Water vapor sorption kinetics of wood modified with glutaraldehyde

The modifying effects of Scots pine (Pinus sylvestris L.) wood with the crosslinking agent glutaraldehyde (GA) on the water vapor sorption kinetics were studied by curve fitting the experimental isotherm sorption data obtained using a Dynamic Vapor Sorption apparatus using the parallel exponential kinetics model (PEK model) and the Hailwood–Horrobin model (H–H model) for the isotherm. Both the H–H model and the PEK model provided good fits to the experimental data. Modification of wood with GA reduced both the time to equilibrium and the equilibrium moisture content (EMC). According to the PEK and H–H models, the reduction in EMC was mainly due to the decrease of moisture content (MC) associated with the slow sorption processes and polylayer water. The fast sorption processes and monolayer water were little affected by GA modification. Compared to the untreated control, the estimated total water absorbed by wood treated to a WPG of 20.9% at 100% RH decreased by 52.2%, by extrapolating the fitted curves derived from the H–H model. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modeling of moisture sorption isotherms of poly(vinyl alcohol)/starch films

Studies on the moisture sorption characteristics of poly(vinyl alcohol)/starch blends for water activity (a_w) values of 0.1–0.9 were performed at 27°C. The equilibrium moisture content at different a_w values was used to fit different sorption isotherm models proposed in the literature. The ranges of a_w applicable for the different sorption isotherms were reported. The model constants of the sorption equations were determined by linear fitting. The value of the coefficient of determination (0.98 ± 0.01) confirmed the goodness of fit of the equations studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3874–3881, 2003     

Moisture-sorption properties and studies on the dilute solution behavior of epoxidized natural rubber ENR 50

Studies of the dilute solution capillary viscosity and moisture sorption of commercial samples of epoxidized natural rubber (ENR 50) were carried out. Dilute solution viscometry of ENR 50 solutions was conducted in xylene, tetrahydrofuran, and methyl ethyl ketone solvents and the degradation due to shearing and oxidation for this rubber was followed. At average elevated temperatures and high relative humidities, epoxidized natural rubber ENR 50 shows high moisture sorption. Moisture sorption measurements at 100% RH and 34°C followed by desorption show near equilibrium moisture intake of 3.402–3.661 g H₂O/100 g rubber, which agrees reasonably well with the estimated value of 4.108 g H₂O/100 g ENR 50. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1633–1644, 1999     

The water vapor sorption behavior of flax fibers—Analysis using the parallel exponential kinetics model and determination of the activation energies of sorption

Sorption kinetic data for the interaction of water vapor with flax (Linum usitatissimum L.) were analyzed used the parallel exponential kinetics (PEK) model, with excellent fits to the data being obtained. The PEK model is the sum of two exponential kinetics processes (fast and slow), which have characteristic times and moisture contents associated with them. The slow adsorption and desorption processes exhibited important differences in their characteristic times, although hysteresis in the moisture contents was found to be predominantly associated with the fast process. The kinetics was examined over a range of relative humidity (RH) values and at different temperatures, enabling the determination of activation energies for the adsorption and desorption kinetic processes throughout the hygroscopic range (from 5–95% RH). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological characterization of cellulose solutions in N‐methyl morpholine N‐oxide monohydrate

Three different modes of rheological properties were measured on 11 and 13 wt % solutions of cellulose in N‐methyl morpholine N‐oxide (NMMO) monohydrate, in which concentration range lyocell fibers of much reduced fibrillation are preferably produced. The dynamic rheological responses revealed that the Cox–Merz rule did not hold for these cellulose solutions. Both cellulose solutions showed a shear thinning behavior over the shear rate measured at 85, 95, 105, and 115°C. However, 13 wt % solution gave rise to yield behavior at 85ºC. The power law index ranged from 0.36 to 0.58. First normal stress difference (N₁) was increased with lowering temperature and with increasing concentration as expected. Plotting N₁ vs shear stress (τ_ω) gave almost a master curve independent of temperature and concentration, whose slope was about 0.93 for both cellulose solutions over the shear rate range observed (τ_ω > 500 Pa). In addition, the cellulose solutions gave high values of recoverable shear strain (S_R), ranging from 60 to 100. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 216–222, 2002     

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture‐sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water‐vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (T_g's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the T_g of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen‐bond strength of the N H groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999     

Structure,Infrared Reflectivity and Microwave Dielectric Properties of (Na0.5La0.5)MoO4–(Na0.5Bi0.5)MoO4 Ceramics

A series of temperature‐stable microwave dielectric ceramics, (1?x)(Na_0.5La_0.5)MoO₄–x(Na_0.5Bi_0.5)MoO₄ (0.0 ≤ x ≤ 1.0) were prepared by using solid‐state reaction. All specimens can be well sintered at temperature of 580°C–680°C. Sintering behavior, phase composition, microstructures, and microwave dielectric properties of the ceramics were investigated. X‐ray diffraction results indicated that tetragonal scheelite solid solution was formed. Microwave dielectric properties showed that permittivity (ε_r) and temperature coefficient of resonant frequency (τ_f) were increased gradually, while quality factor (Q × f) values were decreased, at the x value was increased. The 0.45(Na_0.5La_0.5)MoO₄–0.55(Na_0.5Bi_0.5)MoO₄ ceramic sintered at 640°C with a relative permittivity of 23.1, a Q × f values of 17 500 GHz (at 9 GHz) and a near zero τ_f value of 0.28 ppm/°C. Far‐infrared spectra (50–1000 cm^?1) study showed that complex dielectric spectra were in good agreement with the measured microwave permittivity and dielectric losses.     

WATER SORPTION ISOTHERMS AND GLASS TRANSITION PROPERTIES OF GELATIN

ABSTRACT

The water sorption isotherms of gelatin of different molecular weights (317,700, 228,900, and 197,400) were determined at 50°C using an isopiestic method. The sorption isotherms were modeled using the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–deBoer (GAB) equations. The BET and GAB equations were able to predict the equilibrium moisture content (EMC) with a mean relative error of 5.2 and 5.0%, respectively. The BET monolayer moisture content varied from 4.81 to 5.70% (d.b.) while modeling with the GAB equation predicted monolayer moisture content of 6.14–7.58% (d.b.) depending upon molecular weight. The monolayer moisture content increased with increasing molecular weight. Studies on the effect of moisture content on the “rheological glass transition temperature” (T _g ) showed a smooth increase in the value of T _g as a function of increasing concentration of gelatin solids. This varied from 7 to 35°C at 75% and 97% solids, respectively for the protein sample with MW = 317,700. Pinpointing of the T _g was implemented with the technique of small deformation dynamic oscillation. It was proposed that the “rheological” T _g is the point between the glass transition region and the glassy state. It acquires physical significance by identifying the transition from free volume phenomena of the polymeric backbone in the glass transition region to an energetic barrier to motions in the glassy state involving stretching and bending of chemical bonds.     

Relationship between structure and properties of modified potato starch biodegradable films

Potato starch was gelatinized in the presence of water and varying amounts of glycerol at 90°C. Starch/glycerol films were prepared by casting with water. The addition of glycerol produces a decrease in the crystallinity of the starch in the films. Starch was acetylated (with acetic acid and anhydride) and maleated (with maleic anhydride). Differential scanning calorimetric analysis revealed decrease in the glass transition temperature (T_g) with the chemical modification. The starch modification on the equilibrium moisture content was determined at 25°C. The esterifications produce a decrease in the maximum moisture sorption. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4313–4319, 2006     

Effect of high-pressure processing on moisture sorption properties of brown rice

The effect of high-pressure treatment (0.1 to 500 MPa for 10 min) on the moisture sorption properties of brown rice (Feng Liang You Xiang No. 1) was investigated. Air was maintained at selected conditions (temperature between 20°C and 40°C, equilibrium relative humidity between 11% and 75%) and equilibrium moisture content was measured. The control attained a higher equilibrium moisture content than treated samples, while the 300 MPa treated sample had the lowest. The area of hysteresis of the 300 MPa test sample was the largest and the BET model was applied to determine the monolayer moisture content.     

Temperature-Stable and Low-Loss Dielectrics in the Ca(B'1/2Ta1/2)O3 [B'=Lanthanides, Y, and In] System

The Ca(B′_1/2Ta_1/2)O₃ [B′=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, and In] double perovskite-type ceramics have been prepared by the conventional solid-state ceramic route. The phase purity and surface morphology of the sintered ceramics have been studied by X-ray diffraction (XRD) and scanning electron microscopy methods. XRD study revealed intersubstitution between Ca and B′ ions. Ca(B′_1/2Ta_1/2)O₃ ceramics have relative permittivity (ɛ_r) in the range 23–30, normalized quality factor (Q_u×f) 20 600–59 200 GHz, and temperature coefficient of resonant frequency (τ_f) −6 to −35 ppm/°C. The dielectric properties of Ca(B′_1/2Ta_1/2)O₃ ceramics have been tailored by the addition of positive τ_f materials such as CaTiO₃, TiO₂, Ba(Y_1/2Ta_1/2)O₃, and Ba(Yb_1/2Ta_1/2)O₃, which form a solid solution or a mixture phase with the parent compound. The 0.7Ca(Y_1/2Ta_1/2)O₃–0.3Ba(Y_1/2Ta_1/2)O₃ ceramic has ɛ_r=27.5, Q_u×f=41 900 GHz, and τ_f=−1.2 ppm/°C, and the 0.6Ca(Yb_1/2Ta_1/2)O₃–0.4Ba(Yb_1/2Ta_1/2)O₃ ceramic has ɛ_r=27.7, Q_u×f=48 000 GHz, and τ_f=1.8 ppm/°C.     

Effects of superheated steam treatment on moisture adsorption and mechanical properties of pre-dried rubberwood

Abstract

Rubberwood (Hevea brasiliensis) was treated with superheated steam (140–160?°C) for 1–3?h and then its adsorption ability, mechanical properties, and color changes were investigated. The results of adsorption show decreased equilibrium moisture content (EMC) for all heat-treated cases throughout the hygroscopic range. The Hailwood–Horrobin model was used to analyze the sorption isotherms and determine the monolayer and polylayer moisture contents for untreated and heat-treated rubberwood. The monolayer moisture content clearly decreased with treatment temperature and duration, whereas the reduction in polylayer moisture was relatively smaller. Moreover, the least density of water adsorption sites was found in wood after treatment at 160?°C for 3?h, indicating this as the cause for reduced equilibrium adsorption. All treatment conditions had improved mechanical properties, including compression parallel-to-grain, hardness, and tensile strength. The total color difference of the wood surface increased with increasing temperature and treatment duration.     

Microstructural and Microwave Dielectric Properties of Bi12GeO20 and Bi2O3‐Deficient Bi12GeO20 Ceramics

Bi₁₂GeO₂₀ ceramics sintered at 800°C had dense microstructures, with an average grain size of 1.5 μm, a relative permittivity (ε_r) of 36.97, temperature coefficient of resonance frequency (τ_f) of ?32.803 ppm/°C, and quality factor (Q × f) of 3137 GHz. The Bi_12‐xGeO_20‐1.5x ceramics were well sintered at both 800°C and 825°C, with average grain sizes exceeding 100 μm for x ≤ 1.0. However, the grain size decreased for x > 1.0 because of the Bi₄Ge₃O₁₂ secondary phase that formed at the grain boundaries. Bi_12‐xGeO_20‐1.5x (x ≤ 1.0) ceramics showed increased Q × f values of >10 000 GHz, although the ε_r and τ_f values were similar to those of Bi₁₂GeO₂₀ ceramics. The increased Q × f value resulted from the increased grain size. In particular, the Bi_11.6GeO_19.4 ceramic sintered at 825°C for 3 h showed good microwave dielectric properties of ε_r = 37.81, τ_f = ?33.839 ppm/°C, and Q × f = 14 455 GHz.     

Effects of alkaline conditioning and temperature on the properties of glass fiber polymer composite rebar

This article investigated long term alkaline conditioning and temperature on the physical and mechanical properties of glass fiber‐reinforced polymer (GFRP) composite rebar for structural applications. The GFRP rebar was immersed in alkaline solution (pH ≈ 13) for 23 months at 23°C, and for 24 months at 60°C. The moisture absorption was found to be 0.34% at 23°C after 23 months, and 0.76% at 60°C after 24 months. At both temperatures, moisture absorption did not reach equilibrium which was attributed to two stages non‐Fickian behavior. Glass transition temperature (T_g) of the polymer matrix of rebar that conditioned at 23°C was found to be decreased because of plasticization, whereas T_g of the rebar that conditioned at 60°C was remained greater than the T_g of control rebar due to nonplasticization effect. Shear strength was retained by 83.5% at 23°C and 80.5% at 60°C, flexural strength was retained by 81% at 23°C and 69% at 60°C, and tensile strength was retained by 91.2% at 23°C and 74.3% at 60°C. It was revealed that durability of GFRP rebar in alkaline environment was controlled by the absorbed moisture; this was because the load transfer efficiency of fiber/matrix interface is vulnerable to moisture. POLYM. COMPOS., 37:3181–3190, 2016. © 2015 Society of Plastics Engineers     

Temperature Compensating Microwave Dielectric Based on the (Mg0.95Ni0.05)TiO3–(La0.5Na0.5)TiO3 Ceramic System

The microstructures and microwave dielectric properties of the novel temperature-compensated composite ceramic (1−x)(Mg_0.95Ni_0.05)TiO₃–x(La_0.5Na_0.5)TiO₃ were investigated. Dense and mixed phase samples were produced in the range of 0.05≤x≤0.9. When the x value increased, the quality factor (Q×f) decreased nonlinearly while the dielectric constant (ɛ_r) steadily increased almost linearly due to the compensation effect. The temperature coefficient of resonant frequency (τ_f) was remarkably improved with an increase of (La_0.5Na_0.5)TiO₃ content. With x=0.13, a dielectric constant (ɛ_r) of 23.22, a Q×f value of 86,500 GHz, and a τ_f value of 2.8 ppm/°C was obtained for 0.87(Mg_0.95Ni_0.05)TiO₃–0.13(La_0.5Na_0.5)TiO₃ ceramics sintered at 1275°C for 4 h. Moreover, a band-pass filter with traditional hairpin resonators with a center frequency of 2.4 GHz was designed and fabricated using the proposed dielectric ceramic to study its performance.     

A comparative quality study and energy saving on intermittent heat pump drying of Malaysian edible bird’s nest

This paper aims to study the influence of temperature and relative humidity (RH) during intermittent heat pump drying at 28.6–40.6°C, 16.2–26.7% RH, α?=?0.2–1.0, and the comparison was made against fan drying (27°C, 39.7% RH, α?=?1.00). It was observed that the effects of temperature and RH on drying rate were significant when moisture content was high. Experimental results showed that intermittent heat pump drying at 28.6°C, 26.7% RH, α?=?0.2 of edible bird’s nest greatly reduced effective drying time by 84.2% and color change compared to fan drying, and retained the good energy efficiency.     

Dielectric relaxation spectra of chemically treated woods

The changes in the dielectric properties of absolutely dried Sitka spruce (Picea sitchensis Carr.) wood caused by chemical treatments were investigated. Eight kinds of chemical treatments with various levels of weight percentage gain (WPG) were performed. Through the application of the Cole–Cole circular arc law to the results of the dielectric measurements in the frequency range of 1 kHz to 1 MHz at ?60°C, the relaxation spectrum was calculated. The relaxation magnitude (ε₀ ? ε_∞) was reduced by formalization, acetylation, propylene oxide, and phenol–formaldehyde resin treatments, in which chemical reactions occurred between the OH groups in the cell wall and the added reagents. On the other hand, the generalized relaxation time (τ_m) decreased with increasing WPG, except for acetylation, for which τ_m decreased up to a WPG level of 20% and then increased. In poly(ethylene glycol) impregnation, (ε₀ ? ε_∞) decreased with increasing WPG up to about 50% and then increased, whereas τ_m linearly decreased with increasing WPG. No significant changes in these parameters were recognized for the wood methyl methacrylate composite and heat treatment. With the steam treatment, τ_m increased. The distribution of the relaxation times was broad in acetylation and narrow in propylene oxide treatment and poly(ethylene glycol) impregnation. However, it remained almost unchanged in the other treatments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 37–43, 2005     

Determination of glass transition temperature from dielectric analysis for a series of epoxide oligomers

Dielectric properties have been investigated for a bisphenol-A type epoxide oligomer, whose weight average molecular weight (M?_w) was 9454. The dielectric α-relaxation of the oligomer was found to be governed by the Havriliak–Negami equation as well as the same series of oligomers with smaller M?_ws (388≦M?_w ≦ 3903). The dielectric relaxation times (τ)s for the oligomers with different M?_ws (1396 ≦ M?_w ≦ 9454) can be expressed by the Williams–Landel–Ferry (WLF) equation as a function of the glass transition temperature (T_g) at fixed temperatures from 70 to 100°C. The finding indicates that the T_g of the epoxide oligomer is calculated from the τ through the WLF equation, providing the relation between T_g and τ. The same type of WLF equation was also successfully applied to describe the T_g, dependence of the practical dielectric relaxation time (τ_p), which was obtained from the peak of the dielectric loss vs. frequency curve. The τ_p can be calculated more easily than the τ, based on the Havriliak–Negami equation, not only in the measurement of epoxide oligomer, but also in that of the reactive epoxy resin systems during curing. The T_g of an epoxy–aromatic amine system, which was determined from the τ_p nondestructively detected in the dielectric cure monitoring, was consistent with the T_g experimentally measured by differential scanning calorimetry (DSC).     

Sorption of organic liquids and vapors by rigid PVC

The effects of activity and solvent strength of a number of organic penetrants upon their sorption kinetics and equilibria in poly(vinyl chloride) have been studied by gravimetric vapor and liquid sorption experiments at 30°C. For each solvent, the relation of equilibrium sorption to activity is well approximated by the Flory–Huggins equation with a characteristic value of the interaction parameter χ. The glass transition temperature T_g is depressed in direct proportion to the volume fraction of solvent absorbed; the composition corresponding to a T_g of 30°C, C_g (30°C), is in the range of 0.22–0.30 volume fraction for several common solvents. The form of the sorption kinetics varies with the ratio of the equilibrium sorption to C_g, and thus depends on the combined effects of χ, solvent activity, and plasticizing action. When the equilibrium sorption is less than about C_g/2, kinetics are Fickian, with the very low diffusivities typical of the glassy state; for sorption values between C_g/2 and C_g, anomalous kinetics are observed; and when the sorption is greater than C_g, transport in thin PVC films follows Case II kinetics. At high sorption levels, increasing film thickness produces a shift of the kinetics toward Fickian form with apparent diffusivity values typical of rubbery polymers.     

Letter to the Editor

Abstract

The water sorption isotherms of the Erythrina fusca Lour bark at 30 and 40°C were determined over relative humidity ranging from 55 to 85%. The equilibrium moisture content was determined gravimetrically. The moisture sorption isotherms showed that the equilibrium moisture decreases with increase of temperature. Six models were used for to fit the experimental curves of equilibrium humidity. Parameters of each equation were determined by nonlinear regression analysis. The isosteric heat of moisture sorption was calculated using the Claussius-Clapeyron equation.