ESCA and other morphological investigations of the brittle failure caused by an environmental stress cracking (ESC) of a HDPE milk crate

Abstract

SynopsisThe causes of a drastic reduction in the service life of a HDPE milk crate have been investigated. The mechanism and the type of crate failure have been deduced from a detailed morphological examination of its fracture surface as well as the interior. Various factors responsible for a rapid failure of the milk crate have been identified. An ESCA study of ESC of weathered milk crate surfaces revealed the presence of heavy oxidative degradation on the surface and a diffusion-controlled oxidation mechanism being operative in successive inner layers. The brittleness of this surface layer and formation of sharp cracks therein have been exhibited in SEM micrographs. Optical micrographs clearly show the presence of a surface layer, formed due to degradation, which is nonspherulitic and thus identifiable from the bulk, which is imperfectly spherulitic. Evidence for a migration of polymer additives from bulk to the surface is provided by the ESCA data and the SEM micrographs. DSC thermogram of the microtomed surface layer reveals bimodal endothermic peaks attributed to two phases present in the surface layer-one original phase and the second being degradation-induced. The formation of this brittle surface layer and its effect on the long-term fracture performance of milk crates are discussed, and suggestions for improving their durability are given.

Ageing of thermoplastic umbilical hose materials used in a marine environment I – Polyethylene

“…22 The best performance in terms of ESCR is achieved when HDPE is blended with a high low-molecular weight polymer. Cold drawing and orientation of the polymer was shown to induce orientation and alignment, which changed when the materials were annealed at 75 C. [23][24][25] Extrusion of HDPE in the formation of hose will be expected to impart a certain amount of alignment to the polymer and the quenching process can introduce stresses that have been previously shown to influence the fatigue properties of the polymer system.…”