Effects of expandable graphite on the flame-retardant and mechanical performances of rigid polyurethane foams

Xin-Chao Wang; Ya-Peng Sun; Jie Sheng; Tie Geng; Lih-Sheng Turng; Yong-Gang Guo; Xian-Hu Liu; Chun-Tai Liu

doi:10.1088/1361-648X/ac3b27

Effects of expandable graphite on the flame-retardant and mechanical performances of rigid polyurethane foams

J Phys Condens Matter. 2021 Dec 8;34(8). doi: 10.1088/1361-648X/ac3b27.

Authors

Xin-Chao Wang¹, Ya-Peng Sun¹, Jie Sheng¹, Tie Geng¹, Lih-Sheng Turng², Yong-Gang Guo¹, Xian-Hu Liu³, Chun-Tai Liu³

Affiliations

¹ School of Mechanical & Electrical Engineering, and Henan Provincial Engineering Laboratory of Automotive Composite Materials, Henan University of Technology, Zhengzhou, People's Republic of China.
² Department of Mechanical Engineering, Wisconsin Institute for Discovery, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
³ National Engineering Research Center for Advanced Polymer Processing Technologies, Zhengzhou University, Zhengzhou, People's Republic of China.

PMID: 34794133
DOI: 10.1088/1361-648X/ac3b27

Abstract

Polyurethane foams (PUFs) are found everywhere in our daily life, but they suffer from poor fire resistance. In this study, expansible graphite (EG) as flame retardant was incorporated into PUFs to improve material fire resistance. With the presence of EGs in the PU matrix, bubble size in PUF became smaller as confirmed by the scanning electron microscopy. The mass density of PUFs is directly proportional to the content of EG additive. The compression strengths of EG0/PUF and EG30/PUF decrease from 0.51 MPa to 0.29 MPa. The Fourier transform infrared spectroscopy (FTIR) analysis of RPUFs showed that the addition of EGs did not change the functional group structures of RPUFs. Thermo-gravimetric analysis (TGA) testing results showed that the carbon residue weight of EG30/PUF is higher than other PU composite foams. The combination of TGA and FTIR indicated that the EG addition did not change the thermal decomposition products of EG0/PUF, but effectively inhibited its thermal decomposition rate. Cone calorimeter combustion tests indicated that the peak of the heat release rate of EG30/PUF significantly decreased to 100.5 kW m^-2compared to 390.6 kW m^-2for EG0/PUF. The ignition time of EG/PUF composites also increased from 2 s to 11 s with incorporation of 30 wt% EGs. The limiting oxygen index (LOI) and UL-94 standard tests show that the LOI of EG30/PUF can reach 55 vol%, and go through V-0 level. This study showed that adding EG into PU foams could significantly improve the thermal stability and flame retardancy properties of EG/PUF composites without significantly sacrificing material compression strength. The research results provide useful guidelines on industrial production and applications of PUFs.

Keywords: cone calorimeter; expansible graphite; flame retardancy; polyurethane.