Messi Biology states that compounded rubber is the core intermediate in the production of rubber products. It is made by uniformly mixing raw rubber, compounding agents, and vulcanization systems. Its quality directly determines the performance of terminal products such as tires, hoses, and seals. As an inorganic functional additive, magnesium oxide (MgO) has become an indispensable material in the production of compounded rubber due to its unique chemical and physical properties. It is utilized throughout the processes of processing, vulcanization, and end-product application, playing multiple roles including vulcanization activation, scorch retardation, acid absorption/stabilization, and reinforcement/toughening.
In the vulcanization system of compounded rubber, magnesium oxide acts as an efficient vulcanization activator. Vulcanization is the key step in which rubber molecules cross-link to form a three-dimensional network structure. Magnesium oxide works synergistically with zinc oxide and accelerators to reduce the activation energy of the vulcanization reaction, thereby accelerating the cross-linking process between sulfur and rubber molecular chains. In synthetic rubbers such as chloroprene rubber (CR) and nitrile butadiene rubber (NBR), magnesium oxide is a core vulcanization auxiliary. It can shorten vulcanization time by 20%–30%, improve the uniformity of the cross-linking network, increase the tensile strength of the product by 15%–20%, and simultaneously lower the vulcanization temperature to reduce production energy consumption, meeting the demands of high-efficiency continuous production.
Preventing scorch is another vital function of magnesium oxide in compound processing. Scorch refers to the premature vulcanization of the rubber compound during early stages such as mixing, extrusion, or calendering, which can lead to scrapped materials or product defects. Magnesium oxide possesses endothermic properties and can adsorb free accelerators, delaying early cross-linking reactions and extending the scorch time, thereby widening the processing safety window. At the same time, its excellent dispersion performance helps prevent issues like “raw spots” or white spots, ensuring that compounding agents like carbon black and softeners are distributed more uniformly, which enhances the overall homogeneity of the compounded rubber.
As an efficient acid acceptor, magnesium oxide ensures the long-term stability of compounded rubber. Halogenated rubbers (such as chloroprene rubber and chlorinated butyl rubber) release acidic substances like hydrogen chloride (HCl) during vulcanization and usage. These acids can corrode equipment and degrade rubber molecular chains, leading to aging and cracking of the products. Being alkaline, magnesium oxide can rapidly neutralize these acidic by-products to form stable magnesium salts. This protects the integrity of the rubber cross-linking structure, inhibits aging and degradation, and significantly extends the service life of products—making it particularly suitable for high-end products like cable sheaths and corrosion-resistant seals.
Furthermore, magnesium oxide provides reinforcement and performance optimization for compounded rubber. The addition of appropriate amounts of light or active magnesium oxide can improve the hardness, wear resistance, and dimensional stability of the rubber, enhancing the product’s resistance to deformation. In polar compounds like nitrile rubber, it can reduce the swelling rate in oil media and enhance oil resistance. Compared to traditional reinforcing agents, magnesium oxide combines functionality with filling properties, optimizing formulation costs while ensuring performance, thus offering outstanding cost-effectiveness.
As the rubber industry transitions toward high-end and green development, the quality requirements for compounded rubber continue to rise. Specialized magnesium oxide with high activity, high dispersion, and low heavy metal content has become the mainstream choice in the industry. Its applications are expanding into fields such as new energy vehicle hoses, aerospace seals, and eco-friendly tires. As an “all-around additive” for compounded rubber, magnesium oxide—with its stable performance, multiple functions, and adaptability—supports the improvement of quality and efficiency in rubber products, serving as a vital fundamental material for the high-quality development of the rubber industry.