FLAME RETARDANT NANOFIBERS

Flame retardants (FR) are chemical compounds added with an objective to inhibit/retard the ignition/burning of the plastic. In order to prevent combustion, it becomes mandatory to design a thermally stable polymeric structure that has a lesser probability of decomposing into combustible gases under heat [1].

In the last decade, there is an increasing and urgent need for researchers to investigate and develop improved ways to produce flame retardant materials because of a significant decline increase of the fires in many countries all around the world. Recently, fire hazards have become threats that bring high rates of fatalities and disfiguring burns. The National Fire Protection Association reported 1.3 million fire outbreaks in the U.S. in 2018. These fire outbreaks resulted in 15,200 civilian injuries, 3,120 civilian deaths, and $11.6 billion in property damage. These numbers are still increasing and being unacceptable. To resolve these concerns, several researchers have used nanotechnology to create advanced and innovative fire-retardant solutions [2].

Recent years, thanks to nanoscience and nanofibers, new physical properties, expansion of application scope, and composition between various polymers and plastics could be achieved. On the contrary of micro sized fibers, nanofibers obtained by electrospinning are widely used because they have unique characteristics such as large specific surface area, selective permeability, and strong surface adsorption properties in addition to being lightweight which can keep them in high demand worldwide for various applications including filtration, biomedical applications, packaging, energy, automotive and food industry [3]. However, for more usage, the thermal properties of the nanofibers should be improved. Particularly, they are weak to heat and fire, because mechanical properties of nanofibers may degenerate at high temperatures, and harmful substances are released during the combustion process, which can limit their usage in extensive applications.

To overcome that problem, researchers have been trying different improvement studies to obtain flame retardant nanofibers. Specially, in recent years, a few studies have proven that electrospinning is a suitable and easy method of fabricating flame-retardant (FR) nanofibers. For that purpose, researchers have been using FR additives such as boric acid, chlorine, phosphorus, bromine etc. in the thermoplastic and thermoset polymeric solution to create FR nanofibers [4-5].

For example, in a study, Kim et al developed a multifunctional composite nanofiber by incorporating tannin and reduced graphene oxide to polyurethane (PU) and they improved the flame retardancy and mechanical properties of PU while displaying excellent antibacterial and electrospinning properties. Thanks to this improvement, a new composite nanofiber scaffold was successfully produced and developed, which shows various functionalities in a single material. These nanofibers can potentially be applied in reinforcement, flame retardants that can be used for protective clothing and biomedical fields [6].

In a similar study, Wu et al. [7] manufactured a FR composite by using polyamide 6 (PA6)/nanoclay/intumescent nanocomposite fibers via electrospinning. They claimed that high percentages of nano clay particles improved the electro spinnability of the pristine nanofibers, and pristine nylon-6 samples have a higher degradation temperature than nanocomposite fibers. In addition, FR additives reduced the flammability of the nanofibers.

In another study, Xiao et al. has developed polymer nanofibers with improved flame retardancy via coaxial electrospinning using graphene nanoplatelets hybridized with next generation red phosphorus (NG-RP) and polyamide 66 (PA 66). The incorporation of NG-RP into PA66 improved the flame retardancy and mechanical properties of the nanofibers, as well as maintained the brilliancy and color of the produced nanofibers [8].

Another example of FR nanofibers was developed by Yin et al. [9]. They have manufactured nanofibers with enhanced FR characteristics thanks to electrospinning using multi-walled carbon nanotubes (MWCNT), nanoclay particles, and FR additives. Prepared FR/PA6 nanofibers had lower heat release and flame-retardant properties, that can be attributed to the char residue which served as a protective thermal barrier.

Similarly, in a study Baddam et al focuses on fabricating novel flame-retardant and superhydrophobic nanofibers through the electrospinning of a polymeric solution consisting of recycled expanded polystyrene (EPS), silicon dioxide (SiO2), and boric acid (BA). They concluded that the incorporation of both SiO2 and BA inclusions in EPS gave the best results: a water contact

angle of 156.98◦, a total burning time of 25 s in the flammability test. Thus, the nanofibers obtained in this study are the potential candidates to be used as protective layers in the electronics and packaging industries [10].

The results mentioned above demonstrates that most of the nanoparticles and FR additives can improve the thermal stability and flame-retardant properties of the textile polymers. The main mechanisms behind that feature involved are the formation of a protective barrier layer combined with char promotion and free radical trapping [11].

It is noteworthy to mention that some of the common FRs produce toxic compounds. Additionally, the potential environmental and health concerns associated with the use of nanoparticle have received much attention in the recent years and therefore detailed assessment of their environmental and health impacts is still needed. By the help of electrospinning, researchers have been doing the investigations of non-toxic FR nanofibers therefore this field needs more attention.

The future applications of FR nanofibers are protective clothing, food packaging, householding and energy applications. Although the industrial scale production of FR nanofibers is newly investigated, there is a huge possibility that electrospinning can achieve this goal as it was proven many times that this technique allows larger production rates [12].

References

1. Yan et al. Synthesis of organophosphate-functionalized graphene oxide for enhancing the flame retardancy and smoke suppression properties of transparent fire-retardant coatings, Polym. Degrad. Stab. (2020)

2. “Fire Loss in the United States During 2018” – The National Fire Protection Association

3. Satilmis et al. Development of superhydrophobic electrospun fibrous membrane of polymers of intrinsic microporosity (PIM-2) Eur. Polym. J. (2019).

4. Z. Brahmia et al. Comparative study on fire retardancy of various wood species treated with PEG 400, phosphorus, and boron compounds for use in cement-bonded wood-based products, Surfaces and Interfaces (2020).

5. Zhang et al. An inherently flame-retardant polyamide 6 containing a phosphorus group prepared by transesterification polymerization Polymer (Guildf) (2020)

6. Kim et al. flame retardant, antimicrobial, and mechanical properties of multifunctional polyurethane nanofibers containing tannic acid-coated reduced graphene oxide, Polymer Testing, 2021

7. Wu et al. Flame-retardant polyamide 6/nanoclay/intumescent nanocomposite fibers through electrospinning, Text. Res. J. (2014).

8. Xiao, et al., Core-shell structured polyamide 66 nanofibers with enhanced flame retardancy, ACS Omega (2017).

9. Yin et al. Flame-retardant polyamide 6/carbon nanotube nanofibers: Processing and characterization, J. Eng. Fiber. Fabr. (2015).

10. Baddam et al. Fabrication of flame-retardant and superhydrophobic electrospun nanofibers, Surf. Interf. 2021

11. Norouzi et al. Nanoparticles as Effective Flame Retardants for Natural and Synthetic Textile Polymers: Application, Mechanism, and Optimization, Polym. Rev. 2015

12. inovenso.com

Author:MELİKE GOZUTOK

Article Source:https://www.inovenso.com/flame-retardant-nanofibers/