サステナビリティ
CRISPRによるポリマー編集が世界的なリサイクル活動を変革する可能性
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プラスチックリサイクルの解放
Since their widespread adoption by the manufacturing industry in the 1960s, plastics have become an omnipresent material in our daily lives. They are also the cause of very serious pollution, especially マイクロプラスチック – the broken down, microscopic fragments of plastic polluting the entirety of the Earth and its oceans.
マイクロプラスチックは抗生物質の有効性を低下させることが実証され、胎児や心臓、脳内に存在することが確認され、海洋生物に摂取されているなどの問題があります。
既存のマイクロプラスチック汚染に対処するために、例えばサステナビリティ指標の採用、無毒性の撥水溶剤の使用、あるいはレーザーによる再利用や光駆動光触媒といった方法が検討されています。
一方、エクソンモービルなどの企業が、石油由来プラスチックの低リサイクル率のために訴訟を起こされている。
多くのプラスチック汚染対策はコストがかかり、グローバルな問題に対して多くの国が導入できない、または導入したくないという課題があります。より良い解決策は、プラスチック廃棄物を有価材料に変換し、回収に強い経済的インセンティブを生み出すことです。
(XOM )This is what researchers at Oak Ridge National Laboratory have been working on. They discovered a way to “upcycle plastic waste into higher-performance plastics”, publishing their results in the Journal of the American Chemical Society under the title “Polyalkenamers as Drop-In Additives for Ring-Opening Metathesis Polymerization: A Promising Upcycling Paradigm”1.
従来のリサイクルだけではなぜ不十分なのか？
Plastic is already recycled, but the process is far from perfect. The researchers who worked on this publication describe it accurately as “melt and hope for the best”.
これは問題です。プラスチックリサイクルの各サイクルで、ポリマーの価値が徐々に低下し、結果として得られる製品は耐性、色、耐久性などが劣ります。これは、指向性のない加熱によりプラスチックのポリマー鎖の構造と結合が変化するためです。
したがって、現在のリサイクル技術では、プラスチックは限られた回数しか再利用できず、数回のリサイクルサイクルの後には最終的に廃棄物となります。
さらに、一部のプラスチックはこの方法ではほとんどリサイクルできず、一般的に焼却または埋立てに回されます。
実際、世界のプラスチック生産のうちリサイクルされているのはわずか9％です。
出典: PureCycle Technologies [securities_stock_price_tag symbol="PCT" exchange="NASDAQ"]
リサイクルではなくアップサイクリング
The concept of “upcycling” is that the resulting product of the recycling process is actually superior to the initial material.
This can only be achieved by rearranging in a controlled fashion the polymer chains that form the plastic. This sort of precisely targeted “editing” of the plastic structure has led the researchers to compare their new method to CRISPR、DNAやRNA鎖を自由に改変できる技術.
They worked with molecules poorly or not at all recycled today. This included soft polybutadiene, a common material in rubber tires, and tough acrylonitrile butadiene styrene, used in plastic toys, computer keyboards, ventilation pipes, protective headgear, vehicle trims and molding, and kitchen appliances.
“We’re addressing a significant component of the waste stream with this technology. That’d make a pretty big impact just from conservation of mass and energy from materials that are now going into landfills.”
Jeffrey Foster, Alvin M. Weinberg Distinguished Staff Fellow
The process has a very high “atom economy”, meaning that it recovers in the final product almost all the plastic to recycle that goes in.
仕組み
In order to recreate strong plastic polymers from material to recycle, they first created an additive to add to the existing plastic.
To make the additive, they shredded polybutadiene and acrylonitrile butadiene styrene and immersed it in dichloromethane. The chemical reaction worked at low temperatures (40°C / 104°F) and in less than two hours.
The reaction also needed a catalyst, and ruthenium was used. This is a well-known catalyst in plastic manufacturing and is also used to convert biomass, such as plant oils, into fuels and other high-value organic compounds.
The ruthenium atoms are essentially “carrying” the smaller plastic elements and bringing them to the polymers to make them longer.
The “metathesis” process uses strong double bonds between carbon atoms to increase the chances of chemical reactions.
One part of the method, called ring-opening metathesis polymerization, opens circular carbon molecules and turns them into useful long polymers. Another part, called 交差-メタセシス, inserts chains of polymer sub-units from one polymer chain into another.
出典: Sigma Aldrich
The work was a collaborative task, with some researchers tasked with optimizing polymerization, others using NMR (nuclear magnetic resonance) spectroscopy to analyze the reactions in real time, and others testing the mechanical and thermal properties of final materials.
強力な結果
The Oak Ridge National Laboratory scientists demonstrated that the process, which uses less energy and produces fewer emissions than traditional recycling, efficiently integrates waste materials without compromising polymer quality.
The resulting upcycled plastic displayed strong thermal and mechanical performance, making it superior to the original material, and much superior to plastic recycled with traditional methods.
プラスチックアップサイクリングの次のステップ
すべてのプラスチックのアップサイクリング
This method, now demonstrated for certain plastics, could be expanded to all other plastics. More environment-friendly solvents could be an improvement as well.
“The vision is that this concept could be extended to any polymer that has some sort of backbone functional group to react with.
If scaled up and expanded to employ other additives, broader classes of waste could be mined for molecular building blocks, dramatically reducing the environmental impact of other difficult-to-process plastics.”
Jeffrey Foster, Alvin M. Weinberg Distinguished Staff Fellow
The details of the procedure’s economics also need to be clarified, but it should be okay as it uses low temperature, short reaction time, and a commonly used catalyst.
プラスチック以外へ
The method used worked with plastics but could be deployed to other chemicals as well.
The researchers see it as especially promising for a class of polymer material called thermoset. This includes epoxy resins, vulcanized rubber, polyurethane, and silicone.
Thermoset materials cannot be remelted or reshaped once set, which makes their recycling a challenge.
The upcycling method developed here, attacking the cross-linked molecular structure of plastics, could be applied to the same structure in thermoset materials.
Because the repolymerization process is highly customizable, the final upcycled product could be superior to the original. The upcycled materials might be, for instance, softer and stretchier than the original polymers or, perhaps, easier to shape and harden into durable thermoset products.
結論
Upcycling is a promising option to boost the rate of plastic recycling, as it should provide the economic incentive that was missing until now to get more than 10% of plastic recycled globally.
Reducing plastic usage, removing microplastics, developing bioplastics (see “Top 5 Bioplastics Companies”), and upcycling instead of poor recycling are likely all going to be part of the solution to plastic pollution.
Altogether, they will be a key component in developing a circular economy that is much more resource-intensive and much less polluting.
リサイクル企業
PureCycle Technologies
PCT 価格チャート
PureCycleは、ポリプロピレン（PP）に特化したプラスチックリサイクル企業で、廃棄PPを超純粋なリサイクルPP樹脂に変換します。
彼らは完成品に含まれるすべての添加材（ポリエチレン、固形物、顔料、汚染物など）を“クリーン”にする独自の手法を開発しました。
This extraction process differs from the commonly used mechanical filtration system, which generates too low-quality PP for most industrial applications, even when using high-quality feedstock.
Chemical recycling is another option, but it is far from environmentally friendly and is not cost-efficient.
Purecycleの最終製品は、食品保存容器、加熱・低温殺菌容器、冷凍食品保存容器など、さまざまなPPの一般的用途でFDAに承認されています。将来的には繊維、フィルム包装、注入成形包装、そして自動車用プラスチックへの展開も計画されています。
廃プラスチックのリサイクルに加えて、このプロセスは「バージンPP」よりもエネルギー消費が79％低く、温室効果ガス排出量も35％削減できます。
The company has been building its Ironton pellet production facility, with the first production in 2023年6月, to deploy its recycling process.
It is also building other facilities in North America and Europe, and later on planned in Japan and South Korea with a joint-venture with SK geo centric, aiming to reach 630 million pounds of annual recycling capacity to be reached in 2027
The Ironton facility pellet production reached 3.5 million pounds in Q3 2024, tripling from the quarter before, as well as seeing an increase in the resulting product quality.
Overall, PureCycle is a good company to bet on improving plastic recycling technology, and with the experience to progressively deploy new technology moving away from legacy recycling technology.
研究参考：
1. Jeffrey C. Foster, et al. (2024) Polyalkenamers as Drop-In Additives for Ring-Opening Metathesis Polymerization: A Promising Upcycling Paradigm. Journal of the American Chemical Society 2024 146 (48), 33084-33092 DOI: 10.1021/jacs.4c10588
