Cracking of Poly(Vinylidene Fluoride) Due to Chemical Attack

Abstract

The effects of exposure of poly(vinylidene fluoride) (PVDF) to various chemical solutions has been investigated. Scanning electron microscopy (SEM) was used to examine the exposed samples for signs of chemical attack and cracking, while tensile and flexural bend tests were used to determine the effects of exposure on mechanical properties. Samples exposed to 50% sodium hydroxide exhibited both chemical attack and cracking together with a significant loss in ductility. Exposure to 16% sodium hypochlorite and concentrated sulphuric acid did not give either chemical attack or cracking but exposure to sulphuric acid did cause significant loss of mechanical properties. From the results obtained it was concluded that the cause of cracking in 50% sodium hydroxide was chemical embrittlement, whereby a brittle layer was formed on the surface of the material. This brittle layer subsequently cracked under applied tensile stress. The actual mechanism by which the brittle layer was formed was not established. The cracking was not considered to be due to environmental stress cracking as this requires the simultaneous action of tensile stress and cracking medium.