Characterization of temperature‐dependent moisture diffusivity in PMR‐15 resin

The temperature‐dependent moisture diffusion behavior of high‐temperature polyimide resin, PMR‐15, is presented. Adsorption and high temperature desorption tests are used to experimentally determine moisture diffusivity at several temperatures. Diffusivity is determined from the weight change based on the initial slope and using a nonlinear regression technique with Fickian diffusion assumption. The basic test procedures and diffusivity values are presented in this study. The results also include the relative humidity (RH) dependent equilibrium moisture concentration and a relationship between the RH and equilibrium moisture concentration. As direct measurement at typical operating temperature may be precluded by blistering, an Arrhenius‐type temperature‐diffusivity relationship is used to estimate the temperature‐dependent moisture diffusivity for the PMR‐15 resin. The moisture diffusivity of PMR‐15 tested is estimated to be 6.64 E ?10 m²/s at 288°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Bending-beam study of water sorption by thin poly(methyl methacrylate) films

A bending-beam technique has been employed to study the effects of film thickness (7–55 μm) and rate of cooling during film preparation (～ 6°C/h to a dry ice quench) on sorption characteristics of water by poly(methyl methacrylate) films coated on thin fused quartz beams (? 84 μm thick). In each experiment, the curvature of a polymer coated beam exposed to liquid water was monitored as a function of time by a low power laser pointer. With the use of a transport model which considers the sorption process as the linear superposition of contributions from Fickian diffusion and a first-order polymer molecular relaxation process, the beam curvature data were analyzed to determine the governing transport kinetics and associated transport parameters such as water diffusion coefficient and relaxation rate constant. From curvature analysis for thin films (7–13 μm in thickness), it was found that water diffusion proceeds at early times in a Fickian-like manner with a diffusion constant of 2–4 × 10^?9 cm²/s. At later times, significant relaxation contributions lead to non-Fickian diffusion behavior, an effect that is more pronounced as the film thickness or sample cooling rate decreases. In addition, sorption of water was found to reduce the film stress (initially tensile at ? 10⁸ dyn/cm²) at a rate that increases with sample cooling rate. The high initial film stress not present in free-standing films may account for the relatively higher diffusion coefficient (～ 2 × 10^?8 cm²/s) found here for very thick (55 μm) PMMA coatings. Because the bending-beam technique uses coated samples, it is especially well suited for studying penetrant transport into polymer coatings.     

Effect of hydrophobic hexafluoroisopropylidene group on the water sorption behaviors of rigid poly(p‐phenylene pyromellitimide) polyimide thin films

We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10^?10 to 11.3 × 10^?10 cm²/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003     

Water sorption and water‐resistance properties of poly(vinyl alcohol)/clay nanocomposite films: Effects of chemical structure and morphology

A series of poly(vinyl alcohol)/sodium montmorillonite (PVA/NaMMT) nanocomposite films were prepared via a solution method, and their water sorption and water‐resistant properties were investigated as a function of clay content. The water sorption and water resistance properties were strongly dependent on the chemical structure and film morphology originating from the NaMMT content. The water diffusion coefficient and water uptake of the PVA/NaMMT nanocomposite films were obtained by best fits to a Fickian diffusion model. The diffusion coefficient and water uptake in the PVA/NaMMT nanocomposite films varied between 8.16 × 10⁻¹⁰ and 3.60 × 10⁻¹⁰ cm² s⁻¹ and 35.6 and 29.9 wt%, respectively. Both the diffusion coefficient and water uptake decreased as the content of NaMMT in pure PVA was increased. Additionally, the water resistance pressure (mm) of the PVA/NaMMT nanocomposite films increased with increasing NaMMT content. Contact angle analyses showed that the chemical affinity to water and the surface energy of the nanocomposite films decreased with increasing NaMMT content. Furthermore, the well‐dispersed and exfoliated structure in the nanocomposite films not only induced an increased tortuous path for water molecules to pass through, but also increased the molecular order. However, to enhance the water sorption properties and water resistance of hydrophilic PVA, further studies to increase the dispersion of clay particles and ensure desired morphological qualities such as crystallinity and molecular packing order in the PVA/clay nanocomposite films are required. POLYM. COMPOS., 36:660–667, 2015. © 2014 Society of Plastics Engineers     

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     

Effects of aging and moisture on the dynamic viscoelastic properties of oriental lacquer (urushi) film

The effects of aging and moisture on the dynamic viscoelastic properties of three oriental lacquer films were investigated. With aging over 1000 days at room temperature, the glass‐transition temperature of the lacquer films (T_α) shifted to higher temperatures, the maximum loss tangent (tanδ_α) decreased, and the storage modulus at 20°C (E) increased. These changes were analogous irrespective of lacquers. With increasing moisture content, E decreased and tanδ increased at room temperature. Although the equilibrium moisture content of the virgin lacquer (sap) film was higher than that of the clear lacquer film, its E and tanδ were more stable with an increase of moisture content. It was speculated that the polysaccharides aggregated in the sap film did not effectively contribute to the mechanical properties of the film, while their hygroscopicity resulted in higher moisture content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2288–2294, 2002     

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     

Diffusion of moisture in poly(p-phenylene terephthalamide) film: Analysis by the adsorption-controlled diffusion equation

Diffusion of moisture in poly(p-phenylene terephthalamide) films was observed using a gravimetric method at various vapor pressures at 25°C. The equilibrium moisture regain was 4.9% (g/g) and 4.2% (g/g) at 65% relative humidity for the 16-μm and 50-μm thick film, respectively. These values are slightly larger than regular Kevlar or Kevlar 49 that have the same chemical structure of poly(p-phenylene terephthalamide) (PPTA). The sorption and desorption curves were satisfactorily analyzed by the adsorption-controlled diffusion equation assuming reversible bimolecular kinetics. These results strongly indicate that the interaction between the water molecules and amide groups of polymer plays an important role in the diffusion process and has much effect on the shape of sorption/desorption curves. The diffusion coefficients for the films were in the order from 10^−-11 to 10^−-10 cm²/s, which were also larger than those for Kevlar fibers of 10^−-12 cm²/s. The higher moisture diffusivity in the film reflects sparser molecular packing and existence of interstitial microvoids due to the lower molecular orientation in the noncrystalline region in the PPTA film than in the fiber (Kevlar).     

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 new approach to chemically modified carboxymethyl chitosan and study of its moisture‐absorption and moisture‐retention abilities

A new approach to prepare chemically modified carboxymethyl chitosan (CM) derivatives was reported, from which initially CM was prepared from chitosan, then N‐quaternary ammonium group was introduced by the reaction of CM with 2,3‐epoxypropyl trimethylammonium. The structures of the derivatives were characterized by FTIR, XRD, ¹³C‐NMR, and gel permeation chromatography. The capability of moisture‐absorption and moisture‐retention was investigated. It was found that the moisture‐absorption and moisture‐retention ability of the new derivatives quaternized carboxymethyl chitosan (CMQ) are higher than not only that of CM but also that of chitosan quaternary (Q) and carboxymethyl group and quaternary ammonium group are in synergistic effect. Relationships between molecular structures (including degree of substitution of carboxymethylation group, degree of substitution of quaternary group, and molar mass) and functions of CMQ were also studied. The moisture absorption kinetics of CMQ was discussed and the diffusion of water molecules in it looks likely to be non‐Fickian type. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1303–1309, 2006     

Preparation of poly(vinyl alcohol) films with promising physical properties in comparison with commercial polyethylene film

Poly(vinyl alcohol) (PVA) films with different thicknesses (0.08, 0.2, 0.23, 0.42 mm) were prepared by a casting technique. The transmission and the absorption of the PVA films were measured as functions of the wavelengths. PVA film with a thickness of 0.42 mm showed zero transmission in the wavelength range of 190–350 nm. The transmission spectrum of a commercial polyethylene film with a thickness of 0.21 mm was compared to the transmission spectrum of PVA film with a thickness of 0.42 mm. A correlation was found between the two transmission spectra in the region 190–350 nm and a 20% increase in the transmission of the PVA film in comparison with the transmission of commercial polyethylene in the region 350–1500 nm. The near‐infrared region of the transmission of commercial polyethylene was increased by 15% with respect to the transmission of the PVA film. The stress–strain measurements were done for PVA and commercial polyethylene films. The Young's modulus and the strength at break for PVA films are higher by two orders of magnitude than those for commercial polyethylene film. The strain at break for commercial polyethylene is 17% lower than that for PVA film. Radiation effects on the optical properties of PVA and commercial polyethylene films were investigated. The PVA and commercial polyethylene films were irradiated with a xeon arc lamp at 3.5–5 W/cm². The optical properties for PVA and commercial polyethylene films were studied after irradiation. The obtained results showed that PVA film with a thickness of 0.42 mm gave promising properties which could be used in technological applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1219–1226, 2002     

Gas permeation resistance of a perfluoroalkoxy‐tetrafluoroethylene copolymer

The permeation resistance of perfluoroalkoxy (PFA), a polytetrafluoroethylene (PTFE) copolymer, to various gases was explored. The diffusion and permeability coefficients for hydrogen, oxygen, nitrogen, and air were measured with extruded films using standard manometric techniques. For thicker films, transport properties were independent of film thickness. For the thinnest films, the diffusivity and permeability coefficients were slightly higher because of reduced crystallinity. The solubility of these apolar permeants in PFA was quite low and behaved ideally. Therefore, the permeation characteristics of air could be calculated from those of nitrogen and oxygen. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2122–2125, 2006     

Migration of phthalate and non‐phthalate plasticizers out of plasticized PVC films into air

The aim of the present work is to provide information about the migration of phthalate and non‐phthalate plasticizers generally used in flexible polyvinyl chloride (PVC) applications. Plastisols (pastes) were prepared by mixing PVC, plasticizer, and thermal stabilizer. The plasticized PVC (p‐PVC) films are obtained by gelation at 160°C for 15 min. The p‐PVC films were heat treated at 50, 85, 100, 130, and 160°C up to 420 min to follow the mass loss to find out diffusivity of plasticizer out of films into air and to determine related activation energies. The films having di‐octyl terephthalate (DOTP) and di‐isononyl 1,2‐cyclohexanedicarboxylic acid (DINCH) exhibited the lowest mass loss in general, among the phthalate and non‐phthalate plasticizer having p‐PVC films, respectively, as confirmed by FTIR investigation. The same tendency was observed for diffusion coefficients and for the activation energies of migration. The diffusion coefficients were found to be around 3.5 × 10^?18–2.1 × 10^?17 m²/sec for the studied plasticizers in PVC at 50°C and around 4.0 × 10^?15–9.9 × 10^?14 m²/sec at 160°C. The activation energies for 85–160°C interval were determined to be between 70 and 153 kJ/mol (0.72–1.58 eV) for the plasticizers used herein those could be treated as a homologous series as deduced from the related compensation factors. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Temperature dependence of oxygen diffusion into clay‐doped PS films

Fluorescence technique was employed for the measurement of the diffusion coefficient of oxygen into polystyrene (PS) latex/modified Na‐activated bentonite (MNaLB) clay composite films. Three different MNaLB content (0, 5, and 20 wt%) composite films were prepared from PS/MNaLB mixtures by annealing them at 200°C, above the glass transition temperature of PS for 10 min. To determine the diffusivity of oxygen in PS/MNaLB composite films, diffusion measurements were performed over the temperature range from 25 to 70°C. Pyrene (P) was used as the fluorescent agent. The diffusion coefficients (D) of oxygen were determined by combining the fluorescence quenching method with Fickian transport model, and were found as a function of temperature for each MNaLB content film. The results showed that D values are strongly dependent on both temperature and clay content in composite film. It was also observed that D coefficients obey Arrhenius behavior, from where diffusion activation energies were measured. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Application of osmotic dehydration and microwave drying to strawberries coated with edible films

Osmotic dehydration (OD) is one of the conventional methods to increase the shelf-life of vegetables and fruits. However, the operating conditions can adversely affect the organoleptic and nutritional quality of fresh products due to the high sugar uptake during processing and the loss of water-soluble constituents to the osmotic medium. The application of edible films has attracted interest due to their ability to reduce the entry of solutes and simultaneously increase the removal of water during OD treatments. Microwave (MW) is one of the most effective emerging technologies to accelerate dehydration processes in vegetable matrices. This aspect is particularly relevant in strawberries, given its high content in bioactive and nutritional compounds. Thus, the aim of this paper was to assess the influence of edible film application (alginate–lactate) in strawberry slabs during combined OD-microwaves dehydration processes. Samples of 1?cm thickness were treated with sucrose solution (60°Bx, 40?°C, 4?h) and then were dehydrated in a microwave oven (1.2?W/g). The application of alginate–lactate edible films resulted in similar weight and water losses but lower solids gain compared to uncoated samples during OD treatment. OD pre-treated MW-dried strawberry slabs with moisture contents up to 0.15?kg dry basis were obtained after 100?min of MW drying. Besides, the effective diffusional coefficient (D_e) was estimated for MW drying process, values ranged from 4.5 to 8.8 10^?10 m²/s when shrinkage effect was considered, and from 1.1 to 2.3 10^?9 m²/s for constant thickness assumption.     

Zr4+/Ti4+ Codiffusion Characteristics in Lithium Niobate

Zr⁴⁺/Ti⁴⁺‐codoped LiNbO₃ plates were prepared by local codiffusion of stacked ZrO₂ and Ti metal films coated onto Z‐cut congruent LiNbO₃ substrates in wet O₂ at 1060°C. The metal and oxide films have different thicknesses and coating sequences. After diffusion, the Zr⁴⁺ doping effect on the refractive index of LiNbO₃ and the Li₂O out‐diffusion issue were studied by the prism coupling technique. The codiffusion characteristics of Zr⁴⁺ and Ti⁴⁺ were studied by secondary ion mass spectrometry. The results show that the Zr⁴⁺ doping has little contribution to the refractive index of the crystal. Li₂O out‐diffusion is not measurable. In the Zr⁴⁺‐only diffusion case, the diffusivity of Zr⁴⁺ is four times smaller than that of Ti⁴⁺. In the Zr⁴⁺/Ti⁴⁺ codiffusion case, the Ti⁴⁺ codiffusion assists the Zr⁴⁺ diffusion. The Zr⁴⁺ diffusivity increases linearly by two more times with the increase in initial Ti film thickness from 0 to 200 nm. On the other hand, the Zr⁴⁺ affects the Ti⁴⁺ diffusion little. Neither the ZrO₂ film thickness nor the coating sequence of Ti metal and ZrO₂ oxide films influences the diffusivity of the two ions. All the codiffusion characteristics are explained. A Zr⁴⁺/Ti⁴⁺ codiffusion model is suggested that consists of two independent diffusion equations with a Zr⁴⁺ diffusivity dependent of Ti⁴⁺ concentration and a constant Ti⁴⁺ diffusivity. In addition, the existence of a waveguide in the Zr⁴⁺/Ti⁴⁺‐codoped layer is verified experimentally, and the optical‐damage‐resistant feature of the waveguide is verified by two‐beam hologram recording experimental results.     

Synthesis and properties of radiation‐induced acrylamide–acrylic acid hydrogels

Acrylamide (AAm)/acrylic acid (AAc) hydrogels in the cylindirical form were prepared by γ‐irradiating binary systems of AAm/AAc with 2.6–20.0 kGy γ‐rays. The effect of the dose and relative amounts of AAc and pH on the swelling properties, diffusion behavior of water, diffusion coefficients, and network properties of hydrogel systems was investigated. The swelling capacities of AAm/AAc hydrogels were in the range of 1000–3000%, while poly(acrylamide) (PAAm) hydrogels swelled in the range of 450–700%. Water diffusion into hydrogels was found to be non‐Fickian‐type diffusion. Diffusion coefficients of AAm/AAc hydrogels were found between 0.79 × 10^?5 and 2.78 × 10^?5 cm² min^?1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3570–3580, 2002     

Moisture diffusion in epoxy systems

The moisture diffusion process of an epoxy system is studied as a function of epoxy‐amine stoichiometry and the resulting microstructure. Differences in diffusion behavior are related to the relative importance of diffusion through the low‐density and high‐density microstructural phases for different stoichiometries. Also, changes in saturation level with stoichiometry are explained by competing effects of free volume versus the content of the low‐density phase. Increasing the humidity level causes a corresponding increase in saturation level, while increasing the temperature causes more pronounced non‐Fickian behavior. The effects of absorbed moisture on the thermomechanical properties of the epoxies are also investigated. Reductions in the glass transition temperature, T_g, and moisture‐induced swelling strains are measured after exposure of samples to the three conditioning environments. Moisture‐induced swelling strains increase with increasing moisture content. The reductions in T_g range from 5 to 20°C and are generally larger for amine‐rich samples than for epoxy‐rich and stoichiometric samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 787–798, 1999     

Diffusion Properties of Tm3+ in Congruent LiNbO3 Crystal

Diffusion properties of Tm³⁺ in congruent LiNbO₃ crystal have been investigated, together with other two related issues, i.e., Tm³⁺‐doping contribution to refractive index of LiNbO₃ substrate and Li out‐diffusion. Four X‐cut and four Z‐cut congruent LiNbO₃ substrates locally coated with 15–31 nm‐thick Tm‐metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm³⁺‐doped and Tm³⁺‐free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li₂O contents were evaluated from measured refractive index. The results show that Tm³⁺ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti⁴⁺‐ or Zn²⁺ doping. The Li₂O content at the Tm³⁺‐doped surface equals that at the Tm³⁺‐free surface. The Li out‐diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out‐diffusion is not measurable. At 1130°C, a 30‐h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li₂O content. Secondary ion mass spectrometry was used to study the Tm³⁺ diffusion properties. The results show that the diffused Tm³⁺ ions in all samples follow a complementary error function profile. From measured Tm³⁺ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er³⁺ diffusion. In comparison with Er³⁺ diffusion, the Tm³⁺ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm³⁺ has a lower diffusivity than the Er³⁺, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.