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| 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
Herwig
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Literature:
[1] Sachtling Kunststoff-Taschenbuch
[2] Practical Guide to High Performance Engineering Plastics
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