testing is for the "Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under Accelerated Landfill Conditions"[2]

ASTM D5210-07 testing is for the "Standard Test Method for Determining the Anaerobic Biodegradation of Plastic Materials in the Presence of Municipal Sewage Sludge"[3]

Laboratories performing ASTM testing methods

Biodegradation process of biodegradable additives

A simple chemical equation of the process is:

C6H12O6 → 3CO2 + 3CH4

Interpretation of this process is as follows - In most cases, plastic is made up of hydrophobic polymers. Chains must be broken down into constituent parts for the energy potential to be used by microorganisms. These constituent parts, or monomers, are readily available to other bacteria. The process of breaking these chains and dissolving the smaller molecules into solution is called hydrolysis. Therefore, hydrolysis of these high-molecular-weight polymeric components is the necessary first step in anaerobic biodegradation. Through hydrolysis, the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids.

Acetate and hydrogen produced in the first stages can be used directly by methanogens. Other molecules, such as volatile fatty acids (VFAs) with a chain length greater than that of acetate must first be catabolised into compounds that can be directly used by methanogens.

The biological process of acidogenesis results in further breakdown of the remaining components by acidogenic (fermentative) bacteria. Here, VFAs are created, along with ammonia, carbon dioxide, and hydrogen sulfide, as well as other byproducts. The process of acidogenesis is similar to the way milk sours.

The third stage of anaerobic digestion is acetogenesis. Simple molecules created through the acidogenesis phase are further digested by Acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.

The terminal stage of anaerobic biodegradation is the biological process of methanogenesis. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the biogas emitted. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.[4]

Biodegradable additive manufacturers

References

  1. ↑ "ASTM D5511-12". ASTM International. Retrieved 2012-06-30.
  2. ↑ "ASTM D5526-12". ASTM International. Retrieved 2012-06-30.
  3. ↑ "ASTM D5210-07". ASTM International. Retrieved 2012-06-30.
  4. ↑ "Biodegradable Plastic by Additives". BioSphere Biodegradable Plastic. Retrieved 2012-08-30.
  5. ↑ "Biodegradable Plastic from BioSphere". BioSphere Biodegradable Plastic. Retrieved 2012-08-30.
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