What happens to plastic when it degrades?

Types of plastic degradation

The intact polymer has two broad NMR peaks corresponding to polymer chains. But after exposure to sunlight, the material gives only one sharp peak, “like a needle,” says Liang Luo, an organic materials scientist at Huazhong University of Science and Technology in Wuhan, China. This tells us that its molecular composition has changed.  The sharp NMR peak corresponds to the structure of succinic acid, which is formed during the degradation reaction. The process appears to use photooxidative degradation, in which sunlight irradiation breaks down the double- and triple-bonded carbon structure of the polymer.The end of plastic seas?

The postulated degradation mechanism is totally different from the breakdown of other degradable plastics, e.g., by hydrolysis of ester or amide bonds. The mechanism clearly does not occur in the consumer plastics that litter sunny beaches. It is possible that degradation occurs in other conjugated polymer plastics, but the scientists say they need more work to demonstrate the generality of this mechanism.  Ultimately, the work is an exciting example of degradable conjugated polymers that could be valuable for a variety of applications, such as electronics, in the future. Without a doubt, this ‘near-ideal degradation of plastic’ is a breakthrough in the field.

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Degradation of plastics by microorganisms

From a chemical point of view, it would not be possible to distinguish a petroleum-derived plastic from one produced from biomass, but the uneven distribution of carbon isotopes can be used to elucidate this. Since carbon-14 is formed spontaneously in the atmosphere by cosmic rays, biological tissues have a higher carbon-14 content when living organisms incorporate it from carbon dioxide from photosynthesis. The method of analysis to determine whether a plastic is bio-based measures the beta decay of carbon-14 to distinguish the origin of the plastic in question.

In the case of finished products (bags, disposables, etc.), the thickness of the material is fundamental to the speed of the degradation process. In the case of a range of products to be certified, the thickest product should be used.

Once the material has been received, the first step is to subject it to abiotic degradation tests: high and changing temperature, humidity, oxygen and solar irradiation are the abiotic factors that gradually degrade the plastic outdoors and in some cases, such as oxo-degradable plastics, are necessary for microorganisms to act on them.

How plastic degrades

The first global plastic count was done in 2017 and put the amount of plastic generated up to then at 8.3 billion tons, which is equivalent to the weight of a million Eiffel Towers. Most of all this plastic is no longer used and lies in landfills, beaches or other natural enclaves more or less decomposed.

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The rate at which plastic disintegrates depends on its composition and the environmental conditions to which it is exposed. Thus, for example, the decomposition of plastic that is heavily exposed to the sun and ocean currents will be much faster than that of a plastic object lying in the shade.

Another noteworthy aspect of the yogurt container found a few days ago by Mompó is that it is practically the same as those sold today, which shows that, despite all that has been said about the harmful effect of plastics on the biodiversity of the planet, things have not changed.

The Great Pacific Garbage Patch (GPGP), with 1.8 trillion plastic fragments and a weight of 80,000 tons, is the largest accumulation of floating plastic waste in the sea.

How do plastics fragment and remain in the environment for hundreds of years?

If the garbage truck passes by the block we apparently dispose of the package individually, although it is still a collective problem. But what happens where there is no municipal collection service? It is stored, buried or burned… in any case, it pollutes and affects people, animals and ecosystems in many ways.

Although PET is not considered a hazardous material, excessive consumption of products packaged in PET containers can cause long-term respiratory and skin problems due to the action of “phthalates”, chemical compounds added to make the plastic more flexible and durable, which can be easily released, for example, at high temperatures. When released into the liquid and ingested, these particles accumulate inside the body.

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It should be remembered that most of the high biodiversity areas are surrounded by rural populations, far from the municipalities. In most of them there is no garbage collection service, although even in the most remote areas, delivery trucks from companies that sell bottled beverages (and many other packaged products) arrive and, of course, they are not responsible for the waste they generate. What do the communities do with the PET? They “save” it, bury it or burn it. As we have seen, any option is a problem.