Synthesis of siloxane-containing benzoxazine and its synergistic effect on flame retardancy of polyoxymethylene

A type of trialkoxysilane-containing naphtholoxazine compound (Naph-boz) was successfully synthesized and combined with ammonium polyphosphate/melamine (APP/ME) as an intumescent flame retardant (IFR) to improve the flame-retardant efficiency of polyoxymethylene (POM). The Underwriters Laboratories 94 (UL94) vertical burning test, limiting oxygen index (LOI), cone calorimeter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman spectral analysis were used to study the flame-retardant properties and related mechanism. The results showed that the formulation with 20 wt.% of APP, 6 wt.% of ME, and 4 wt.% of Naph-boz passed UL94 V-1 rating, and the LOI value was improved to 40.3%. Compared with pure POM, the IFR with Naph-boz had greater reduction in peak heat release rate (lower 74.9%) and total heat release (lower 40.2%). SEM images showed that compact and reinforcing charred layer was formed during the POM/IFR/4Naph-boz samples combustion, which was beneficial at reducing and maintaining low combustion parameters throughout the cone calorimeter test. The synergistic flame-retardant effect between Naph-boz and APP/ME was considered as the reason for the improvement in flame retardancy POM. Furthermore, because of the Naph-boz was conducive to the compatibility between the flame retardants and matrix, the notched Izod impact strength of POM/IFR/4Naph-boz composite was higher than that of POM/IFR system.