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5
Corrosion of Polymer (Plastic) Materials
As discussed previously, metallic materials undergo a specific corrosion rate
as a result of an electrochemical reaction. Because of this, it is possible to
predict the life of a metal when in contact with a corrodent under a given set
of conditions. This is not the case with polymeric materials. Plastic materials do not experience a specific corrosion rate. They are usually completely
resistant to chemical attack or they deteriorate rapidly. They are attacked
either by chemical reaction or by solvation. Solvation is the penetration of
the plastic by a corrodent, which causes softening, swelling, and ultimate
failure. Corrosion of plastics can be classified in the following ways as to the
attack mechanism:
1. Disintegration or degradation of a physical nature due to absorption,
permeation, solvent action, or other factors
2. Oxidation, where chemical bonds are attacked
3. Hydrolysis, where ester linkages are attacked
4. Radiation
5. Thermal degradation involving depolymerization and possibly
repolymerization
6. Dehydration (rather uncommon)
7. Any combination of the above
Results of such attacks will appear in the form of softening, charring, crazing, delamination, discoloration, dissolving, or swelling.
The corrosion of polymer matrix composites is also affected by two other
factors: the nature of the laminate and, in the case of the thermoset resins,
the cure. Improper or insufficient cure time will adversely affect the corrosion resistance, whereas proper cure time and procedures will generally
improve the corrosion resistance.
All polymers are compounded. The final product is produced to certain
specific properties for a specific application. When the corrosion resistance of
a polymer is discussed, the data referred to are that of the pure polymer. In
many instances, other ingredients are blended with the polymer to enhance
certain properties, which in many cases reduce the ability of the polymer to
resist attack of some media. Therefore it is essential to know the makeup of
any polymer prior to its use.
5
Corrosion of Polymer (Plastic) Materials
As discussed previously, metallic materials undergo a specific corrosion rate
as a result of an electrochemical reaction. Because of this, it is possible to
predict the life of a metal when in contact with a corrodent under a given set
of conditions. This is not the case with polymeric materials. Plastic materials do not experience a specific corrosion rate. They are usually completely
resistant to chemical attack or they deteriorate rapidly. They are attacked
either by chemical reaction or by solvation. Solvation is the penetration of
the plastic by a corrodent, which causes softening, swelling, and ultimate
failure. Corrosion of plastics can be classified in the following ways as to the
attack mechanism:
1. Disintegration or degradation of a physical nature due to absorption,
permeation, solvent action, or other factors
2. Oxidation, where chemical bonds are attacked
3. Hydrolysis, where ester linkages are attacked
4. Radiation
5. Thermal degradation involving depolymerization and possibly
repolymerization
6. Dehydration (rather uncommon)
7. Any combination of the above
Results of such attacks will appear in the form of softening, charring, crazing, delamination, discoloration, dissolving, or swelling.
The corrosion of polymer matrix composites is also affected by two other
factors: the nature of the laminate and, in the case of the thermoset resins,
the cure. Improper or insufficient cure time will adversely affect the corrosion resistance, whereas proper cure time and procedures will generally
improve the corrosion resistance.
All polymers are compounded. The final product is produced to certain
specific properties for a specific application. When the corrosion resistance of
a polymer is discussed, the data referred to are that of the pure polymer. In
many instances, other ingredients are blended with the polymer to enhance
certain properties, which in many cases reduce the ability of the polymer to
resist attack of some media. Therefore it is essential to know the makeup of
any polymer prior to its use.