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A siloxane compound (MVC) and a bi-group phosphaphenanthrene/triazine compound (TGD) were employed in epoxy thermosets to explore high-efficiency flame retardant systems. With only 1wt% MVC and 3wt% TGD, an epoxy thermoset passed UL 94 V-0 rating test and achieved a limiting oxygen index value of 34.0%, exhibiting an excellent flame retardant effect. The MVC/TGD system not only decreased the peak value of heat release rate and effective heat of combustion but also imparted an improved charring ability to thermosets, thereby outstandingly reducing the flammability of 1%MVC/3%TGD/EP. Compared with the fire performance of 4%TGD/EP and 4%MVC/EP, the MVC/TGD system showed an obvious flame retardant synergistic effect, mainly depending on the general improvement of flame inhibition, charring and barrier effects of the thermoset during combustion. Evolved gas analysis combinedwith condensed-phase pyrolysis product Analysis jointly revealed the details of the changed pyrolysis mode.
A phosphaphenanthrene and triazinetrione group containing flame retardant (TAD) is combined with organically modified montmorillonite (OMMT) in epoxy resin thermosets (EP) to improve the performance of the flame-retardant system. When only 1 wt% OMMT/4 wt% TAD is introduced into the EP, the limited oxygen index (LOI) rises from 26% to 36.9% and a V-0 rating is achieved in a UL 94 test. The decomposition and pyrolysis products in the gas phase and condensed phase were characterized using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The influence on the decomposition of EP, such as the increase in char yield, is limited with the incorporation of OMMT; a large amount of the phosphorus is released into the gas phase. The flame-retardant effect evaluation based on cone calorimeter data testified that OMMT improves the protective-barrier effect of the fire residue of OMMT/TAD/EP on the macroscopic scale, while TAD mainly causes flame inhibition. The fire residues showed a corresponding macroscopic appearance (digital photo) and microstructure (scanning electron microscope [SEM] results). The protective barrier effect of OMMT and the flame-inhibition effect of TAD combined to exert a superior flame-retardant effect, resulting in sufficient flame-retardant performance of OMMT/TAD/EP
Scientific publications addressing the durability of the flame retardance of cables during their long-term application are rare and our understanding lacks. Three commercial flame retardants, aluminum hydroxide, aluminum diethyl phosphinate (AlPi-Et), and intumescent flame retardant based on ammonium polyphosphate, applied in ethylene-vinyl acetate copolymer (EVA) model cables, are investigated. Different artificial aging scenarios were applied: accelerated weathering (UV-irradiation/temperature/rain phases), humidity exposure (elevated temperature/humidity), and salt spray exposure. The deterioration of cables’ surface and flame retardancy were monitored through imaging, color measurements, attenuated total reflectance Fourier transform infrared spectroscopy, and cone calorimeter investigations. Significant degradation of the materials’ surface occurred. The flame retardant EVA cables are most sensitive to humidity exposure; the cable with AlPi-Et is the most sensitive to the artificial aging scenarios. Nevertheless, substantial flame retardance persisted after being subjected for 2000 h, which indicates that the equivalent influence of natural exposure is limited for several years, but less so for long-term use.
The durability of flame retardancy is a challenge for cables over long lifetimes. The degradation of flame retardance is investigated in two kinds of exposures, artificial weathering and humidity. In this basic study, typical mineral flame retardants in two polymers frequently used in cable jackets are investigated to get the fundamental picture. Aluminum hydroxide (ATH) and magnesium hydroxide (MDH) are compared in ethylene‐vinyl acetate (EVA), and further in EVA and linear low‐density polyethylene (LLDPE) cables containing the same ATH. The changes in chemical structure at the surface are studied through attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), the formation of cracks, and changes in color are investigated. The cone calorimeter and a bench scale fire testing cable module are utilized to evaluate the fire behavior of the cables. Although the flame retardancy deteriorated slightly, it survived harsh exposure conditions for 2000 h. Compared to EVA/MDH and LLDPE/ATH, the fire behavior of EVA/ATH is the least sensitive. Taken together, all of the results converge to estimate that there will be no problem with flame retardancy performance, for materials subjected to natural exposure for several years; the durability of fire retardancy is questionable for longer periods, and thus requires further investigation.