A Synergistic Flame Retardant System Based on Expandable Graphite, Aluminum (Diethyl-)Polyphospinate and Melamine Polyphosphate for Polyamide 6

Abstract

Expandable graphite (EG), aluminum (diethyl)polyphosphinate (AlPi) and melamine polyphophate (MPP) was used as flame retardant multi-material additive in a polyamide 6 (PA6) matrix. Flame inhabitation performances were conducted by cone calorimeter, LOI and UL-94 tests, synergisms identified analyzed by TGA-FTIR and TGA-GC/MS and effects found were comprehensively discussed. SEM images were used for char residue characterization. For PA6 containing 20 wt.% EG and 5 wt.% AlPi/MPP (3:2), a well working synergism in limiting oxygen indices could be identified exhibiting the highest oxygen index (OI) measured: 46%. The study shows that the synergism due to the partial substitution of EG by AlPi/MPP can be attributed to two effects: (1) When PA6/AlPi/MPP mixtures decompose predominantly CO2 evaporates in early decomposition stages. CO2 evaporations was found to be sensitive to the heating rate applied, whereas specifically high heating rates increased the CO2 yield measured. (2) Solid decomposition products of AlPi/MPP act as “glue” between expanded graphite and thus increase the mechanical residue stability.

Expandable Graphite, Aluminum Diethylphospinate and Melamine Polyphosphate as Flame Retarding System in Glass Fiber-Reinforced PA6

“…No changes within the chemical decomposition pathway were found. [ 10 ] AlPi/MPP mixtures combined with EG were studied as a synergistic multi-material mixture in PA6 [ 11 ]. The general decomposition modes as well as the flame retardancy effects of PA6/AlPi/MPP mixtures have been described in detail in [ 5 , 7 , 11 ].…”

“…[ 10 ] AlPi/MPP mixtures combined with EG were studied as a synergistic multi-material mixture in PA6 [ 11 ]. The general decomposition modes as well as the flame retardancy effects of PA6/AlPi/MPP mixtures have been described in detail in [ 5 , 7 , 11 ]. Net MPP is known to accelerate the decomposition process in PA6 due to an early de-polymerization mode.…”

“…Within this paper, we provide insights into a multi-material flame retarding system for a glass fiber-reinforced polyamide 6 grade based on EG as the main ingredient, as well as an AlPi/MPP mixture as a minor component. The study corresponds to knowledge gained from non-reinforced PA6/EG/AlPi/MPP systems published in [ 10 , 11 ] and intends to research the same system in glass fiber-reinforced PA6. Fire performance was investigated by cone calorimetry, UL-94 and LOI fire testing.…”

“…For PA6, systems based on aluminum diethylphosphinate (AlPi) [ 5 , 6 ], melamine polyphosphate (MPP) [ 5 , 7 ], red phosphorus and ammonium polyphosphate (APP) [ 8 , 9 ] have been found to be specifically effective. More recently, published studies on the use of a higher temperature stable EG grade in PA6 also showed promising flame retarding properties, specifically in cone calorimeter tests [ 10 , 11 ]. The performance of a flame retardant additive system does not only depend on the chemistry itself, but also on physical factors (e.g., fillers) which influence the exchange of recuperated heat and generated flammable gases over time.…”

“…As a non-phosphorus alternative, expandable graphite has recently been studied as a flame retardant additive in PA6 compounds [ 10 , 11 ]. When exposed to heat, an intercalated blowing agent expands the graphite flakes into a worm-like structure several hundred times the original volume.…”