While other factors (such as strength, friction or surface quality) often dominate the material selection, chemical environment and resistance should always be taken into account. Chemicals are a common cause of plastic product failure. Frustratingly, such problems often emerge only after a delay when the product is already on the market.
Typically, failures occur when amorphous plastics are combined with continuous stress, and an unaccounted-for chemical substance acts as a catalyst. A classic example involves internal stress caused by amorphous plastic shrinking around a metal insert with residual machining oil on its surface.
How to Assess Chemical Resistance in your design?
Explore and understand your product's chemical environment, and incorporate this into both your material selection process as and test plan.
Chemical compatibility charts are available online. They may be challenging to interpret without a broader understanding of chemical terminology. Don't let this discourage you.
Identify a reference product that has proven its durability in a similar application and service environment.
When possible, prefer semi-crystalline plastics. These are generally more resistant to chemicals than amorphous ones. However, every thermoplastic has its susceptibility.
If transparency is required, you are likely to choose an amorphous grade. Be cautious—especially polycarbonate (PC), despite its strength and impact resistance, is prone to chemical damage.
For challenging conditions, you can consider high-performance plastics like PEEK, PPS, or PPA. These are rarely necessary for common consumer products but  in certain demanding cases they reduce the risk of chemical damage.
Leverage the expertise of material suppliers to identify suitable materials based on reference products or specific performance requirements.
Avoid and minimize continuous stress. Combined with chemical exposure this easily leads to Environmental Stress Cracking (ESC), a common cause of failure. Also, remember internal stress. Follow standard principles of plastic product design, such as ensuring uniform wall thickness, avoiding sharp corners, and allowing proper cooling.
Account for elevated temperatures in your design and test plans, as they accelerate the effects of chemicals.
A simple test setup for chemical compatibility
You can assess a material's chemical sensitivity through a simple stress test. For example:
Prepare 10 material samples and apply continuous stress (e.g., wrap them around a round tube).
Apply the chemical substance in question to the stressed area of five samples, leaving the other five as controls.
Accelerate the reaction by placing all samples in an oven
Gradually increase the temperature until cracks begin to form.
If you can identify a pattern in crack behavior, you can evaluate the material and substance compatibility. Â
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