{"id":3366,"date":"2021-12-09T10:00:00","date_gmt":"2021-12-09T10:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=3366"},"modified":"2021-11-25T06:00:16","modified_gmt":"2021-11-25T06:00:16","slug":"new-recyclable-thermoset-polymer-is-based-off-of-wood-lignin","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/new-recyclable-thermoset-polymer-is-based-off-of-wood-lignin\/","title":{"rendered":"New Recyclable Thermoset Polymer Is Based Off of Wood Lignin"},"content":{"rendered":"\n

Materials scientists and engineers would be the first to tell you that there are primarily two kinds of polymers in the world: thermoplastics<\/em> and thermosets<\/em>. Thermoplastics are polymers that can \u201csoften\u201d when heated then harden when cooled; these polymers make up most of the consumer plastics that we know of, like the polyethylene<\/em> (PE) in plastic bags<\/a> and the poly(ethylene terephthalate)<\/em> (PET) in your soda bottles<\/a>.<\/p>\n\n\n\n

Now, thermosets on the other hand are polymers who undergo a \u201ccuring\u201d process; unlike their thermoplastic cousins, these polymers do not \u201csoften\u201d when heated, and instead just decompose. This is also usually an irreversible process, meaning these polymers can rarely be recycled through simple heating and remolding. These polymers include the rubber<\/em> in your car\u2019s tires, and the epoxy resin<\/em> in your nearest composite glass window.<\/p>\n\n\n\n

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Vulcanized rubber tires are examples of thermosetting polymers; these polymers break down when exposed to heat, and the process is often irreversible. (Onyeador, 2020) <\/figcaption><\/figure><\/div>\n\n\n\n

These thermosets often need the presence of a curing agent, like a catalyst or even just heat, to begin the crosslinking <\/em>process of a desired prepolymer resin. Crosslinking meshes ang entangles the long chains of polymer molecules together, much like the metal mesh of a chain link fence; it\u2019s this process that makes thermosetting polymers very strong and durable, and imparts upon them properties like chemical resistance.<\/p>\n\n\n\n

You see, in contrast to thermoplastic polymers that really just rely on intermolecular forces to stick together, thermosets link their polymers with one another by chemical bonding; this is why your plastic bag simply \u201cmelts\u201d when heated, while your rubber tire burns to an irreparable state. Heating can permanently break the chemical bonds of most thermosets.<\/p>\n\n\n\n

Or, at least, that\u2019s how things would go in the world if a group of researchers from Stockholm University didn\u2019t have anything to say about it. You see, these particular scientists devised an ingenious thermosetting polymer that cures and performs just the way you\u2019d expect a thermoset to, but with a catch\u2014this thermoset is based off of lignin<\/em>, an organic polymer that forms most of the support structures in plants. Their novel findings were published in the journal ACS Applied Materials & Interfaces<\/em>.<\/p>\n\n\n\n

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Scientists hold a sample of the lignin-based thermoset from the new study; this particular thermoset can be broken down by heat, then recycled. (Sipponen, 2021) <\/figcaption><\/figure><\/div>\n\n\n\n

The researchers combined lignin with a \u201cnon-toxic crosslinking chemical\u201d derived from ethylene glycol<\/em>, and was mixed then simply cured to allow crosslinking to occur. The lignin, surprisingly enough, didn\u2019t need any chemical modification to allow for this process\u2014it was just simply heated together with the crosslinking agent.<\/p>\n\n\n\n

The result is a black polymer that allows for \u201c[tuning] the material properties, [which] opens many opportunities to commercial applications,\u201d according to co-author Mohammad Morsali. For example, the new thermoset was used as an adhesive by modifying the lignin-to-crosslinking-agent ratio to be 50% lignin by weight prior to curing. The result was an adhesive that was capable of bonding even two metal plates of aluminum.<\/p>\n\n\n\n

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Study co-author Mohammad Morsali showcases an adhesive derived from their new thermoset, which was able to bind two aluminum plates together. (Sipponen, 2021) <\/figcaption><\/figure><\/div>\n\n\n\n

The icing on this thermosetting cake is the fact that the polymer can simply be broken down thermally, and can then be reused multiple times, and was said to retain strength that\u2019s comparable to those of common engineering plastics despite the reforming.<\/p>\n\n\n\n

Said co-author Professor Mika Sipponen: “The material that we developed is perfectly in line with the current move towards sustainable circular materials. Owing to its design consisting of so-called dynamic covalent bonds<\/em>, the material can be formed over and over again by relatively mild heating.”<\/p>\n\n\n\n

Fellow co-author Dr. Adrian Moreno continued: “We were amazed by the performance of the new materials, and one of the striking aspects of our results is the simplicity and material-efficiency of the synthetic process. In contrast to earlier examples we do not need any chemical modification or fractionation of the lignin but can simply cook it with the cross-linker in a one-pot reaction.\u201d<\/p>\n\n\n\n

(For more polymer news, check out our piece on the true dangers of microplastics in our infants<\/a>, as well as polymers being used as a basis for \u201cflexible\u201d supercapacitors<\/a>.)<\/p>\n\n\n\n

References<\/h2>\n\n\n\n