What Are The Latest Advances in Flame Retardant Technology at Home And Abroad

What Are the Latest Advances in Flame Retardant Technology at Home and Abroad

Polymer materials, one of the three major materials alongside ceramic and metal materials, are widely used in almost every aspect of human work and life. However, most polymer materials are carbon-based polymers, making them highly flammable when exposed to open flames, posing a serious threat to human life and property. Therefore, research into the flame retardant properties of polymers is essential.

Based on the combustion characteristics of polymer materials, various methods can be employed to interrupt the combustion process and achieve flame retardancy. In 1930, the antimony oxide-chlorinated paraffin synergistic flame retardant system was discovered and successfully applied to some polymer materials. In the 1950s, Hooker Chemical Company developed flame-retardant unsaturated polyesters using reactive monomers containing chlorinated phosphoric acid. Subsequently, new reactive flame retardant monomers containing bromine and phosphorus emerged. In the 1980s, discussions on toxicity and environmental issues in the flame retardant field led to halogen-free, smoke-suppressing, and low-toxicity flame retardants becoming new development goals. With the rapid development of polymer materials, research on flame retardant technology and mechanisms has become increasingly extensive and in-depth. Various flame retardant technologies have been explored based on gas-phase, condensed-phase, and heat exchange interruption mechanisms. In recent years, composite flame retardant, synergistic flame retardant, and macromolecular flame retardant technologies have garnered significant attention. This article provides an overview of the recent progress in these flame retardant technologies both domestically and internationally.

I. Composite Flame Retardant Technology

1. Layered Double Hydroxides (LDHs)  

Layered double hydroxides (LDHs) are layered inorganic nanomaterials with compositions and structures similar to aluminum hydroxide (Al(OH)₃, ATH) and magnesium hydroxide (Mg(OH)₂, MH). They combine the advantages of both and are free of toxic substances, making them ideal green flame retardants for smoke suppression. The flame retardant mechanism of LDHs involves decomposition during combustion into CO₂, H₂O, and metal oxides. CO₂ and H₂O dilute flammable gases and O₂, reducing combustion temperature, while metal oxides promote char layer formation, isolating O₂ and heat, thereby slowing substrate degradation.

2. Nanoporous Metal-Organic Framework Materials (MOFs)  

MOFs are porous organic-inorganic hybrid materials formed by self-assembly of organic ligands with metal ions or clusters. Their design is flexible and their structure is tunable. By modifying organic ligands or metal coordination sites, MOFs with specific properties can be obtained, indicating broad application potential. Zeolitic imidazolate frameworks (ZIFs), combining the advantages of traditional MOFs and zeolites, are formed by self-assembly of transition metals with imidazole-containing organic ligands. They are easy to synthesize, stable, have regular pores, diverse structures, and high catalytic activity.

3. Polyhedral Oligomeric Silsesquioxanes (POSS)  

POSS is a novel siloxane-based flame retardant with an organic-inorganic hybrid structure. It improves flame retardancy while enhancing mechanical, processing, and thermal properties of polymers. POSS, with its hybrid, cage-like, and nanostructured features, increases polymer thermal stability, flame retardancy, and mechanical performance while reducing dielectric constant. POSS and its derivatives, as halogen-free flame retardants, represent a major category of novel halogen-free flame retardants and are widely used.

4. Graphene Nanosheets (GNS)

GNS are two-dimensional nanosheet materials composed of a single layer of carbon atoms. GNS and their derivatives exhibit excellent flame retardant properties due to their nano-effects, especially when combined with inorganic nanomaterials to form versatile flame retardant materials. Compared to traditional carbon-based flame retardants (e.g., graphite, expanded graphite, oxidized graphite), GNS's unique two-dimensional nanostructure offers higher flame retardant efficiency. Compared to carbon nanotubes, GNS is more cost-effective for industrial applications.  

The flame retardant mechanism of GNS and its derivatives includes:  

- Promoting the formation of dense, continuous char layers during combustion, providing physical isolation.  

- High specific surface area effectively adsorbs flammable organic vapors or hinders their release and diffusion.  

- Active groups on GNS and GO surfaces decompose and dehydrate at low temperatures, releasing gases that absorb heat and reduce polymer matrix temperature while diluting O₂ concentration.  

- Interaction with polymer chains forms a three-dimensional network structure, preventing melt dripping and improving flame retardancy.

II. Synergistic Flame Retardant Technology

One of the latest international research hotspots in halogen-free flame retardants is the use of multiple flame retardant elements to compensate for the shortcomings of single elements, balancing flame retardant dosage, performance, and cost to meet growing environmental and safety requirements. Researchers have extensively studied synergistic effects of various flame retardant systems, such as hydroxide synergistic flame retardancy, phosphorus-nitrogen synergistic flame retardancy, phosphorus-silicon synergistic flame retardancy, and nanoparticle composite flame retardant systems.

1. Metal Hydroxide Synergistic Flame Retardancy  

Metal hydroxides, including ATH and MH, are among the most environmentally friendly flame retardants as they produce no harmful substances during flame retardancy. Their decomposition products can absorb harmful gases and smoke generated during polymer combustion. Common halogen-free composite flame retardants are categorized into layered materials, phosphorus-containing compounds, and rare earth oxides.

2. Phosphorus-Nitrogen Synergistic Flame Retardancy  

Phosphorus-nitrogen synergy has become a key direction in phosphorus- and nitrogen-based flame retardant research and development, offering an environmentally friendly and halogen-free option in many fields. The flame retardant mechanism involves a combination of condensed-phase and gas-phase flame retardancy. During combustion, flame retardants decompose to form inorganic acids like phosphoric acid or polyphosphoric acid, creating a protective layer on the substrate surface to isolate air. Simultaneously, they release non-flammable gases like ammonia, nitrogen, water vapor, and nitrogen oxides, blocking oxygen supply and achieving flame retardancy. For example, water-soluble phosphorus-nitrogen synergistic intumescent flame retardants (PEIPO) for water-blown flexible PU foams are prepared using polyethyleneimine and phosphorus intermediate precursors.

3. Other Synergistic Systems  

Alkyl hypophosphite flame retardants, known for their thermal stability, high phosphorus content, and excellent flame retardant performance, are widely used but expensive. Their mechanical performance is not ideal when used alone, so they are often combined with nanoparticles or inorganic flame retardants. Linear or branched alkyl hypophosphites are the most widely used, with AlPi applied in polyesters and polyamides (PA). For instance, AlPi and triethylenglycol triglycidate (TGIC) synergistically flame retard polyamide 6 (PA6). When the total mass fraction of AlPi and TGIC is 11% with a mass ratio of 97:3, UL-94 V-0 rating and LOI of 30.3% are achieved. Another example involves blending ammonium polyphosphate (APP), aluminum hypophosphite (AHP), and melamine cyanurate (MCA) with polypropylene (PP). When the total flame retardant mass is 30% with a ratio of m(APP):m(AHP):m(MCA) = 4:1:1, ideal flame retardancy is achieved, with LOI of 33% and UL-94 V-0 rating.

III. Macromolecular Flame Retardant Technology

Macromolecular flame retardants are synthesized by chemically reacting small-molecule flame retardants into macromolecular structures, resulting in compounds rich in flame retardant elements with good compatibility with polymers. For example, an inorganic-organic hybrid macromolecular flame retardant—hexa[4-(N-phenylamino-DOPO-methylene)phenoxy]cyclotriphosphazene (DOPO-PCP)—is synthesized via substitution, condensation, and addition reactions for DGEBA flame retardancy. Another example involves introducing hindered amine groups with free radical scavenging functions into intumescent flame retardants (IFR) to create a novel macromolecular intumescent flame retardant (HAPN), which is used with APP to flame retard PP.

Flame retardants have evolved significantly with the widespread application of polymer materials. As environmental awareness grows, demand increases for efficient, non-toxic, polymer-compatible, low-migrating, and cost-effective eco-friendly flame retardants. New flame retardant varieties and emerging technologies are continuously emerging. Synergistic and macromolecular flame retardant technologies are advancing toward higher efficiency, lower toxicity, and environmental friendliness. Future research directions include ultrafine design, microencapsulation, synergistic combinations of different flame retardants, macromolecular flame retardant structural design, and surface modification technologies for polymer flame retardant materials. With ongoing research progress, flame retardants are poised for vigorous development.

YINSU Flame Retardant New Material Co., Ltd. has achieved remarkable results in the field of flame retardants. Its microcapsule-coated red phosphorus flame retardant adopts the original multi-layer microcapsule coating process, which is characterized by high phosphorus content, low additive amount, low smoke density, etc., which can significantly reduce the cost of the material, and at the same time, improve the dispersion and compatibility, and ensure that the material appearance is flat and bright. In addition, the composite antimony flame retardants of YINSU Flame Retardant Company, such as T series, not only maintain the flame retardant effect of traditional antimony trioxide, but also significantly reduce the cost of raw materials, with excellent processing performance and environmental compliance, are suitable for a wide range of plastic substrates, and are widely used in wires and cables, electronic and electrical appliances, and automotive interiors and other industries. With their advantages of high efficiency flame retardancy, environmental compliance and cost optimization, these products have become the ideal choice for many industries to enhance the flame retardancy of their products.