Characterization of Pores in Dense Nanopapers and Nanofibrillated Cellulose Membranes: A Critical Assessment of Established Methods

Abstract

Nanofibrillated cellulose (NFC) is a natural fibrous material that can be readily processed into membranes. NFC membranes for fluid separation work in aqueous medium, thus in their swollen state. The present study is devoted to a critical investigation of porosity, pore volume, specific surface area, and pore size distribution of dry and wet NFC nanopapers, also known as membranes, with various established techniques, such as electron microscopy, helium pycnometry, mercury intrusion, gas adsorption (N2 and Kr), and thermoporometry. Although these techniques can be successfully applied to inorganic materials (e.g., mesoporous silica), it is necessary to appraise them for organic and hydrophilic products such as NFC membranes. This is due to different phenomena occurring at the materials interfaces with the probing fluids. Mercury intrusion and gas adsorption are often used for the characterization of porosity-related properties; nevertheless, both techniques characterize materials in the dry state. In parallel, thermoporometry was employed to monitor the structure changes upon swelling, and a water permeance test was run to show the accessibility of the membranes to fluids. For the first time, the methods were systematically screened, and we highlighted the need of uniform sample treatments prior to the measurements (i.e., sample cutting and outgassing protocols) in order to harmonize results from the literature. The need for revising the applicability range of mercury intrusion and the inappropriateness of nitrogen adsorption were pointed out. We finally present a table for selecting the most appropriate method to determine a desired property and propose guidelines for results interpretation from which future users could profit.

Enhancing Insulating Performances of Presspaper by Introduction of Nanofibrillated Cellulose

“…Before the test, presspaper samples were dried at 105 °C for 12 h. Figure 3 presents the pore size distributions of reference presspaper and NFC modified presspaper. For reference presspaper, air voids with diameter higher than 50 μm are ascribed to the interspaces between different small pieces of test samples [27]. The cumulative pore volume results also support this.…”

Nanocellulose in Sensing and Biosensing

“…12,17,18,25,36,46,48,[50][51][52][53][54] Due to their multi-performance character and variety of morphologies -e.g., nanocrystals, nanofibrils, nanofilms and electrospun cellulose fibers and different forms -e.g., papers, transparent films, hydrogels, aerogels, spherical particles, etc-,NCs have acquired increasing attention in numerous applications such as biomaterials engineering, biomedicine, energy (batteries and solar cells), membranes, opto/electronic devices, polymer nanocomposites, textiles and clothing, food, medical, cosmetic and pharmaceutical products, packaging industries, etc. 12,[17][18][19]21,24,25,[32][33][34]42,46,[54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] In order to improve and also to impart new certain properties to the surface of NCs for desired applications, according to the targeted applications, several strategies have been engineered to tune some interfacial, mechanical and optical properties of NCs and their compatibility, processability and reactivity using wide variety of materials such as hydrophobic matrices and various types of nanoparticles (NPs) and(bio)molecules. The chemical modification or functionalization of the hydroxyl groups onto the surface of NCs can offer specific functional groups via non-covalent surface modification (through adsorption of surfactants, oppositely charged entities/polyelectrolytes), sulfonation, TEMPO-mediated oxidation, esterification, etherification, silylation...…”

Mechanical response of multi-layer bacterial cellulose nanopaper reinforced polylactide laminated composites

“…1) can be observed, suggesting little or no impregnation of the BC nanopaper(s). This is attributed to the high viscosity of molten PLLA (>5000 Pa s at 180 °C) [23] and the small pore size of the nanocellulose network [24]. In this context, the reinforcing effect of the laminated composites stems from BC nanopapers instead of individual BC nanofibres [14].…”