Renewing PET – New Types of Environmentally Sustainable Plastics

In the USA more than 13 billion plastic bottles are disposed of each year. Most plastic beverage bottles are made from PET. After being emptied and hopefully tossed in the waste bin the beverage bottle may end up being recycled. While plastics are recyclable, the resulting materials are limited to “second generation reuse” only, such as fleece clothes, carpet and other ‘second-life’ products. This means that at the final end of the life-cycle the materials made from recycled plastic bottles are ultimately disposed in landfills. Although there is a tendency to re-use recycled PET in new beverage bottles, such as the PlantBottle of Coca-Cola, only a relatively small percentage is added to the virgin resins used. In the United States, up to 63 lbs of plastic packaging per capita is discarded each year, instead of being repeatedly recycled.
This might come to an end.

In a paper published in the American Chemical Society journal “Macromolecules”, scientists from IBM and Stanford University detail discoveries that could lead to the development of new types of biodegradable, biocompatible plastics. The breakthrough also could lead to a new recycling process that has the potential to significantly increase the ability to recycle and reuse common PET and plant-based plastics in the future.

In general, mechanical, rather than chemical, recycling is used for PET because ….it’s too expensive to break the polymer down into its chemical parts, according to the National Association for PET Container Resources. There are two existing methods for accomplishing the chemical reaction, but they are very energy-intensive and have been abandoned because of the cost. Even with the use of existing catalysts to help the recycling reactions along, these processes must be done at high temperatures and under great pressure, and take a long time.

The researchers describe in their paper several new developed catalysts, one of which can be used to chemically recycle PET in a short time at 75 ºC. PET is made from two feedstocks, one of them an organic acid, the other ethylene glycol, which is relatively inexpensive. The catalyst works in an ethylene glycol solution. When shredded water bottles are placed in the solution, the catalyst causes the organic acid in the plastic to react with the ethylene glycol in solution to make PET that is of the same quality of which the bottle was made originally.

Jim Hedrick, a researcher at IBM’s Research facility in San Jose, CA, (Monica M. Davey/Feature Photo Service for IBM)

A major focus of the research has been on ring-opening polymerization, a strategy dominated by metal oxide or metal hydroxide catalysts. The research shows that organic catalysts both exhibit activities that rival the most active metal-based catalysts, and provides access to polymer architectures that are difficult to access by conventional approaches. This discovery and new approach using organic catalysts could lead to well-defined, biodegradable molecules made from renewable resources in an environmentally responsible way.

The paper also describes recycling or degradation strategies that would enable a “closed-loop” life cycle for materials that meet the needs of the marketplace while helping to minimize the environmental footprint left for future generations.
The PET-recycling catalyst, a type of molecule called a carbene, was inspired by vitamin B1, says Stanford chemistry professor Robert Waymouth. The Stanford and IBM researchers guessed that a similar organic small molecule might be good at catalyzing reactions that string esters together to make long polymers.

The IBM researchers will now collaborate with the King Abdulaziz City for Science and Technology in Saudi Arabia to test the chemical recycling of PET on a larger scale. In initial tests, they will focus on breaking down the polymer into its constituents. However, the company has also had good results using its organic catalysts to de-polymerize PET to make specialized materials such as feedstocks for high-strength plastics that are more valuable but are expensive to make using other pathways.

“You start with trash, and build it back up into higher value materials,” says Robert Allen, senior manager of advanced materials chemistry at IBM Almaden.

If the new catalysts have “even a modicum of success, it would be big news,” says Dennis Sabourin, executive director of the National Association for PET Container Resources.

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8 responses to “Renewing PET – New Types of Environmentally Sustainable Plastics

    • Mike, we are not talking about simple recycling here. It is a cradle-to-cradle system: ……. discoveries that could lead to the development of new types of biodegradable, biocompatible plastics. The breakthrough also could lead to a new recycling process that has the potential to significantly increase the ability to recycle and reuse common PET and plant-based plastics in the future.
      Up till now recycling creates second-generation products and not cradle-to-cradle.

  1. Pingback: Renewing PET – New Types of Environmentally Sustainable Plastics Book university·

  2. 13 billion bottles, 63 pounds per capita… all good to bring up on the supply side of recycling and useless without a source.

    And I don’t care if its you on the back of an envelope or a National Science Foundation study. Cite a source…

  3. Dear Anton, I’ve been reading your blog for some month – it’s really interesting to have some themes together. In germany, you’re focussed on pet cycle and recycling generally, its good to see how the situation in another country is

  4. Hello,

    I read your artical in this website and i need help to find answers for the follwoing questions:

    Define the chemical reactions in your plant and where these occur (main desired and undesired reactions). Include: balanced equations, phase of species, enthalpy of reaction, etc..
    How do impurities affect the process chemistry?
    Define the kinetic rate or equilibrium constant equation for the reactions. Include, if possible now, a model which predicts the behaviour of your reactions under different operating conditions of temperature, pressure, pH, etc.
    What is a typical yield of desired product? What is the selectivity of desired product over a key undesired product? What is typical % conversion of the feed?
    What are the normal operating conditions (normal operating range of T, P, pH, etc..) of typical units? Is there a reason why this combination of operating conditions is considered optimal?
    What type of catalyst, if any, is used? What are the distinguishing characteristics of this catalyst? How often does the catalyst need to be replaced? What does it cost?

    Thank you,

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