The traditional expansion flame retardant system, represented by ammonium polyphosphate (APP, acid source) - pentaerythritol (PER, carbon source) - melamine (MEL, gas source), has defects such as poor water resistance, insufficient thermal stability, component migration, mismatched heating timing of the three components, large addition amount, and loose carbon layer.
1、 Breakthrough in acid source: traditional acid source: ammonium polyphosphate APP. The disadvantage is high water solubility and easy water separation; The thermal decomposition temperature is relatively low (about 210 ℃), and many engineering plastics decompose prematurely at processing temperatures; The release rate of phosphorus is difficult to regulate; Poor compatibility with non-polar resins.
1. Piperazine pyrophosphate (PAPP)
Phosphorus nitrogen integration, with a thermal decomposition temperature raised to 280-300 ℃, suitable for high processing temperature resins such as PP and PA.
The hydrolysis stability is significantly better than that of APP, with resistance to migration and precipitation.
Not only does it release phosphoric acid to catalyze the formation of carbon, but the piperazine ring also participates in crosslinking, strengthening the carbon layer skeleton.
Shortcomings: Weak foaming alone, often requiring a combination of gas sources and carbonization aids
2. Cyclophosphazene derivatives ◦
Circular P-N skeleton with high thermal stability; Hydroxyl and amino groups can be introduced into the side chain, while also participating in carbonization and gas production.
Integrate the acid source and some char sites onto the same molecule to narrow the temperature window difference between the three components.
3. Organic phosphonic acids, phosphonates (phenylphosphonates, phytates) ◦
There are stable P-C covalent bonds, and the hydrolytic stability is much higher than that of P-O-NH type APP.
The temperature range for acid release can be regulated to avoid premature acid release during the processing.
Some phosphonic acid species also possess the ability to quench free radicals in the gas phase, breaking through the limitations of traditional acid sources that only have condensed phase catalysis.
4. Microcapsule modification APP ◦
Coat APP particles with melamine formaldehyde, epoxy resin, and silica.
Not changing the APP kernel, but significantly reducing water solubility, improving compatibility, and suppressing premature decomposition during processing.
Belonging to a low-cost modification route, but still physically coated, there is a risk of shell damage during long-term use.
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