Phosphorus-based halogen-free flame retardants are a type of highly efficient flame retardant additives with phosphorus as the core component and no halogens. They are widely used in polymer materials, electronic appliances, building materials and other fields. Its classification and characteristics can be systematically analyzed from the following dimensions:
First, classification system
Inorganic phosphorus-based flame retardants
Representative substances: red phosphorus, ammonium polyphosphate (APP), aluminum hypophosphite, diammonium hydrogen phosphate, etc.
Mechanism of action:
Condensed phase flame retardancy: When heated, it decomposes to form strong dehydrating agents such as phosphoric acid and metaphosphoric acid, promoting the formation of a dense carbonized layer on the material surface and isolating oxygen and heat transfer.
Gas-phase flame retardancy: Some inorganic phosphorus compounds release non-flammable gases (such as ammonia), diluting the concentration of flammable volatile substances.
Application fields: Thermoplastic plastics (such as PP, PE), engineering plastics (PA, PBT), coatings, rubber, etc.
Organophosphorus-based flame retardants
Representative substance:
Phosphate esters: Triphenyl phosphate (TPP), triphenyl phosphate (TCP), resorcinol bis (diphenyl phosphate) (RDP).
Phosphonate esters: Dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP).
Phosphine oxides: triphenylphosphine oxide (TPPO), bisphenol A bis (diphenylphosphine oxide) (BDP).
DOPO compounds: 9, 10-dihydro-9-oxa-10-DOPo oxide (DOPO) and its derivatives.
Mechanism of action:
Gas-phase flame retardancy: Decomposition generates PO· free radicals, which capture H· and OH· free radicals in the combustion chain reaction and interrupt the combustion cycle.
Condensed phase flame retardancy: Promotes the carbonization of materials and forms an insulating barrier.
Application fields: polycarbonate (PC), epoxy resin, polyurethane foam, textiles, etc.
Second, core features
High-efficiency flame retardant performance
Low addition amount: Phosphorus-based flame retardants significantly reduce the flammability of materials through the dual effects of the gas phase and the condensed phase. For example, the addition amount of red phosphorus in PP only needs 5%-10% to reach UL-94 V-0 grade.
Carbon formation efficiency enhancement: Organophosphorus flame retardants (such as DOPO derivatives) can form cross-linked structures with high-molecular chains, enhancing the strength and thermal stability of the carbon layer.
Environmental Protection and Safety
Halogen-free feature: It does not contain halogen elements such as bromine and chlorine, thus avoiding the release of highly toxic gases like dioxins during combustion.
Low smoke and low toxicity: The main decomposition products are phosphate, carbon dioxide and water vapor, significantly reducing smoke density and toxicity (for example, the smoke density of TPP is 40% lower than that of decabromodiphenyl ethane).
Material compatibility and processability
Compatibility optimization
Inorganic phosphorUs-Based series: The interfacial binding force with polymers is improved through microencapsulation techniques (such as coating with red phosphorus), reducing migration and precipitation.
Organophosphorus series: Flexible chain segments (such as long-chain alkyl groups) or reactive groups (such as epoxy groups) are introduced into the molecular structure to enhance compatibility with the matrix.
Processing stability: Some organophosphorus-based flame retardants (such as DMMP) have low melting points and high solubility, which are convenient for blending and processing with resins.
Multifunctional synergy effect
When combined with nitrogen-based/silicon-based systems: When APP is compounded with melamine cyanurate (MCA), it can form a porous carbon layer through expansion and foaming, increasing the flame retardant efficiency by more than 30%.
In combination with inorganic fillers: After APP is compounded with nano-montmorillonite (MMT), the density of the carbon layer increases, and the peak heat release rate (PHRR) decreases by 50%.
Third, typical application scenarios
The field of electronics and electrical appliances
PC/ABS alloy: Flame-retardant with BDP or RDP, meeting the requirements of UL-94 V-0 grade and GWIT 775℃, and used in mobile phone casings and printer components.
Wire and cable: APP is compounded with magnesium hydroxide to prepare low smoke zero halogen flame retardant sheath material, which has passed the IEC 60332-3-24 vertical burning test.
The field of transportation
New energy vehicle battery pack: DOPO-based flame retardants are compounded with epoxy resin to enhance thermal runaway safety and pass the GB/T 31467.3 needle-puncture test.
Interior material of high-speed rail: Microencapsulated red phosphorus flame-retardant polypropylene, meeting the EN 45545-2 HL3 flame-retardant standard.
The field of building materials
Polyurethane insulation board: The oxygen index (LOI) of the polyurethane foam with DEEP added reaches 28%, and the smoke density grade (SDR) is ≤75, meeting the requirements of Grade B1 of GB 8624-2012.
Epoxy floor coating: TPPO modified epoxy resin, with wear resistance improved by 20% and flame retardant grade reaching UL-94 V-0.
