Plant acid makes carbon fiber less flammable, more recyclable
Carbon fiber composite materials may be light and strong, but making them resistant to fire has been a bit of a challenge. Now, though, Korean scientists have discovered that a plant-derived substance both keeps them from burning and makes them easier to recycle.
In the past, halogen was added to carbon fiber composites in order to make them flame-resistant. Its use for that purpose was ultimately banned worldwide, however, due to the fact that it produced toxic substances when the materials were incinerated for recycling. That incineration process burned away the epoxy resin in the composites, leaving only bits of the carbon fibers behind.
Led by Dr. Yong-Chae Jung, researchers at the Korea Institute of Science and Technology (KIST) recently tried using tannic acid in place of halogen. Tannic acid is an abundant natural polyphenol, which is produced by plants.
When added to epoxy resin, the acid improved that resin's ability to bond with the carbon fibers. More importantly, though, the tannic acid charred when exposed to flames – this formed a charred layer on the surface of the carbon fiber, which kept flame-feeding oxygen from getting into the material. As a result, the composite was both stiff and flame-resistant.
Additionally, the material can be thoroughly recycled simply by placing it in water that's in a supercritical fluid state – this means that the liquid's temperature and pressure are being kept above a specific critical level. The composite dissolves within "tens of minutes" of immersion, allowing over 99 percent of both the fibers and the resin to be recovered.
What's more, the reclaimed resin can be used to produce carbon quantum dots, which are currently utilized in items such as LEDs and organic solar cells.
"We have created a composite material with an expanded range of application that is a dramatic improvement over conventional carbon fiber-reinforced plastic in terms of flame-retardancy, mechanical rigidity, and recyclability," says Dr. Jung. "These improved traits are significant in that they determine the range of application of said composite material."
A paper on the research was recently published in the journal Composites Part B: Engineering.