Review: Embrittlement in organic coatings
Failure is defined by a coating’s purpose, but a crack is a failure in almost every application. Cracks cause problems in service when they first arise, well before they are widespread. By itself, degradation of a polymer coating can cause cracks or adhesive failure, but several other sources of stress are possible. How do these stresses arise and how do coating properties change during service resulting in cracks?
Polymers become brittle
Moisture can produce swelling or blistering, entailing compressive stresses, but often tensile stresses also result at the same time. Environmental stress cracking causes embrittlement in polymers due to a combination of plasticisation and swelling caused by moisture. Seemingly small stresses, from thermal mismatch or bending, can initiate failure by repetition or due to a stress concentration. Polymers become brittle, manifested in several ways. Modulus and tensile strength may increase, but elongation and fracture surface energy diminish considerably.
Not only do all these factors affect the overall coating film, but they also affect the internal integrity between the binder and other ingredients and thus failure can be initiated internally before it become apparent externally.
The review has been published in Progress in Organic Coatings,Volume 172, November 2022.