Antioxidants (AO)
- The role of antioxidants is to prevent the oxidation of polymers.
- These are the substances which easily get self oxidised, although in some cases antioxidants act by combining with the oxidised polymer to give a stable product.
- Antioxidants generally belong to the class of phenols, aromatic amines and salts and condensation products form by reacting aminophenols and amines with aldehyde, ketone and thiocompounds.
- On the basis of protection mechanism antioxidants are classified into two categories viz
2) Peroxide decomposers.
1) Kinetic chain breaking antioxidants
These are also called chain terminators or chain scavengers. These antioxidants scavenges some of all low molecular free radical and polymeric radical.
2) Peroxide decomposers
These decompose the hydroperoxy group present in the polymer.
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| Peroxide decomposers. |
- On commercial basis antioxidants are classified into two types.
2) Secondary antioxidants.
1) Primary antioxidants.
These inhibit oxidation by chain termination reaction. These include substances with reactive OH and NH groups. Inhibition occurs through transfer of proton to free radical. The resulting radical is stable and unable to abstract proton from polymer chain.
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| Primary antioxidants. |
2) Secondary antioxidants.
Secondary antioxidants are frequently called hydroperoxide decomposers. These convert hydroperoxide into unreactive, unradical and thermally stable product.Organophosphorus and thiosynergistic compounds are used as hydroperoxide decomposers.
- Secondary antioxidants are combined with primary antioxidants to yeild synergistic stabilization effect.
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