Plastic Fundamentals

What is Environmental Stress Cracking and How do I Stop it?

By Dr. Duane Priddy Sr. · Published February 17, 2021

Pictured: Polymer chains are entangled like spaghetti. Stress pulls them apart.

Rigid plastics parts get their strength by the entanglement of the long polymer chain molecules that make up the plastic. Over time, the long polymer chains gradually disentangle from each other during the use of the plastic part causing the plastic part to become weaker and weaker.

Environmental stress cracking is the result of two things acting together: tensile stress in the part, and contact with a chemical that the plastic does not tolerate. Neither alone is usually enough, which is why a part can serve for years and then crack soon after it meets the wrong cleaner, caulk or sealant. Prevention has two levers. Lower the stress the part carries, from service loads and from residual moulding stress, and verify that every chemical touching it is compatible with that specific plastic.

CPVC environmental stress cracking explained