Hindered phenolic antioxidants for protection of polymers

oktober 5, 2022
blog

Hindered phenolic antioxidants are compounds that have substituents on one or both sides of the hydroxyl group of the benzene ring. According to the number of hindered phenolic functional groups in its molecule, it is generally divided into mono-hindered phenolic and poly-hindered phenolic. In this article we will explain the mechanism of hindered phenolic antioxidants for protection of polymers.

What is the mechanism of polymer aging?

During use or storage, polymers undergo a degradation reaction due to heat, light, ozone oxidation or metal ion catalysis. Then the properties of the product are reduced, such as discoloration, tacky, hard brittle or crack. As a results, loss of value in use.
In the radical chain oxidation of polymer, hindered phenolic antioxidant supplies protons to form phenolic oxygen free radicals. Since the free radicals form a conjugated system with the benzene ring, it is stable and has low activity, which can slow down the oxidation induction processing. At the same time, the phenolic oxygen radical also has the ability to scavenge free radicals, which can terminate the oxidation chain reaction.

The main types and applications of hindered phenolic antioxidants

Mono-phenol antioxidant

Mono-phenol antioxidants have only one hindered phenolic unit. It is mostly anti-staining and no pollution. But the molecular weight is small, easy to volatile, so that the antioxidant effect is reduced. It can only be applied to systems that do not require high weather resistance. For example, some Omnistab products in this category are:

  • Omnistab AN 1076; Excellent compatibility with most polymer materials, low volatility, good resistance to precipitation. For example, PP, PE, PVC, PA, ABS, PS, PVC, SBS, PU, PET, PMMA.
  • Omnistab AN 1135; High activity liquid hindered phenolic antioxidants with good dispersion. For instance, PUR, PMMA, PVB, coatings, and adhesives.
  • Omnistab AN 565; Suitable for the processing of unsaturated rubber. It is effective in stabilizing the therm-oxygen aging and degradation of elastomer and can prevent the gel phenomenon. Applications with SBS, SIS, TPE, BR, SBR and other rubbers.

Bis-phenol antioxidant

Bisphenol antioxidants refer to phenolic antioxidants that directly link two hindered phenolic units with alkyl or sulfur bonds. Compared with the monophenol type, the bisphenol type has a higher molecular weight, which improves the thermal stability, so it has a better anti-aging effect. Two Omnistab Bis-phenol antioxidants are:

  • Omnistab AN 1035; Belongs to thio-hindered phenolic antioxidant, provides processing stability for polymers. It’s widely used in PE wire and cable, or PP, HDPE and PUR.
  • Omnistab AN 1024; A metal passivator with the dual functions of anti-oxidation and metal deactivation

Poly-phenol antioxidant

Polyphenol antioxidants contain more than two hindered phenolic units in their molecular structures. Three Omnistab products which are Poly-phenol antioxidants:

  • Omnistab AN 1010; High effective hindered phenolic antioxidant with low volatility and odorless. Excellent in PP, PE, PVC, PA, PBT, PET and adhesives.
  • Omnistab AN 1330; Particularly suitable for polyolefin products with high demands on water extraction resistance and discoloration. Applications with PP, HDPE, TPE, ABS, PVC.
  • Omnistab AN 3114; Its effect is excellent in polyolefin. Omnistab AN 3114 has a synergistic effect with UV absorbers or phosphite esters.

Guidelines for use of hindered phenol antioxidants

Synergistic effect is obtained when hindered phenol antioxidants are used in combination with phosphite ester or thioester antioxidant! Hindered phenolic antioxidants act as chain terminators by scavenging free radicals. However, hindered phenols cannot break down hydroperoxides, so they must often be used with auxiliary antioxidants (such as phosphite esters or thioesters) and HALS.

Would you like to know more about the process or receive a recommendation for a specific application? get in touch with us and we will be happy to help you. Try us!

Frequently asked questions

What is hindered phenolic?

Compounds that have substituents on one or both sides of the hydroxyl group of the benzene ring. According to the number of hindered phenolic functional groups in its molecule, it is generally divided into mono-hindered phenolic and poly-hindered phenolic.

What do phenolic antioxidants do?

In the radical chain oxidation of polymer, hindered phenolic antioxidant supplies protons to form phenolic oxygen free radicals. Since the free radicals form a conjugated system with the benzene ring, it is stable and has low activity, which can slow down the oxidation induction processing. At the same time, the phenolic oxygen radical also has the ability to scavenge free radicals, which can terminate the oxidation chain reaction.

Examples of phenolic antioxidants?

1. Omnistab AN 1076; Excellent compatibility with most polymer materials, low volatility, good resistance to precipitation.
2. Omnistab AN 1135; High activity liquid hindered phenolic antioxidants with good dispersion.
3. Omnistab AN 565; Suitable for the processing of unsaturated rubber. It is effective in stabilizing the therm-oxygen aging and degradation of elastomer and can prevent the gel phenomenon.
4. Omnistab AN 1035; Belongs to thio-hindered phenolic antioxidant, provides processing stability for polymers.
5. Omnistab AN 1024; A metal passivator with the dual functions of anti-oxidation and metal deactivation.
6. Omnistab AN 1010; High effective hindered phenolic antioxidant with low volatility and odorless.
7. Omnistab AN 1330; Particularly suitable for polyolefin products with high demands on water extraction resistance and discoloration.
8. Omnistab AN 3114; Its effect is excellent in polyolefin. Omnistab AN 3114 has a synergistic effect with UV absorbers or phosphite esters.

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