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ShareAugust 1, 2007 — Chemical Engineers developed a way to break down plastic bottles made from polyethylene terephthalate -- or PET, and recycle it back into high value uses like more soda bottles, water bottles, beer bottles. Inside the recycling plant's extruder, water is removed from ground up plastic. Then, the plastic is melted and chemically broken down -- in a process called depolymerization. The breakthrough in this process is to be able to go from chips of this plastic to the recycled material in about five minutes.
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Here's a loaded question -- do you recycle? Even if you recycle -- do you know where your plastic bottles go? Are they made into more bottles or something else? The answer may surprise you!
Recycled bottles are not made into new bottles -- they're used for lower grade plastics to build things like playgrounds -- but a new machine may change that!
"What you want to do, ideally, is take that material and recycle it back into high value uses like more soda bottles, water bottles, beer bottles", said George Roberts, a chemical engineer at North Carolina State University.
Roberts and his team developed a way to break down bottles made from polyethylene terephthalate -- or PET. Right now, this type of plastic is non-biodegradable and costs too much to recycle back into food-grade bottles.
"You're trying to complete that loop, then you don't have to make new bottles," said Joan Patterson, also a chemical engineer at North Carolina State University.
Inside the recycling plant's extruder, water is removed from ground up plastic.
Then, the plastic is melted and chemically broken down -- in a process called depolymerization.
"This is where the reaction begins and continues along the length of the extruder this way," said Patterson.
"The breakthrough in this process is to be able to go from chips of this plastic to the recycled material in about five minutes," said Roberts.
Good news considering Americans go through two and a half million plastic bottles every hour! Every year we make enough plastic to shrink-wrap Texas ý and most of it ends up in our landfills. But if every American household recycled just one out of every ten plastic bottles they used, we'd keep 200-million pounds of plastic out of landfills each year.
The Material Research Society contributed to the information contained in the TV portion of this report.
BACKGROUND: Chemical engineers at North Caroline State University have developed a more efficient way to chemically recycle your soda bottles back into new ones. Many companies are interested in the new process, both in the US and internationally, because of its potential for increased efficiency and increased value of the end product. NCSU is working with a startup company called DPoly Systems to commercialize the technology.
WHAT IS PET? All plastics are synthetic polymers, a high-molecular weight chemical compound made up of linked molecules called monomers. The combining of monomers to form a polymer chain is called 'polymerization'. Polyethylene perepthalate (PET) is a common plastic used in beverage bottles. Like most plastics, the bottles are non-biodegradable and will just sit in landfills if we don't recycle them. In addition, the PET bottle market continues to grow rapidly; in Europe, even beer is packaged in plastic bottles. PET is made out of petroleum, so more efficient recycling of old PET bottles would help reduce out dependence on oil.
THE PROBLEM: Recycling is an excellent concept, but we often waste more energy in reprocessing our recyclables than we are gaining. Furthermore, to date no one has found a cost-effective means of recycling food containers into new food containers. More efficient processes will bring us closer to the goal of not wasting our resources. Although there is a demand for recycled bottle-grade PET, the high cost of cleaning post-consumer beverage bottles, strict FDA requirements, and outmoded technology have favored the use of virgin PET over recycled bottle PET in the manufacturing of beverage bottles. Instead, most beverage bottles collected for recycling are reprocessed into non-food products such as fiber and strapping.
HOW IT WORKS: The NCSU researchers have developed a new chemical reprocessing method that uses a twin-screw extruder as a chemical reactor. The solid plastic pieces are melted down and then react chemically with ethylene glycol, reducing the molecular weight. Supercritical carbon dioxide lowers the viscosity even more, so that the plastic emerges as something more similar to water, rather than a strand of plastic. This is called 'depolymerization'. They then remove impurities and 're-polymerize' the material, resulting in resin that is purer and therefore more valuable to processors that incorporate post-consumer PET into their products. The technique takes 10 minutes, compared to two to four hours for conventional batch processing, in which the PET is placed in an autoclave, heated for five hours, them cooled down. The extruder runs continuously, reducing energy losses, and is capable of handling large amounts of polymer in a very short time frame.
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