Abstract
In this study, alkali and alkaline earth metal chlorides with different cationic radii (LiCl, NaCl, and KCl, MgCl2, and CaCl2) were used to gain insight into the behavior of cellulose solutions in the presence of salts. The specific focus of the study was on the evaluation of the effect of salts’ addition on the sol–gel transition of the cellulose solutions and on their ability to form monoliths, as well as the evaluation of the morphology (e.g., specific surface area, pore characteristics, and microstructure) of aerocelluloses prepared from these solutions. The effect of the salt addition on the sol–gel transition of cellulose solutions was studied using rheology, and morphology of resultant aerogels was evaluated by scanning electron microscopy and Brunauer–Emmett–Teller analysis, while the salt influence on the aerocelluloses’ crystalline structure and thermal stability was evaluated using powder X-ray diffraction and thermogravimetric analysis, respectively. The study revealed that the effect of salts’ addition was dependent on the component ions and their concentration. The addition of salts in the amount below certain concentration limit significantly improved the ability of the cellulose solutions to form monoliths and reduced the sol–gel transition time. Salts of lower cationic radii had a greater effect on gelation. However, excessive amount of salts resulted in the formation of fragile monoliths or no formation of gels at all. Analysis of surface morphology demonstrated that the addition of salts resulted in a significant increase in porosity and specific surface area, with salts of lower cationic radii leading to aerogels with much larger (~ 1.5 and 1.6-fold for LiCl and MgCl2, respectively) specific surface area compared to aerocelluloses prepared with no added salt. Thus, by adding the appropriate salt into the cellulose solution prior to gelation, the properties of aerocelluloses that control material’s performance (specific surface area, density, and porosity) could be tailored for a specific application.Graphic abstract
Highlights
Biodegradable and non-toxic natural polymeric materials have attracted considerable attention in multiple industries in today’s world, due to a serious environmental pollution created by synthetic plastics
We investigated the effect of the addition of sodium chloride (NaCl) salt on aerocellulose properties and found that the addition of 5 wt% of NaCl resulted in an increase of the specific surface area by * two-fold, and a slight increase in the porosity of cellulose aerogels (Parajuli et al 2020)
Despite the same amount of Microcrystalline cellulose (MCC) used for the preparation, aerocelluloses prepared with added monovalent salts appeared bigger in size than the control sample, following the trend ACel-KCl [ ACel-NaCl [ ACel-LiCl [ control (Fig. 1)
Summary
Biodegradable and non-toxic natural polymeric materials have attracted considerable attention in multiple industries in today’s world, due to a serious environmental pollution created by synthetic plastics. The products based on aerocelluloses range from high-value products in pharmaceutical and biotech industries (e.g., drug delivery vehicles, cell storage/growth devices, tissue engineering scaffolds (Pircher et al 2015; Chin et al 2016; Cai et al 2014) to medium- or low-value products (e.g., adsorbents (Dassanayake et al 2016), oil/water separation agents (Liao et al 2016), chromatographic systems (Luo and Zhang 2010), catalysts (Schestakow et al 2016b), heat insulation materials (Lazzari et al 2019), metal nanoparticle/metal oxide carriers (Wan et al 2016; Tian et al 2017), and energy absorbers (Li et al 2018)) For all these applications, the specific surface area, porosity and pore size distribution are undoubtedly the most meaningful morphological characteristics of the materials, as they define the product performance. The ability to control these intricate aerocelluloses’ features is of particular interest
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