Enhancement of Flame Retardant Performance of Bio-Based Polylactic Acid Composites with the Incorporation of Aluminum Hypophosphite and Expanded Graphite

Abstract

A series of flame retarding biodegradable polylactic acid composites (FR-PLA) based on aluminum hypophosphite (AHP) and expanded graphite (EG) were prepared by the melt-compounding method. The effect of AHP and EG on the flame retardancy and thermal stability of PLA were investigated by thermogravimetric analysis (TGA), UL-94 vertical burning test, limiting oxygen index, microscale combustion calorimetry and cone calorimeter testing. The gas products of PLA and FR-PLA composites were investigated by TG-IR technology. TGA results showed that the FR-PLA composites presented higher char residue and reduced mass loss rate than neat PLA. Significant improvement of flame retardancy of PLA/AHP/EG composites indicated an excellent synergistic effect between AHP and EG. Cone calorimeter tests gave clear evidence that the combination of AHP and EG resulted in a significant reduction of the heat release rate (HRR) and total heat release (THR). TG-IR revealed that the combination of AHP and EG resulted in significant decrease of gas products. The char residue of FR-PLA composites were also investigated by scanning electron microscope, Fourier transform infrared spectra spectroscopy and X-ray photoelectron spectroscopy. Based on the analysis, possible flame retardant mechanism was discussed.

Keywords:

• Polylactic acid
• flame retardant
• aluminum hypophosphite
• expanded graphite
• polymer-matrix composites

Acknowledgments

This research was supported by National Basic Research Program of China (973 Program) (2012CB719701), National Natural Science Foundation of China (No. 11125210), the Fundamental Research Funds for the Central Universities (WK2320000014), the joint fund of Guangdong province and CAS (No. 2010A090100017), and the Opening Project of State Key Laboratory of Fire Science of USTC (HZ2010-KF06).