Preparation of Carbon Fibers from Cellulose Acetate.

[NNadir]

The paper to which I'll briefly refer is this one: Carbon Fibers Made from Cellulose Acetate as a Green Polymer Precursor Fabian Straske, Shakir Zainuddin, Antoine Viard, Günter Motz, and Thomas Scheibel ACS Sustainable Chemistry & Engineering 2024 12 (15), 5780-5787

Cellulose is by far, the most abundant polymer on Earth. Currently carbon fibers are made from dangerous fossil fuels. The carbon in them is thus not dumped into the planetary atmosphere, but is effectively sequestered by use.

From the introductory text:

Carbon fibers (CFs) show high strength, lightweight, good electrical and thermal conductivity, as well as corrosion resistance. (1?3) Therefore, they are used in a broad range of applications in textile industries, (4?6) filter systems, (7,8) reinforcement of concrete as construction materials, (9) as well as automotive and aircraft industries, (10?12) enabling the replacement of materials like steel and aluminum. Over 90% of the currently available CFs are made from petrochemically based precursors with poly(acrylonitrile) (PAN) being the most important precursor material. (13,14) Wet spinning is used to produce precursor fibers made of PAN, which are subsequently carbonized at temperatures of 1350 °C and above in an inert atmosphere. (11,15?17)

Cellulose as a renewable resource, in contrast, has been known to be the longest-in-use CF precursor material and can be obtained from plants as an inexhaustible resource for the manufacturing of CFs. Low carbon yields and in contrast promising results using PAN-based precursors resulted in the switch of precursor materials from cellulose to PAN. (18)

Nowadays, interest in cellulose precursors has arisen again due to economic as well as ecological reasons. The carbonization of petrochemical-based PAN produces toxic gases such as ammonia, hydrogen cyanide, and various lower nitriles, (19) which require extensive exhaust gas treatment. The gases released during the carbonization of cellulose are less toxic in comparison. (20) Therefore, precursor filaments made of biorenewable materials possess significant advantages and should be considered as an alternative to the cost-intensive unsustainable resources, which supports a revival of cellulose as a precursor. (21,22)
Cellulose can be obtained from renewable resources like plants and microorganisms as the product of fermentation. (22,23) Therefore, cellulose could be an inexhaustible raw material to produce carbon fiber precursors, making cellulose-based CF more sustainable compared to those produced from PAN. (21,22) Since cellulose shows poor solubility in most solvents, cellulose derivatives with higher solubility like cellulose acetate (CA) have been used to manufacture cellulose fibers. Cellulose acetate is made from cellulose by acetylation by using acetic acid. The production of cellulose fibers can be achieved by spinning CA solutions and subsequent deacetylation of the gained fibers in a NaOH/ethanol bath. (24) Regenerated cellulose fibers, such as viscose, can be used as CF precursors as well. However, their production is based on dissolving pulp solubilized by forming sodium xanthate with carbon disulfide, followed by spinning into a coagulation bath of sulfuric acid. During the production of CA, no large amounts of carbon disulfide and sulfuric acid are necessary, making the manufacturing of CA-based CFs more cost-effective and sustainable. (22,25?27)

The potential of CA as a valuable precursor for CFs has been previously investigated using electrospinning yielding carbon fiber meshes. (24,28,29) Functionalized nonwoven meshes, nanocomposites, or vertically aligned arrays made of carbon nanofibers have been shown to act as supercapacitor electrodes, (22,30) superoleophilic materials for oil–water separation, (31) and neuro-electrophysiological activity sensors. (32) Further carbon fibers were produced using cellulose acetate spinning dopes with embedded nanocrystalline cellulose... (33)

The process of performing this task involves the use of a tube furnace, which in theory might be fueled by nuclear heat. The temperature was 1400 °C, temperatures readily accessible from nuclear fuels.

The process of making cellulose acetate involves the use of acetic anhydride, which in theory, but not generally in industrial practice, can be synthesized from methane produced by the hydrogenation of carbon dioxide, followed by carbonylation of the methane, a well understood industrial process.

The carbon yield of the process is about 20%, and presumably generates carbon dioxide and/or carbon monoxide of biological origin, that can thus be recycled into the process.

It's never going to be a big deal, but every little bit helps.

[Bernardo de La Paz]

1. Interesting. Thank you. . . . nt