Near infrared (NIR) spectroscopy compared with thermogravimetric analysis as a tool for on‐line prediction of water diffusion in polyamide 6,6

NIR spectroscopy in the transmission mode and thermogravimetric analysis were used to predict diffusion of water into polyamide 6,6 samples immersed in water at 40, 60, 75 and 90 °C for different periods of time. The sorption curves between 40 and 75 were sigmoidal indicating that the surface concentration was time dependent. The sorption curves were readily fitted by the use of a time‐dependent surface concentration and a water‐concentration‐dependent diffusivity. The zero‐concentration water diffusivity decreased non‐linearly and the activation energy of diffusion increased from 24 to 58 kJ mol^?1, with decreasing temperature. The surface concentration relaxation time decreased rapidly. The sorption of water in thick polyamide samples was readily characterized by FT‐NIR spectroscopy. The accuracy and feasibility of this method was similar to conventional thermogravimetric methods. The greatest advantage of FT‐NIR, however, is the possibility of detecting and monitoring the moisture concentration on‐line and in a non‐destructive way. © 2002 Society of Chemical Industry     

Moisture diffusion properties of HFPE‐II‐52 polyimide

Moisture diffusion properties of the polyimide HFPE‐II‐52 were determined using weight gain, weight loss, and swelling experiments over a temperature range of 25–200°C. Below 100°C, diffusivity was measured using standard weight loss and weight gain methods. Above 100°C, diffusivity is found by weight loss experiments performed by placing moisture saturated samples in an oven and recording weight loss dynamically. The diffusivity of the polyimide was found to obey the Arrhenius relation over the entire range of temperature. Weight gain experiments were performed to determine the equilibrium level of moisture absorbed by the polyimide as a function of relative humidity. Swelling experiments were performed to measure swelling strain as a function of moisture absorption. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3471‐3479, 2006     

Experimental determination of concentration‐dependent carbon dioxide diffusivity in LDPE

In this work, we experimentally determine the concentration‐dependent diffusivity of carbon dioxide in low‐density poly(ethylene) (LDPE). For this purpose, experiments are carried out to obtain pressure‐decay data for isothermal diffusion of the gas in the polymer. Based on a detailed mass transfer model, variational calculus is used to establish the conditions necessary to yield the concentration‐dependent diffusivity that enables the model‐predicted mass of absorbed gas in polymer to match with the experimental counterpart. A computational algorithm is implemented to solve the model and the conditions and obtain the diffusivities. Determined at 120 and 130°C for four different pressures in the range 0.352 to 1.232 MPa, the diffusivities are strong unimodal functions of gas concentration in polymer and of the order 10^?9 m² s^?1. Mathematical correlations are developed to calculate the diffusivity at a given temperature, pressure, and gas concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of hygrothermal aging on dimensional stability of thin injection‐molded short glass fiber reinforced PA6 materials

The hygrothermal aging of short glass fiber reinforced polyamide 6 materials (PA6/GF) is a major problem for thin‐walled components used in the automotive sector. In this work, the thickness and glass fiber content of PA6/GF materials were varied and exposed to hygrothermal aging. The temperature and relative humidity were chosen to range from ?40 to 85°C and 10% RH to 85% RH respectively, according to automotive requirements for components in the passenger compartment. For the absorption of moisture, the diffusion behavior could not be generally described by Fick's law. However, the results indicate that the diffusion behavior is dependent on the relative humidity and thickness of the PA6/GF material. The morphology of the test specimen, which is influenced by injection molding, was also found to affect the diffusion behavior. The states of equilibrium for moisture absorption are strongly dependent on the relative humidity during hygrothermal aging and less dependent on the temperature. The maximum absorbed humidity was found at a temperature of 65°C and 85% RH, which was higher than at 85°C and 85% RH because of reduced contrary aging processes, such as postcrystallization. In certain climatic conditions and test specimen thicknesses, there was a characteristic overshoot in the mass change. This behavior could be attributed to a different degree of crystallization and lower glass fiber content. Both moisture absorption and an overshoot of the mass affected the dimensional stability of the test specimens. This effect on dimensional stability could be correlated with the glass fiber orientation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42245.     

Effects of prior aging at 288°C in argon environment on time‐dependent deformation behavior of a thermoset polymer at elevated temperature,Part 2: Modeling with viscoplasticity theory based on overstress

The viscoplasticity based on overstress (VBO) is augmented to model the effects of prior isothermal aging in an argon environment on the inelastic deformation behavior of PMR‐15 neat resin, a high‐temperature thermoset polymer. VBO is a unified state variable theory with growth laws for three state variables: the equilibrium stress, the kinematic stress and the isotropic stress. A systematic model characterization procedure based on a limited number of well defined experiments is employed to determine the VBO parameters. Experimental findings presented in Part I reveal the equilibrium stress and the kinematic stress to be affected by prior aging. Based on the experimental results, the isotropic stress is developed as a function of prior aging time. In addition, several VBO model parameters are made dependent on prior aging time. Comparison with experimental data demonstrates that the modified VBO successfully predicts the inelastic deformation behavior of the PMR‐15 polymer subjected to prior isothermal aging for up to 2000 h. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hygrothermal aging and tensile behavior of injection‐molded rice husk‐filled polypropylene composites

The effect of the filler volume fraction on the tensile behavior of injection‐molded rice husk‐filled polypropylene (RH–PP) composites was studied. Hygrothermal aging behavior was also investigated by immersing the specimens in distilled water at 30 and 90°C. The kinetics of moisture absorption was studied from the amount of water uptake by specimens at regular interval times. It was found that the diffusion coefficient and the maximum moisture content are dependent on the filler volume fraction and the immersion temperatures. Incorporation of RH into the PP matrix has led to a significant improvement in the tensile modulus and a moderate improvement in the tensile strength. Elongation at break and energy at break, on the other hand, decreased drastically with the incorporation of the RH filler. The extent of deterioration incurred by hygrothermal aging was dependent on the immersion temperature. Both the tensile strength and tensile modulus deteriorated as a result of the combined effect of thermal aging and moisture attack. Furthermore, the tensile properties were not recovered upon redrying of the specimens. Scanning electron microscopy was used to investigate the mode of failure of the RH–PP composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 742–753, 2001     

Adsorption of butanol from aqueous solution onto a new type of macroporous adsorption resin: Studies of adsorption isotherms and kinetics simulation

BACKGROUND: Owing to the rapid depletion of petroleum fuel, the production of bio‐butanol has attracted much attention. However, low butanol productivity severely limits its potential industrial application. It is important to establish an approach for recovering low‐concentration butanol from fermentation broth. Experiments were conducted using batch adsorption mode under different conditions of initial butanol concentration and temperature. Batch adsorption data were fitted to Langmuir and Freundlich isotherms and the macropore diffusion, pseudo‐first‐ and second‐order models for kinetic study. RESULTS: The maximum adsorption capacity of butanol onto KA‐I resin increase with increasing temperature, ranged from 139.836 to 304.397 mg g^?1. The equilibrium adsorption data were well fitted by the Langmuir isotherm. The adsorption kinetics was more accurately represented by the macropore diffusion model, which also clearly predicted the intraparticle distribution of the concentration. The effective pore diffusivity (D_p) was dependent upon temperature, but independent of initial butanol concentration, and was 0.251 × 10^?10, 0.73 × 10^?10, 1.32 × 10^?10 and 4.31 × 10^?10 m² s^?1 at 283.13, 293.13, 303.13 and 310.13 K, respectively. CONCLUSION: This work demonstrates that KA‐I resin is an efficient adsorbent for the removal of butanol from aqueous solutions and available for practical applications for future in situ product recovery of butanol from ABE fermentation broth. Copyright © 2012 Society of Chemical Industry     

Impression creep of PMR‐15 resin at elevated temperatures

The polyimides formed from the polymerization of monomeric‐reactants (PMR) approach have been increasingly used as matrix materials in fiber‐reinforced composites on aerospace and space structures for high temperature applications. The performance of PMR‐based structures depends on the mechanical durability of PMR resins at elevated temperatures, including creep and stress relaxation. In this work, the creep behavior of PMR‐15 resin was studied using the impression technique in the temperature range of 563–613 K and the punching stress range of 76–381 MPa. It was found that there existed a steady state creep for the creep tests performed at temperatures of 563 K and higher, from which a constant impression velocity was calculated. The steady state impression velocity increased with temperature and punching stress with the stress exponent in the range of 1.5–2.2. The average of the apparent activation energy of the PMR‐15 was calculated as 122.7 ± 6.1 kJ/mol. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Moisture diffusion through vinyl ester nanocomposites made with montmorillonite clay

Moisture diffusion was studied through vinyl ester samples containing up to 5 wt% of organically treated montmorillonite. Two different kinds of clay surface treatment were employed to make the clay compatible with Derakane^TM 411‐350 vinyl ester resin. The nanocomposites were characterized using differential scanning calorimetry (DSC), mechanical property measurements, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). TEM pictures showed that the clay platelets were either exfoliated or intercalated, and the two different surface treatments resulted in different dispersion characteristics. All the samples were post cured, and the diffusivity of moisture was measured by soaking the samples in 25°C water and noting the increase in weight with increasing time of immersion. It was found that water diffusivity decreased with increasing clay content, and it was reduced to half its value in the neat resin when the clay content was only 1 wt% regardless of the nature of clay surface treatment. However, the equilibrium moisture content, the glass transition temperature, and the elastic modulus all increased with increasing amounts of clay.     

Theoretical analysis and experimental study on SO2 adsorption onto pistachio‐nut‐shell activated carbon

The adsorption study of SO₂ onto the activated carbon prepared from pistachio‐nut shell was studied theoretically and experimentally. A single‐particle sorption model known as concentration‐dependent surface diffusivity micropore, surface and macropore diffusion control model incorporating micropore, macropore and surface diffusions, together with a nonlinear isotherm at the micropore mouth, has been derived and solved by a finite difference method. The effects of different types of nonlinear isotherms and concentration dependent surface diffusivities have been thoroughly studied. The effects of adsorbate concentration and temperature on adsorption were studied experimentally. Good agreement was found between the model predictions and the experimental results. The value of the tortuosity factor and the extracted diffusion coefficients obtained are consistent with their corresponding values reported. © 2008 American Institute of Chemical Engineers AIChE J 2009     

Water absorption and hygrothermal aging study on organomontmorillonite reinforced polyamide 6/polypropylene nanocomposites

The water absorption and hygrothermal aging behavior of organomontmorillonite (OMMT) reinforced polyamide 6/polypropylene (PA6/PP ratio = 70/30), with and without maleated PP (MAH‐g‐PP), was studied at three different temperatures (30, 60, and 90°C). The water absorption and hygrothermal aging response of the composites was studied and analyzed by tensile tests and morphology assessment (scanning electron microscopy and transmission electron microscopy), indicating the effect of the immersion temperature, OMMT, and MAH‐g‐PP compatibilizer. The mathematical treatment used in analyzing the data was the single free phase model of diffusion, which assumed Fickian diffusion and utilized Fick's second law of diffusion. The kinetics of water absorption of the PA6/PP nanocomposites conformed to Fickian law behavior, whereby the initial moisture absorption follows a linear relationship between the percentage gain at any time t and t^1/2 (the square root of time), followed by saturation. It was found that the equilibrium moisture content and the diffusion coefficient are dependent on the OMMT loading, MAH‐g‐PP concentration, and immersion temperatures. Both the tensile modulus and strength of the PA6/PP nanocomposites deteriorated after being exposed to hygrothermal aging. MAH‐g‐PP acted as a good compatibilizer for PA6/PP/OMMT nanocomposites, which was attributed to its higher retention ability in modulus and strength (in the wet and redried states), lower equilibrium moisture content, and reduced water diffusivity of the nanocomposites. Morphological sketches for both uncompatibilized and MAH‐g‐PP compatibilized PA6/PP/OMMT nanocomposites, toward water uptake are proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 780–790, 2005     

Modeling changes in the modulus of poly(ε‐caprolactone) due to hydrolysis and plasticization

The evolution of the flexural modulus of poly(ε‐caprolactone), prepared with a tin(II) 2‐ethylhexanoate catalyst, was measured in terms of the polymer molecular weight and moisture content. Changes in the polymer molecular weight were observed, but these did not result in a loss of modulus. Fickian diffusion was used to characterize the absorption of moisture into the polymer. The maximum moisture content and moisture diffusivity constant of the polymer were determined to be 0.62% and 2.039 × 10^?5 mm²/s, respectively. Reductions in the polymer modulus from 0.5 to 0.4 GPa were attributed to water plasticization. An empirical expression for the polymer modulus as a function of immersion time was developed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A SIMPLIFIED MODEL FOR DETERMINATION OF MOISTURE DIFFUSIVITY OF DATE FROM EXPERIMENTAL DRYING CURVES

ABSTRACT

Experimental drying curves for Tunisia Deglet Nour dates were obtained in a laboratory dryer under different drying conditions The air temperature was varied from 30 to 69^°C, relative humidity from 11.6 to 47.1 % and air velocity from 0.9 to 2.7 m/s. A numerical method to obtain a solution of a diffusion equation in which the diffusivity depends upon temperature and moisture content has been proposed to investigate the moisture movement in a date by assuming the sample to be a homogenous infinite cylinder. To rind the fitting moisture and temperature dependent diffusivity, the calculated drying curves are compared with the observed drying curves and an empirical equation for the moisture diffusivity of the date has presented as a function of temperature and moisture. It has been shown that the moisture distribution in the date during drying can be obtained by using the empirical equation presented.     

Experimental investigation of moisture diffusion in short‐glass‐fiber‐reinforced polyamide 6,6

Moisture diffusion in polyamide 6,6 (PA66) and its short glass fiber‐reinforced composites has a great influence on their mechanical properties and service lives under hydrothermal environments. Hence, the moisture diffusion in neat PA66 and its composites was studied comprehensively in this study with the general Fickian model. To systematically investigate the effects of the fiber content, humidity, temperature, and humidity–temperature coupling effect on the diffusion coefficient and equilibrium concentration, gravimetric experiments for the PA66 composites were carried out under different hydrothermal conditions. The results show that the equilibrium moisture concentration depended on the relative humidity and fiber content but only depended weakly on temperature. The diffusion velocity was affected by the three aforementioned factors with different trends. The analysis of variance demonstrated that the humidity–temperature coupling effect played an important role in the diffusion process. The regression analysis gave the corresponding quadratic regression equations. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42369.     

Drying characteristics and modeling of yam slices under different relative humidity conditions

The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20, 30, and 40%, temperature of 60°C, and air velocity of 1.5 m/s had an insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH led to a rapid increase in sample’s temperature. The higher sample temperature could provide an additional driving force to water diffusion and thereby promote the moisture movement, which could minimize the negative effect of lower the drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity, and mass transfer coefficient ranged from 0.1024 to 0.1182, 1.1133 × 10^?10 to 8.8144 × 10^?9 m²/s, and 1.8992 × 10^?9 to 1.7364 × 10^?7 m/s, respectively. A rather high correlation coefficient of determination (R² between 0.9871 and 0.9971) was determined between the experimental and predicted moisture contents. The present findings contribute to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying.     

Studies on molecular transport of n‐alkanes through poly(tetrafluoroethylene‐co‐propylene) elastomeric membrane

Molecular transport of a series of n‐alkanes through commercial TFE elastomer (FA 150L) has been studied in the temperature range 30–50 °C using sorption‐gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes and temperature. The diffusion coefficients at 30°C varied from 4.53 × 10^?8 cm²/s (n‐heptane) to 0.18 × 10^?8 cm²/s (n‐hexadecane). The liquid concentration profiles have also been computed using analytical solution of Fick's equation with the appropriate initial and boundary conditions and these were presented as a function of penetration depth of molecular migration and time of immersion. These results have been discussed in terms of molecular size of alkanes as well as temperature. In all the liquid penetrants, the transport phenomenon was found to follow the anomalous behavior. From the temperature dependence of diffusion and permeation coefficients, the Arrhenius activation parameters have been estimated. These parameters do not exhibit any systematic variation with the size of the penetrants. The resulting low diffusion coefficients, contribute to the superior barrier performance of the membrane, is due, in part, to the high glass transition temperature of Aflas? TFE elastomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2228–2235, 2006     

Synthesis and physicochemical study of bisphenol‐C‐formaldehyde‐toluene diisocyanate polyurethane–jute and jute–rice husk/wheat husk composites

Bisphenol‐C‐formaldehyde‐toluene‐2,4‐di isocyanate polyurethane (PU) has been synthesized at room temperature and used for the fabrication of jute and jute–rice husk/wheat husk hybrid composites. PU–jute and PU–jute–RH/WH composites were prepared under pressure of 30.4 MPa at room temperature for 8 h, while PU–jute–RH/WH composites were prepared under same pressure at 110°C for 5 h. PU–jute composite has good tensile strength and flexural strength (50–53 MPa), while PU–jute–RH/WH hybrid composites have moderate tensile strength (9–11 MPa) and a fairly good flexural strength (15–31 MPa). Composites possess 1.1–2.2 kV electric strength and 0.94–1.26 × 10¹² ohm cm volume resistivity. Water absorption in PU–jute composite is different in water (9.75%), 10% HCl (12.14%), and 10% NaCl (6.05%). Equilibrium water uptake time in salt environment is observed 96 h, while in pure water and acidic environments it is 192 h. In boiling water equilibrium water content and equilibrium time are found to be 21.7% and 3 h, respectively. Water absorption increased 2.2 times in boiling water, whereas equilibrium time reduced 64 times. Thus, PU–jute composite has excellent hydrolytic stability against boiling water, 10% HCl, and 10% NaCl solutions. Fairly good mechanical and electrical properties and excellent hydrolytic stability of composites signify their usefulness for low cost housing units and in electrical and marine industries. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2363–2370, 2006     

Effects of prior aging at 288°C in argon environment on time‐dependent deformation behavior of a thermoset polymer at elevated temperature,part 1: Experiments

The inelastic deformation behavior of PMR‐15 neat resin, a high‐temperature thermoset polymer, aged at 288°C in argon environment for up to 2000 h was investigated. The experimental program was designed to explore the in?uence of prior isothermal aging on monotonic loading and unloading at various strain rates. In addition, the relaxation response and the creep behavior of specimens subjected to prior aging of various durations were evaluated. All tests were performed at 288°C. The time‐dependent mechanical behavior of the PMR‐15 polymer is strongly influenced by prior isothermal aging. The elastic modulus increased and the departure from quasi‐linear behavior was delayed with prior aging time. Stress levels in the region of inelastic flow increased with prior aging time. Furthermore, prior aging significantly decreased the polymer's capacity for inelastic straining, including the material's capacity to accumulate creep strain. Conversely, the relaxation response was not affected by the prior aging. © 2009 Wiley Periodicals, Inc.? J Appl Polym Sci, 2009     

Determination of Chemical Tracer Diffusion Coefficients for the La‐ and Ni‐site in La2NiO4+δ Studied by SIMS

Chemical (impurity) tracer diffusion of Pr, Nd, and Co into polycrystalline La₂NiO_4+δ was done at 950°C–1350°C in air, argon, and intermediate pO₂ (5.5 × 10^?3 atm O₂), and diffusion coefficients were extracted from depth profiles determined by Secondary Ion Mass Spectrometry (SIMS). The Pr and Nd profiles have only one broad region, corresponding to bulk diffusion, whereas the Co tracer depth profile has two distinct regions with different slopes, where the outer shallow region represents bulk diffusion and the inner region with deep penetration depths represents grain‐boundary diffusion. It is thus concluded that the diffusivity on the Ni‐site is enhanced by grain‐boundary diffusion. The bulk diffusion was evaluated using the solution of Fick's second law for thin‐film source, and the grain‐boundary diffusion was evaluated according to Whipple‐Le Claire's equation. The average apparent activation energies for Pr and Nd bulk diffusion are 165 ± 15 kJ/mol, for Co bulk diffusion 295 ± 15 kJ/mol, and for Co grain‐boundary diffusion 380 ± 20 kJ/mol. Qualitatively, the diffusivities and activation energies follow levels and trends in agreement with those from other experimental techniques. The apparent lack of—in fact reverse—correlation between activation energy and level of diffusivity is discussed in terms of a possibility that the faster species (Ni) reach equilibrium defect concentrations while the slower (La) is in effect frozen in.     

Molecular transport of aromatic hydrocarbons through lignin‐filled natural rubber composites

The diffusion and transport of organic solvents through lignin‐filled natural rubber composites have been studied in the temperature range 25–45°C. The diffusion of aromatic solvents through these samples were studied with special reference to the effect of filler concentration, penetrant size, and temperature. Transport coefficients such as diffusion, permeation, and sorption coefficients were estimated. The van't Hoff relationship was used to determine the thermodynamic parameters. The first order kinetic rate constant has been evaluated. A correlation between theoretical and experimental sorption results was evaluated. POLYM. COMPOS., 28:15–22, 2007. © 2007 Society of Plastics Engineers