Alcohol formula

Polyvinyl alcohol precursor increases carbon fiber yield

Researchers from Indonesia and Norway published an article in the journal polymers in which polyvinyl alcohol is used as the basis for the synthesis of carbon nanofibers with the addition of silver nitrate.

Study: Improvement of carbon-nano fiber yield with electrospun iodinated PVA/silver nanoparticles as precursor via low-temperature one-step synthesis. Image Credit: whitehoune/Shutterstock.com

Introduction to carbon nanofibers

Carbon nanofibers (CNF) are attractive for use as reinforcement in polymeric materials in engineering fields, supercapacitors, high temperature fillers and enzymes due to their strong tensile qualities.

The desire for CNF as a reinforcement is expected to grow, even though the technologies often used to synthesize CNF, such as chemical vapor deposition (CVD), are considered difficult and somewhat expensive.

Both polymer and electrodeposition have been extensively researched as a precursor and as a technique.

FTIR spectra of (a) pure PVA, (b) PVA/AgNO3 nanofiber, (c) iodinated PVA/AgNO3 nanofiber, (d) iodinated PVA nanofiber, (e) CNF and (f) CNF/Ag.

Figure 1. FTIR spectra of (a) pure PVA, (b) PVA/AgNO3 nanofiber, (vs) Iodinated PVA/AgNO3 nanofiber, (D) Iodinated PVA nanofiber, (and) CNF, and (F) CNF/Ag.

© Gea S, et al. (2022)Importance of polymers

Polymers with long hydrocarbon groups are often used as intermediates in the manufacture of carbon fibers.

Many monomers, including poly(acrylonitrile), poly(vinyl alcohol), poly(amic acid), and phenolic resin yielded more than 50% carbon when synthesized in acetone cyanide with acrylonitrile (HCN).

With a high carbon content of up to 54.5%, polyvinyl alcohol (PVA) is considered a precursor.

It also has high water solubility, is non-toxic and functions as a reducing agent. Moreover, these properties increase the number of carbon fibers synthesized and decrease the processing cost.

As a result, thermal combustion of PVA above 400°C may result in decreased CNF yield, necessitating the use of another pre-preparation procedure to address this issue.

SEM morphological images of (a) PVA nanofiber;  (b) PVA/AgNO3 nanofiber;  (c) iodinated PVA nanofiber;  (d) iodinated PVA/AgNO3 nanofiber, and the diameter-size distributions of (e) PVA nanofiber;  (f) PVA/AgNO3;  (g) iodinated PVA nanofiber;  and (h) iodinated PVA/AgNO3 nanofiber.

Figure 2. SEM morphological images of (a) PVA nanofiber; (b) PVA/AgNO3 Nanofiber; (vs) iodinated PVA nanofiber; (D) Iodinated PVA/AgNO3 nanofiber, and the diameter-size distributions of (and) PVA nanofiber; (F) PVA/AgNO3; (g) iodinated PVA nanofiber; and (h) Iodinated PVA/AgNO3 nanofiber. © Gea S, et al. (2022)

Formation of carbon fibers

Several attempts have been made to identify alternative pre-preparation procedures, including those related to functional components and inclusion of metals via electrospinning and traditional processes.

Since carbon fiber synthesis typically involves three processes: stabilization, carbonization, and sometimes graphitization, a sequence of pre-treatment procedures are implemented to preserve stability, resulting in increased CNF yield.

Metal ions have been shown to have a favorable effect on the thermal degradation and carbonization of PVA. Metals used in electrospinning accelerate the gelatinization system and improve electrical characteristics.

UV-Vis spectra of carbon nanofibers of (a) PVA and (b) PVA/AgNO3.

Picture 3. UV-Vis spectrum of carbon nanofibers of (a) PVA and (b) PVA/AgNO3. © Gea S, et al. (2022)

Importance of silver nanoparticles

Silver nanoparticles are gaining importance due to their wide range of biological applications.

The antibacterial properties of silver nanoparticles have been used to suppress bacterial growth in a variety of applications, including orthopedic surgeries, wound repair and care, and health technologies.

They are the most commonly used sterilizing nanoparticles in commercial and medical products like textiles, canned reusable grocery bags, refrigerator panels and hygiene products.

These nanomaterials have been shown to have enzymatic oxidation capabilities for biological agents as well as for industrial compounds such as benzene. Silver nanoparticles are also commonly used as surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF) (MEF) sensors.

In the most recent study, AgNO3 is used as silver nanoparticle (SNP) resource for thermal cracking of PVA substrate. To develop a porous structure, iodination inside the PVA and electrospinning are recommended as pretreatment techniques.

TEM images of (a) carbon nanofiber from iodinated PVA nanofiber, (b) carbon nanofiber with silver nanoparticle from iodinated PVA/AgNO3, (c) silver nanoparticle and (d) particle distribution of diameter.

Figure 4. TEM images of (a) Carbon nanofiber from iodinated PVA nanofiber, (b) carbon nanofiber with silver nanoparticle from iodinated PVA/AgNO3(vs) silver nanoparticle, and (D) particle distribution diameter. © Gea S, et al. (2022)

Experimental results

When the negatively charged electrons of the hydrophilic groups of PVA reacted with the positive ions of Ag, physical and chemical interactions were observed.

It has been claimed that hydrogen bonds form between the hydroxyl groups of PVA and the polymer units of the fluid (water), as well as the nitrate ion of AgNO3.

SEM photos demonstrated the impact of Ag and iodine deposition on the electrospun nanofibers.

The PVA polymer generated nanofibers with variable diameters ranging from 20 to 160 nm. Because the inclusion of metals improved conductance and adhesion, the widths of PVA/AgNO3 the fibers were noticeably more uniform.

Addition of AgNO3 increases the conductivity of the solution. Based on experimental investigations, the amount of AgNO3 at a weight fraction of 0.2 percent was found to be the best formulation where clumping could be prevented.

Raman spectroscopy has been used to determine the graphitic structure of carbon fibers. During the experiments, a one-step heat treatment reduced the diameter of the iodinated electrospun fibers by half.

To conclude, carbon nanofibers were efficiently synthesized from PVA with the inclusion of silver nanoparticles in the form of AgNO3 via a one-step pyrolysis procedure.

DTG thermogram of PVA nanofiber, iodinated PVA nanofiber, PVA/AgNO3 nanofiber and iodinated PVA/AgNO3 nanofiber.

Figure 5. DTG thermogram of PVA nanofiber, iodinated PVA nanofiber, PVA/AgNO3 Nanofiber and iodized PVA/AgNO3 Nanofiber. © Gea S, et al. (2022)

Continue Reading: High thermal effects on concrete reinforced with carbon nanotubes

Reference

Gea S, et al. (2022) Improved yield of carbon-nano fibers with electrospun iodinated PVA/silver nanoparticles as precursor via low-temperature one-step synthesis. Polymers. 14(3). 446. Available at: https://www.mdpi.com/2073-4360/14/3/446

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