Heat of Decomposition and Fire Retardant Behavior of Polyimide-Graphene Nanocomposites

Caroline J Akinyi,Jude O Iroh

doi:10.3390/en14133948

Abstract

Polyimide is a high-performance engineering polymer with outstanding thermomechanical properties. Because of its inherent fire-retardant properties, polyimide nanocomposite is an excellent material for packaging electronic devices, and it is an attractive electrode material for batteries and supercapacitors. The fire-retardant behavior of polyimide can be remarkably improved when polyimide is reinforced with multilayered graphene sheets. Differential scanning calorimetry and thermogravimetric analysis were used to study the heat of decomposition and gravimetric decomposition rate, respectively, of polyimide-graphene nanocomposites. Polyimide/graphene nanocomposites containing 10, 20, 30, 40, and 50 wt.% of multilayered graphene sheets were heated at a rate of 10 and 30 °C/min in air and in nitrogen atmosphere, respectively. The rate of mass loss was found to remarkably decrease by up to 198% for nanocomposites containing 50 wt.% of graphene. The enthalpy change resulting from the decomposition of the imide ring was found to decrease by 1166% in nitrogen atmosphere, indicating the outstanding heat-shielding properties of multilayered graphene sheets due to their high thermal conductivity. Graphene sheets are believed to form a continuous carbonaceous char layer that protects the imide ring against decomposition, hence decreasing initial mass loss. The enthalpy changes due to combustion, obtained from differential scanning calorimetry, were used to calculate the theoretical heat release rates, a major parameter in the determination of flammability of polymers. The heat release rate decreased by 62% for composites containing 10 wt.% of graphene compared to the neat polyimide matrix. Polyimide has a relatively lower heat of combustion as compared with graphene. However, graphene significantly decreases the mass loss rates of polyimide. The combined interaction of graphene and polyimide led to an overall decrease in the heat release rate. It is noted that both mass loss rate and heat of combustion are important factors that contribute to the rate of heat released.

Highlights

Polymer nanocomposites are a class of flame retardant technology that was discovered in the early 1990s and has been shown to result in dramatic decreases in peak heat release rates [1,2]
It was observed that the initial stage of degradation of polyimide follows the same pathway in both nitrogen and oxygen and this is not affected by the presence of graphene
Graphene was shown to lower the rate of mass loss of the composites by up to 198% at PI-50 wt.% graphene as it acts as a heat shield, protecting the underlying polymer matrix from external heat flux

Summary

Introduction

Polymer nanocomposites are a class of flame retardant technology that was discovered in the early 1990s and has been shown to result in dramatic decreases in peak heat release rates [1,2]. Nanocomposites enhance flame retardancy by forming a barrier around the underlying polymer, which slows down the mass degradation and heat release rates [4,5,6,7]. When used in the fabrication of polymer nanocomposites, it results in the improvement of mechanical, electrical, thermal, and gas barrier properties of the polymers. The addition of nanofillers, such as graphene, to organic polymers has resulted in the improvement of thermal stability because of the mass transport barrier to volatiles generated during thermal decomposition and thermal isolation effect of sheets [23,24]. The thermal stability and combustion properties of milligram-sized samples were obtained using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)

Materials and Methods

Findings

Conclusions