Magnesium oxide exhibits excellent anti-yellowing and life-extending functions in polyurethane sponges through multiple pathways: “acid neutralization + adsorption + free radical inhibition + thermal stability.” It is particularly suitable for demanding applications in industries such as indoor furniture, automotive interiors, and packaging cushioning.
1. Neutralizing Acidic Degradation Products:
Polyurethane materials are prone to generating trace amounts of acidic substances (such as carboxylic acids, hydrogen chloride, etc.) under heat, oxygen, and ultraviolet radiation. These acidic substances accelerate degradation and trigger yellowing.
Magnesium oxide, being a basic oxide, can effectively neutralize these acidic byproducts, inhibiting discoloration reactions catalyzed by acid.
2. Adsorbing Moisture and Carbon Dioxide:
Moisture and CO₂ in the air can react with polyurethane to form carbamates and other substances, which also lead to yellowing.
Magnesium oxide has good hygroscopic and CO₂ adsorption capabilities, which can slow down these reactions and delay yellowing caused by hydrolysis.
3. Inhibiting Free Radical Reactions:
Under ultraviolet irradiation or high temperatures, free radicals are easily generated in polyurethane materials, inducing molecular chain scission and color changes.
Magnesium oxide has a certain ability to capture free radicals, which can reduce free radical chain reactions and lower the yellowing rate.
4. Enhancing Thermal Stability:
Under thermal aging conditions, polyurethane decomposition is accelerated, producing colored impurities.
Magnesium oxide can improve the overall thermal stability of the material, inhibit high-temperature decomposition reactions, and reduce thermal yellowing phenomena.
5. Synergistic Effect with Halogenated Flame Retardants:
If halogenated flame retardants are used in polyurethane sponges, thermal degradation easily releases strongly acidic substances such as HCl, triggering more severe yellowing.
Magnesium oxide can neutralize HCl through a neutralization reaction, inhibiting discoloration caused by halogen removal, and is particularly suitable for flame-retardant sponge systems.