Linear Viscoelastic Behavior of n ‐Alkane Diluted Polyethylene Melts: Sorption, Desorption, and Oscillatory Rheometry

ABSTRACT

The strategic modification of polymer melt rheology through the incorporation of low‐molecular‐weight diluents is critical for optimizing industrial processes such as foam extrusion and devolatilization. This study systematically elucidates the influence of a homologous series of n ‐alkanes ( C ₁₀ – C ₁₈ ) on the linear viscoelastic properties of high‐density (PE‐HD) and linear low‐density polyethylene (PE‐LLD) melts. To address the experimental challenges posed by volatile components, a rigorous methodological framework was established, integrating gravimetric sorption and desorption kinetics with oscillatory parallel‐plate rheometry. Gravimetric analysis substantiated that the diluent mass fraction in the molten state is primarily governed by macromolecular architecture, with the short‐chain branched PE‐LLD demonstrating a markedly higher sorption capacity than the linear PE‐HD due to an enhanced specific free volume. Controlled desorption experiments allowed for the reproducible adjustment of sub‐saturation concentrations, where drying kinetics followed a first‐order exponential decay. Rheological characterization revealed a pronounced, concentration‐dependent reduction in melt viscosity. The application of the Time‐Concentration Superposition (TCS) principle enabled the model‐independent derivation of horizontal ( a _c ) and vertical ( b _c ) shift factors. The established methodology provides a rigorous framework for dilution‐assisted rheology modification while outlining clear boundaries for probing future multi‐regime scaling transitions.