Inorganic hydroxides are the most widely used basic category in halogen-free flame retardant systems, among which aluminum hydroxide (ATH) and magnesium hydroxide (MH/MDH) are the two core varieties. With the advantages of low smoke, non-toxicity, environmental compliance, and controllable cost, they are widely used in plastics, rubber, wire and cable, building materials, and other fields. Many users easily confuse the two during material selection. In fact, they differ significantly in thermal decomposition characteristics, processing compatibility, flame retardant efficiency, and applicable scenarios. Blindly applying them can easily lead to processing decomposition, product foaming, failure to meet flame retardant standards, decreased mechanical properties, and other problems. Only by precisely matching the substrate and production process can the flame retardant effect and overall cost be balanced.
Their most core difference lies in thermal decomposition temperature and processing compatibility.Aluminum HydroxideIts initial decomposition temperature is about 180-230°C; during decomposition, it rapidly releases water of crystallization to carry away heat, while generating an aluminum oxide heat-insulating layer. It has fast heat absorption, outstanding smoke suppression, and low raw material cost, making it the most widely used general-purpose flame retardant filler in the industry. However, its decomposition temperature is relatively low, so it is not suitable for resin systems processed above 220°C. High-temperature processing can easily cause product foaming, pores, premature powder decomposition and failure, etc. It is mostly used in low-temperature processing fields such as soft PVC, ordinary polyolefins, and low-temperature silicone rubber.Magnesium HydroxideIts initial decomposition temperature is about 330-340°C, more than 100°C higher than that of aluminum hydroxide, and the total heat absorbed per unit mass during decomposition is higher. At high temperatures, it forms a dense magnesium oxide protective layer, providing better flame retardancy and smoke suppression. It can stably adapt to high-temperature processing systems such as PP, PA engineering plastics, high-temperature silicone rubber, and crosslinked cable compounds, avoiding premature decomposition and failure during processing. However, magnesium hydroxide has higher raw material cost and greater powder hardness, causing more obvious wear to extruder and injection molding machine screws. Moreover, at the same flame retardant rating, its impact on mechanical properties such as tensile and impact properties is slightly greater than that of aluminum hydroxide. In the industry, both powders are usually surface-modified with silane coupling agents to greatly improve compatibility with the polymer matrix, reduce precipitation and blooming, and simultaneously improve mechanical properties and flame retardant efficiency.
In actual industrial selection, precise matching can be made according to processing temperature, substrate type, and cost positioning. For soft materials and low-end extruded products with processing temperatures within 200°C, the ATH system is preferred, with outstanding cost-effectiveness; for engineering plastics, high-temperature rubber, thin-wall injection molded parts with processing temperatures above 230°C, the MH system is preferred to ensure stable processing and reliable flame retardant effect. For mass production scenarios requiring balanced performance, a proportional compounding scheme of ATH and MH can also be adopted to achieve the optimal balance between cost and temperature resistance.HongtaiWe can provide aluminum hydroxide and magnesium hydroxide flame retardant products with different particle sizes and different degrees of surface modification, suitable for the flame retardant modification needs of various plastic and rubber systems. The entire product series complies with RoHS and REACH environmental standards.
Overall, aluminum hydroxide excels in low cost and good smoke suppression, and is the first choice for low-temperature general-purpose flame retardant scenarios; magnesium hydroxide excels in temperature resistance and high-temperature flame retardant efficiency, making it suitable for high-end high-temperature processing scenarios. As downstream industries' demand for halogen-free flame retardant materials continues to become more segmented, the two flame retardants are no longer simply substitutes; they increasingly leverage their respective advantages through compounding and synergy, becoming the core support of inorganic halogen-free flame retardant systems.
