Triazine-Based Compounds and Their Application in Halogen-Free Intumescent Flame Retardant Systems
Triazines are a class of nitrogen-containing organic compounds, including the following three isomers: 1,3,5-triazine, 1,2,4-triazine, and 1,2,3-triazine. Among these, 1,3,5-triazine is the most common. Compounds such as melamine and melamine cyanurate fall within the category of triazine-based compounds. The effectiveness of triazine-based compounds in flame retardancy has gained market recognition and has become a key research focus in recent years.
Triazine-based compounds are rich in tertiary carbon structures, offering excellent char-forming properties. They are chemically stable, decomposing only when heated above 150°C in concentrated sulfuric acid. Serving as prepolymers for many oligomers and polymers, they can be readily synthesized into compounds with relatively high molecular weights, aligning with the development trend of macromolecular flame retardant technology.
Triazine-based flame retardants include melamine (MEL) and its salts, melamine cyanurate (MCA) and its derivatives, as well as cyanuric acid and its derivatives. This article focuses on novel triazine-based compounds and their application in halogen-free intumescent flame retardant (IFR) systems.
Using a blend of cycloalkane oil-modified SEBS and polypropylene (O-SEBS/PP) as the matrix, an intumescent flame retardant was formulated by combining a triazine-based char-forming foaming agent (CFA), ammonium polyphosphate (APP), and SiO₂ for flame retarding the O-SEBS/PP system. The IFR system alone was insufficient to address the flame retardancy of O-SEBS/PP materials. An O-SEBS/PP/IFR system with 35 wt% IFR addition only achieved a UL94 V-1 rating (1.6mm thickness). When IFR was combined with aluminum hypophosphite (AHP) at a mass ratio of 8:1 for flame retarding O-SEBS/PP, the O-SEBS/PP/FR material with a total additive content of 28 wt% and 1.6mm thickness achieved a UL94 V-0 rating. Parameters such as peak heat release rate (PHRR) and total heat release (THR) were significantly reduced.
The results indicate that O-SEBS/PP composites are inherently difficult to flame retard, and IFR alone exhibits low efficiency for this system.
To improve the flame retardant efficiency of IFR in this system, aluminum hypophosphite (AHP) was introduced. The flame-retardant O-SEBS/PP composite contained approximately 69% matrix resin, consisting of 46% SEBS (with 50% oil extension) and 23% PP. The total flame retardant additive (IFR + AHP) content was 30%. Within this, the mass ratio of CFA to APP was maintained at 1:4, SiO₂ addition was 5% of the IFR mass, and the remainder comprised different mass ratios of AHP and IFR. Antioxidant 1010 and zinc stearate were each added at 0.5%.
Data on the flame retardant performance of O-SEBS/PP composites with different AHP:IFR mass ratios show that as the proportion of IFR increases, the limiting oxygen index (LOI) of the material first increases and then decreases. All formulations passed the UL94 V-0 rating (1.6mm). When the mass ratio of AHP to IFR was 1:8, the composite achieved the highest LOI value of 34.8% and a vertical burning time of 1.5 seconds, indicating this as the optimal ratio between AHP and IFR.