Disadvantages
Easy to absorb moisture: This is the biggest pain point of the app. Type I APP is particularly evident, as water absorption not only affects the electrical properties of the material, but also leads to foaming and bubbling during the extrusion process.
Poor compatibility with polymers: APP is an inorganic substance with poor compatibility with non-polar polyolefins such as PP and PE, and poor dispersion can affect its mechanical properties.
Migration and precipitation: In humid environments, the APP may migrate to the surface of the material, causing "frost" and a decrease in flame retardancy.
It is precisely because of these drawbacks that the modification of apps has become a top priority in research.
APP's "Transformation" Technique: A Comprehensive Review of Modified Technologies
In order to better serve flame retardant materials, researchers and engineers have invented various modification methods for the APP.
① Coupling agent modification
Treating APP with coupling agents such as silane and titanate can improve its compatibility with polymers and enhance the mechanical properties of the material.
② Melamine modification
Melamine reacts with APP, partially replacing ammonium ions in APP to generate melamine modified ammonium polyphosphate (MAPP). MAPP has higher thermal stability and reduced moisture absorption, making it particularly suitable for flame retardancy of materials such as polypropylene.
③ Microencapsulation modification
This is currently the hottest modification direction. Wrap the APP with materials such as melamine formaldehyde resin, epoxy resin, polyurethane, etc. to form microcapsules. This can both isolate moisture and improve compatibility with polymers. For example, by using in-situ polymerization method to coat melamine formaldehyde resin on the surface of APP, the solubility of the coated APP in 25 ℃ water can be reduced from 2.5g/100mL of pure APP to 0.25g/100mL.
④ Piperazine modification
Some teams have developed piperazine modified ammonium polyphosphate (Pi APP), which introduces piperazine structures into the APP through liquid-phase or solid-phase reactions. The initial decomposition temperature of Pi APP (L-Pi-APP is 304 ℃, S-Pi-APP is 221 ℃) can be adjusted, and the residual carbon content is increased by 8% to 18% compared to pure APP.
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