Halogen-free flame retardants have advantages such as environmental friendliness, low toxicity and high efficiency in the application of engineering plastics, but they also have disadvantages such as large dosage and relatively poor compatibility with plastics. The following is a detailed introduction:
First, types of halogen-free flame retardants
Inorganic flame retardants: such as aluminium hydroxide (ATH), magnesium hydroxide (MDH), etc. ATH has three functions: flame retardancy, smoke suppression and filling, and is hailed as a “pollution-free flame retardant”. MDH has the advantages of good thermal stability and no generation of toxic gases, and is an environmentally friendly green flame retardant.
Expandable graphite flame retardant: It is made by acidifying natural graphite with concentrated sulfuric acid and then expanding it. It has the characteristic of rapid expansion at high temperatures and can extinguish the flame through the instantaneous increase in volume when a fire occurs.
Nitrogen-based flame retardants: such as melamine (MA) and its salts (cyanuric acid salts, phosphates, guanidine salts and dicyandiamide salts), etc. Nitrogen-based flame retardants have the advantages of low volatility, non-toxicity, halogen-free, low smoke, and no generation of corrosive gases. They are often used in combination with other flame retardants.
Silicon-based flame retardants: They are divided into two major categories: inorganic silicon and organic silicon flame retardants. Silicone flame retardants are a new type of halogen-free flame retardants, featuring high efficiency, non-toxicity, low smoke, anti-dripping and pollution-free properties.
Phosphorus-based flame retardants: including inorganic phosphorus and organic phosphorus flame retardants. Red phosphorus is an inorganic phosphorus flame retardant with excellent performance, but it is prone to moisture absorption, oxidation and the release of highly toxic gases. Therefore, microencapsulation surface treatment is often adopted to improve its performance. Ammonium polyphosphate (APP) is also a kind of inorganic phosphorus flame retardant with good performance, featuring excellent thermal stability and low toxicity.
Second, the application effect of halogen-free flame retardants in engineering plastics
Environmental friendliness: Halogen-free flame retardants do not contain halogen elements and do not release harmful substances during combustion. They comply with environmental protection requirements such as ROHS and REACH and are not subject to export restrictions in developed countries.
Low toxicity: The combustion products contain few toxic substances, reducing the potential harm to human health.
Flame retardant performance: By adding special halogen-free flame retardants, the flame retardant performance of engineering plastics is stable, with low smoke and low odor when burning.
Processing performance: Halogen-free flame-retardant plastics are easy to be formed through injection molding, extrusion and other processing techniques, and will not corrode the mold surface.
