On the characterization of viscoelastic behaviours of ultra-high molecular polyethylene composite with 1-ethyl-3-methylimidazolium ethyl sulfate ionic liquid

Introducing ionic liquids (ILs) into ultra-high molecular polyethylene (UHMWPE) is a promising approach to improving the processibility of UHMWPE. To have a comprehensive understanding of the role of ILs in affecting the properties and molecular structures of UHWMPE, we conducted a systematic study on the viscoelastic behaviours of UHMWPE/IL composites with various ILs content at room temperature. Stress relaxation tests were performed under constant tensile strain (\({\varepsilon }_{0}=\) 0.47%). Constant strain-rate tests were also performed at five strain rates over the range of 2 × 10^–3 s⁻¹ to 1.7 × 10^–1 s⁻¹. To have deeper insights into the phenomena and the structure–property relationship, theoretical modelling based on the generalized Maxwell model was employed to study the time-dependent relaxation modulus. The modelling results suggest decreased elasticity and viscosity by the addition of ILs, indicating weakened bonding and enhanced motions of chain segments. Moreover, experimental yield stresses from the constant strain-rate tests were modelled by the cooperative model, which is based on the Eyring’s activation theory and takes the cooperative motion of chain segments into accounts. Analysis of the modelling results also shows that ILs increased the effective volume and decreased the energy barrier required to activate chain motions, confirming the enhanced mobilities of chain segments of UHMWPE by the addition of ILs.