Biodegradable additives
Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product.
[2] Good biodegradable additives expedite the rate of degradation by reducing the strength of certain properties of the polymers and increasing their attractiveness to microorganisms.
For example, Brevibacillus borstelensis, Rhodococcus rubber, Pseudomonas chlororaphis, and Comamonas acidovorans TB-35 have all been shown experimentally to use direct action to consume polyethylene.
[5] Once hydrolysis or oxidation occurs, the microorganisms can act directly on the lower molecular weight products and utilize the carbon in these fragments as a source of energy.
[citation needed] Common enzymes involved in microbial plastic biodegradation include lipase, proteinase K, pronase, and hydrogenase, among others.
Common electron acceptors used by anaerobic bacteria are sulfate, iron, nitrate, manganese and carbon dioxide.
[5] The presence of a continuous starch phase allows direct consumption of the plastic by microorganisms because the material becomes more hydrophilic.
Cornplast, produced by the National Corn Grower Association (USA), is a specific starch additive that can be used to increase the biodegradability of synthetic polyethylene.
50%-50% by weight blends of Cornplast with both LDPE and HDPE have been studied to determine the effectiveness of starch as a biodegradable additive.
This strain of bacteria can grow in both marine and terrestrial conditions and is able to use a variety of sugars, hydrocarbons, and carboxylic acids as nutritional sources.
Geobacillus thermoleovorans successfully attaches to the surface of poly(lactic acid), and experiments show that this colonization will increase the rate of microbial degradation of the plastic.
[9] Pro-oxidant additives increase the rate of both thermo-oxidation and photo-oxidation, resulting in a larger amount of low molecular extractable compounds.
[10] Microbial strains can then efficiently attack the carbon in these low molecular weight fragments of the large chain polymers.
Polyethylene is a very common polymer used in many everyday plastic products, such as water bottles, grocery bags, and drain pipes.
Fe complexes increase the rate of photooxidation by providing a source of radicals for the initiation step in the process of creating smaller molecular weight fragments.
[11] The use of such OXO-biodegradation additives was banned in the EU in 2019[12] due to concerns that treated plastics do not fully biodegrade and instead result in the accelerated formation of microplastics.
[14] Some important physical properties that can be measured experimentally are tensile strength, molecular weight, elasticity, and crystallinity.
Measuring the physical appearance of the plastic before and after potential microbial biodegradation can also provide insight into the efficacy of the degradation.
[8] Another way to determine the efficacy of biodegradation is by measuring the amount of carbon dioxide and/or methane produced by the microorganisms that are degrading the plastic.
Typically, samples are buried in biologically active soil for six months and are exposed to air to ensure that there is sufficient oxygen so that the aerobic mechanism of degradation can occur.
Burning plastics leads to significant amounts of air pollution, which is harmful to human and animal health.
