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We are all familiar with the popular foam insulation material polystyrene when it comes to protecting consumer goods and its application in the food industry in the form of plastic pallets and containers. The flame retardancy of this material is discussed in Materials Magazine.

Research: Effective expanded graphite coating on polystyrene beads can improve flame retardancy. Image Credit: Sima/Shutterstock.com

In recent years, this widely used synthetic polymer material has been mainly used in construction because expanded polystyrene (EPS) is used as an insulation board system for floors, walls, and roofs in homes and commercial buildings. However, one of the main disadvantages of EPS is that it is highly flammable and can be ignited at relatively low temperatures.

Therefore, a team of researchers from the Korea Institute of Civil Engineering and Construction Technology designed a flame-retardant coating using expanded graphite (EG) and a process to uniformly coat the coating on the surface of polystyrene beads. Their goal is to use the coating to improve the flame retardancy of commercial EPS beads to provide an effective fire safety solution.

An example of coating polystyrene beads with a flame-retardant coating solution. Image source: Bae, M et al., materials

Although EPS panels are being deployed on construction sites around the world, safety standards regarding non-combustibility are usually different. In South Korea, the government has begun to implement material standards, which means that these materials must pass at least a semi-incombustibility test to be suitable for on-site use.

However, most commercial EPS panels have not passed the current safety standards, which is why Korean researchers completed their tasks. Under the leadership of senior researcher Dr. Jaesik Kang, the team aims to add a "monomer that can impart flame retardancy to the polymer backbone to prepare flame retardant polymers," Kang explained.

According to the THR of the foam insulation sample of the cone calorimeter. Image source: Bae, M et al., materials

Expanded graphite (EG) has been identified as a good candidate for the intended application due to its unique characteristics. When in contact with the heat of the fire, graphite will expand and produce an expansion layer, thereby preventing the spread of the flame, thereby minimizing one of the biggest dangers of fire burning-the release of toxic smoke.

Although the toxicity level of EPS itself is equal to or lower than that of natural or organic materials, the spread of fire in buildings can cause other building materials (including chemical coatings and adhesives) to release toxic fumes. Therefore, due to the low flame retardant efficiency of EPS, it is necessary to improve safety standards and design methods to do this.

As the name suggests, expanded graphite has the ability to expand, which contributes to its flame retardant effect. Graphite has a special layered structure, which helps molecules to be inserted between graphite layers. Therefore, when the material comes into contact with fire, the graphite layer will be pushed away like an accordion.

In order to evenly spread EG on the beaded surface of EPS, the team made a flame-retardant solution prepared from a water-soluble composition of EG and other additives. The result is a flame-retardant expanded polystyrene block (FR-EPS).

"The flame retardant coating solution contains 10-30wt% porous particles, 5-20wt% starch, 20-50wt% EG-made flame retardant and 20-30wt% water based on the binder. A total of 0.1 to 3 wt% % Silane (organosilicon compound) and 3 to 15% by weight thermosetting resin as additives," Kang explained.

In the study, the material was tested under ambient air conditions according to KS F ISO 5660-1, which is the ISO fire response test standard. For comparison, the team used various EPS blocks of various compositions that were not treated with EG, and then measured the results according to the fire resistance index (FRI).

FR-EPS sample after cone calorimeter test. Image source: Bae, M et al., materials

Then the material is subjected to horizontal and vertical burning tests. In general, FR-EPS based on EG shows a better performance level, "Compared with the FRI value of other polystyrene composite materials, the FRI value of FR-EPS proves the'excellent' level and has a higher level of performance. FRI value," Kang said.

Although some commercially available EPS products exhibit a high level of self-extinguishing in the horizontal combustion test, their level is still very low in the vertical test. However, FR-EPS confirmed a high level of self-extinguishing in both horizontal and vertical tests-improving the latter's two levels.

FR-EPS has also passed the semi-incombustibility standard in the regulations, thus showing that the EPS coated with a water-soluble flame retardant made of expanded graphite meets good fire safety standards.

Kang and his team successfully produced an effective flame retardant coating based on expanded graphite to improve the flame retardancy of expanded polystyrene beads. The introduction of stricter policies and such methods to improve the flame retardancy of buildings will inevitably create a safer environment for people living and working in buildings.

Bae, M. Lee, H. Cui, G. Kang, J. Effective expanded graphite coating on polystyrene beads to improve flame retardancy. Materials 2021, 14, 6729. https://www.mdpi.com/1996-1944/14/21/6729

EUMPS, "The Behavior of EPS in the Event of Fire". August 2002. [https://eumeps.construction/content/8-downloads/4-documents/1-fire-safety/eps-behaviour-in-case-of-fire.pdf: Accessed in November 2021]

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David is an academic researcher and interdisciplinary artist. David's current research explores how science and technology, especially the Internet and artificial intelligence, can be put into practice to influence a new shift towards utopianism and the reemergence of commons theory.

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