A Synergistic Flame Retardant System Based on Expandable Graphite, Aluminum (Diethyl-)Polyphospinate and Melamine...

Area of Science:

• Materials Science
• Polymer Chemistry
• Fire Safety Engineering

Background:

• Polyamide 6 (PA6) is a widely used polymer requiring improved flame retardancy for safety-critical applications.
• Flame retardant additives are crucial for enhancing the fire safety of polymers like PA6.
• Synergistic effects between different flame retardants can lead to superior performance compared to individual components.

Purpose of the Study:

• To investigate the flame retardant properties of a multi-material additive system in a PA6 matrix.
• To identify and analyze the synergistic effects between expandable graphite (EG), aluminum diethylpolyphosphinate (AlPi), and melamine polyphosphate (MPP).
• To evaluate the impact of these additives on the fire behavior and char residue of PA6.

Main Methods:

• Flame retardancy was assessed using cone calorimeter, Limiting Oxygen Index (LOI), and UL-94 tests.
• Synergistic effects were analyzed through Thermogravimetric Analysis coupled with Fourier-Transform Infrared Spectroscopy (TGA-FTIR) and Gas Chromatography-Mass Spectrometry (TGA-GC/MS).
• Char residue morphology was characterized using Scanning Electron Microscopy (SEM).

Main Results:

• A formulation of PA6 with 20 wt.% EG and 5 wt.% AlPi/MPP (3:2 ratio) demonstrated significant flame retardant synergy.
• The optimal formulation achieved the highest measured Oxygen Index (OI) of 46%.
• Analysis revealed that CO2 evolution in early decomposition stages and enhanced mechanical stability of the char residue contributed to the observed flame retardancy.

Conclusions:

• Partial substitution of EG with AlPi/MPP in PA6 creates a synergistic flame retardant system.
• The synergistic mechanism involves enhanced CO2 release during decomposition and improved char structure integrity.
• This multi-material additive approach offers a promising strategy for improving the fire safety of polyamide 6.