Synthesis of a phosphorus and sulfur-containing aromatic diamine curing agent and its application in flame retarded epoxy resins

A novel curing agent of epoxy resins (EPO), bis(3-amino-2-thienyl) phenylphosphine oxide (ABTPPO), was synthesized and characterized by Fourier transform infrared spectroscopy, H-1 nuclear magnetic resonance (NMR), C-13 NMR, and P-31 NMR. ABTPPO was used as a flame retardant curing agent, and a novel halogen-free flame retardant EPO composite was prepared. The flame retardant properties of ABTPPO-cured EPO were evaluated in terms of limiting oxygen index and vertical burning test (UL-94), while the combustion and thermal degradation behaviors were investigated by cone calorimeter test (CONE) and thermogravimetric analysis, respectively. The cured EPO composite passed the UL-94 V-1 and V-2 rating when the sample thickness is 3.0 and 1.6mm, respectively, and the limiting oxygen index value reached 38.3%. The morphological structures of char residue tested by scanning electron microscopy demonstrated that ABTPPO benefited to the formation of a more compact and homogeneous char layer on the materials' surface during burning, which protected the underlying matrix from decomposition and enhanced the flame retardancy of materials. The cured EPO showed excellent fire performance after the water resistance test because of the low water uptake (0.6wt%), which demonstrated that the flame retardant EPO composite possessed excellent water resistance property. Copyright (C) 2014 John Wiley & Sons, Ltd.