Tags: Flame Retardant Materials, Flame Retardants, Magnesium Hydroxide, Magnesium, Plastics
[Introduction] Magnesium hydroxide (MH) is an environmentally friendly, green inorganic flame retardant characterized by excellent flame retardancy, smoke suppression, and filling effects.
China Powder Network News: Plastics are essential materials in industrial production and daily life. However, plastics are highly flammable and generate a significant amount of toxic smoke and harmful substances during combustion. Effectively improving the flame retardancy of plastics is a critical issue to be addressed in practical applications. Magnesium hydroxide (MH) is an eco-friendly green inorganic flame retardant with excellent flame retardant, smoke suppressant, and filling properties. It possesses a high decomposition temperature, produces no toxic or harmful pollutants upon decomposition, and can be used synergistically with other flame retardants to achieve enhanced effects.
Application of Magnesium Hydroxide Flame Retardants in PP (Polypropylene)
PP is widely used in automotive, construction, and other sectors due to its low toxicity, low cost, excellent electrical insulation, good processability, and chemical corrosion resistance. However, PP is highly flammable with a fast burning rate, producing molten droplets and releasing large amounts of toxic smoke during combustion. Therefore, enhancing the thermal and flame resistance of PP is crucial. Chen Lingzhi et al. prepared an activated carbon-modified MH flame retardant using magnesium sulfate, ammonia, and activated carbon, applying it to PP polymers. The results showed that by incorporating the modified MH flame retardant into PP, the Limiting Oxygen Index (LOI) increased from 19.6% to 28.9%, significantly improving its flame retardant performance.
Application of Magnesium Hydroxide Flame Retardants in PS (Polystyrene)
PS is characterized by its low price, ease of processing, corrosion resistance, high impact strength, and durability, making it widely used in construction, decoration, electronics, and transportation. However, PS has a low LOI value and is highly flammable, continuing to burn even after the ignition source is removed. It releases massive heat and toxic smoke during combustion and produces severe melt dripping, which limits its application. Researchers added MH to PS to study changes in flame retardancy. The results indicated that as the MH dosage increased, CO2 production during thermal degradation decreased, char residue rose sharply, and the content of volatile and semi-volatile substances increased. This suggests that the addition of MH alters the flame retardancy of PS, increases its combustion temperature, and modifies its combustion mechanism.
Application of Magnesium Hydroxide Flame Retardants in PVC (Polyvinyl Chloride)
PVC is another common general-purpose thermoplastic used in films, pipes, wall panels, and electrical materials (especially cable insulation). It is categorized into rigid PVC and soft PVC. Rigid PVC, which contains fewer plasticizers, has better flame retardancy than soft PVC. However, since PVC contains chlorine, it releases hydrogen chloride gas and large amounts of toxic smoke during combustion. Therefore, while improving the flame retardancy of PVC, attention must also be paid to smoke suppression.
MH flame retardants can improve the flame retardancy of PVC while reducing toxic gas emissions. Wu Jianning et al. used different modifiers for the surface treatment of MH and studied its effects on the mechanical properties and flame retardancy of PVC. The results showed that zinc stearate provided the best modification effect, achieving an oil absorption value of 33.39%. The resulting MH particles were uniformly dispersed with significantly reduced agglomeration. This significantly improved the flame retardancy of PVC, although it had some impact on the material’s tensile strength.
Application of Magnesium Hydroxide Flame Retardants in PE (Polyethylene)
PE is favored in construction, electrical, and medical industries due to its excellent processability, electrical insulation, mechanical properties, and resistance to high and low temperatures. However, its LOI value is only about 17.4%, making it highly flammable. Improving PE’s flame retardancy is a major research focus. Common flame retardants for PE include halogen-based, phosphorus-nitrogen-based, and inorganic types like aluminum/magnesium. MH is particularly favored for its low cost and environmental friendliness.
Tao Jun studied the mechanical, electrical, thermal stability, and flame retardant properties of PE composites using MH with three different particle sizes. The results showed that MH significantly enhances the flame retardancy and thermal stability of PE. When the MH particle size was 3.1 μm, the composite exhibited the best comprehensive performance: a tensile strength of 16.1 MPa, elongation at break of 400%, an LOI of 22.3%, a Peak Heat Release Rate (PHRR) of 270 kW/m², and a volume resistivity of 5.2×10¹³ Ω·m.
Challenges and Prospects of Magnesium Hydroxide Flame Retardants
While magnesium hydroxide is a green, eco-friendly flame retardant with good effects and low cost, it faces challenges. As an additive flame retardant, high loading levels are required to meet stringent flame retardancy standards. Furthermore, MH is highly polar and hydrophilic, making it difficult to disperse in polymer matrices. It tends to agglomerate, leading to poor compatibility with plastics. This results in decreased mechanical strength, reduced processability, and poor flowability of the composite materials, limiting its large-scale application.
Future research should focus on:
- Ultrafining: Reducing MH to sub-micron or nano-scales.
- Surface Modification: Developing new surface modifiers to improve compatibility.
- Synergistic Compounding: Combining MH with other flame retardants.
- Microencapsulation Technology: To enhance performance and integration.
By improving flame retardant efficiency while minimizing the impact on the mechanical properties of plastics, the application of MH in the plastics industry can be further expanded.