Disadvantages
High hygroscopicity: This is the primary drawback of APP. It is particularly pronounced in Type I APP; moisture absorption not only impairs the material’s electrical properties but also causes foaming or blistering during the extrusion process.
Poor compatibility with polymers: As an inorganic substance, APP has poor compatibility with non-polar polyolefins (such as PP and PE); poor dispersion can adversely affect mechanical properties.
Migration and blooming: In humid environments, APP may migrate to the material’s surface, leading to “blooming” and a reduction in flame-retardant performance.
It is precisely because of these shortcomings that the modification of APP has become a top priority in research.
The “Transformation” of APP: A Review of Modification Techniques.
To enable APP to better serve as a flame retardant, researchers and engineers have developed various modification methods.
I. Coupling Agent Modification
Treating APP with coupling agents such as silanes or titanates enhances its compatibility with polymers and improves the material’s mechanical properties.
II. Melamine Modification
Melamine reacts with APP, partially replacing the ammonium ions within the APP structure to form melamine-modified ammonium polyphosphate (MAPP). MAPP exhibits superior thermal stability and reduced hygroscopicity, making it particularly suitable for the flame retardancy of materials like polypropylene.
III. Microencapsulation Modification
This is currently a highly popular area of modification research. APP particles are encapsulated using materials such as melamine-formaldehyde resin, epoxy resin, or polyurethane to form microcapsules. This process effectively isolates the APP from moisture while improving its compatibility with polymers. For instance, when melamine-formaldehyde resin is coated onto the APP surface via in-situ polymerization, the solubility of the modified APP in water at 25°C drops from 2.5 g/100 mL (for pure APP) to 0.25 g/100 mL.
IV. Piperazine Modification
Several research teams have developed piperazine-modified ammonium polyphosphate (Pi-APP) by introducing piperazine structures into APP through liquid-phase or solid-phase reactions. The initial decomposition temperature of Pi-APP is tunable (304°C for L-Pi-APP and 221°C for S-Pi-APP), and the char residue yield is increased by 8%–18% compared to pure APP.
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Post time: Sep-09-2026
