Spectroscopic and Thermodynamic Study of Biopolymer AdsorptionPhenomena in Heterogeneous Solid?Liquid Systems

摘要

Molecular selective adsorption processes at the solid surface ofbiopolymers in mixed solvent systems are poorly understood due to manifoldinteractions. However, the ability to achieve adsorptive fractionation of liquid mixturesis posited to relate to the role of specific solid?liquid interactions at the adsorbentinterface. The hydration of solid biopolymers (amylose, amylopectin, cellulose) inbinary aqueous systems is partly governed by the relative solvent binding affinities withthe biopolymer surface sites, in accordance with the role of textural and surfacechemical properties. While molecular models that account for the surface area andsolvent effects provide reliable estimates of hydration energy and binding affinityparameters, spectroscopic and thermal methods offer a facile alternative experimentalapproach to account for detailed aspects of solvation phenomena at biopolymerinterfaces that involve solid?liquid adsorption. In this report, thermal and spectroscopicmethods were used to understand the interaction of starch- and cellulose-basedmaterials in water?ethanol (W?E) binary mixtures. Batch adsorption studies in binaryW?E mixtures reveal the selective solvent uptake properties by the biomaterials, in agreement with their solvent swelling inpure water or ethanol. The nature, stability of the bound water, and the thermodynamic properties of the biopolymers invariable hydration states were probed via differential scanning calorimetry and Raman spectroscopy. The trends in biopolymer?solvent interactions are corroborated by dye adsorption and scanning electron microscopy, indicating that biopolymeradsorption properties in W?E mixtures strongly depend on the surface area, pore structure, and accessibility of the polar surfacegroups of the biopolymer systems, in agreement with the solvent-selective uptake results reported herein.