The Korea Institute of Science and Technology (KIST) announced that a research team from the Advanced Composite Materials Research Institute led by Dr. Yong chae Jung has developed a flame-retardant carbon fiber reinforced composite material (CFRP) that uses tannic acid extracted from plants. At the same time, the group also proposed an environmentally friendly material recycling method.
CFRP is a composite material containing carbon fiber, which is 4 times lighter than steel but 10 times stronger than steel. It is widely used in aerospace, automotive, shipbuilding and sports equipment industries. From the structural point of view, CFRP is composed of carbon fiber and epoxy resin, and its function is similar to that of steel and cement in concrete structures. In order to achieve a certain mechanical strength, the carbon fiber and epoxy resin in CFRP must be firmly bonded together. In addition, CFRP must be fire-resistant because it is often used in applications closely related to daily life, such as building materials. In order for CFRP to exert such characteristics, it is sometimes necessary to synthesize it with additives.
Since CFRP has heat resistance, it can be made fireproof by adding halogen flame retardants. However, the use of halogens in CFRP is banned globally, because such chemicals produce toxic substances when they are incinerated and recycled. Therefore, the current task is to use non-toxic and safe materials to make fireproof CFRP
Jung Yong-chae, the principal researcher of the KIST Advanced Composites Institute, tried to use an environmentally friendly substance, tannin, to improve the mechanical strength and flame retardancy of CFRP. The characteristic of tannic acid is that it can be closely combined with carbon fiber, and it will turn into charcoal when burned. The charred tannic acid will act as a barrier to prevent the inflow of external oxygen. By using tannic acid to make epoxy resin and blending it into carbon fiber, KIST's research team successfully developed a strong flame-retardant CFRP.
Unlike traditional epoxy resins that are susceptible to heat, epoxy resins made of tannic acid are flame-retardant and require no additives, which means that toxic substances generated when CFRP is incinerated for recycling will no longer be a problem. In addition, because traditional CFRP is incinerated, the performance of its epoxy resin will decrease and cannot be fully recycled. The research team also proposed a new recycling method.
By dissolving CFRP in water in a supercritical fluid state (such as temperature and pressure exceeding a set level), more than 99% of CFRP can be recovered without reducing the performance of carbon fiber. The study also found that the dissolution of epoxy resin will produce a substance called "carbon dots", which can be used as electronic materials (photoelectric, sensing, biological imaging, etc.). Unlike the incineration recycling method, the incineration epoxy resin can only recover incomplete carbon fiber, and this new recycling method can recover all the components of the composite material.