Due to its excellent flame retardant and thermal insulation properties, magnesium oxide (MgO) is commonly used as a flame retardant in various applications such as building materials, cables and wires, automotive industry, electrical equipment and textiles and furniture, etc. So far, the flame retardant properties of MgO in a variety of polymer matrices have been widely studied, including but not limited to polyamide (PA), polycarbonate (PC), and polyethylene terephthalate (PET), etc.
MgO Used in Flame Retardant PA Composites
Magnesium oxide flame retardant plays an extremely important role in polyamide 6,6 (PA66). Research shows that micron-sized MgO can be combined with aluminum diethylphosphinate (AlPi) as a synergist to synergistically enhance the flame retardant properties of PA66. When the total loading amount is only 10 wt%, the synergistic system of AlPi and MgO improves the flame retardant performance of the PA66 matrix. The composite's limiting oxygen index (LOI) value is as high as 32.3%, and the sample in the vertical combustion test obtained the UL-94 V-0 rating with a thickness of 1.6 mm.
Proposed mechanism of PA66 composites. [1]
MgO Used in Flame Retardant PC Composites
Magnesium oxide is commonly used as a flame retardant additive in polycarbonate composites. Quanxiao Dong et al. developed a flame-retardant PC/MgO nanocomposite with high flame retardancy through melt blending method. A small amount of MgO (2wt%) can significantly enhance the flame retardancy, and the LOI value of PC significantly increases from 26.5 to 36.8. In this work, MgO affects the flame retardant properties of PC through the following two aspects: on the one hand, MgO catalyzes thermo-oxidative degradation and accelerates the thermal protection/mass loss barrier on the burning surface; on the other hand, the filler reduces the initial stage of activation energy and improves the thermal stability of the final stage. [2]
MgO Used in Flame Retardant PET Composites
The introduction of multi-component flame retardant systems into PET polymer substrates can effectively improve its thermal stability and fire resistance, even for recycled PET. Red phosphorus/magnesium oxide and red phosphorus/iron oxide combined flame retardant systems can enhance the fire retardant properties of PET. Among them, metal oxides (MgO and Fe2O3) act as synergists, and their combination with red phosphorus can produce a synergistic effect on fire resistance. However, the mechanisms of action of MgO and Fe2O3 are not similar. MgO can form a three-dimensional network by interacting with the acidic functional groups of PET chains. While Fe2O3 is converted into Fe3O4 and FeO, and promotes the oxidation of red phosphorus to obtain the chemical structure present in the charcoal layer formed after partial combustion of PET. [3]
MgO Used for Flame Retardant Modification of Cellulose Fibers
The LOI value of cellulose fiber is only 19, so flame retardants need to be introduced to give cellulose fiber flame retardancy. In addition to MgO, an acid-resistant MgO microcapsule was also prepared for doping into cellulose fibers through a blending wet spinning process. The incorporation of MgO significantly improves the flame retardant properties of the prepared cellulose fibers. In addition, because MgO microcapsules have better acid resistance, they can promote the flame retardancy of cellulose fibers more effectively than pure microcapsules. Specifically, the addition of Mg2+ ions to cellulose fibers reduces the thermal decomposition temperature inside the cellulose fibers, catalyzes the dehydration and decarboxylation reactions, thereby promoting the formation of more carbon and non-flammable small molecules, while reducing the production of levoglucosan and flammable volatiles. [4]
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References
- Zhaoshun Zhan, et al. Mater. Res. Express, 2019, 6, 115317.
- Dong Q, et al. Journal of applied polymer science, 2012, 123(2), 1085-1093.
- Laoutid F, et al. Fire and Materials: An International Journal, 2006, 30(5), 343-358.
- Li X, et al. Carbohydrate polymers, 2017, 176, 246-256.
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