Technical Insights into LSHF Flame Retardants for Industrial Professionals

Technical Insights into LSHF Flame Retardants for Industrial Professionals

Low-smoke, halogen-free flame-retardant materials are a type of flame-retardant material that does not release halogens (such as fluorine, chlorine, bromine, iodine, etc.) when burned, produces low smoke, and has low toxicity. They are widely used in fields with high requirements for safety and environmental protection. The following is a detailed introduction from three aspects: basic knowledge, issues in application, and new development materials.

I. Basic Knowledge of Low-Smoke, Halogen-Free Flame-Retardant Materials

1. Core Definitions and Characteristics

The core requirements for low-smoke, halogen-free flame-retardant materials are:

• Halogen-free: Does not contain halogen elements (such as chlorine and bromine in traditional halogen-containing flame-retardant materials), and does not produce corrosive toxic gases such as hydrogen chloride (HCl) and hydrogen bromide (HBr) during combustion.

• Low Smoke: Low smoke generation during combustion (typically measured by smoke density rating SDR, generally requiring ≤50), reducing visibility loss and escape difficulties during fires.

• Flame Retardant: Achieves a certain flame retardant rating (e.g., UL94 V-0, GB/T 2408 V-0 grade) through the addition of flame retardants or structural design, delaying or preventing flame spread.

2. Main Composition and Flame Retardant Mechanism

Low-smoke halogen-free flame-retardant materials typically use polymers as the base material (such as polyethylene (PE), polypropylene (PP), polyolefin elastomers (POE), etc.) combined with halogen-free flame retardants. Their flame-retardant mechanisms primarily include:

• Cooling effect: Flame retardants (such as magnesium hydroxide, aluminum hydroxide) decompose when heated, absorbing heat and lowering the surface temperature of the material to inhibit combustion.

• Dilution effect: The inert gases produced by decomposition, such as water vapor and carbon dioxide, dilute the concentration of oxygen and combustible materials, interrupting the combustion chain.

• Char formation effect: Flame retardants (such as phosphorus-based or silicon-based compounds) promote the formation of a dense char layer on the material surface, isolating heat and oxygen and preventing further flame spread.

• Synergistic effect: Combining multiple flame retardants (e.g., phosphorus-nitrogen compounds, silicon-phosphorus compounds) enhances flame retardancy through synergistic effects (e.g., reducing the amount of single flame retardant added while improving material performance).

3. Typical Application Areas

The core advantage of low-smoke, halogen-free flame-retardant materials is “safety + environmental protection,” so they are primarily used in scenarios with strict fire safety requirements:

• Electrical cables: building wiring, rail transportation (subways, high-speed rail), automotive wiring harnesses, etc. (toxic gases from burning cables are a primary cause of death in fires, and low-smoke, halogen-free materials can reduce this risk).

• Building materials: wall insulation panels, flooring, pipes, etc. (high-rise buildings, hospitals, schools, and other densely populated areas have particularly high demand).

• Electronics and appliances: smartphone/computer casings, charging station components, internal insulation parts of appliances, etc. (reducing smoke and toxic hazards in electrical fires).

• Transportation: ship and aircraft interior components (in enclosed spaces, low-smoke, halogen-free materials can extend escape window time).

II. Major Issues in Application

Despite the significant advantages of low-smoke, halogen-free flame-retardant materials, the following bottlenecks still exist in practical applications:

1. Conflict between mechanical properties and flame-retardant performance

To achieve flame-retardant effects, halogen-free flame retardants (such as magnesium hydroxide, aluminum hydroxide) typically require high addition levels (sometimes exceeding 50%). However, excessive filling disrupts the continuity of the polymer matrix, leading to:

• Reduced tensile strength and impact strength (easily brittle, such as cable sheaths prone to cracking).

• Reduced flexibility (e.g., pipes and seals lose elasticity, affecting installation and service life).

2. Poor processing performance

• High-filler-content flame retardants increase melt viscosity, leading to higher energy consumption during extrusion, injection molding, and other processing steps, and may cause precipitation phenomena (where flame retardant particles precipitate to the surface, affecting appearance and performance).

• Some flame retardants (e.g., phosphorus-based) decompose easily at high processing temperatures, requiring strict temperature control, which increases production complexity.

3. High cost

• High-performance halogen-free flame retardants (such as new phosphorus-based or silicon-based compounds) are significantly more expensive than traditional halogen-containing flame retardants (such as bromine-based compounds).

• To balance mechanical properties, additives such as compatibilizers and lubricants must be added, further increasing material costs.

• High processing difficulty reduces production efficiency, indirectly increasing overall costs.

4. Insufficient weather resistance and stability

• Some halogen-free flame retardants (such as magnesium hydroxide) have poor water resistance, and prolonged exposure to humid environments may cause the material to absorb moisture and degrade in performance.

• Under aging conditions such as ultraviolet light and high temperatures, the interface between the flame retardant and the polymer matrix is prone to failure, leading to a decline in flame retardant performance (e.g., affecting the service life of outdoor electrical cables).

III. New Material Developments and Technological Trends

In response to the above issues, recent research and industrialization of low-smoke halogen-free flame-retardant materials have focused on “high performance, low cost, and environmental friendliness.” The following are several representative new development directions:

1. Efficient Composite Flame-Retardant Systems

Reducing the amount of flame retardant added through “synergistic effects” while enhancing both flame-retardant and mechanical properties is the most mature technical approach currently available:

• Phosphorus-nitrogen composite systems: Combining phosphorus-based compounds (e.g., phosphates, red phosphorus) with nitrogen-based compounds (e.g., melamine, guanidine salts), where nitrogen-based compounds promote char formation of phosphorus-based compounds, and phosphorus-based compounds enhance the flame-retardant efficiency of nitrogen-based compounds, allowing a 10%-20% reduction in additive dosage (e.g., in PP materials, phosphorus-nitrogen composite flame retardant can achieve UL94 V-0 rating with a 25% addition, and tensile strength is 15% higher than that of a single phosphorus-based system).

• Silicon-phosphorus composite system: Silicon-based compounds (such as siloxanes, nano-silica) improve material processing flowability while synergistically forming char with phosphorus-based compounds, enhancing material impact resistance and weatherability (suitable for electronic appliance housings).

2. Nano-Composite Flame-Retardant Materials

Utilizing the high specific surface area and interfacial effects of nanoparticles to optimize material performance:

• Nano-flame retardants: Convert magnesium hydroxide and aluminum hydroxide into nano-sized particles (particle size 50–100 nm) to minimize disruption to the polymer matrix while enhancing flame retardancy (e.g., a 30% addition of nano-magnesium hydroxide achieves the same flame retardancy as 40% of traditional micron-sized particles, with a 20% increase in impact strength).

• Nano-reinforcing phases: Incorporating carbon nanotubes, graphene, etc., into flame-retardant materials to compensate for the mechanical property degradation caused by flame retardants using their high strength characteristics, while promoting char formation (e.g., in a PE/graphene/phosphorus-based composite system, tensile strength increases by 30%, and smoke density decreases by 15%).

3. Bio-Based Low-Smoke Halogen-Free Flame-Retardant Materials

In line with the “dual carbon” trend, environmentally friendly flame-retardant materials are prepared using renewable biomass raw materials (such as starch, cellulose, and plant oils):

• Matrix modification: Using bio-based polymers such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA) as the matrix to replace traditional petroleum-based polymers (such as PE, PP), which inherently possess biodegradability.

• Bio-based flame retardants: Using natural products (such as phytate and chitosan) as flame retardants, and enhancing flame retardancy through chemical modification (such as the reaction between phytate and nitrogen-based compounds). For example, the PLA/phytate-melamine composite system achieves a flame retardancy rating of UL94 V-0 and can degrade by over 30% in soil within six months.

4. Functionalized Custom Materials

Developing specialized materials tailored to specific application requirements:

• High-temperature and low-temperature resistant type: Incorporating high-temperature resistant resins (e.g., polyether ether ketone PEEK) into the flame-retardant system, suitable for new energy vehicle battery packs (operating in environments from -40°C to 120°C).

• High-transparency type: Combining transparent flame retardants (such as organophosphorus compounds) with transparent polymers (such as PC, PMMA) for transparent partitions in rail transit applications (flame-retardant without compromising transparency).

• Self-healing type: Incorporating reversible crosslinking agents (such as disulfide compounds) to enable material repair through heating or light exposure after damage, extending service life (suitable for wire and cable sheathing).

As safety and environmental standards rise globally, low-smoke, halogen-free (LSHF) materials are essential for wire and cable applications in construction, rail transit, and electric vehicles. Addressing industry challenges in balancing flame retardancy with mechanical properties and processability, Guangzhou Yinsu Flame Retardant offers specialized solutions. Our portfolio includes Microencapsulated Red Phosphorus Masterbatch FRP-950X for enhanced safety and char formation. Antimony Trioxide Replacement T3 for halogen-free synergy. As well as a variety of highly effective organophosphorus flame retardants ADP. These enable superior UL94 V-0 performance while meeting stringent environmental requirements for safer cable solutions.