1. Classification by chemical composition
Inorganic flame retardant
Hydroxides, such as aluminum trihydroxide (ATH) and magnesium hydroxide (MH), decompose endothermically upon heating and release water vapor, diluting combustible gases. They have advantages such as environmental friendliness, non-toxicity, and low cost. However, large addition amounts (typically 30%-60%) may affect the mechanical properties of materials.
Oxides and salts: such as antimony trioxide (Sb₂O₃), zinc borate, barium metaborate, etc., are often used as synergists in combination with halogenated flame retardants to enhance the flame retardant effect.
Others: such as red phosphorus, ammonium polyphosphate (APP), magnesium carbonate, etc. Among them, red phosphorus has high flame retardant efficiency and requires a small amount of addition, but it is prone to oxidation and moisture absorption, and needs to be modified before use.
Organic flame retardant
Halogenated flame retardants: Mainly composed of brominated (such as decabromodiphenyl ether, tetrabromobisphenol A) and chlorinated (such as chlorinated paraffin) compounds, they exhibit high flame retardant efficiency. However, they may release toxic gases (such as dioxins) during combustion, making them environmentally unfriendly and gradually subject to restrictions.
Phosphorus-based flame retardants: including inorganic phosphorus (such as red phosphorus, APP) and organic phosphorus (such as phosphates, phosphonates), which achieve flame retardancy by promoting char formation and forming a thermal insulation layer. Some varieties exhibit both gas-phase and condensed-phase flame retardant effects.
Nitrogen-based flame retardants: such as melamine and melamine cyanurate (MCA), release non-flammable gases (such as NH₃) when heated, diluting the oxygen concentration. They are often used in conjunction with phosphorus-based flame retardants to form an intumescent flame retardant system.
Intumescent flame retardant (IFR): Consisting of an acid source (such as APP), a carbon source (such as pentaerythritol), and a gas source (such as melamine), it expands upon heating to form a porous carbon layer, providing thermal and oxygen insulation. It is an environmentally friendly, halogen-free flame retardant, widely used in materials such as polyolefins.
2. Classification by usage
Additive flame retardant
It is added through physical mixing before plastic processing, offering convenience and strong applicability, accounting for 80%-90% of the total flame retardant content. It is commonly used in thermoplastic materials such as polyethylene (PE) and polypropylene (PP). However, it may affect the processability, mechanical properties, and electrical properties of the material.
Reactive flame retardant
The molecule contains reactive functional groups that can chemically bond to polymer chains, providing a durable flame retardant effect with minimal impact on material properties. It is primarily used in thermosetting plastics such as epoxy resin and polyurethane. The disadvantage is that there are fewer varieties and limited applications.
3. Classification by Environmental Friendliness
Traditional flame retardants: Mainly halogen-based, they exhibit high flame retardant efficiency, but pose significant environmental and toxicity concerns. Some of them have been restricted for use by regulations such as the EU RoHS.
Environmentally friendly flame retardants: including halogen-free flame retardants (such as phosphorus-based, nitrogen-based, silicon-based, and intumescent types) and nano-flame retardants (such as nano-magnesium hydroxide and nano-silica), which are characterized by low smoke, low toxicity, and high efficiency, are the current mainstream development trend.
4. Classification by mechanism of action
Gas-phase flame retardant: For example, halogenated flame retardants decompose into hydrogen halides (HX) upon heating, which capture free radicals and interrupt the combustion chain reaction.
Condensed phase flame retardant: such as phosphorus-based and intumescent flame retardants, which promote the dehydration and carbonization of materials to form a thermal insulation layer.
Synergistic flame retardancy: For example, the combination of Sb₂O₃ and halogenated flame retardants significantly enhances flame retardant efficiency.
Shall I compile a classification and comparison table of plastic flame retardants to help you quickly grasp the characteristics and applicable scenarios of various flame retardants?
Classification of plastic flame retardants
Plastic flame retardants are key additives that enhance material safety by inhibiting or delaying the combustion of polymers. They are widely used in various fields such as electronics and electrical appliances, building materials, and transportation. According to existing information, flame retardants can be classified from multiple dimensions, and the
following is a systematic overview:
I. Classification by chemical composition
Inorganic flame retardant
Hydroxides, such as aluminum trihydroxide (ATH) and magnesium hydroxide (MH), decompose upon heating, absorbing a large amount of heat and releasing water vapor to dilute combustible gases. They possess advantages such as environmental friendliness, non-toxicity, and low cost. However, they require high filler content (30%-60%), which may affect material processing and mechanical properties.
Oxides and salts: such as antimony trioxide (Sb₂O₃), zinc borate, barium metaborate, etc., have weak flame retardant effects themselves, but when used in conjunction with halogenated flame retardants, they significantly enhance the stability of the char layer.
Other inorganic substances: such as red phosphorus, ammonium polyphosphate (APP), magnesium carbonate, etc. Among them, red phosphorus has high flame retardant efficiency and requires a small amount of addition, but it is prone to oxidation and moisture absorption, and needs to be surface modified before use.
Organic flame retardant
Halogenated flame retardants: Primarily consisting of brominated compounds (such as decabromodiphenyl ether and tetrabromobisphenol A) and chlorinated compounds (such as chlorinated paraffins), they exhibit high flame retardant efficiency, require minimal addition, and exert minimal impact on material properties. However, they may release toxic gases (such as dioxins and hydrogen halides) during combustion, posing poor environmental friendliness. Some of these compounds have been restricted for use by the EU RoHS directive.
Phosphorus-based flame retardants: including inorganic phosphorus (such as red phosphorus, APP) and organic phosphorus (such as triphenyl phosphate, TCPP). Their mechanism of action is to promote the dehydration and carbonization of materials, forming a thermal insulation layer. Some varieties can also capture free radicals in the gas phase.
Nitrogen-based flame retardants, such as melamine and melamine cyanurate (MCA), release non-flammable gases (such as NH₃) when heated, diluting the oxygen concentration. They often work synergistically with phosphorus-based flame retardants to form an intumescent flame retardant system.
Intumescent flame retardant (IFR): Consisting of an acid source (such as APP), a carbon source (such as pentaerythritol), and a gas source (such as melamine), it expands upon heating to form a porous carbon layer, achieving thermal and oxygen insulation. It is an environmentally friendly, halogen-free flame retardant, widely used in polyolefin materials.
II. Classification by usage
Additive flame retardant
It is physically mixed into the resin before plastic processing, offering convenience and strong adaptability, and accounts for 80%-90% of the total market. It is commonly used in thermoplastics such as PE, PP, PVC, etc. The disadvantage is that when the addition amount is large, it may reduce the mechanical properties, electrical properties, and processing fluidity of the material.
Reactive flame retardant
The molecule contains reactive functional groups that can chemically bond to polymer chains, becoming part of the material structure, with a durable flame retardant effect and minimal impact on performance. It is mainly used in thermosetting plastics such as epoxy resin and polyurethane. However, due to complex synthesis and limited varieties, its application proportion is relatively low (about 10%-20%).
III. Classification by Environmental Friendliness
Traditional flame retardants: Mainly halogen-based, they have high flame retardant efficiency, but they also have problems such as toxicity, high smoke production, and corrosive combustion products, which are gradually being replaced.
Environmentally friendly flame retardants: including halogen-free flame retardants (such as phosphorus-based, nitrogen-based, silicon-based, and intumescent types) and nano-flame retardants (such as nano-magnesium hydroxide and nano-silica), which are characterized by low smoke, low toxicity, and high efficiency, are currently the mainstream direction of research and development and application.
IV. Classification by mechanism of action
Gas-phase flame retardant: For example, halogenated flame retardants decompose into hydrogen halides (HX) upon heating, which capture combustion free radicals and interrupt the chain reaction.
Condensed phase flame retardant: Such as phosphorus-based and intumescent flame retardants, which promote dehydration and carbonization of materials, forming a dense carbon layer to isolate heat and oxygen.
Synergistic flame retardancy: For example, when Sb₂O₃ is compounded with halogenated flame retardants, volatile antimony halides and antimony oxyhalides are generated, which absorb heat and dilute combustible gases, significantly enhancing flame retardant efficiency.
