On the nanostructure of micrometer-sized cellulose beads

Abstract

The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately, dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material. We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m(2) g(-1) in cellulose bead sample type MT50 and from 417 to 220 m(2) g(-1) in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected. The SAXS results were compared with Brunauer-Emmett-Teller results from nitrogen sorption measurements and with mercury intrusion experiments.

Functional Cellulose Beads: Preparation, Characterization, and Applications

“…However, dry-state measurements are possible as well, which enables evaluation of the effect of different drying procedures on pores of different sizes. 132 Another method that can be applied for measuring pore size distribution of cellulose beads in the wet state is the spin echo NMR technique. 133 This exploits the delayed diffusion of water molecules near the pore walls compared to the molecules further away from the wall.…”

“…Thus, alternative methods, where pores sizes are measured directly in the wet state, can provide additional complementary information. Small angle X-ray scattering (SAXS) has been used to determine pore sizes and surface areas of never dried cellulose beads. , The technique is based on the measurement of different electron densities between the pore wall and the water phase, and it likewise assesses closed pores and pore sizes from 2 to 200 nm, meaning that comparison with the above-mentioned techniques is difficult. However, dry-state measurements are possible as well, which enables evaluation of the effect of different drying procedures on pores of different sizes …”

Zn2+-loaded cellulose beads stabilized by chitosan and prepared via freeze-drying for removing human testosterone in plasma

“…Freeze-drying method is seldom used to prepare cellulose beads for adsorption due to it can destroy the structure of the beads [22]. Our study indicates after freeze-dried and swelled, the adsorbent can restore spherical shape and their adsorption capacity is also improved.…”

“…As a representative technique to prepare porous material [19], freeze-drying is used to enhance adsorption capacity of some material, such as chitosan/cellulose composite [20] and cellulose nano-fibrils [21]. However, the method is ruled out for preparation of cellulose beads due to it can destroy the structure of the beads [22]. Cellulose beads have very good swelling behaviour [23] and the adsorbent for hemoperfusion can be used at wet-state.…”

Nanostructured Cellulose II Gel Consisting of Spherical Particles

“…Comparable results were calculated from nitrogen sorption experiments according to BET and BJH theories to obtain surface area and pore size distribution, respectively. The freeze-drying of the alcogel (FD- t BuOH) yielded an open-porous structure with a high surface area of 298 m 2 /g, which is higher than the surface area of commercial cellulose beads (121–201 m 2 /g) and better comparable to CNF (249 m 2 /g) and TEMPO-oxidized CNF (284–349 m 2 /g). , In contrast to that, the cryogel that was freeze-dried from water (FD-water) had a small surface area of only 10 m 2 /g, which is in the range of microcrystalline cellulose powder (1–20 m 2 /g) . Although CNF and FD- t BuOH feature comparable surface areas, the reactivity towards azidopropyl triethoxysilane is significantly higher in case of the cellulose II gel …”