Influence of Dissolution Temperature and Storage Time on Hydroxyethyl Cellulose Viscosity: Insights Into Molecular Structure Evolution

In this paper, the structures and molar substitutions (MS) of the two HECs are first determined by Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) dissolution, and Gel Permeation Chromatography (GPC) characterization. By analyzing two HEC variants with differing viscosities across various concentrations, temperatures, and storage durations, this study finds that viscosity is significantly affected by dissolution temperature and storage time, with these effects dependent on the MS degree of HEC. For low MS HEC, the viscosity remains stable at high dissolution temperatures (40–90 °C) in dilute solutions (0.1–1.5% w/v) but decreases in concentrated environments. In contrast, highly viscous HEC (0.1–1.0% w/v) shows minimal viscosity changes in dilute conditions, with reductions occurring in concentrated solutions. Increasing dissolution temperature causes a shift in molecular conformation from a loose random nematic structure to a more compact one, resulting in larger spacing between molecular chains, reduced interaction forces, and lower viscosity. Over time, low MS HEC transitions from a random coil to a compact structure, while high MS HEC maintains its disrupted form. This work enhances the understanding of HEC behavior under varying conditions and provides a theoretical foundation for optimizing its applications in diverse fields.