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Adhesives Ingredients

Antioxidants for Adhesives

Adhesives and their raw materials react like other organic materials with oxygen in a process called autoxidation. This guide offers you an extended overview of Antioxidants in the adhesives & sealant industry. You will be able to select the antioxidant you need from the different antioxidant families mentioned here. This guide will also take a look into antioxidant benefits and applications. You can also check how to test and determine the efficiency of the antioxidant(s) you have selected.

Secondary Antioxidants

  1. Mechanism
  2. Organophosphorus Compounds
  3. Thiosynergists
Mechanism
    Secondary antioxidants, frequently referred to as hydroperoxide decomposers, decompose hydroperoxides into non-radical, non-reactive, and thermally stable products.

    They are often used in combination with primary antioxidants to yield synergistic stabilization effects.

Hydroperoxide decomposers prevent the split of hydroperoxides into extremely reactive alkoxy and hydroxy radicals. Organophosphorus compounds and Thiosynergists antioxidants widely used hydroperoxide decomposers.

Organophosphorus Compounds

Organophosphorus compounds are secondary antioxidants that decompose peroxides and hydroperoxides into stable, non-radical products. They are extremely effective stabilizers during processing and are normally used in combination with a primary antioxidant. 

Trivalent phosphorus compounds are excellent hydroperoxide decomposers. Generally, phosphites (or phosphonites) are used and react according to the following general reaction, generating phosphates.


Some of these compounds are sensitive to water and can hydrolyze, leading to formation of acidic species. While the addition of an acid scavenger can minimize the effect, the industry has generally converted to hydrolysis-resistant compounds.

Commercially available phosphites differ by the nature of the aryl groups. Some typical structures are shown below.


Thiosynergists

Among sulfur-based hydroperoxide decomposers, esters of 3,3-thiodipropionic acid play an important role. Thiosynergists react according to the following general reaction, generating sulfoxides and sulfones.


Although thiosynergists do not improve the melt stability of polymers during polymer processing, they are very efficient for long-term thermal aging applications. Sulfur based hydroperoxide decomposers are mainly used in combination with hindered phenol antioxidants.

The most common commercially available thiosynergists are based on either lauric or stearic acid.

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