On the aggregative behavior of 4-O-Methyl-D-Glucurono-D-Xylan in aqueous solution: from optimized solvation at hot temperature to cold gelation

The physicochemical characterization of aqueous solutions of 4-O-methyl-D-glucurono-D-xylan (MGX), extracted from beech wood sawdust, has been conducted by Size Exclusion Chromatography (SEC) on-line coupled with Multi Angle Light Scattering (MALS) analyses. The chromatograms clearly evidence a strong aggregative behavior with the presence of two populations: the first one, less predominant (6.7–25 wt%), is made of large size structures, with number average molar mass (Mn) and mass average molar mass (Mw) higher than 10 ⁶ g.mol ^− 1 , while the second one, more predominant (75–93.3 wt%), is made of chains displaying relatively lower molar masses. In this study, we demonstrate that suitable solvation conditions can be reached through heating at 80°C in pure water. In this case, the 2nd population accounts for 93.3 wt% of the sample, with molar masses of 22.700 and 36.900 g.mol ^− 1 respectively for Mn and Mw, corresponding to those from the literature obtained in non-aggregative conditions (i.e. DMSO or aqueous alkaline media). Conversely, stronger aggregation has been evidenced with lower solvation temperature, higher MGX concentration or in the presence of salts (notably with KCl). Finally, an unexpected cold gelation of semi-dilute concentrated MGX aqueous solution (150 g.L ^− 1 ) has been observed through rheology with a large hysteresis, characterized by a G’/G’’ crossing at 15.5°C when cooling and at 37.5°C when heating back to the initial temperature of 50°C.