Halogen-free flame retardants are widely used in polycarbonate (PC), featuring environmental friendliness and excellent flame retardant performance. The following is an introduction from several aspects including application advantages, common types, application effects, technical challenges and development trends:
Application advantages
Environmental friendliness: Halogen-free flame retardants do not contain halogen elements, thus avoiding the toxic gases produced by halogen elements during combustion, such as hydrogen chloride and hydrogen bromide, which may cause harm to human health in case of fire. Moreover, they meet environmental protection requirements and reduce potential risks to the environment and human health.
Flame retardant performance: By adding halogen-free flame retardants, polycarbonate materials can to a certain extent slow down the spread of flames and heat release, thereby enhancing the fire safety of the materials.
Thermal stability: Halogen-free flame retardants enable polycarbonate to maintain good stability at high temperatures, making it less prone to melting and helping to preserve structural integrity in the event of a fire.
Common types
Silicone halogen-free flame retardants: such as FR3040, are long-lasting halogen-free flame retardants suitable for both transparent and opaque polycarbonate, and are highly efficient and low-additive flame retardants for thin-walled PC products.
Sulfonate flame retardants: The mechanism of action is divided into three levels. At the initial stage of combustion, the flame retardant decomposes to form sulfuric acid, which catalyzes the dehydration and cross-linking of polycarbonate molecular chains, rapidly forming a dense carbon layer on the material surface. In the mid-term stage, sulfur dioxide gas is released to dilute the oxygen concentration and simultaneously capture the free radicals produced by combustion. In the later stage, the carbon layer continues to thicken, just like putting on heat-insulating armor for the material, keeping the internal temperature below 400℃.
High-molecular polymer solid halogen-free flame retardants of phosphorus and nitrogen, such as FR-106, are specifically designed for polycarbonate alloys (PC/ABS) and polyphenylene oxide alloys (PPO/HIPS), facilitating the addition of materials and enhancing temperature resistance, and can bring superior high-temperature resistance in the used resins.
New solid phosphate ester flame retardants: They have many advantages such as low volatility and migration, good thermal stability, the ability to enhance PC, and convenient treatment.
Reactive phosphorus-based flame retardants: For instance, by introducing triphenylphosphine oxide (TPO) units into the PC chain segment, PC can be endowed with permanent flame retardancy. However, the preparation process is complex, product quality is difficult to control, and its industrial value remains to be evaluated.
Application effect
Transparent halogen-free flame-retardant PC plastic: It maintains the high transparency of PC material, making the appearance of the product clear and not affecting the visual effect. It can be used to manufacture the casings of electronic devices, such as computers and mobile phones, to enhance the environmental friendliness and safety of the products. It can also be used to produce transparent fireproof isolation boards, window materials, etc., which not only ensures a wide field of vision but also enhances safety in case of fire. It can also be used for interior trim parts of automobiles, aircraft interiors, etc., to improve the survival rate of passengers on transportation vehicles in case of fire. And it is used in the production of protective glasses, face masks, etc., providing transparency while offering flame and heat protection.
High-strength halogen-free flame-retardant PC formula: Such as the Edgetek™ halogen-free flame-retardant polycarbonate (PC) formula from Evant, it meets the UL94 V-0 high flame-retardant grade requirements. Combining high strength, high fluidity and long-term stability, it provides a safer and more sustainable material option for key structural components of servers. The composite system of PC+40% glass fiber (GF) is adopted. By optimizing the material ratio, it maintains high strength while endowing the material with excellent impact resistance, ensuring that the component is not prone to deformation under high temperature or load, and can also meet the application requirements in frequent plugging and unplugging or vibration environments.
Technical challenges
The contradiction between thermal stability and flame retardant efficiency: Some phosphorus-based flame retardants may decompose prematurely at processing temperatures, affecting their flame retardant performance.
Maintenance of material light transmittance: After adding flame retardants, the light transmittance of polycarbonate may decrease, affecting the appearance and usage effect of the product.
Cost control: The new type of silicone flame retardant is relatively expensive, which increases the production cost.
Development trend
Bionic structural design: Drawing on the interlaced and laminated structure of nacre, a barrier layer with alternating organic and inorganic distribution is constructed; Simulate the hollow structure of polar bear hair and develop a porous flame-retardant system.
Intelligent early warning system integration: Embedding graphene sensor networks into materials to achieve early fire early warning functions.
