Study of Hydrophilic Properties of Polysaccharides

Abstract

In this research, the structural characteristics, specific surface area, sorption of water vapor, and wetting enthalpy of various polysaccharides (cellulose, hemicelluloses, starch, pectin, chitin, and chitosan) have been studied. It was confirmed that crystallites are inaccessible for water, and therefore water molecules can interact only with polar groups in noncrystalline (amorphous) domains of biopolymers. The isotherms of water vapor sorption for various polysaccharides had sigmoid shapes, which can be explained by the absorption of water molecules in heterogeneous amorphous domains having clusters with different packing densities. The method of contributions of polar groups to sorption of water molecules was used, which allowed to derivate a simple calculating equation to describe the shape of sorption isotherms. The wetting of biopolymers with water was accompanied by a high exothermic thermal effect, in direct proportion to the amorphicity degree. The sorption values and wetting enthalpies of amorphous domains of biopolymers were calculated, which allowed to find the hydrophilicity index and compare the hydrophilicity of the various polysaccharides.

Hygroscopy as an Indicator of Specific Surface Area in Polymer Materials

“…The maximum values W h for starch, as for cellulose, did not exceed 30–33% with water activity close to 1. Similar values of water vapor sorption capacity for different polysaccharides are given in [ 44 ]. For potato starch, maximum W h values varied from 40 to 45%, and for microcrystalline cellulose, wood pulp, and cotton fibers, the W h range was from 18 to 32%.…”

Study of Isotherms of Water Vapor Sorption for Hydrophilic Polymers

“…For some samples, at high φ-values above 0.9, a deviation of the experimental isotherm from the calculated one is observed. It is known that for cellulose and other polysaccharides this phenomenon is caused by capillary condensation [6,23,25]. In the case of water-soluble polymers, such as PV, at high φ-values above 0.9, the dissolution process of the polymer in absorbed water begins, which also leads to anomalies in the sorption isotherm.…”

Study of sorption of alcohols vapors by cellulose

“…The crystallinity (X) and amorphicity (Y) degrees of the samples were determined by the method of wide-angle X-ray scattering (WAXS) [9]. The specific surface area, Ssp (H), was measured using adsorption of inert hexane vapor [10]. The content of α-cellulose was determined according to TAPPI standard method T-203 [11].…”

“…The sigmoid isotherms are usually explained by multilayer adsorption of sorbate molecules on the surface of pores. However, the absorption process of polar sorbates (e.g., water vapor) by amorphous domains (AD) of semicrystalline cellulose also gives a sigmoid isotherm of type II [6,7,10]. In addition, for various cellulose sorbents at high relative vapor pressures, Р/Ро ≥ 0.9, the adsorption or absorption can be accompanied by capillary condensation.…”

“…Structural studies have shown that amorphous domains of cellulose have a heterogeneous packing since they consist of densely and loosely packed clusters with different energies of hydrogen bonds [10]. The densely packed clusters accounting about 80 vol.…”