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High Heat Additives Selection

Additives used with commodity polymers cannot give the best results with high temperature polymers. This is because of the lack of high temperature stability of these traditional additives. This fact has led to the development of specific additives that can be used with high temperature polymers. This guide will review the three main high heat additives: antioxidants, flame retardants and processing aids used with high heat polymers. Read on and uncover the features they offer in several high temperature polymers.

Antioxidants


Antioxidants protect the polymers against thermally induced oxidation. Oxidation can lead to several undesirable effects such as:
  • Discolorationhigh temperature polymer degradation
  • Changes in melt viscosity and
  • Deterioration of mechanical properties

The result is a limited useful life of the polymer or final article. Polymers can undergo oxidative degradation during high temperature melt processing operations, end-use and long-term storage operations. Since high temperature polymers are usually processed at temperatures more than 300°C, degradation is an important factor to be addressed.

Different antioxidant additives are most effective in different temperature ranges. The following Table summarizes some common antioxidant materials and their useful temperature ranges.

Effective Temperatures for Antioxidants

Antioxidant

Temp. Range (°C)

Hindered Amine

< 150

Hindered Phenol

150 - 300

Thioesters

< 150

Phosphites

175 - 300

Hydroxylamines

175 - 300




The table above shows that hindered amines can be effectively used for lower temperature processes. But cannot be utilized with high temperature polymers. On the other hand, phosphites and hydroxylamines have been specifically developed for use with high temperature polymers.

One of the most common phosphites for use with high temperature polymers is an alkyl-aryl phosphite. It functions by the decomposition of hydroperoxide intermediates in the oxidation process. It is effective with most high temperature polymers. It serves to lower the changes in the melt viscosity and also reduces discoloration effects.

Challenges with Antioxidants


alkanolamine component in mixture with phosphitePhosphites undergo undesired hydrolysis on exposure to moisture or water during storage or handling. This diminishes the activity of the stabilizer. Also, it means that their ability to absorb significant amount of moisture, such as polyamides, will be low. This problem has been addressed by incorporating an alkanolamine component into a mixture with the phosphite. Such compositions exhibit improved performance compared to the phosphite stabilizer alone.

In high temperature polymers, antioxidants suffer from the challenge of different processing methods used with the different polymers. Each of the different methods have unique time and temperature profiles associated with them. Thus, production methods for the aerospace industry vary from those in the electronics industry. The antioxidant stabilizer material must provide stability to the polymer in these processing scenarios.

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