• Breaking down plastic into its constitue

    From ScienceDaily@1:317/3 to All on Thursday, March 24, 2022 22:30:44
    Breaking down plastic into its constituent parts

    Date:
    March 24, 2022
    Source:
    ETH Zurich
    Summary:
    A team of ETH researchers led by Athina Anastasaki have succeeded
    in breaking down plastic into its molecular building blocks and in
    recovering over 90 percent of them. A first step towards genuine
    plastic recycling.



    FULL STORY ==========================================================================
    The chemical industry has a long tradition of producing polymers. This
    involves turning small molecular building blocks into long chains of
    molecules that bond together. Polymers are the basis of all kinds of
    everyday plastics, such as PET and polyurethane.


    ========================================================================== However, while the formation of polymers is well established and well researched, scientists have given little attention to how polymer chains
    are broken down (a process called depolymerisation) to recover their
    individual building blocks -- monomers. One reason for this is that
    breaking down polymers is a complex process. Whether a polymer can be
    broken back down at all into its constituent parts depends on which of
    the different polymer manufacturing processes were used. Another reason
    is that the depolymerisation processes used to date require a lot of
    energy, which has made them economically unviable.

    Added to this is the fact that recycled polymers are usually only used
    in the manufacture of low-value products.

    Breaking down polymers is the goal Athina Anastasaki, Professor of
    Polymeric Materials at ETH Zurich, wants to change this. She has set
    herself the goal of producing polymers that can be easily broken down
    into their building blocks so that they can be fully recycled.

    The materials scientist has been able to take a first important step
    in this direction: A study by her group has just been published in
    the Journal of the American Chemical Society. In it, Anastasaki and her colleagues show that they can break down certain polymers into their basic building blocks -- monomers - - and recycle them for use in materials
    for further applications.

    The polymers broken down are polymethacrylates (e.g. Plexi Glass) that
    were produced using a specific polymerisation technique called reversible addition- fragmentation chain-transfer polymerisation -- otherwise known
    as RAFT. This relatively new method, which is now also attracting the
    interest of industry, produces polymer chains of uniform length.



    ========================================================================== First success The researchers at ETH Zurich have succeeded in recovering
    up to 92 percent of the building blocks of polymethacrylates without
    adding a catalyst that would enable or accelerate the reaction. "Our
    method could conceivably be developed even further to involve the use
    of a catalyst. This could increase the amount recovered even more,"
    says Anastasaki.

    The chemical group present at the end of a polymer chain is
    crucial for the polymer's breakdown. By heating the polymer solvent
    mixture to 120DEGC, the researchers created what are referred to as
    "radicals" at the end of a polymethacrylate chain, which triggered the depolymerisation. Researchers at the Australian National University in
    Canberra were able to confirm the results mathematically.

    Producing the same or a different product According to Anastasaki, the
    building blocks recovered in this way can be used to produce the same
    polymer or a completely different product -- an insoluble hydrogel that
    can also be broken down into its monomers. The newly created products
    are of similar quality to the original ones. This is in contrast to
    previous products made from recycled polymers.



    ==========================================================================
    But there is a catch: "Products made with RAFT polymerisation are more expensive than conventional polymers," says Anastasaki. To address this drawback, she and her group are already working on expanding the method
    for large-scale applications, which will make it more competitive and
    the resulting products cheaper. The researchers also aim to increase
    the amount retrieved and recover all the building blocks of a polymer.

    The materials scientist is also researching whether other polymers
    can be depolymerised. She is particularly interested in polystyrene, a widespread, low-cost plastic that is used in many areas of everyday life (Styrofoam).

    Method will not resolve the plastics problem in the short term Even if
    this new method raises hopes of solving humankind's plastic waste problem, Anastasaki dismisses the idea for the time being. There is no quick
    fix to the problem. She goes on to say. "It will take a lot of time and research before the process is established in the chemical industry." Nor
    will it get rid of plastic waste: today's polymers cannot be broken down
    in this way. Some new, suitable polymers have to come into circulation
    before their building blocks can be recovered. But the method has one advantage: no new chemical plants are needed for its introduction and use.

    "We are only at the beginning of our research into depolymerisation. There
    are over 30,000 studies on developing new polymerisation strategies,
    with only a handful of them addressing the subject of monomer recovery,"
    says Anastasaki.


    ========================================================================== Story Source: Materials provided by ETH_Zurich. Original written by
    Peter Rueegg. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Hyun Suk Wang, Nghia P. Truong, Zhipeng Pei, Michelle L. Coote, and
    Athina Anastasaki. Reversing RAFT Polymerization: Near-Quantitative
    Monomer Generation Via a Catalyst-Free Depolymerization
    Approach. Journal of the American Chemical Society, 2022 DOI:
    10.1021/jacs.2c00963 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220324104451.htm

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