Chemical resistance: What must be considered when selecting?

In numerous industrial applications, the chemical resistance of a material is a decisive selection criterion. Whether in medical technology, plant engineering, food processing or the chemical industry – materials regularly come into contact with aggressive substances. Choosing an unsuitable material can lead to corrosion, material failure or dangerous leaks. It is therefore essential to assess resistance to acids, alkalis, solvents and other chemicals precisely.

What does chemical resistance mean?

Chemical resistance is the ability of a material to permanently retain its mechanical and physical properties when in contact with chemical substances. This concerns, for example:

• Dimensional stability
• Tensile strength
• Impermeability to diffusion
• Surface condition

A resistant material shows no cracks, swelling or material changes even under prolonged exposure. Concentration, temperature, duration of exposure and the physical state of the chemical play an important role here.

Overview: chemical resistance of engineering plastics

The following table provides an initial overview of the resistance of selected plastics to typical chemicals (at room temperature):

Plastic	Acids	Alkalis	Alcohols	Ketones	Oils & greases
PE-HD	good	very good	good	poor	good
PP	very good	very good	good	poor	good
PVC-U	very good	good	good	satisfactory	very good
PVDF	very good	very good	very good	good	very good
PTFE	excellent	excellent	excellent	very good	very good
PA6	satisfactory	poor	good	poor	good
POM	good	poor	good	poor	very good
PC	poor	poor	good	poor	good
PMMA	poor	poor	satisfactory	poor	poor

Note: These values are general guidelines. A practical material selection requires individual tests under the real conditions of use.

Important selection criteria

When assessing chemical resistance, you should consider the following factors:

Concentration and temperature

The higher the concentration of a chemical and the higher the temperature, the more aggressive its effect on the material. For example, sulphuric acid at low concentration is compatible with many plastics, but at high concentration it is highly corrosive.

Contact time and exposure

Short-term contact can be tolerated by many materials. For continuous exposure – for instance in pipelines or storage tanks – a chemical-resistant plastic is required.

Mechanical load

Combinations of chemical and mechanical load (e.g. pressure, tension or vibration) can significantly reduce resistance. The material must therefore be suitable not only chemically but also mechanically.

Diffusion behaviour

Some chemicals penetrate apparently impermeable materials (permeation). This behaviour must be tested, particularly with gaseous media or thin-walled components.

Industry-specific recommendations

Chemical industry

• Use of PTFE, PVDF or PFA with highly aggressive media
• Piping systems made of PP-H or PVDF

Food processing

• PE-HD or PP due to good resistance to cleaning chemicals
• Materials must also be food-safe (FDA/EU 10/2011)

Medical technology

• Materials such as PEEK, PVDF or PTFE, as they can be autoclaved and are resistant to disinfectants

Water treatment

• PVC-U, PE, PP and PVDF for tanks, pipes, filter systems
• Important: check resistance to chlorine, ozone or sodium hydroxide solution

Mechanical and plant engineering

• POM, PA, PBT or PPS with oily or greasy media
• high rigidity required where mechanical load occurs at the same time

Conclusion

Chemical resistance is a central selection criterion for engineering plastics – especially in safety-critical or hygiene-relevant applications. A well-founded material choice must always take into account the specific chemical, its concentration, temperature and other application parameters. Standard values and tables provide guidance, but do not replace individual material testing in the specific case of use.

FAQ

Which type of plastic is considered the most resistant to chemicals? PTFE (Teflon) offers one of the broadest chemical resistances of all.

How do I recognise whether a plastic is chemical-resistant? Manufacturer data sheets provide information. Resistance tables and, if necessary, laboratory tests are also important.

Are there universal plastics for all chemicals? No. Even PTFE has limits – e.g. with molten alkali metals or certain organic solvents at high temperatures.

Are bio-based plastics chemical-resistant? Usually less so. Their resistance is often lower than that of conventional engineering plastics.