Constructing Cellulose Diacetate Aerogels with Pearl-Necklace-Like Skeleton Networking Structure

Cellulose and its derivative aerogels have attracted much attention due to their renewable and biodegradable properties. However, the significant shrinkage in the supercritical drying process causes the relatively high thermal conductivity and low mechanical property of cellulose and its derivatives aerogels. Considering the pearl-necklace-like skeleton network of silica aerogels, which can improve thermal insulation property and mechanical property. Herein, we propose a new strategy for fabricating cellulose diacetate aerogels (CDAAs) with pearl-necklace-like skeletons by using tert-butanol (TBA) as exchange solvent after experiencing the freezing-drying course. CDAAs obtained have the low density of 0.09 g cm−3, the nanopore size in the range of 10–40 nm, the low thermal conductivity of 0.024 W m−1 K−1 at ambient conditions, and the excellent mechanical properties (0.18 MPa at 3% strain, 0.38 MPa at 5% strain). Ultimately, CDAAs with moderate mechanical property paralleled to cellulose-derived aerogels obtained from supercritical drying process are produced, only simultaneously owning the radial shrinkage of 6.2%. The facile method for fabricating CDAAs could provide a new reference for constructing cellulose/cellulose-derived aerogels and other biomass aerogels.

The Chemistry and Physics of Aerogels

Discover a rigorous treatment of aerogels processing and techniques for characterization with this easy-to-use reference. Presents the basics of aerogel synthesis and gelation to open porous nanostructures, and the processing of wet gels like ambient and supercritical drying leading to aerogels. Describes their essential properties with their measurement techniques and theoretical models used to analyse relations to their nanostructure. Linking the fundamentals and with practical applications, this is a useful toolkit for advanced undergraduates, and graduate students doing research in material and polymer science, physical chemistry, and chemical and environmental engineering.

Extrusion-Based 3D Printing for Highly Porous Alginate Materials Production

Three-dimensional (3D) printing is a promising technology for solving a wide range of problems: regenerative medicine, tissue engineering, chemistry, etc. One of the potential applications of additive technologies is the production of highly porous structures with complex geometries, while printing is carried out using gel-like materials. However, the implementation of precise gel printing is a difficult task due to the high requirements for “ink”. In this paper, we propose the use of gel-like materials based on sodium alginate as “ink” for the implementation of the developed technology of extrusion-based 3D printing. Rheological studies were carried out for the developed alginate ink compositions. The optimal rheological properties are gel-like materials based on 2 wt% sodium alginate and 0.2 wt% calcium chloride. The 3D-printed structures with complex geometry were successfully dried using supercritical drying. The resulting aerogels have a high specific surface area (from 350 to 422 m2/g) and a high pore volume (from 3 to 3.78 cm3/g).

Synthesis of Monolithic TiO2 Aerogels With Relatively Low Shrinkage and Improved Formability Assisted by CTAB

Monolithic TiO2 aerogels without severe shrink were obtained by the sol-gel method with the addition of the surfactant cetyltrimethylammonium bromide (CTAB) to control the hydrolysis and polycondensation process and acetonitrile solvent as the solvent to improve the crystallinity. After CO2 supercritical drying, the shrinkage ratio of monolithic TiO2 aerogels modified by CTAB decreased by up to ∼26.9%, compared with the pure TiO2 aerogel. Their apparent densities were all lower than 300 g/cm3. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR) and BET Specific Surface Area Analysis were used to analyze the as-synthesized samples. The results revealed that all the samples were anatase-TiO2 phase with nanoporous network structures. The specific surface areas reached 250.2 m2/g confirmed by the BET (Brunaur–Emmett–Teller method) analysis. However, TiO2 aerogels without the addition of CTAB showed evident agglomeration and collapse of the network in comparison with CTAB-added samples. To further study the structure-property relationship, the photocatalysis performance of as-synthesized and 300°C-calcined aerogels was carried out contrastively. Interestingly, the influences of the CTAB adding amount of as-synthesized and calcined TiO2 aerogels are negative and positive, respectively, which is probably due to the synergistic effect of CTAB hindrance and grain refinement. Potentially, This kind of TiO2 aerogels assisted by CATB with low density, small shrinkage, improved formability, high specific surface area and fine crystalline grain may be applied in various applications, such as electrochemistry, photocatalysis, etc.

PVDF HFP_RuO2 Nanocomposite Aerogels Produced by Supercritical Drying for Electrochemical Oxidation of Model Tannery Wastewaters

A supercritical CO2 drying process was used to prepare an innovative nanocomposite, formed by a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF HFP) aerogel loaded with RuO2 nanoparticles. The produced nanocomposites, at 10% and 60% w/w of RuO2, were tested for the electrochemical oxidation of model tannery wastewaters. The effect of the electrochemical oxidation parameters, like pH, temperature, and current density, on tannic acid, intermediates, and chemical oxygen demand (COD) removal, was investigated. In particular, the electrolysis of a simulated real tannery wastewater, using PVDF HFP_RuO2 60, was optimized working at pH 10, 40 °C, and setting the current density at 600 A/m2. Operating in this way, surfactants, sulfides, and tannins oxidation was achieved in about 2.5 h, ammonium nitrogen oxidation in 3 h, and COD removal in 5 h. When chloride-containing solutions were tested, the purification was due to indirect electrolysis, related to surface redox reactions generating active chlorine. Moreover, sulfide ions were converted into sulfates and ammonium nitrogen in gaseous N2.

Development of a New Silica Aerogel-Polypropylene Foam Composite as a Highly Flexible Thermal Insulation Material

A new flexible thermal insulation sheet, a composite of silica aerogel with polypropylene (PP) foam, has been developed. Even though a large volume ratio of silica aerogel (97%) was included, the composite showed high flexibility. Thermal conductivity of the composite was 0.016 W/(m⋅K) at 298 K, which is as low as silica aerogel monolith. Silica aerogel flaking, which has been a problem in practical applications, is very low in this composite due to skin layers of the polymer-foam composite. A supercritical drying process for rolled sheets of the material for large-scale production is also described. Simulations of extraction of 2-propanol from a silica alcogel revealed that rolled composite sheets with small spaces between the sheet composite are able to dry in a reasonable extraction time. These findings led to effective on production of this material on a pilot industrial scale.

The effect of the drying method on the cell wall structure and sorption properties of waterlogged archaeological wood

Drying is a process affecting various wood properties, including its structure, moisture behaviour and mechanical properties. Since waterlogged wooden artefacts usually constitute priceless objects of cultural heritage, understanding the effect of drying on the complex interactions between the wood ultrastructure and the resulting properties is necessary to ensure their proper conservation. Hence, this was the aim of the present study, with a particular emphasis on the influence of drying conditions on the relations between the cell wall structure, dimensional stability and hygroscopicity of degraded archaeological wood. The choice of the particular drying methods was dictated by their final effect on wood appearance (dimensions). The results obtained clearly show that depending on the drying method applied, the resulting material differs significantly in structure, dimensions and sorption properties, despite the same degree of wood degradation. Air- and oven-drying resulted in the highest wood shrinkage, lower porosity, and a decreased number of free hydroxyls in the wood cell wall. The best wood dimensional stabilisation and the highest porosity were ensured by freeze- and supercritical drying. No correlations were found between wood structure and moisture behaviour. The outcome of the research may be useful for conservators who plan to provide the artefacts with proper storage conditions and effective conservation/reconservation.