Inorganic Flame Retardants vs. Organic Flame Retardants:
Understanding the Two Approaches to Fire Protection for Polymer Materials
I.Inorganic Flame Retardants: The Silent "Heat Insulation Masters"
Inorganic flame retardants are mostly metal hydroxides, inorganic salts, or minerals. They extinguish fires physically by absorbing heat, dehydrating, diluting oxygen, and forming a coating layer.
Advantages
1.High thermal stability: Most can withstand processing temperatures above 300℃.
2.Low toxicity and low smoke: Do not release corrosive gases during combustion, aligning with environmental trends.
3.Low cost: Extremely cost-effective compared to some organic flame retardants.
4.Smoke suppression effect: Some varieties, such as aluminum hydroxide and zinc borate, can significantly reduce smoke.
Disadvantages
1.High addition amount: Usually requires 30%~60% to achieve a flame retardant rating, which severely sacrifices the material's mechanical properties.
2.Poor compatibility: The interface between inorganic particles and the polymer matrix is weak, easily leading to brittleness in the material.
3.Moisture Absorption: Some salts (such as ammonium polyphosphate) are prone to absorbing moisture, affecting electrical properties.
II.Organic Flame Retardants: Precise "Chemical Vanguards"
Organic flame retardants block the combustion chain in the gas or condensed phase through chemical reactions. They are highly efficient, require only small amounts, and are the mainstay of modified plastics.
Advantages
1.High Flame Retardant Efficiency: Typically, adding 5%~20% can achieve UL94 V-0, with minimal impact on the mechanical properties of the substrate.
2.Good Compatibility: Organic structures are similar to polymers, making them easy to disperse.
3.Flexible Design: Different flame-retardant elements (Br, P, N, etc.) can be introduced through molecular design to achieve synergistic effects.
Disadvantages
1.Environmental Risk: Some brominated flame retardants (such as polybrominated diphenyl ethers and hexabromocyclododecane) are listed as persistent organic pollutants under the Stockholm Convention and are being phased out.
2.Release of Toxic Gases: Combustion may produce corrosive or toxic gases such as HBr and dioxins.
3.High Cost: Especially some new organophosphorus and phosphazene flame retardants, which are quite expensive.
III.The "Chemical Reaction" of Inorganic and Organic Elements—Synergistic Flame Retardancy
Using them alone often has limitations, but combining them often produces a 1+1>2 effect. For example:
Halogen-Antimony Synergy: Brominated flame retardants + antimony trioxide generate antimony trihalides in the gas phase, simultaneously playing a quenching and isolating role.
Phosphorus-Nitrogen Synergy: APP + triazine charring agent. APP acts as an acid and gas source, while the triazine charring agent acts as a char source. During combustion, an expanded foam char layer is formed, providing heat and oxygen insulation.
Nano Synergy: Adding a small amount of montmorillonite or hydrotalcite to the intumescent flame retardant system can significantly enhance the density of the char layer and improve flame retardant efficiency.
IV.How to Choose?—Practical Advice Based on Application Scenarios
Many engineers struggle with which type to choose. The key lies in your matrix, processing conditions, and target grade.
Polyolefins (PP, PE): For general packaging films, bromine-based + antimony compounds are the most economical; for outdoor products or those with high environmental requirements, intumescent flame retardants (APP + triazine charring agent) or magnesium hydroxide are used; XPS insulation boards previously used HBCD, but are now forced to switch to methyl octabromoether or brominated SBS.
Engineering plastics (Nylon, PBT): After glass fiber reinforcement, the efficiency of MCA decreases, requiring the use of MPP or alkyl phosphinates (ADP). ADP and MPP blends are currently the mainstream halogen-free solution.
Polyurethane foam: Flexible foams often use TCPP and TDCP (but TDCP is restricted due to health concerns); rigid foams can use TCPP, phosphorus-containing polyols, or expandable graphite.
