Korean Researchers Develop Recyclable Flame-Retardant Composite for Mobility

Updated on September 01, 2026 • 7 min read

Researchers at the Korea Research Institute of Chemical Technology (KRICT) have developed a recyclable self-reinforced composite that achieves UL-94 V-0 flame-retardant performance, targeting one of the difficult trade-offs in thermoplastic composite development: combining fire resistance, mechanical performance, processability and recyclability in the same material system.

The technology uses high-density polyethylene (HDPE) fibers and films together with a low-cost, low-molecular-weight polyolefin additive. According to the research team, the additive improves interlayer bonding and flame-retardant dispersion during manufacturing but can largely be removed during recycling.

The researchers report an approximately 40% improvement in adhesion between the film and reinforcing fibers and removal of more than 90% of the additive during recycling.

The work, led by Dr. Jin Chul Kim, Dr. Ji-Eun Jeong and Dr. Young-Jae Jin at Korea Research Institute of Chemical Technology (KRICT), was published in Composites Part B.

Why Flame-Retardant Composites Are Difficult to Recycle

Fire performance and recyclability do not naturally arrive together in conventional composite structures.

Many applications requiring high flame resistance have traditionally used thermoset fiber-reinforced composites. Once a thermoset matrix has undergone crosslinking and cured, it cannot simply be remelted and reshaped in the way a conventional thermoplastic can.

That characteristic provides useful thermal and dimensional stability, but complicates end-of-life processing.

Thermoplastic composites offer a different route because the polymer matrix can potentially be reheated and reprocessed. However, introducing large quantities of flame-retardant additives creates another materials-engineering problem.

High filler loading can increase viscosity during processing, interfere with impregnation or consolidation and reduce mechanical performance. Poorly dispersed particles can also produce local inconsistencies within the composite.

The KRICT team therefore focused not only on making an HDPE composite flame retardant, but on managing the interaction between processing, reinforcement, additives and subsequent recycling.

HDPE Fibers and Films Form a Self-Reinforced Composite

Instead of combining carbon or glass fibers with a polymer matrix, the researchers developed a self-reinforced composite (SRC) based on HDPE fibers and films.

In self-reinforced polymer composites, the reinforcement and matrix are based on the same polymer family or chemically compatible materials.

The KRICT process stacks HDPE fibers and films to produce the composite structure.

This architecture is particularly interesting from an end-of-life perspective because it avoids introducing a fundamentally different reinforcing material that would subsequently have to be separated from the polymer matrix.

The challenge is achieving sufficient consolidation without damaging the reinforcing fibers.

For a useful laminate to form, the intermediate polymer needs enough flow during processing to fill gaps and establish strong interfaces while the reinforcement retains its structural function.

Polyolefin Additive Performs Three Functions

The research team’s low-molecular-weight polyolefin additive was introduced into the intermediate film and performs three reported functions.

First, it increases material flow during processing, helping the film establish closer contact with the HDPE fibers.

Second, it improves the dispersion of flame-retardant particles, reducing their tendency to agglomerate.

Third, the additive was selected so that it can largely be removed through washing during recycling.

This combination addresses a significant materials-processing issue.

Adding flame retardants can solve one performance requirement while creating problems elsewhere in the material system. If particles increase viscosity or concentrate unevenly, consolidation and mechanical properties can suffer.

According to KRICT, introducing the new additive increased adhesion between the film and fibers by approximately 40% compared with the formulation without the additive.

Composite Reaches UL-94 V-0 With 40 wt% Flame Retardant

The researchers incorporated as much as 40 wt% flame retardant into the composite.

Such a high loading would normally be expected to create substantial challenges for mechanical properties and processing.

However, KRICT reports that the resulting material retained its mechanical properties while reaching UL-94 V-0, the highest classification within the UL-94 vertical burning test cited by the researchers.

V-0-rated specimens must extinguish rapidly under the prescribed test conditions and must not produce flaming drips that ignite the cotton indicator positioned below the specimen.

For transportation applications, however, UL-94 V-0 should not be interpreted as complete qualification for a specific component. Automotive and mobility applications can require additional fire, smoke, toxicity, thermal-aging and application-specific testing.

KRICT says further flame-retardancy testing for industrial applications is planned.

More Than 90% of Additive Removed During Recycling

Perhaps the more distinctive aspect of the research is what happens after the composite reaches the end of its first use cycle.

The researchers compared their formulation with material containing a conventional commercial additive.

According to KRICT, more than 40% of the conventional additive remained after recycling, adversely affecting the recovered material.

With the newly developed additive system, more than 90% of the additive could be removed.

The researchers subsequently recovered material reported to have color and strength comparable with virgin plastic.

This is important because recyclability is not determined simply by whether a thermoplastic can technically be melted again.

Repeated processing can introduce contamination, residual additives, polymer degradation and changing material properties. These effects can progressively reduce the quality and potential applications of recycled material.

Designing additives with their eventual removal in mind introduces end-of-life requirements much earlier into composite formulation.

Professor’s Analysis: Designing the Interface for Both Manufacturing and Recycling

The most interesting aspect of the KRICT work is not simply that the researchers produced a flame-retardant thermoplastic composite.

It is that the same additive has been designed to help manufacturing and then largely disappear when the material reaches recycling.

That represents an important shift in how composite constituents can be considered.

During manufacturing, the additive is useful. It improves flow, supports particle dispersion and contributes to better fiber-film contact.

During recycling, retaining the same additive becomes undesirable. It therefore needs to be efficiently removed so that the recovered polymer can approach the properties of the original material.

This creates a kind of temporary processing functionality.

For future recyclable composites, this principle could be significant. Engineers may increasingly need to evaluate not only what a sizing, binder, compatibilizer or processing aid contributes during production, but also what happens to that chemistry during the second and third material lifecycle.

The self-reinforced HDPE architecture provides another advantage from this perspective.

A conventional GFRP or CFRP structure inherently contains two substantially different material classes. Recovering value from both constituents can require separation or dedicated recycling routes.

A self-reinforced polymer composite potentially simplifies that material architecture.

But significant questions remain before this laboratory result becomes an automotive structural material.

Repeated recycling behavior needs to be established. Flame retardants must not progressively accumulate through multiple recycling loops. Long-term mechanical behavior, temperature exposure, environmental aging and component-scale manufacturing also need evaluation.

And because HDPE has fundamentally different stiffness and temperature-performance characteristics from carbon fiber/epoxy, glass fiber composites and metals, the technology will need to be matched carefully to appropriate structural applications.

The research should therefore be viewed as a materials-platform development rather than a direct replacement for existing automotive structural composites.

Next Step Is Industrial Validation

KRICT plans additional flame-retardancy testing as well as studies examining whether flame retardants accumulate during repeated recycling.

The researchers also intend to work with industrial partners on material characterization and demonstration programs aimed at next-generation mobility applications, including electric vehicles.

Those studies will be important in determining where the material can realistically sit between conventional polymers, thermoplastic composites, thermoset composites and metallic structures.

If the approach scales successfully, its larger contribution may be the demonstration that composite formulation can be engineered around manufacturing performance and end-of-life recovery simultaneously, rather than treating recyclability as a problem to solve only after the component has been produced.