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

Florian Tomiak,Klaus Rathberger,Dietmar Drummer,Angelina Schoeffel

doi:10.3390/polym13162712

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.

Highlights

Polyamide 6 (PA6) is one of the most important representatives of engineering polymers and used in a wide range of technical applications
The study shows that the synergism due to the partial substitution of expandable graphite (EG) by aluminum (diethyl)polyphosphinate (AlPi)/melamine polyphophate (MPP) can be attributed to two effects: (1) When polyamide 6 (PA6)/AlPi/MPP mixtures decompose predominantly CO2 evaporates in early decomposition stages
We present the flame retardant performance and decomposition processes of a multi-material system based on EG, AlPi and MPP in a PA6 matrix

Summary

Introduction

Polyamide 6 (PA6) is one of the most important representatives of engineering polymers and used in a wide range of technical applications. Within this paper we discuss an efficient multi-material flame retarding system for polyamide 6 based on expandable graphite (EG) as main ingredient as well as AlPi/MPP mixtures as synergistic component. The effect of AlPi and MPP as flame retardant additives in GF and non-GF polyamides has been studied. MPP performs less effective in PA6 due to the depolymerization mode of decomposition [20] and is, mostly used as synergist in multi-material systems [21]. MPP is reported to be an effective synergist with multiple phosphor-based additives, whereas for glass fiber reinforced PA6/AlPi/MPP combinations show good performances in Cone Calorimeter, limiting oxygen index (LOI) and UL-94 fire tests. We present the flame retardant performance and decomposition processes of a multi-material system based on EG, AlPi and MPP in a PA6 matrix. Synergistic effects were mostly found in LOI tests for formulations containing EG as main ingredient, as well as AlPi/MPP mixtures at a ratio of 3:2 as synergist

Materials and Preparation

Fire Testing

Decomposition Analytics

Thermal Decomposition

Char4Residue Analysis 75