Experimental and numerical study on water sorption over modified mesoporous silica

–SO₃H modified mesoporous silica adsorbent with water sorption capacity and fast desorption kinetics for water sorption was synthesized and studied via a combined experimental and numerical approach. Mesoporous silica was synthesized using sol–gel method in H₂SO₄ medium. The water adsorption isotherms and kinetics over the silica were evaluated by a dynamic water vapor sorption analyzer. Mesoporous silica was modeled using annealing simulation with CVFF forcefield. –SO₃H modified mesoporous silica was modeled by the attachment of –SO₃H to the surface hydroxyl groups and validated. Simulation results show water sorption capacity at low relative humidity (RH) increases with –SO₃H loading on mesoporous silica. Energy distribution of intermolecular interaction and micro-view of water sorption over –SO₃H modified mesoporous silica reveal that although strong interaction (intermolecular interaction of ?40 to ?20 kcal/mol) between hydrophilic groups (–SO₃H) with water can increase water sorption capacity at low RH, weak H₂O–H₂O interaction (intermolecular interaction of ?20 to ?10 kcal/mol) dominated water sorption capacity at both low and high RH.     

Properties of nitrocellulose‐coated and polyethylene‐laminated chitosan and whey films

Chitosan (chitosan acetic acid salt) and whey (65% protein) films were coated with a nitrocellulose lacquer or laminated with polyethylene to enhance their water resistance and gas barrier properties in humid environments. The barrier properties were measured by the Cobb₆₀ test and water‐vapor (100% relative humidity) transmission and oxygen (90% relative humidity) permeability tests. Mechanical properties were obtained with tensile tests. Packaging properties were studied with crease and folding tests. The Cobb₆₀ test revealed that the coated films were resistant to liquid water, at least for a short exposure time, if the coating thickness was at least 10–17 μm. Water‐vapor transmission rates comparable to those of polyethylene‐laminated films were obtained for coated chitosan at a coating thickness of 5–7 μm. The coated films possessed low oxygen permeability despite the high humidity. Coated films dried for 3 weeks showed oxygen permeabilities at 90% relative humidity that were similar to values for dry ethylene‐co‐vinyl alcohol at 0% relative humidity. The lacquer partly penetrated the whey films, and this led to excellent adhesion but poor lacquer toughness. The lacquer coating on chitosan was tougher, and it was possible to fold these films 90° without the coating fracturing if the coating thickness was small. The coated whey films were readily creasable. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 985–992, 2001     

The effect of triethyl citrate on the dispersibility and water vapor sorption behavior of polylactic acid/zeolite composites

The aim of this study was to investigate the water vapor adsorption behavior and mechanical properties of poly (lactic acid) (PLA)/zeolite (5, 10, or 15 phr) composites prepared with triethyl citrate (TEC; 20 phr) via a melting process. TEC was used to improve the flexibility of the PLA and the dispersibility of the zeolite in TEC-zeolite suspensions that were ultra-sonicated. It was found that zeolite was uniformly dispersed in the PLA matrix, and the interfacial adhesion between the PLA matrix and zeolite was enhanced by TEC. In addition, the tensile strengths and Young's modulus of the composites improved with increasing zeolite content. The PLA/zeolite composites prepared with TEC had increased water vapor permeability and contact angles compared to neat PLA and standard PLA/zeolite due to the presence of TEC. In particular, TEC accelerated the hydrolysis of the PLA surface in a high humidity environment, resulting in an improvement in water vapor sorption capacity. At the same zeolite content of 15 phr, the equilibrium moisture content (EMC) values of PLA/zeolite films prepared with TEC increased by up to 39.25 mg/g whereas those prepared without TEC only increased by up to 24.33 mg/g. The results suggest the possibility of applying PLA/zeolite films prepared with TEC as a flexible active packaging material.     

The stable hydrogen and oxygen isotope variation of water stored in polyethylene terephthalate (PET) bottles

A set of bottled waters from a single natural spring distributed worldwide in polyethylene terephthalate (PET) bottles has been used to examine the effects of storage in plastic polymer material on the isotopic composition (delta18O and delta2H values) of the water. All samples analyzed were subjected to the same packaging procedure but experienced different conditions of temperature and humidity during storage. Water sorption and the diffusive transfer of water and water vapor through the wall of the PET bottle may cause isotopic exchange between water within the bottle and water vapor in air near the PET-water interface. Changes of about +4 per thousand for delta2H and +0.7 per thousand for delta18O have been measured for water after 253 days of storage within the PET bottle. The results of this study clearly indicate the need to use glass bottles for storing water samples for isotopic studies. It is imperative to transfer PET-bottled natural waters to glass bottles for their use as calibration material or potential international working standards.     

Investigation of Moisture Sorption,Permeability, Cytotoxicity and Drug Release Behavior of Carrageenan/Poly Vinyl Alcohol Films

This work describes moisture sorption behavior and water vapor permeability of glutaraldehyde-crosslinked carrageenan/polyvinyl alcohol (Carr/PVA) films. The moisture uptake has been studied under various relative humidity (RH) and the data obtained has been interpreted in the terms of various isotherm models such as GAB, Oswin and Halsey models. The moisture permeability through the films has been characterized in the terms of various parameters like water vapor transmission rate (WVTR), permeance (P) and water vapor permeability (WVP). It was found that these parameters are greatly affected by the degree of crosslinking of the films. Finally, the model drug Gentamycin Sulphate was loaded in to the films and its release was monitored kinetically in the physiological buffer (PF) at 37°C. The films exhibited diffusion controlled release mechanism. The films are non-cytotoxic.     

Electrospun zirconium hydroxide nanoparticle fabrics as sorptive/reactive media

Good quality adsorbent fabrics were electrospun from slurries of zirconium hydroxide nanoparticles and polyvinyl butyral (PVB) in alcohols. The as-spun fabrics had very high porosity, about 80 vol%, and high zirconium hydroxide content, 50–95 wt%. The porosity and mechanical strength of the fabrics could be modified via compaction and/or exposure to alcohol vapor. SO₂ sorption capacity of the fabrics was high at 1.6–1.9 mol/kg and was relatively independent of the sample pretreatment, unlike the capacity of the pristine nanoparticles, which decreased when the powder was stored in a low relative humidity atmosphere. The as-purchased zirconium hydroxide nanoparticles contained about 45 wt% of water, equivalent to the formula ZrO₂·5.6H₂O. In contrast, the electrospun composite fabrics contained only 25 wt% of mostly coordinated water, leading to the formula ZrO₂·2.2H₂O. The presence of PVB binder inhibited the rehydration/dehydration processes and stabilized the SO₂ sorption capacity of the composite fibers. The electrospun fabrics could find applications as conformable, flexible filters in civilian and military applications.     

Antimicrobial nanocomposite films made of poly(lactic acid)–cellulose nanocrystals (PLA–CNC) in food applications—part B: effect of oregano essential oil release on the inactivation of Listeria monocytogenes in mixed vegetables

Antimicrobial nanocomposite films containing oregano essential oil (EO) were prepared by solvent casting. Film matrix was composed of supramolecular poly(lactic acid)–cellulose nanocrystals (PLA–CNC) nanocomposite. Bioactive PLA–CNC–oregano films were prepared by incorporating oregano EO as an antimicrobial agent. Resulting films were then converted into packaging applied on mixed vegetables as a food model and stored for 14 days at 4 °C to determine their antimicrobial capacity against Listeria monocytogenes, their physico-chemical/structural properties and their total phenols (TP) release during storage, in order to evaluate the effect of oregano EO. It was observed the addition of oregano EO did not affect the water vapor permeability (WVP) of films, but increased their elongation at break (Eb) and reduced their tensile strength (TS) and tensile modulus (TM) at day 0. However, TS, TM, Eb and WVP values of control and bioactive films were increased slightly after 14 days of storage. FTIR analysis allowed characterizing the molecular interactions of oregano EO with PLA–CNC matrix via the identification and interpretation of their respective vibration bands. Microbiological analysis of mixed vegetables inoculated with L. monocytogenes (3 log CFU g^?1) indicated that PLA–CNC–oregano films induced a quasi-total inhibition of bacteria in vegetables at day 14 and therefore demonstrated a strong antimicrobial capacity in situ. The percentage of TP release from bioactive films was determined by Folin–Ciocalteu’s method and results showed that TP release increased continuously from day 0 to day 14, up to 16.6 % at day 14. These results allowed demonstrating the strong antimicrobial capacity of PLA–CNC–oregano films for food packaging applications in vegetable produce.     

Water sorption in hybrid silica gels containing colloidal nontronite

Hybrid silica gels (HSGs) were prepared according to an acid-catalyzed sol–gel method using tetraethoxysilane (TEOS) as silica precursors and colloidal suspension of nontronite clay mineral. The silica surfaces were hydrophilic in relation to silanol groups and it was of interest to increase hydrophobicity by substituting silanol by methylated groups through addition of methyltrimethoxysilane (MTMS) in a molar ratio TEOS: MTMS equaled to 1:0.4. The aim of the present paper was to predict effects of water content in soil on HSG hydration by characterizing HSG water desorption and sorption with dynamic vapor sorption device. From desorption kinetics, TEOS HSGs showed higher ability to water surface evaporation and diffusion compared to the TEOS–MTMS HSGs. After complete dehydration, water sorption isotherms Type II were obtained for HSGs. Isotherms were fitted with Brunauer-Emmett-Tellet (BET) and Guggenheim, Andersen, de Boer (GAB) models. The higher monolayer values of water adsorbed for HSGs containing nontronite suggested a major influence of clay minerals on overall hydration. However, the water binding energy depended upon the nature of silica matrix indicating weaker bonds with methylated groups at solid surface in MTMS–TEOS HSGs. Apparent water sorption diffusivities, D_app were calculated according to Fick’s diffusion model. Maximal D_app values were obtained in the range 0.2??.3 a_w after which the D_app decreased in relation with capillary condensation.     

Water Sorption Properties and Antimicrobial Action of Zinc Oxide Nanoparticles-Loaded Cellulose Acetate Films

In this work, ZnO nanoparticles loaded cellulose acetate (ZOLCA) films have been prepared and characterized by XRD, SPR and SEM analysis. The moisture permeation properties of the films have been investigated. The GAB isotherm model has been found to fit well on the moisture uptake data obtained at different temperatures. The monolayer sorption capacity χ_m was found to decrease from 0.059 to 0.0079 g water/g dry film with increase in temperature from 20 to 37°C. The isosteric heat of sorption, when studied in the lower water activity range of 0.04 to 0.10, was evaluated to be 46.55 to 87.29 kJ/mol. The water vapor permeability across the ZOLCA films was found to increase with temperature and activation energy of moisture sorption process was found to be 48.57 kJ/mol. These films have shown excellent antibacterial action against model bacteria E-Coli when investigated by qualitative and quantitative methods. Films exhibit great potential to be used as edible films to protect food stuff against microbial infections.     

Online Preconcentration Using Surfactant Coated Alumina Modified with 1,5-Diphenylthiocarbazone and Determination of Cadmium in Environmental Samples by Flame Atomic Absorption Spectrometry

A rapid and sensitive method for the determination of trace levels of cadmium in cigarettes, soil, and blood samples by flame atomic absorption spectrometry (FAAS) has been developed. It is based on the online sorption of Cd(II) ions on a minicolumn packed by sodium dodecyl sulfate–coated alumina modified with dithizone. The optimum experimental parameters for the adsorption and desorption of cadmium were investigated. The recovery obtained was found to be 96% with preconcentration factor of 150. The calibration curve was linear between 50–600 µg/L Cd with a detection limit of 3 µg/L, sample frequency of 30 h^?1 and reuse of column for 10 times without loss of sensitivity. The accuracy of the method was confirmed by applying the standard addition method and quantitative recoveries (95–99%) were obtained.     

Highly Selective and Sensitive Preconcentration of Mercury Ion and Determination by Cold Vapor Atomic Absorption Spectroscopy

Abstract

A simple and selective method based on a sodium dodecyl sulfate (SDS)–coated chromosorb P modified by 2‐mercaptobenzoxazole (MBO) has been developed to selectively separate and concentrate ultra trace amounts of mercury(II) ions for its highly sensitive measurement by cold vapor atomic absorption spectrometry (CVAAS).

The mercury ions were adsorbed quantitatively on SDS‐coated chromosorb due to its complexation with MBO, while the retained Hg²⁺ ions were then stripped from the column with minimal amounts of 2 M nitric acid in acetone. The eluting solution was sent to CV‐AAS for evaluating Hg²⁺ ion content and results indicate that the calibration curve was linear for Hg²⁺ ion in the range of 0.05–85.6 ng mL^?1 and 0.09–9.6 µg mL^?1 of Hg²⁺ ions. Maximum capacity of the SDS‐coated chromosorb modified with 40 mg of the ligand was found to be 498±30 µg of mercury(II), the limit of detection was 0.01 ng mL^?1, and enrichment factors were about 300, which make it suitable it for dilute solution analysis. The method was successfully applied to the determination of Hg²⁺ ion content in real samples.     

Characterization of the transition between the monohydrate and the anhydrous citric acid

The knowledge of the thermodynamic parameters related to the hydration of organic solid phases is paramount to exert a very good control over this transition during industrial production or storage. To study this phenomenon, the citric acid was chosen as a model compound. By an original combination of gravimetric and thermal analyses (dynamic vapor sorption and discontinuous isoperibolic thermal analysis, respectively) with structural determination (prototype of in situ X-ray diffractometer) the hydrate/anhydrate transition of the citric acid was thermodynamically characterized by determining: (i) the temperature associated to the peritectic transition <CA, 1H₂O> ? <CA> + H₂O_l, as well as (ii) the minimum relative humidity of hydration, and (iii) the critical relative humidity of deliquescence versus temperature. All these studies lead to the proposition of phase diagram between citric acid and water as a function of temperature and partial vapor pressure of water.     

Carbon dioxide, ethylene and water vapor sorption in poly(lactic acid)

The objective of this work is to study the gas/vapor sorption in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio using a quartz crystal microbalance (QCM). For that purpose, the sorption of carbon dioxide, ethylene and water vapor in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio, in temperature range from 283 to 313 K and up to atmospheric pressure was measured. The measured isotherms indicate that the sorption mechanism is sorbate dependent, since carbon dioxide and ethylene seem to have predominantly a Langmuir type of mechanism while water is predominantly Henry controlled. Two temperature protocols were used and only ethylene sorption is affected by them. Comparisons with previously measured gas sorption data in PLA 80:20 using the same temperature protocol indicate that the l:d ratio plays a dominant role in gas/vapor sorption in PLA.     

Moisture sorption isotherms of whole and fractionated date-pits: Measurement and theoretical modelling

Moisture sorption properties of whole date-pits (WDP) and three fractionated date-pits; defatted date-pits (DDP), residue (REP) and supernatant (SUP) fractions were studied. Sorption isotherms were measured using Differential Thermal and Humidity chamber at different temperatures (10, 30, 50, 70 and 90 °C) and relative humidity ranged from 0.05 to 0.9. Crossovers of isotherm curves were observed for all fractions between different temperatures. At 30 °C, BET-monolayers of WDP, DDP, REP and SUP were 4.9, 4.2, 3.8 and 3.2 g/100 g ds, respectively. The complete isotherms (i.e. 0.05–0.90 water activity) were modelled by GAB with high coefficient of determination (i.e. 0.944 to 0.999). In the cases of WDP and DDP, the isosteric heat plots showed increasing trends with the decreased moisture and peaks at moisture 0.025 and 0.040 g/100 g ds. Unlike all fractions, DDP isokinetic temperatures T_is (i.e. 97.4 °C) was lower than isobound temperatures T_ib (i.e. 145.0 °C) indicating complete removal of bound water occurred at higher temperature as compared to the temperature when all reactions reached at the same. The moisture sorption isotherm characteristics could be used in determining the end point of drying and storage stability as well as packaging design of the date-pits and their fractions.     

Thermodynamic analysis of sorption isotherms of bentonite

Sorption isotherms of water vapour on commercial bentonite clay are determined at T = (303, 323, and 343) K. The sorption isotherms have a sigmoid shape (Type II). At a given water activity, moisture content decreases with increasing temperature. Hysteresis between adsorption and desorption isotherms is shown over most the range of water activity varying from 0.1 to 0.9. The fitting of the experimental data by using two theoretical models (Guggenheim–Anderson–DeBoer (GAB) and Henderson) shows that the two models reproduce experimental data with acceptable accuracy. The GAB model, however, is largely superior. The isosteric sorption enthalpy is determined and its dependency on the amount of water retention is investigated. It is found that the enthalpy reaches a maximum value when a monolayer of water covers the adsorbant surface. The enthalpy decreases asymptotically to a finite value when the amount of adsorbed water increases.     

Ascorbic acid biosensor based on laccase immobilized on an electrode modified with a self-assembled monolayer and coated with functionalized quantum dots

Laccase was immobilized on an electrode modified with a cysteine self-assembled monolayer and coated with functionalized quantum dots. The immobilized laccase is capable of directly transferring an electron. Immobilized laccase retained its activity to oxidize ascorbic acid (AA), and the apparent Michaelis–Menten constant was found to be 0.47 mM. The modified electrode was used to determine AA in the 10 to 140 μM concentration range, with linear response curve and a detection limit of 1.4 μM (s/n?=?3).     

Thermal crystallization kinetic and electrical properties of partly crystallized amorphous indium oxide thin films sputtering deposited in the presence or the absence of water vapor

Partly crystallized amorphous indium oxide thin films were deposited under water vapor atmosphere by magnetron sputtering. XRD analysis revealed that appropriate water vapor could suppress the film’s crystallinity. In situ thermal crystallization process was monitored by high-temperature XRD. The crystallization data were analyzed using the Kolmogorov–Johnson–Mehl–Avrami equation. The kinetic exponent n is determined to be approx. 1/2 and 3/2 for film deposited in the absence and the presence of water vapor, respectively. The activation energy of crystallization for film deposited under 1 × 10^?5 Torr water vapor pressure was determined to be 30.7 kJ mol^?1, which is higher than 18.9 kJ mol^?1 for film deposited in the absence of water vapor. The increased activation energy caused by the chemically bonded hydrogen and embedded O–H bonds from the water vapor resulted in the suppression of crystallization. Introduction of appropriate water vapor during the deposition decreased the resistivity because of the increase of Hall mobility. The resistivity of the films after annealing increased due to the evaporation of water vapor resulted in crystal defects.     

Impacts of delignification and hot water pretreatment on the water induced cell wall swelling behavior of grasses and its relation to cellulolytic enzyme hydrolysis and binding

The relationships between biomass composition, water retention value (WRV), settling volume and enzymatic glucose yield and enzyme binding is investigated in this work by employing grasses pretreated with combinations of alkaline hydrogen peroxide (AHP) delignification and liquid hot water pretreatment that result in significant alterations of cell wall properties and subsequent enzymatic hydrolysis yields. Specifically, these cell wall treatments are performed on corn stover and switchgrass to generate material with a range of lignin (6–35 %) and xylan (2–28 %) contents as well as a range of other properties such as carboxylic acid content, water binding affinity and swellability. It was determined that WRV and settling volume are predictors of glucose yield (R² = 0.900 and 0.895 respectively) over the range of materials and treatment conditions used. It was also observed that mild AHP delignification can result in threefold increases in the WRV. Dynamic vapor sorption isotherms demonstrated that AHP-delignified corn stover exhibited an increased affinity for water sorption from the vapor phase relative to untreated corn stover. These results indicate that these water properties may be useful proxies for biomass susceptibility to enzymatic deconstruction.     

Fourier transform infrared study on the sorption of water to various kinds of polymer thin films

The state of sorbed water and the sorbing processes of water to various polymer thin films were studied with Fourier transform infrared (FTIR) spectroscopy. To prepare the polymer films, we used poly(ethylene glycol)s of different molecular weights and various kinds of vinyl polymers, such as poly(2‐methoxyethyl acrylate). The O? H stretching band of water sorbed in the films increased gradually on contact with water vapor at 50% relative humidity and leveled off. When O? H stretching bands of water sorbed to polymer films were compared, the peak positions and profiles of water sorbed to the polymeric materials with the same hydrogen‐bonding site were similar. A hybrid density‐functional method supported the assignment of the peaks. Furthermore, the diffusion coefficient (D) of water vapor in the polymer films was estimated by time‐resolved measurements of the sorbed water at the very initial stage (0–830 s). It was clearly shown that the D values of water vapor in the polymer materials with a strong hydrogen‐bonding site were smaller than those in hydrophobic polymers. The usefulness of the FTIR technique to investigate water sorption to polymer materials was definitely demonstrated. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2175–2182, 2001     

Microfibrillated cellulose (MFC): pullulan bionanocomposite films

The aim of this work was to develop and characterize microfibrillated cellulose (MFC)/pullulan bionanocomposites. Fourier transform infrared spectroscopy suggested that the affinity between the two polymers resulted in new hydrogen bonding of the nanocomposite materials compared to pristine pullulan. At the same time, an increase in crystallinity was observed proportional to the amount of MFC used, as shown by the X-ray analyses. Accordingly, final films showed improved mechanical properties proportionally to the filler loading, with impressive elastic modulus and tensile strength of ~4.50 GPa and ~60 MPa, respectively, for the sample containing 10 % MFC. However, as demonstrated by the moisture sorption isotherms, the addition of MFC did not help reduce the amount of water adsorbed by the samples. In addition, the oxygen and water vapor permeability data clearly showed that final films still suffered high relative humidity values, whereas their barrier performance toward oxygen was excellent under dry conditions, with O₂ permeability coefficients (P′O ₂) comparable with those of common high barrier films/coatings. Finally, while the nanocomposites in the form of films had high haze values (from 23 to 40 %), the same nanocomposites in the form of coatings were decidedly more transparent, which suggests that their use as thin layers could be more suitable when the “see-through” capability must be preserved, for example in food packaging applications.