Synergic effects of dimethyl methylphosphonate (DMMP) and nano-sized montmorillonite (MMT) on the flammability and mechanical properties of flax fiber reinforced phenolic composites under hydrothermal aging

Abstract

In this study, a phosphorus-containing flame retardant (FR) DMMP was applied to solve the flammability of flax fiber reinforced phenolic composites (FFRPCs), and the phenolic resin was further modified with nano-sized MMTs in order to enhance the flame retardancy. The water absorption performance of the composites was obtained by weighing method and the flammability of the composites was evaluated through the vertical burning test and limiting oxygen index (LOI) test. The effect of water absorption on the interlaminar properties of the composites was investigated. Then, the morphology of the composites and thermal stability of the composites were analyzed with the aid of scanning electronic microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and cone calorimeter test before and after water immersion. The results revealed that using DMMP to pretreat flax fiber is a simple and effective method to improve the flame retardancy of FFRPCs. Adding MMTs into the phenolic resin facilitated the formation of more carbonization layers within the composites during burning, which would synergistically retard flame with the DMMP. On the other hand, it restrained water absorption of the composites and hindered the precipitation of DMMP from the composites to some extent. Therefore, the effects of water absorption on the reduction of the flammability and mechanical properties of DMMP/MMT treated composites were less than those being merely treated by DMMP due to less water absorption of the composites by adding MMTs.