Thermoplastic Elastomers:
Antioxidants in Styrene Block Copolymers (SBS, SIS) – Part 4
Styrene block copolymers such as SBS (Styrene-Butadiene-Styrene) and SIS (Styrene-Isoprene-Styrene) are susceptible to thermal and oxidative degradation. To ensure longer service life, color stability, and mechanical resistance, antioxidants are used.
1. Primary Antioxidants – Free Radical Scavengers
These antioxidants interrupt the chain reaction of free radicals, protecting the polymer from oxidative degradation:
Hindered Phenols prevent degradation at moderate temperatures. They are effective in SBS/SIS for consumer goods, packaging, and soft-touch applications.
Additives from the WTH product range: WTH-AN 1010, WTH-AN 1076
Thioether-Phenol Combinations enhance long-term protection, particularly for thermally stressed applications.
Additive from the WTH product range: WTH-Chemnox AN-1520
2. Secondary Antioxidants – Peroxide Decomposers
These prevent thermal degradation by breaking down hydroperoxides:
Phosphite Antioxidants are particularly effective in extrusion and injection molding of SBS/SIS, stabilizing the material during processing and preventing yellowing.
Additive from the WTH product range: WTH-Chemnox AN 168
Thioether Antioxidants are effective in high-temperature applications with significant ozone and UV exposure, such as DLTDP (Dilaurylthiodipropionate) and DSTDP (Distearylthiodipropionate).
3. Synergistic Combinations for Maximum Protection
A combination of primary and secondary antioxidants is often the best choice:
- WTH-AN 1010 + WTH-AN 168 → Prevents thermal and oxidative degradation.
- WTH-AN 1076 + DLTDP → Ideal for high-temperature applications.
- HALS + Phenol Antioxidants → Optimal for UV-sensitive applications.
Conclusion
For SBS and SIS TPEs, hindered phenols (e.g., WTH-AN 1010) are ideal for long-term protection. When combined with phosphite antioxidants (WTH-AN 168), thermal stability during processing is also improved. For applications exposed to high UV or ozone levels, HALS or thioether antioxidants are recommended.
