Biomass-derived plastics are limited by their low heat resistance. Now, collaborative research between the Japan Advanced Institute of Science and Technology (JAIST) and the University of Tokyo (U-Tokyo) has successfully developed a technology to convert cellulosic biomass into aromatic polymers.
Polymers with an aromatic backbone are characterized by high levels of heat resistance – examples of traditional polymers with an aromatic structure are shown in Table 1.
Currently available bioplastics (eg PLA, PHA, PA11) are mostly aliphatic and thus exhibit poor thermostability. Developing aromatic heterocyclic monomers from biomass is difficult, due to the difficulty of controlling their structure.
Two specific aromatic molecules, 3-amino-4-hydroxybenzoic acid (AHBA) and 4-aminobenzoic acid (ABA) were produced from kraft pulp, an inedible cellulosic feedstock by Professor Ohnishi and his research team at U-Tokyo. Recombinant microorganisms enhanced the productivity of the aromatic monomers selectively and inhibited the formation of side products.
Professor Kaneko and his research team in JAIST then chemically converted AHBA into 3,4-diaminobenzoic acid (DABA), which was subsequently polymerized into poly(2, 5-benzimidazole) (ABPBI) via polycondensation and processed into thermoresistant film.
It was found that incorporating a very small amount of ABA with DABA dramatically increases the heat-resistance of the resulting copolymer. The team claims to have produced film with the highest thermostable plastic on record (Fig 1).
Density functional theory (DFT) calculations confirmed the small ABA incorporation strengthened the interchain hydrogen bonding between imidazoles.
Organic plastic superior in thermostability (over 740°C), was developed from inedible biomass feedstocks without using heavy inorganic fillers and thus lightweight in nature.
|Table 1 Characteristics of biomass polymers and traditional high heat resistance plastics|
|Short Name||Chemical structure||Commercial Name||Characteristics||Biomass-based?|
|PLA (polylactic acid)||(C3H4O2)n – Lactide is also the IUPAC-approved class name for cyclic dimers and higher cyclic oligomers of lactic acid (dilactide, trilactide, …) and of other hydroxycarboxylic acids||Bio-Flex (FKur)||Range from amorphous glassy polymer to semi-crystalline and highly crystalline polymers with a glass transition 60–65°C, a melting temperature 130-180°C, and a tensile modulus 2.7–16 GPa. Used as a feedstock material in desktop fused filament fabrication 3D printers and as medical implants (anchors, screws, plates, pins, rods and mesh)||Yes|
|Fozeas (Mitsubishi Chemical)|
|LLC Ingeo (NatureWorks)|
|Ceramis-PLA (Alcan Packaging)|
|PHA||Polyhydroxyalkanoates||BioMatera||Biodegradable plastics which can be either thermoplastic or elastomeric, with melting points ranging from 40 to 180°C.||Yes|
|TianAn Biologic Materials|
|Tianjin GreenBio Materials|
|PA11 (Nylon 11)||Poly(ω-undecanamide), Poly(imino-1-oxoundecamethylene), Poly[imino(1-oxoundecane-1,11-diyl)]||Rilsan (Arkema)||Produced from castor beans, Nylon 11, due to its low water absorption, increased dimensional stability when exposed to moisture, heat and chemical resistance, flexibility, and burst strength, is used in various applications for tubing in preference to Nylon 6||Yes|
|DABA||3,4-diaminobenzoic acid||JAIST/U-Tokyo (in development)||Aromatic produced from biomass, claimed to be the highest thermostable plastic on record||Yes|
|PBO||poly(p-phenylene-2,6-benzobisoxazole||Zylon (Toyobo)||Thermoset liquid-crystalline polymer with very high strength with excellent thermal stability||No|
|PBI||polybenzimidazole||Celazole (Aetna)||Highest performance engineering thermoplastic available, offering the highest heat resistance and mechanical property retention over 200°C of any unfilled plastic||No|
|Polyimide||poly (4,4′-oxydiphenylene-pyromellitimide)||Kapton (Du Pont)||Stable (in isolation) across a wide range of temperatures, from −269 to +400°C||No|
Ultrahigh Thermoresistant Lightweight Bioplastics Developed from Fermentation Products of Cellulosic Feedstock, Aniruddha Nag et al. Advanced Sustainable Systems, issue 2000193, 2020, DOI: 10.1002/adsu.202000193.
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