Aug 31: Korean researchers have developed, for the first time, a recyclable flame-retardant composite that overcomes a fundamental limitation of conventional flame-retardant composites, which cannot be recycled once cured, while maintaining excellent flame resistance.
A research team led by Dr. Jin Chul Kim, Dr. Ji-Eun Jeong, and Dr. Young-Jae Jin at the Korea Research Institute of Chemical Technology has developed a self-reinforced composite fabrication technology that simultaneously achieves improved processability, flame retardancy, and recyclability simply by adding a low-cost, low-molecular-weight polyolefin additive.
The technology is expected to enable the use of lightweight and recyclable components in next-generation mobility applications such as electric vehicles, which have traditionally relied on metals or non-recyclable thermoset fiber-reinforced composites.
Fiber-reinforced composites, a type of thermoset composite material, have been widely used in products that require high flame resistance, including automotive components, electronic circuit boards, and electrical outlets. Because their shape becomes permanently fixed after curing, they can maintain their structural integrity even in high-temperature environments such as fires.
However, once cured, these materials cannot be melted again even when heated and therefore must be landfilled or incinerated at high temperatures. With the growing emphasis on carbon neutrality, regulations on and replacement of “non-recyclable materials” have become inevitable, creating an urgent need for composite materials that are reprocessable while also providing flame retardancy and processability.
To address this challenge, the research team developed a self-reinforced composite by stacking layers of high-density polyethylene fibers and films, which can be reprocessed when heated.
The researchers added a small amount of a low-cost, low-molecular-weight polyolefin additive to the intermediate film, enabling it to perform three functions simultaneously. The additive makes the material more flowable so that the film and fibers adhere tightly without gaps; helps the flame-retardant particles disperse uniformly without agglomerating; and can be effectively removed by washing during recycling.
Interlayer adhesion is a key factor determining the durability and safety of composite components. With the new additive, the adhesion between the film and fibers improved by approximately 40% compared with the material without the additive. In addition, although incorporating as much as 40 wt% flame retardant would normally cause a substantial decline in strength and flexibility, the composite achieved the highest flame-retardant rating, UL-94 V-0, without compromising its mechanical properties.
UL-94 V-0: The highest rating under the UL-94 vertical burning test established by Underwriters Laboratories. Materials rated V-0 rapidly self-extinguish after ignition and do not produce flaming drips that ignite combustible materials below.
Meanwhile, materials containing a conventional commercial additive retain more than 40% of the additive during recycling, resulting in a significant deterioration in material properties. In contrast, more than 90% of the additive used by the research team could be removed, enabling the recovery of high-purity recycled material with color and strength comparable to those of virgin plastic.
The research team plans to conduct additional flame-retardancy tests for industrial applications and follow-up studies to ensure that flame retardants do not accumulate during repeated recycling. The team also plans to accelerate the commercialization of structural composites for next-generation mobility applications through collaboration with potential industrial users on material property evaluation and demonstration studies.
The research was published in March in Composites Part B (Impact Factor: 14), an international journal ranked in the top 1% by Journal Citation Reports.