How to improve chemical resistance?

Chemical resistance of plastics refers to a plastic's ability to maintain its integrity and properties when exposed to various chemicals. This includes resistance to degradation, leaching, swelling, or loss of mechanical properties when exposed to them.

Chemical resistance in plastics isn’t just a matter of choosing the right material for a particular solvent—it’s also a matter of time, stress, and internal structure. While many plastics are rated for resistance to certain chemicals, long-term exposure—especially under mechanical stress—can lead to unexpected failures. 

Plastic parts often contain internal stresses from shrinkage during molding. These residual stresses act as weak points in the material. Over time, if the part is exposed to a chemical agent, it can gradually weaken the intermolecular bonds—particularly along the chains that are already under the most stress. As the chemical attack progresses, these highly stressed polymer chains may begin to break, transferring the load to the surrounding material. 

This chain reaction can lead to a phenomenon called crazing, where fine surface cracks develop in the direction of stress. Crazing is often an early warning sign of chemical-induced degradation. If exposure continues, these micro-defects can propagate, ultimately resulting in part failure.

Image credits: Curbell plastics¹