Layered double hydroxides (LDHs) are nano-layers materials used as fillers for epoxy resins to enhance fire resistant performance. The LDHs were modified with four different anions based on organophosphate ester compounds, namely bis-2 ethyl hexyl phosphate (BEHP), phytate (Phy), glycerophosphate (GP) and diphenyl phosphate (DPP). All the LDHs were prepared by a co-precipitation method. For the LDHs synthesis, the decarbonation, pH, aging time and precipitating agent affected the formation of LDHs.
The layers of the modified LDHs are based on hydroxides of magnesium and aluminium. For the modification with the BEHP, GP or DPP anions, they intercalated in the interlayer spaces of LDHs. Meanwhile, the modification of LDH with the Phy anions resulted in the exfoliation of layers. The water molecules also were adsorbed on the surface of LDHs and intercalated among the metal hydroxides layers.
Afterwards, the 1 wt%, 5 wt% and 10 wt% of the pristine LDHs and the modified LDHs were incorporated into epoxy resins of diglycidyl ether of bisphenol A (DGEBA) cured with 4,4'-diamino diphenylmethane (DDM) or 4,4'-diamino diphenyl sulfone (DDS). The LDHs did not influence significantly on the mechanical properties and the interference with the polymer chains movement. However, they increased the storage modulus and the loss modulus in the glassy state of the epoxy nanocomposites. Furthermore, the modified LDHs were able to decrease the thermal decomposition temperature of epoxy resins. The increase of LDHs contents contributed to the rise of char residues.
In the DDM curing system, the loadings of modified LDHs at 5 wt% were sufficient for the stop of combustion. Meanwhile, the 5 wt% modified LDHs could delay the combustion of epoxy resins cured with DDS; however, they were not self-extinguished. It needed to load the modified LDHs at 10 wt% to provide the survived epoxy nanocomposites.
