The Effects of a Macromolecular Charring Agent with Gas Phase and Condense Phase Synergistic Flame Retardant Capability on the Properties of PP/IFR Composites.

Anxin Ding,Ziheng Sun,Jihui Wang,Xia Han,Aiqing Ni,Hongda Chen

doi:10.3390/ma11010111

Abstract

In order to improve the efficiency of intumescent flame retardants (IFRs), a novel macromolecular charring agent named poly(ethanediamine-1,3,5-triazine-p-4-amino-2,2,6,6-tetramethylpiperidine) (PETAT) with gas phase and condense phase synergistic flame-retardant capability was synthesized and subsequently dispersed into polypropylene (PP) in combination with ammonium polyphosphate (APP) via a melt blending method. The chemical structure of PETAT was investigated by Fourier transform infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance (NMR) spectroscopy. Thermal properties of the PETAT and IFR systems were tested by thermogravimetric-derivative thermogravimetric analysis (TGA-DTG) and thermogravimetry–Fourier transform infrared spectroscopy (TG-FTIR). The mechanical properties, thermal stability, flame-retardant properties, water resistance, and structures of char residue in flame-retardant composites were characterized using tensile and flexural strength property tests, TGA, limiting oxygen index (LOI) values before and after soaking, underwritten laboratory-94 (UL-94) vertical burning test, cone calorimetric test (CCT), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDXS), and FTIR. The results indicated that PETAT was successfully synthesized, and when the ratio of APP to PETAT was 2:1 with 25 wt % loading, the novel IFR system could reduce the deterioration of tensile strength and enhance the flexural strength of composites. Meanwhile, the flame-retardant composite was able to pass the UL-94 V-0 rating with an LOI value of 30.3%, and the peak of heat release rate (PHRR), total heat release (THR), and material fire hazard values were considerably decreased compared with others. In addition, composites also exhibited excellent water resistance properties compared with traditional IFR composites. SEM-EDXS and FTIR analyses of the char residues, as well as TG-FTIR analyses of IFR were used to investigate the flame-retardant mechanism of the APP/PETAT IFR system. The results indicated that the efficient flame retardancy of PP/IFR composites could be attributed to the synergism of the free radical-quenching and char layer-protecting mechanisms in the gas phase and condense phase, respectively.

Highlights

Polypropylene (PP) has been widely used in various fields such as the automobile industry, appliances, and in electric shell and packaging materials, etc. [1,2,3]
The thermal properties of PETAT and intumescent flame retardants (IFRs) systems were tested by thermogravimetric-derivative thermogravimetric analysis (TGA-DTG) and thermogravimetry–Fourier transform infrared spectroscopy (TG-FTIR)
In order to address the issue of low efficiency of intumescent flame retardants (IFRs), a novel

Summary

Introduction

Polypropylene (PP) has been widely used in various fields such as the automobile industry, appliances, and in electric shell and packaging materials, etc. [1,2,3]. The neat PP resin cannot meet all requirements because of its low flame retardancy and poor thermal resistance properties. Halogenated flame retardants are not able to be applied to materials in many fields, even though they have highly efficient flame retardancy with a gas phase flame-retardant mechanism during polymer combustion [7,8,9]. This is because researchers have certified that halogens and their derivatives are toxic and carcinogenic to humans. Intumescent flame retardants (IFRs) have attracted considerable attention from researchers due to their low smoke, halogen-free, anti-dropping, environmental-friendly properties. During the combustion of the PP/IFR composites, IFR can involve PP in a series of chemical reactions to form a compact and continuous intumescent carbonaceous layer which acts as a barrier to protect the inside material from combustion with a condense phase flame-retardant mechanism [13,14]

Methods

Results

Conclusion