Intumescent flame retardants (FR) are considered to be one of the development directions of halogen-free flame retardant materials due to their high flame retardant efficiency, low smoke, non-toxicity, and non-corrosive gas release. However, due to the poor compatibility of intumescent flame retardants with polypropylene, moisture absorption, and easy precipitation, surface modification of intumescent flame retardants, synergistic effects of different flame retardants, and development of new intumescent flame retardants have become the main development trends of intumescent flame retardant technology.
Intumescent Flame Retardants: A Focus on Halogen-Free Materials
Intumescent flame retardants (IFR) represent a key direction for halogen-free flame retardant materials because of their high efficiency, low smoke production, and non-toxic, non-corrosive nature. Poor compatibility with polypropylene, moisture absorption, and easy precipitation lead researchers to focus on surface modification, synergistic effects, and developing new IFRs.
Mechanism of Flame Retardance
IFR typically contains phosphorus, nitrogen, and carbon. Components include a carbonizing agent, a dehydrating agent, and an expanding agent. Ammonium polyphosphate serves as the acid source, pentaerythritol as the carbon source, and melamine as the gas source. As temperatures rise, the carbon source undergoes esterification and dehydration cross-linking reactions, forming a carbonized product. Gases from the gas source create a closed, porous carbon layer, which isolates heat and blocks oxygen, leading to self-extinguishing behavior.
Common Formulas
Adjusting the ratios of carbon, acid, and gas sources creates different IFRs. Traditionally, a 3/1/1 ratio provides effective flame retardation. Pentaerythritol, mannitol, and sorbitol serve as carbon sources. Triazine polymers, with their stable rings, are gaining interest as new carbonizers. Common acid sources include ammonium polyphosphate, zinc borate, and magnesium ammonium phosphate. Gas sources may use melamine, dicyandiamide formaldehyde resins, and others.
Single-Component IFRs
Single-component IFR integrates all roles into one. This reduces the need for multiple additives, improves water resistance, and enhances thermal stability. These can graft onto polypropylene monomers, improving compatibility. However, their flame retardant efficiency is lower. Pentaerythritol diphosphate melamine salt (PDM) is a notable example with commercial success abroad.
Synergistic Additives
To boost IFR’s efficiency, additives like zeolites, metal compounds, and rare earth oxides are employed. Nanoparticles such as montmorillonite, hydrotalcite, and carbon nanotubes enhance flame retardation. These additives improve polypropylene’s flame retardancy, heat release inhibition, and thermal stability.
New Processing Technologies
Techniques including nano-scaling, surface modification, and microencapsulation address issues like poor thermal stability, moisture absorption, and inadequate flame retardant efficiency. These advancements aim to enhance overall IFR performance.
Baozhuan New Material Technology Co., Ltd. has been focusing on the research and development of environmentally friendly halogen-free flame retardants for more than ten years. The company’s environmentally friendly flame retardant product series include melamine polyphosphate, piperazine pyrophosphate system compound flame retardants,phosphorus-nitrogen intumescent compound flame retardant, environmentally friendly and efficient flame retardant,and phosphorus nitrogen compound flame retardants. These flame retardants not only have the characteristics of high flame retardant efficiency, good thermal stability, no precipitation, good water resistance, good color stability, light aging resistance and low smoke and non-toxicity, but also can make the material reach the UL 94 V-0 level flame retardant standard by adding an appropriate amount.
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