New Recycling Technologies Needed to Combat Plastic Pollution
by Jazmin Becerril Gonzalez, age 14
Recycling plastic has become a big issue in today’s world. Millions of tons of plastics enter landfills while few are recycled. In fact, there are only two kinds of plastics that are commonly recycled in the United States. These plastics are polyethylene terephthalate (PET) and high-density polyethylene (HDPE) which are the main components of soda bottles, milk jugs and detergent containers. Due to limited recycling capabilities and low recycling rates, scientists are developing new technologies to improve recycling in the future.
The main issue in recycling involves processing and sorting the material. Typically, plastics are sorted at a recovering facility where they are shredded, melted and remolded. However, this only works well for products such as bottles and containers while other packaging or plastic film materials take more effort. There are several types of plastic being used in the production of such material..
Geoffrey Coates, a chemist at Cornell University in Ithaca, N.Y., states, “Most plastics are like oil and water.” Plastics don’t easily combine and some objects are made of multiple types of plastic. This makes separating the different plastics in products very difficult.
One chemical engineer, George Huber at the University of Wisconsin-Madison, has developed a method to combat this issue. In his research, he used various liquids to dissolve plastics in order to separate them. Specifically, in his tests, he worked on separating plastics in food packaging film. This film has three types of plastic: PET, polyethylene, and ethylene vinyl alcohol (EVOH). The film was stirred with a liquid called toluene and then placed into another chemical to remove the EVOH. Eventually the other two plastics were recovered by using antisolvent chemicals. His work was recognized in Science Advances last November 18th.
In addition to Huber’s work, Coates has created a method using chemicals called “compatibilizers'' which help different kinds of plastics combine. Specifically, Coates has created a chemical that can blend polyethylene and polypropylene which makes plastic stick together. This could ease the work in recycling as these two types make up most plastic trash. This new design allows for collection of these materials in an organized fashion.
Although developing new strategies to sort plastic is important, creating ways to properly reuse old plastics is also critical. One growing issue is the amount of chemicals in plastic trash. Recycled plastic comes with lots of impurities such as dyes, flame retardants and additives. Additionally, recycled plastic is usually weaker compared to new plastics, making it difficult to reuse them more than once.
To confront these issues in recycling, chemical recycling is a growing method used in industries. A French company named Carbios uses enzymes to break down PET into two monomers: ethylene glycol and terephthalic acid. While the enzyme does break down PET, it is not perfect and studies are being performed to redesign the active site of the enzymes to increase productivity. One study was able to break down 90 percent of colored PET bottles in 10 hours using a new enzyme. Furthermore, the purified monomers were used to make new bottles that ended up being just as strong as the original.
Along with chemically recycling PET, other studies propose advanced ways to recycle polyethylene. Susannah Scott at the University of California, Santa Barbara, developed a method to decompose polyethylene into alkylaromatics under mild conditions. Alkylaromatics are ingredients used in soaps and other products. To start the process, polyethylene is placed with platinum in a chemical reaction chamber at 280 degrees Celsius for 24 hours. This process breaks the bonds in polyethylene and releases hydrogen, overall breaking the plastic into small pieces. These fragments are around 30 carbon atoms long and form rings which are the alkylaromatic compounds.
With the growing amount of plastic used on a daily basis, new methods are being developed to ensure that plastics are recycled properly. Scientists are creating ways to strengthen recycled plastics back to their original form. A new form of plastic called poly(diketoenamine)s or PDKs could potentially be recycled infinitely. This plastic simply needs to be placed in an acidic solution in order to break down into its monomers. Afterwards, these monomers could be reassembled to create new plastics for the future. Although this is a potential solution for plastic consumption, it is still being studied heavily and continued research is being performed in order to combat the world’s growing plastic waste issues.
[Source: Science News for Students]