How Do Antioxidants Improve the High-Temperature Stability of Polyurethane?

At 120°C for 500 hours, polyurethane without antioxidants loses 40% of its tensile strength, whereas the antioxidant-treated sample loses only 8%—a striking contrast that highlights the vital role antioxidants play in thermal stabilization systems for polyurethane.

Thermo-oxidative degradation is the major limiting factor for polyurethane in high-temperature environments. As temperature rises, polymer chains are attacked by oxygen, triggering chain scission and free radical propagation reactions that sharply degrade material performance. Antioxidants intervene in this oxidative process, forming a multi-layer thermal defense system within the polyurethane.

Multiple Mechanisms of Antioxidant Protection

1.Enhanced Thermal Stability

 *Hindered phenol antioxidants (e.g., Irganox 1010) donate active hydrogen atoms to terminate free radical chains. Adding just 0.3% of a hindered phenol can extend polyurethane’s oxidation induction time at 150°C to 3.5 times that of untreated samples.

 *Phosphite antioxidants (e.g., Ultranox 626) convert unstable hydroperoxides (ROOH) into inert alcohols, effectively preventing secondary oxidation.

2.Dual Strategy for Yellowing Suppression

 *Sumilizer GA-80 chelates trace metal ions like Fe and Cu (as low as 5 ppm), blocking metal-catalyzed oxidation routes.

 *In combination with light stabilizers (e.g., Tinuvin 770), the yellowing index (ΔE) can be maintained below 2.0 after 1,000 hours of UV aging—a 75% improvement over untreated samples.

3.Synergistic Antioxidant Systems

An optimal antioxidant formulation usually includes:

 *Primary antioxidants (phenols): Ensure long-term thermal stability; recommended at 0.1–0.5%.

 *Secondary antioxidants (phosphites): Protect during processing; optimal when used at a 1:2 ratio with primary antioxidants.

 *Metal deactivators (e.g., oxanilides): Especially useful in metal-filled systems; can double or triple high-temperature service life.

Representative Performance Enhancement Cases

1.Heat Resistance & Anti-Core Burning Performance

 SARANOX® PU368 demonstrated excellent performance under continuous heat aging at 180°C:

*Over 90% tensile strength retention after 100 hours

*Yellowing index (ΔYI) of thick sections (10 mm) kept below 3.0, effectively solving the “burned core” issue

*When blended with amine antioxidants, service life in automotive engine compartments (peak 135°C) extends up to 8,000 hours

2.Processing Stability

 Antioxidant U-5068L performs remarkably in multiple processing cycles:

*After five 220°C extrusions, melt flow index (MFI) variation remains under 5%

*In 150°C aging, MFI fluctuations are within ±8% even after 1,000 hours

*After 2,000 hours of thermal aging, color difference (ΔE) remains under 4.0

From molecular mechanisms to macro-level performance improvements, antioxidants provide reliable protection for polyurethane in high-temperature applications.

As polyurethane expands into high-temperature sectors such as new energy and electronic encapsulation, more efficient and long-lasting antioxidants are in demand. The future lies in next-generation antioxidants that offer both thermal durability and long-term stability, unlocking new frontiers for polyurethane innovation.