Production of Microplastics
Understanding the production of microplastics is the first step to determining how to reduce the pollution caused by them. Primary microplastics such as nurdles and microbeads are specifically manufactured to have a size of less than 5mm in diameter. These microplastics can be made out of many different polymers.
Polyethylene terephthalate is one polymer used to make nurdles. Ethylene glycol ((CH₂OH)₂) and terephthalic acid (C₆H₄(CO₂H)₂) are combined under high temperatures at a low atmospheric pressure. This creates long chains of monomers. These polymer chains grow in length as they are exposed to heat. The liquid is then extruded and shaped as it cools. This process creates small pellets that can later be used to create larger plastic materials.
One way that secondary microplastics are formed is through photodegradation. Photodegradation occurs when some polymers are exposed to ultraviolet rays. The ultraviolet light is able to target the tertiary carbon bonds in these polymers. This reaction creates free radicals, which then bind with the oxygen in the air to create carbonyl groups within the polymers. This makes the synthetic polymer extremely brittle, and easily broken. Some polymers that undergo this process are Low Density Polyethylene and Polypropylene.
A similar way in which synthetic polymers can be degraded chemically is through photolysis. Photolysis is when a polymer absorbs a photon of a wavelength between 290-700 nm. This insites an unstable excited state within the molecule. Simultaneously light is being absorbed by triplet oxygen, which produces singlet oxygen, which is highly reactive. The excited state of the molecule in the presence of singlet oxygen creates a situation in which polymers can spontaneously decompose.
Synthetic polymers can also be degraded physically. Plastics are easily crushed, and due to the rigid structure of many of them, they splinter easily. Weather conditions can contribute to the break down of synthetic polymers, as heavy rain and wind can be strong enough to crack plastics.
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