Antioxidants and Light Stabilizers

Like other polymer materials, polyurethane foam is prone to aging under external factors such as light and heat, leading to yellowing and a decline in its physical properties. Adding antioxidants, UV absorbers, and other anti-aging additives can mitigate these effects.

Adding small amounts of antioxidants to polyurethane raw materials or formulations can effectively inhibit thermal oxidative degradation. The role of antioxidants is to prevent polymer chain scission reactions and the formation of hydrogen peroxide induced by oxygen.

Hindered phenolic compounds are the most commonly used antioxidants for polyurethane materials. Examples include:

• 1,3,5-Trimethyl-2,4,6-tris(3',5'-di-tert-butyl-4-hydroxybenzyl)benzene
• 2-(2'-Hydroxy-3'-tert-alkylbenzyl)anisole
• Tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (Antioxidant 1010)
• Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Antioxidant 1076)
• 2,6-Di-tert-butyl-4-methylphenol (Antioxidant 264)

Phosphite antioxidants, such as tris(2,4-di-tert-butylphenyl) phosphite, are also commonly used.

Aromatic isocyanate raw materials, such as diphenylmethane diisocyanate, tend to yellow and undergo chemical reactions during storage and use under the influence of light, heat, oxygen, and moisture. This can lead to the formation of insoluble substances and a decrease in isocyanate content. Adding antioxidants and anti-aging agents like triphenyl phosphite, trinonylphenyl phosphite, or tris(2,4-di-tert-butylphenyl) phosphite can reduce these effects. Combining phosphites with substituted phenols enhances polyurethane's weather resistance and UV stability. These phosphite antioxidants are often used with anti-aging agents like 2246 or Antioxidant 300 [4,4'-thio-bis(6-tert-butyl-3-methylphenol)] for better results.

Polyether polyols can also oxidize under the effects of air, heat, and moisture. After prolonged storage, their color may yellow, and their acid value may increase, which negatively impacts polyurethane foam production, particularly soft foam. Adding anti-aging agents can raise the initial oxidation temperature by 30–50°C, improving the raw materials' and foam products' oxidative resistance. Common antioxidants include 2,6-di-tert-butyl-p-cresol (BHT, Antioxidant 264) and 2,2'-methylenebis(4-methyl-6-tert-butylphenol). Mixed antioxidants perform better, with a typical usage level of 0.1%–0.3% of the polyether. Among the most effective antioxidants for polyether-based flexible polyurethane foams are 2,6-di-tert-butyl-p-cresol and 4,4'-di-tert-octyl-diphenylamine, which help reduce core discoloration and spontaneous combustion risks.

Light Stabilizers (UV Absorbers)

Light stabilizers improve polyurethane's light stability. Various types of light stabilizers are available, including:

• Benzophenone-type UV absorbers: 2-Hydroxy-4-methoxybenzophenone, 2-Hydroxy-4-n-octoxybenzophenone (UV-531)
• Hindered amine light stabilizers (HALS): Decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidyl) ester
• Benzotriazole-type UV absorbers: 2-(2'-Hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole (UV-326), Bis(2'-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-327)

The typical dosage in foam products ranges from 0.1% to 0.5%.

Combining antioxidants and light stabilizers yields a synergistic effect, providing superior protection against aging and UV degradation.