Novel epoxy/expandable graphite halogen-free flame retardant composites−preparation, characterization, and properties

In this work, expandable graphite (EG) was grafted using a coupling agent, 3-isocyanatopropyltriethoxysilane (IPTS). EG has a -O-C2H5 (-OEt) functional group which reacts with a polymer matrix through the sol-gel reaction. EG was functionalized by the coupling agent to form a covalent bonding between organic and inorganic phases, increasing the compatibility between the fillers and polymer, and thereby enhancing the thermal stability of the composites. FT-IR and X-ray photoelectron spectroscopy (XPS) were adopted to characterize the grafting reaction between IPTS and EG. Thermogravimetric analysis (TGA), the derivative of thermogravimetric weight (DTG) and the difference between the thermogravimetric weights (TG△) were employed to calculate the thermal stability of the composites. The limiting oxygen index (LOI) was utilized to classify the composites by flame retardancy. A scanning electron microscope (SEM) was applied to observe their morphology, and the behavior of expansion was discussed after the materials were burnt. TGA/MS was used to analyze the gas products during thermal degradation. The results demonstrate that functionalized EG can improve the thermal stability of composites and increase the flame retardancy.