On the BET Surface Area of Nanocellulose Determined Using Volumetric, Gravimetric and Chromatographic Adsorption Methods

Volumetric N2 adsorption at −196°C is generally accepted as “gold standard” for estimating the Brunauer-Emmet-Teller (BET) surface area of nanocellulose. It is unclear however, whether the BET surface area of nanocellulose obtained at such low temperatures and pressures is meaningful at an absolute sense, as nanocellulose is used at ambient temperature and pressure. In this work, a systematic evaluation of the BET surface area of nanocellulose using highly crystalline bacterial cellulose (BC) as model nanocellulose was undertaken to achieve a comprehensive understanding of the limitations of BET method for nanocellulose. BET surface area obtained using volumetric N2 adsorption at −196°C was compared with the BET surface area acquired from gravimetric experiments based on n-octane adsorption using dynamic vapour sorption (DVS) and n-octane adsorption determined by inverse gas chromatography (iGC), both at 25°C. It was found that the BET surface area calculated from volumetric N2 adsorption data was 25% lower than that of n-octane adsorption at 25°C obtained using DVS and iGC adsorption methods. These results supported the hypothesis that the BET surface area of nanocellulose is both a molecular scale (N2vs n-octane, molecular cross section of 0.162 nm2vs 0.646 nm2) and temperature (−196°C vs 25°C) dependent property. This study also demonstrates the importance of selecting appropriate BET pressure range based on established criteria and would suggest that room temperature measurement is more relevant for many nanocellulose applications.

Dynamic vapour sorption protocols for the quantification of accessible hydroxyl groups in wood

This study investigated several key parameters of deuterium exchange measurements in a dynamic vapour sorption apparatus to optimise the measurement protocol for hydroxyl (OH) group accessibility determination. The impact of changing the sample mass, the deuterium oxide (D2O) vapour exposure time and the rate of change in moisture content (dm dt−1) during the drying steps on the measured OH group accessibility were analysed. A sample mass of more than 10 mg, an exposure to D2O vapour of at least 10 h and a dm dt−1 of 0.0005% min−1 over a 10-min period during the drying steps gave the most reliable results. We also investigated the necessity of adding a method stage that eliminates the effect of inclusion compounds (ICs). The addition of an initial drying and wetting stage enabled the release of entrapped solvents.

Quantifying the hygroscopic properties of cyclodextrin containing aerosol for drug delivery to the lungs

The hygroscopic growth factor for individual aqueous 2-hydroxypropyl β-cyclodextrin droplets has been measured and compared with dynamic vapour sorption measurements.

Composite silicone-SAPO-34 foams: experimental characterization for open cycle applications

In this work, novel composite silicone-SAPO-34 foams have been prepared and experimentally characterized for application in desiccant open cycles. Water adsorption isotherms of several samples have been measured by a gravimetric dynamic vapour sorption analyser at 30°C and 70°C up to the relative humidity RH= 75%, representing typical process and regeneration air conditions in desiccant evaporative cooling cycles. Adsorbent foams manufactured with 20%, 40% and 60% weight fraction of SAPO-34 have been compared with the pure SAPO-34 powder. Results highlighted that the prepared foams adsorb a significant amount of water, according to the initial mass fraction of zeolite used in the compound. Moreover, the tested foams exhibited sufficiently fast water sorption rate for practical application in a desiccant open cycle system.

Surface Properties and Reactivity of Phosphate-based Glasses by Inverse Gas Chromatography and Dynamic Vapour Sorption

The chemical durability of phosphate-based glasses (PGs) in an aqueous environment is crucial in determining their dissolution properties and their ultimate performance in vivo. In this study, inverse gas chromatography (IGC) and dynamic vapour sorption (DVS)were used to investigate the short-term aqueous interactions of PG particles doped with SiO2 and TiO2 (50P2O5-40CaO-xSiO2- (10-x)TiO2, where x=7, 5, 3, and 0 mol%). IGC was used to evaluate the solubility parameter and surface energy of PGs. A good correlation between the polar parts of the solubility parameter and surface energy with glass transition temperature (Tg) and dissolution rates was demonstrated. DVS was applied to monitor the sorption characteristics of the PG particles. An increase in silica content resulted in greater vapour sorption and mass change. Nuclear magnetic resonance spectroscopy data of the PGs post exposure to vapour demonstrated that increased SiO2 content disrupted the glass network and formed protonated phosphate species. Fourier transform infrared spectroscopy verified the presence of non-reacted water molecules in the PGs depending on SiO2 content. Moreover, there was a good correlation between the values measured through IGC and DVS, demonstrating the ability of both techniques in predicting the dissolution properties of PGs as consequence of alterations in their chemistry.

Sorption-Related Characteristics of Surface Charred Spruce Wood

Surface charring of wood is a one-sided thermal modification process that can be used to create a hydrophobic, durable surface to exterior claddings. Spruce (Picea abies L.) wood samples were charred with a hot plate and several time-temperature combinations while using simultaneous surface compression. Temperature profile, water sorption, cupping after water exposure and density profile were measured. Furthermore, changes in the microstructure and surface functional groups were investigated by scanning electron microscopy and photoacoustic FT-IR spectroscopy. Results show that surface charring notably improves the hydrophobicity measured by contact angle, water floating and dynamic vapour sorption. Increased holding time during charring reduced the sorption but at the same time increased the dimensional instability measured by cupping. The density profile showed a shifting density peak with more severe modification regimes, indicating a more porous surface. The PAS-FTIR showed increased aromaticity of the surface that was also present in the pyrolysis zone beneath the surface in samples modified with longer holding time. Higher modification temperature affected the sorption as well as cupping positively but it is possible similar results can be obtained with lower temperature and longer holding time.

How silanization influences aggregation and moisture sorption behaviours of silanized silica: analysis of porosity and multilayer moisture adsorption

Based on the results of nitrogen adsorption and dynamic vapour sorption as well as analysis by the Hailwood–Horrobin (H-H) model, the effects of γ-methacryloxypropyltrimethoxysilane (MPTS) on the agglomeration and moisture sorption properties of fumed silica particles were investigated. After adding various concentrations (2%, 4%, 6% and 8%) of MPTS, different degrees of silanization were obtained by showing various ─OH group contents on the silica surface, which resulted in silica agglomerates with different porous structures. The bigger mesopores in the unmodified silica agglomerates became smaller and finally disappeared after MPTS modification and the Bruanuer–Emmett–Teller surface area decreased more gradually with an increase in MPTS concentration. The H-H model fitted the sorption isotherms very well, and both hydrated water and dissolved water showed decreasing trends with the increase in MPTS concentration, showing reduced hygroscopicity. Up to 6% MPTS, the ─OH groups decreased with increasing MPTS concentration, as indicated by reduced K h and W parameters, while at 8% MPTS an extensive self-condensation of MPTS occurred. Adsorption hysteresis appeared for moisture sorption on silanized silica, especially at low relative humidity values and at low MPTS concentrations, which could be explained by a synergistic effect of the surface ─OH group content and pore characteristics. These results could aid our understanding of the applications of silane-modified silica particles.