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.
Benzoxazine monomers of traditional bisphenol-A benzoxazine (BA-a) and bisphenol-A benzoxazine containing trialkoxysilane (BA-a-Si) were synthesized and incorporated into polyoxymethylene/ammonium polyphosphate/melamine (POM/APP/ME) to improve the fire retardancy of POM. The flame retardation, thermal, and mechanical properties of POM composites were evaluated by cone calorimeter, limiting oxygen index (LOI), and the Underwriters Laboratories-94 (UL-94) vertical burning tests, as well as thermogravimetric analysis and mechanical tests. Addition of BA-a-Si (2 wt%) into POM could simultaneously improve its flame retardancy (UL-94 vertical burning rating to V-0 rating and LOI value reached 52.1%) and notched impact strength
In this work, three kinds of APP, coated with melamine (MF-APP), silane (GW-APP), epoxy (MC-APP) were employed to compound with novolac resin (Novolac) and melamine (ME), aimed to study the effect of the modified APP on the flame-retardant performance, mechanical properties, and thermal stability of polyformaldehyde (POM). The results showed that composites with modified APP exhibited better flame retardant and mechanical performance than that with unmodified APP. In contrast, GW-APP had the best synergistic effect with Novolac and ME, and POM/GW-APP composites reached UL-94 V-0 rating and its limit oxygen index (LOI) value was up to 34.0%. The morphology of the carbon layer showed that the silane coating material can promote the charring process in condensed phase better than epoxy and melamine coating materials in flame retardant POM system, leading to the formation of integrated char layers with more quantity and higher quality, which effectively delayed the mass and heat transfer during combustion.
A novel intumescent flame retardant (IFR) composed of ammonium polyphosphate (APP), benzoxazine containing trialkoxysilane (BA‐a‐Si) and melamine (ME), is compounded with different specifications of MoS2 as synergist to flame retard polyformaldehyde (POM). The flame retardancy and mechanism of the composites are analyzed by limiting oxygen index (LOI), vertical combustion (UL‐94) and cone calorimeter. At the same time, the mechanical properties and lubricating properties are tested by electromechanical testing machine and wear testing machine. The experimental results show that MoS2 has a good synergistic effect with IFR, and the smaller the average particle size of MoS2 is, it seems to be more beneficial to improve the flame retardancy of POM composites. Only a small amount of MoS2 (0.8 wt%) is needed to synergize with IFR, the flame retardant POM composite (FR‐POM) can achieve UL‐94 (3.2 mm) V‐0 rating, LOI of 62.5%, and heat release rate reduction of 25.3%, total smoke release decreased by 29.5%. In addition, from the mechanical properties analysis, it is found that the microscale MoS2(M2) can better improve the bending and tensile properties of the FR‐POM composites, while the nanoscale MoS2(N80) is more helpful to improve the lubricating properties.
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