Leila Dehabadi

Polysaccharide-based materials and their adsorption properties in aqueous solution.

Polysaccharides (PS) of cellulose, soluble, corn- and maize-derived starches with variable amylose/amylopectin content were cross-linked with epichlorohydrin (EPI) to form polymeric adsorbents. The properties of the cross-linked PS-EPI materials were prepared by varying the synthesis conditions (nature of polysaccharide, temperature, and reagent ratios) to afford network polymer materials with tunable properties. The optimized polymers were obtained at a reaction temperature (50-54 °C) according their yield were characterized using spectroscopic (IR and NMR) methods, and thermal gravimetric analysis (TGA). The textural and adsorptive properties of the polymers were evaluated using nitrogen gas and dye-based methods using p-nitrophenol. Solvent uptake, nitrogen adsorption, and aqueous dye sorption show that the amylose and amylopectin content in the PS-EPI copolymers display a complex relationship with their physicochemical properties. Polymers with greater cross-linking did not show incremental changes in water or dye uptake. Structural variation of the polysaccharide (i.e. branching, molecular weight, and relative amylopectin/amylose content) contributed to the sorption properties by modifying their textural properties and surface chemistry.

Macromolecular hydration phenomena

Water plays an important role in the physicochemical and mechanical properties of Nafion (poly tetrafluorosulfonic acid) and cellulosic materials. Due to the strong influence of hydration on the properties of these materials, the mechanism and molecular-level understanding of hydration processes are the subject of ongoing interest in food, environmental and energy science. Nafion is a sulfonated tetrafluoroethylene polymer that represents a prototypical polymer electrolyte membrane (PEM) material. PEMs are often composed of a hydrophobic backbone with a strongly hydrophilic region (e.g., sulfonic acid moieties), which are directly attached to the backbone or through a pendant group. The application of Nafion in fuel cells as PEMs necessitate that the hydration properties of the membrane play an important role for maintaining high proton conductivity and mechanical properties. Cellulose on the other hand is one of the most abundant and low-cost renewable biopolymers with unique hydration properties. The hydration of cellulose impacts its biodegradability, recyclability and tunable physicochemical properties for various applications employing composite materials, pharmaceutical delivery systems, paper production, fibers and biofuel production. One of the challenges in the development and valorization of cellulose-based materials relates to its insolubility in aqueous media and conventional solvents. Therefore, evaluation of the hydration properties of Nafion and cellulose materials is required in order to characterize their physicochemical properties. Studies of the hydration properties of these materials include dielectric, spectroscopic techniques (NMR and IR), dynamic vapor sorption, differential scanning calorimetry (DSC), viscometry and computer simulations to determine the structural, kinetic and thermodynamic properties associated with such hydration processes. DSC is a sensitive and versatile thermal analysis method for the study of hydration phenomena, thermal behavior and thermodynamic state of water in hydrated macromolecular systems. The aim of this mini-review is to provide an overview of recent DSC studies relevant to aspects of hydration phenomena for Nafion and cellulose. This overview will contribute to an improved understanding of the hydration properties of Nafion and cellulose materials for applications that involve hydration phenomena.

Starch Particles, Energy Harvesting, and the “Goldilocks Effect”

This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption–desorption performance. SP15 has a particle diameter (dp) of 15 μm with a surface area (SA) of 2.89 m2/g and a pore width (Pw) of 80 Å. Microporous starch particles (SP15) were compared with high amylose starch (HAS15; SA = 0.56 m2/g, dp = 15 μm, Pw = 46 Å) and silica gel (SG13; SA = 478 m2/g, dp = 13 μm, Pw = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP15, HAS15, and SG13. The water swelling (%) for SP15 was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS15 and SG13, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP15 system was much improved (4–31%) over the HAS15 and SG13 systems at controlled operating conditions. SP15 is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption–desorption properties, herein referred to as the “Goldilocks effect”. This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications.