Sunday, 18 April 2021

Rules of Thumb for Oxidative Stability of Polymers


Rules of Thumb for Oxidative Stability of Polymers

Hello and welcome to a new rule of thumb blog post. Today we discuss the governing rules for oxidative stability of polymers.

Apart from thermal aging, environmental influences (e.g. ultraviolet light) or attack by chemicals can cause oxidative degradation of macromolecules.

There are 5 chemical rules which steer the oxidative stability of polymers and when correctly applied can elongate the lifetime of the plastic part:

1)    Bond strength: high bond strengths found in the carbon fluorine bond (C-F) are better than bond strengths of C-H or C-C.

2)    Aromatic groups: aromatic compounds (contain one or more rings with pi electrons delocalized all the way around them) are more stable compared to methylene groups.

3)    Also, aromatic C-H bonds are better than aliphatic C-H bonds.

4)    Oxidation resistance: C=O bonds have a better oxidation resistance compared to methylene.

5)    Decomposition path: unzipping reactions should be not easily possible (no easy chemical decomposition pathway).

For example, polyamides may have a high melt temperature (due to hydrogen bonding) however they may have a poor oxidative stability caused by the presence of aliphatic C-H. Therefore incorporation of oxidative stabilizers can improve the continuous use temperature of polyamides. 

More rule of thumb posts can be found here.

Thank you for reading and #findoutaboutplastics

Greetings

Herwig Juster

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Literature:

[1] Sachtling Kunststoff-Taschenbuch

[2] Practical Guide to High Performance Engineering Plastics

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