Hindered phenolic antioxidants are compounds having 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 single hindered phenolic and multi-hindered phenolic. In this article, we will explain the mechanism by which hindered phenolic antioxidants protect polymers.
What is the mechanism of polymer aging?
During use or storage, polymers can undergo degradation reactions due to heat, light, ozone oxidation or metal ion catalysis. The properties of the product then decrease, such as discoloration, stickiness, brittleness, or cracking. As a result, the use value is lost.
In the radical chain oxidation of polymers, hindered phenolic antioxidants donate protons to form phenolic oxygen radicals. Since the free radical and the benzene ring form a conjugated system, it has good stability and low activity, which can slow down the oxidation-induced process. At the same time, phenolic oxygen radicals also have the ability to scavenge free radicals, which can terminate the oxidation chain reaction.
Main types and applications of hindered phenolic antioxidants
Monophenolic antioxidants have only one hindered phenolic unit. Mainly anti-staining, no pollution. However, the molecular weight is small and volatile, which reduces the antioxidant effect. It can only be used in 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 precipitation resistance. Such as PP, PE, PVC, PA, ABS, PS, PVC, SBS, PU, PET, PMMA.
Omnistab AN 1135; highly active liquid hindered phenolic antioxidant with good dispersibility. For example, PUR, PMMA, PVB, coatings and adhesives.
Omnistab AN 565; suitable for processing unsaturated rubbers. It can effectively stabilize the thermo-oxidative aging and degradation of elastomers, and can prevent the phenomenon of gelation. Suitable for SBS, SIS, TPE, BR, SBR and other rubbers.
Bisphenol antioxidant
Bisphenol antioxidants refer to phenolic antioxidants in which two hindered phenol units are directly connected by an alkyl bond or a sulfur bond. Compared with the monophenolic type, the bisphenolic type has higher molecular weight and improved thermal stability, so it has better anti-aging effect. The two Omnistab bisphenol antioxidants are:
Omnistab AN 1035; is a sulfur hindered phenolic antioxidant that provides processing stability to polymers. Widely used in PE wire and cable, or PP, HDPE, PUR.
Omnistab AN 1024; a metal passivator with dual functions of anti-oxidation and metal passivation
Polyphenol Antioxidant
Polyphenol antioxidants contain more than two hindered phenol units in their molecular structure. Three Omnistab products, which are polyphenol antioxidants:
Omnistab AN 1010; Low volatility, odorless, highly potent hindered phenolic antioxidant. Excellent in PP, PE, PVC, PA, PBT, PET and adhesives.
Omnistab AN 1330; especially suitable for polyolefin products requiring high resistance to water extraction and discoloration. Application with PP, HDPE, TPE, ABS, PVC.
Omnistab AN 3114; it works extremely well in polyolefins. Omnistab AN 3114 is synergistic with UV absorbers or phosphites.
Guidelines for the use of hindered phenolic antioxidants
The combined use of hindered phenolic antioxidants and phosphite or thioester antioxidants can produce synergistic effects! Hindered phenolic antioxidants act as chain terminators by scavenging free radicals. However, hindered phenols cannot decompose hydroperoxides, so they must often be used with secondary antioxidants (such as phosphites or thioesters) and HALS.
Would you like to learn more about the process or receive application-specific advice? Contact us and we will be happy to assist you. try us!
