Polyethylene Melt Rupture and Slip in Simple Shear: A Visual and Mechanistic Study

Melt rupture of a bimodal molecular weight distribution polyethylene is studied under simple shear via flow visualization techniques for the first time. We demonstrated that this catastrophic failure is not exclusive to extensional flows. It was found that melt rupture is a time‐dependent phenomenon occurring after steady‐state plateau in slip velocity and stress. The rupture happens at the three‐phase (polymer‐air‐plate) common line and propagates through the specimen. The common line recedes slightly and stops slipping just before the onset of rupture. The presence of polytetrafluoroethylene lubrication (low surface energy coating) changes the nature of the slip mechanism toward adhesive failure and accelerates melt rupture in terms of time‐to‐rupture‐onset (at the same nominal shear rate). Surface roughness reduces the time to rupture onset but without affecting the nature of the slip. A time‐dependent phenomenon at the interface like fractionation or changes in conformation and entanglement density of the interfacial chains is likely the reason for the transition from slip to melt rupture. This conclusion holds substantial industrial relevance, especially since the prevailing approach to prevent rupture involves promoting slip and reducing stress. However, our research demonstrates that even after achieving a relatively high steady‐state slip velocity, rupture can occur.