Influence of High‐Energy Ball‐Milling on the Rheological Properties of Molded Ultra High Molecular Weight Polyethylene and Its Correlation With the Structural Alteration

ABSTRACT In this work, the influence of high‐energy ball‐milling on the rheological properties of molded ultra‐high molecular weight polyethylene (UHMWPE) was explored and correlated with its structural alterations. The effect of ball‐milling on material properties was primarily analyzed through shear rheology. Notably, both shear and absolute value of complex viscosities decreased by more than 10 orders of magnitude with increasing ball‐milling time; however, the rate of reduction becomes less pronounced beyond 30 min of milling. Linear viscoelastic measurements and time–temperature superposition (TTS) studies revealed a distinct shift from a reptation‐dominated terminal region and rubbery plateau to a Rouse‐dynamics‐dominated high‐frequency transition region in the 30min ball‐milled specimen compared with the neat UHMWPE. This transition suggested a decrease in entanglement density and the formation of shorter chains due to chain scission. This is further supported by a significant increase (greater than sevenfold) in the molecular weight between entanglements for the 30 min ball‐milled specimen compared with the neat one. Microstructural evidence revealed that the particle morphology evolves from initially spherical to lamellar and flake‐like structures, resulting from particle flattening and chain interdiffusion during milling, followed by delamination and fragmentation. In addition, X‐ray diffraction analysis indicated the evolution of a prominent monoclinic phase following ball‐milling. Thermal analysis revealed a slight decrease in crystallinity from ~59% for neat UHMWPE to ~51% after 30 min of milling. Dynamic mechanical analysis further supports the rheological findings, demonstrating a reduction in storage modulus and overall stiffness, which is attributed to decreased entanglement density and possible chain shortening.