Surface Segmental Mobility and Adhesion—Effects of Filler and Molecular Mass

The adhesion of thin films of poly(methyl acrylate) (PMA) on glass slides in contact with tape has been measured as a function of thickness, molecular mass, and amount of silica-based filler. In all cases studied the polymer thin-film, tape-peel tests resulted in linear force-velocity plots. The best-fit lines were extrapolated to find the fracture energies at zero velocity. For thin layers of rubbery PMA on glass slides the PMA-tape fracture energies were found to decrease (from 55–20 J/m²) with increasing PMA thickness (50–1000 nm). Thin films made from glassy poly(methyl methacrylate) (PMMA) were found to have no thickness dependence and much higher fracture energies (～ 140 J/m²). The effect of PMA molecular mass was found to be smaller than the effect of film thickness. Including silica in the films at low levels dramatically increased the fracture energies, with a maximum (182 J/m²) found with 5.2% silica. With larger amounts of silica, the fracture energy declined significantly.     

Cohesive Zone Models of Polyimide/Aluminum Interphases

The fracture energy required to delaminate PMDA/ODA polyimide films from aluminum substrates was determined using the circular blister test. Films were prepared by spin coating the polyamic acid of PMDA and ODA onto polished aluminum substrates, by vapor co-deposition of PMDA and ODA monomers onto polished aluminum substrates, or by spin-coating the polyamic acid onto polished aluminum substrates that were first coated with thin layers of γ-aminopropyltriethoxysilane (γ-APS). Elastic and elastoplastic analyses were used to extract the fracture energies from the blister test results. Elastoplastic analysis provided fracture energies that ranged from 579 J/m² for spin-coated films on polished substrates to 705 J/m² for vapor-deposited films on polished substrates and to 750 J/m² for spin-coated films on silanated substrates. These values were intermediate between those provided by the two different elastic analyses. Differences in fracture energy determined by the three different analysis methods were related to plastic deformation in the films and, in the case of the two elastic analyses, to differences in the approach used to extract the fracture energy from experimental results. Failure of specimens prepared by spin-coating PMDA/ODA films onto aluminum substrates occurred cohesively within the polymer, near the interface between well imidized polymer in the bulk of the films and poorly imidized polymer in a layer near the aluminum surface. For the case of specimens prepared by vapor codeposition of PMDA and ODA monomers, failure occurred within the vapor deposited films, close to the aluminum/film interface. Failure of spin-coated films on silanated substrates occurred mostly within the γ-APS but leaving 'islands' of polyimide and silane on the aluminum.     

A Modified Silane Treatment for Superior Hydrolytic Stability of Glass Reinforced Composites

A silicon tetrachloride-modified silane treatment of E-glass particles and fibers improved the hydrolytic stability of the glass reinforced composites by creating a water-resistant silane copolymer interphase of approximately 30 Angstroms thickness. SEM observation of E-glass particulate reinforced dimethacrylate-based resin composites showed that strong interfacial adhesion was maintained even under 72 hours of exposure to boiling water, while interfacial adhesion in the conventionally-treated materials was destroyed under the same conditions. Interfacial fracture energy was measured using an embedded single fiber fragmentation test. In the initial dry state, no interfacial debonding was observed in either the modified or conventionally-treated microcomposites, indicating strong interfacial adhesion in both cases. However, after exposure to boiling water for 24 hours, debonding occurred in both cases, with interfacial fracture energies of 281 J/m² and 54 J/m² for the modified and conventionally-treated interfaces, respectively. The improvement in hydrolytic stability of the interface is believed to be caused by a higher degree of crosslinking in the silane layer and the replacement of at least some of the hydroxyl groups on the glass surface by covalent O—Si—O bonds.     

Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300-400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.     

GRAIN GROWTH AND DENSIFICATION IN PALLADIUM OXIDE PARTICLES DURING SPRAY PYROLYSIS

A model for aerosol-phase densification of particles during their synthesis by spray pyrolysis is presented. The model was used to describe the evolution of the specific surface area of PdO powders synthesized at temperatures between 400 to 800 °C (residence times 27.9 to 22.7 s). Surface areas and grain sizes ranged between 56 m²/g and 4 nm at 400 °C to 3.2 m²/g and 40 nm at 800 °C The characteristic coalescence lime was determined as: τ= 1.7 x 10¹³T d³ exp(1.3 x 10⁵/RT) [for lattice diffusion] and t = 2.7 x 10¹⁹Td⁴exp (1.6 x 10⁵/RT) [for grain boundary diffusion] (τ is in seconds, Tin degrees Kelvin, R is 8.314J/(mol.K)and d is in meters), but the data and model did not allow identification of the specific mechanism. The model provides a general approach for correlating changes in particle surface area with reactor operating conditions that is applicable to a wide variety of materials.     

The fracture toughness and fatigue crack propagation behaviour of annealed PET

The fracture toughness of poly(ethylene terephthalate) (PET) is correlated with various morphologies produced upon annealing. Annealing PET at a Hoffman regime III crystallization temperature (120°C) or inducing solid-state polymerization result in materials of high fracture toughness (K_c = 8.7 MPa m^1/2 and 9.5 MPa m^1/2, respectively); these high toughness values are related to multiple-crazing mechanisms produced by high tie-molecule densities. Annealing fully dried PET at 200°C transforms the material to a Hoffman regime I/II structure, and the fracture toughness decreases to 6.5 MPa m^1/2. Hydrolysis also reduces the fracture toughness (K_c < 3 MPa m^1/2). In these low toughness materials, multiple crazing is not observed. In addition, the fatigue crack propagation response of PET is found to be superior in samples annealed to produce high fracture toughness as compared with samples annealed to produce low fracture toughness values.     

Thin Layer Drying Models for Osmotically Pre-dried Young Coconut

Thin layer convection drying was performed on osmotically pre-dried young coconut, strips, both thin and thick. A drying air temperature range of 50-70°C and an airflow of 0.25 m s^-1 was used to dry samples soaked in three sugar solution concentrations (40, 50, and 60°B) during the osmotic drying phase, with the convection drying alone serving as control. An analysis of variance (ANOVA) revealed that sugar concentration and thickness significantly affected osmotic drying rates as shown by their final moisture contents. While the drying air temperature and slab thickness significantly affected the average drying rate and the sugar concentration was an insignificant factor during convective drying phase. Effective diffusivity of water during hot air drying varied from 1.71 to 5.51 × 10^-10 m²s^-1 over the temperature range investigated, with energy of activation equal to 1173.0 kJ/kg. Three mathematical models available in the literature were fitted to the experimental data, with the Page model giving better predictions than the single or double term exponential model. The temperature dependence of the diffusivity coefficients was satisfactorily described by a simple Arrhenius type relationship.     

Mechanism of Through Air Drying of Paper: Application in Hybrid Drying

During through air drying the internal sheet drying history develops as a succession of local moisture content profiles in the sheet thickness dimension. These profiles were determined by interrupting the through drying of 180 g/m² 6-ply sheets, then quickly delaminating and determining the moisture content of each 30 g/m² ply. On the through flow inlet side of the sheet, large moisture differences, about 0.4-0.6 kg/kg dry per 30 g/m² ply, develop and move into the interior of the sheet provided that local moisture content is in the range 0.45-1.75 kg/kg. On the through flow exit side, moisture gradients only become significant for moisture content below about 1.25 kg/kg. From the through flow exit side of the sheet much of the water is removed by diffusion to the flow entry side where most evaporation into the through flow occurs. The kinetics of through drying reflect the interaction between these two mechanisms, local evaporation into the through flow and thickness direction diffusion. The moisture diffusivity-moisture content relation controls this balance. In any combination with cylinder drying to give some kind of hybrid dryer, through drying should be at the dry end where air permeability is highest and cylinder drying rate is lowest.     

Strengthening interfaces between biaxial oriented PET and PSMA: Effects of nitrogen plasma and bonding treatments

The fracture toughness, G_c, of the interface between a nitrogen plasma-treated poly(ethylene terephthalate) (PET) film and a poly(styrene-co-maleic anhydride) (PSMA) substrate was measured by using asymmetric double cantilever beam method. The effects of plasma treatment condition on PET films and post-plasma bonding treatment of the bi-material on the adhesion and the failure mechanism were investigated. For a given plasma pressure and energy, the amount of incorporated nitrogen on the PET surface as determined from X-ray photoelectron spectrometry (XPS) increased with increasing plasma treatment time and reached a plateau value of 7.7 at.%. XPS measurement showed that the incorporated nitrogen was primarily in the form of amine and amide. For bonding temperatures between 130 °C and 160 °C, the fracture toughness increased with increasing nitrogen incorporation on PET surface and reached a saturation G_c which significantly depended on the bonding temperature. The saturation G_c increased from 10 J/m² at 130 °C to 40 J/m² at 140 °C, reached a maximum of 120 J/m² at 150 °C, and then decreased to 60 J/m² at 160 °C. The location of failure also changed drastically with the bonding temperature. SEM and XPS measurements showed that for bonding temperature < 140 °C, failure occurred at the PET/PSMA interface. For bonding temperature = 150 °C, the interfacial adhesion exceeded that of the cohesive strength of PET film and failure occurred within the PET film. At the bonding temperature of 160 °C, failure occurred within PSMA bulk material. XPS measurement was used to measure the areal joint density, Σ_cross of PSMA chains pinned on the functionalized PET film surface. A transition in areal joint density below which G_c scales linear with Σ_cross and above which G_c scales with was found. The transition was identified as the transition from the pure chain scission of in situ formed copolymers to plastic deformation of the interface.     

Effect of Pulsed Electric Field and Osmotic Dehydration Pretreatment on the Convective Drying of Carrot Tissue

The influence of pulsed electric field (PEF) and subsequent centrifugal osmotic dehydration (OD) on the convective drying behavior of carrot is investigated. The PEF was carried out at an intensity of E = 0.60 kV/cm and a treatment duration of t_PEF = 50 ms. The following centrifugal OD was performed in a sucrose solution of 65% (w/w) at 40°C for 0, 1, 2, or 4 h under 2400 × g. The drying was performed after the centrifugal OD for temperatures 40-60°C and at constant air rate (6 m³/h).

With the increase of OD duration the air drying time is reduced spectacularly. The dimensionless moisture ratio Xr = 0.1 is reached for PEF-untreated carrots after 370 min of air drying at 60°C in absence of centrifugal OD against 90 min of air drying after the 240 min of centrifugal OD. The PEF treatment reduces additionally the air drying time. The total time of dehydration operations can be shortened when OD time is optimized. For instance, the minimal time required to dehydrate untreated carrots until Xr = 0.1 is 260 min (120 min of OD at 40°C and 140 min of drying at 60°C). It is reduced to 230 min with PEF-treated carrots.

The moisture effective diffusivity D_eff is calculated for the convective air drying based on Fick's law. The centrifugal OD pretreatment increases drastically the value of D_eff. For instance, 4 h of centrifugal OD permitted increasing the value of D_eff from 0.93 · 10^-9 to 3.85 · 10^-9 m²/s for untreated carrots and from 1.17 · 10^-9 to 5.10 · 10^-9 m²/s for PEF-treated carrots.     

Influence of Edible Films upon the Moisture Loss and Microstructure of Dietetic Sucrose-Free Sponge Cakes during Storage

The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = q_oe^-kt. The values of rate constants 'k', in day^-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10^-3, for bound water is (3.07 ≤ k_w ≤ 6.26) × 10^-2, for slightly bound water is (4.22 ≤ k₁ ≤ 8.49) × 10^-2 and for strongly bound water is (2.02 ≤ k₂ ≤ 5.62) × 10^-2 as compared to 18.53 × 10^-3, 7.16 × 10^-2, 9.04 × 10^-2, and 5.36 × 10^-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage.     

Osmotic Dehydration of Apple Cylinders: I. Conventional Batch Processing Conditions

Osmotic drying was carried out, with cylindrical samples of apple cut to a diameter-to-length ratio of 1:1, in a well-agitated large tank containing the osmotic solution at the desired temperature. The solution-to-fruit volume ratio was kept greater than 30. A modified central composite rotatable design (CCRD) was used with five levels of sucrose concentrations (34-63°Brix) and five temperatures (34-66°C). Kinetic parameters weight reduction (WR), moisture loss (ML), solids gain (SG) were considered. A polynomial regression model was developed to relate moisture loss and solids gain to process variables. A conventional diffusion model involving a finite cylinder was also used for moisture loss and solids gain, and the associated diffusion coefficients were computed. The calculated moisture diffusivity ranged from 8.20 × 10^-10 to 24.26 × 10^-10 m²/s and the solute diffusivity ranged from 7.82 × 10^-10 to 37.24 × 10^-10 m²/s. Suitable ranges of main parameters were identified for OD kinetics further study.     

First Principles Study of the Aluminum-Cubic Boron Nitride Interface

A plane wave density functional methodology, with the local density approximation for the elemental constituents, was used to investigate the structure, bonding, and adhesion of atomic-scale interfaces between aluminum and cubic-boron nitride (c-BN). Two fully periodic interfaces, Al(110)-c-BN(110) and Al(001)-c-BN(110), were constructed for this purpose. Interfacial bonding, examined with contours of the charge density difference and electron localization function, was found to be stronger between Al-N pairs than Al-B pairs. The computed work of separation ( W_s ) values were 2.25 J/m² for Al(110)-c-BN(110) and 2.65 J/m² for Al(001)-c-BN(110). The higher adhesion in the latter interface is attributed to a higher planar density of interfacial Al atoms. The computed W_s values were compared with values from first principles calculations on other aluminum-ceramic interfaces. The possibility of adhesive transfer during tensile debonding was qualitatively investigated.     

Soft and Hard Adhesion

The force needed to pull a cylindrical stud from a soft elastomeric film depends on their elastic and geometric properties. For a rigid stud and a thick elastomeric film, the pull-off stress (σ) depends on the elastic modulus (E) of the film and the radius (a) of the stud as σ ∼ (E/a)^1/2 (soft adhesion). However, when the film is very thin, the pull-off stress is significantly higher than the case with thick films, and its value depends on the elastic modulus and the thickness (h) of the film as σ ∼ (E/h)^1/2 (hard adhesion). Here, we study the pull-off behavior of a soft cylindrical stud, one flat end of which is coated with a high modulus thin baseplate. As the flexural rigidity of this baseplate is varied, we observe the transition between the two types of adhesion. We present a simple physical interpretation of the problem, which could be of value in understanding various biofouling and adhesive situations.     

Assessment of Osmotic Process in Combination with Coating on Effective Diffusivities during Drying of Apple Slices

The effect of carboxymethyl cellulose (CMC) coating on the mass exchanges during the osmotic dehydration of apples and its effect on the quality of final product were studied. Coating semi-rings of apple with CMC solution (1%) was found to prevent solute uptake and to reduce salt diffusion coefficient from 4.35 × 10^-10 m²/s to 2.86 × 10^-10 m²/s. However, coating did not significantly affect the diffusivity of water. The effective diffusivity of salt and consequently solids gain were found to be depended on the concentration of CMC solution in the range of 0-1%. Increasing the concentration of CMC further from 1% had no effect on the mass exchanges during the osmotic process. Maximum performance ratio, defined as water loss/solids gain, and the lowest solids diffusion was observed for coated samples (with 1% CMC solution) treated with an osmotic solution containing glucose syrup (50%) and NaCl (2%).     

Drying Characteristics of Barley Grain Dried in a Spouted-Bed and Combined IR-Convection Dryers

A study was performed to determine the drying characteristics and quality of barley grain dried in a laboratory scale spouted-bed dryer at 30, 35, 40, and 45°C and an inlet air velocity of 23 m/s^-1, and in an IR-convection dryer under an infrared radiation intensity of 0.048, 0.061, 0.073, and 0.107 W cm^-2 at an air velocity of 0.5 m/s^-1. The results show that the first, relatively short, phase of a sharp decrease in the drying rate was followed by the phase of a slow decrease. The time of barley drying depended on temperature of inlet air in a spouted-bed dryer and on radiation intensities in an IR-convection dryer. Barley drying at 45°C in a spouted-bed dryer was accompanied by the lowest total energy consumption. The average specific energy consumption was lower and the average efficiency of drying was higher for drying in a spouted-bed dryer. The effective diffusivities were in the range 2.20-4.52 × 10^-11 m² s^-1 and 3.04-4.79 × 10^-11 m²/s^-1 for barley dried in a spouted-bed and in an IR-convection dryer, respectively. There were no significant differences in kernel germination energy and capacity between the two drying methods tested.     

VOLATILE ORGANIC COMPOUND (VOC) REMOVAL BY ADSORPTION ONTO ACTIVATED CARBON FIBER CLOTH AND ELECTROTHERMAL DESORPTION: AN INDUSTRIAL APPLICATION

Previous studies have shown good adsorption of volatile organic compounds (VOC) present in air onto activated carbon fiber cloths (ACFCs). In a chemical plant, a treatment process was carried out to control a gaseous emission (flow close to 100 m³ h^-1) loaded with methylene chloride at concentrations ranging between 3 and 30 g m^-3. A final mass flow lower than 100 g h^-1 was required in the outlet emission. Two identical cylindrical ACFC modules worked alternately in an adsorption-desorption cycle. The outlet pollutant mass flow was found to be less than 4 g h^-1. After saturation of the adsorbent, the module was electrothermally regenerated. Desorbed methylene chloride was recovered in a cryogenic trap and reused in the chemical processes of the plant. This system worked continuously for more than 18 months (24 h per day) with no operating problems and giving good performance in terms of VOC outlet emission concentrations.     

Preparation, structural and optical characterization of BaWO4 and PbWO4 thin films prepared by a chemical route

Polycrystalline BaWO₄ and PbWO₄ thin films having a tetragonal scheelite structure were prepared at different temperatures. Soluble precursors such as barium carbonate, lead acetate trihydrate and tungstic acid, as starting materials, were mixed in aqueous solution. The thin films were deposited on silicon, platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and specular reflectance infrared Fourier transform spectroscopy, respectively. Nucleation stages and surface morphology evolution of thin films on silicon substrates have been studied by atomic force microscopy. XRD characterization of these films showed that BaWO₄ and PbWO₄ phase crystallize at 500 °C from an inorganic amorphous phase. FTIR spectra revealed the complete decomposition of the organic ligands at 500 °C and the appearance of two sharp and intense bands between 1000 and 600 cm⁻¹ assigned to vibrations of the antisymmetric stretches resulting from the high crystallinity of both thin films. The optical properties were also studied. It was found that BaWO₄ and PbWO₄ thin films have Eg=5.78 eV and 4.20 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of BaWO₄ and PbWO₄ thin films.     

Drying Kinetics of a Porous Spherical Particle and the Inversion Temperature

A model is presented for drying of a single porous particle with superheated steam and humid air. Experimental data for spherical porous ceramic particle reported in the literature were used for the validation of the model. An inversion temperature at which the evaporation rates within superheated steam and humid air are equal was predicted. The effect of thermophysical properties of the particle (permeability 10^-14 - 10^-17 m², diameter 3 × 10^-3 - 10 × 10^-3 m) and operating variables (gas mass flux 0.26 - 0.78 kg m^-2 s^-1, drying agent temperature 120-200°C) is tested. The inversion temperature is shown to be affected by the thermophysical properties of the porous particle and of the drying agent.     

MOISTURE MEASUREMENT BY FT-IR-SPECTROSCOPY

This contribution reports on the use of a FT-IR-spectrometer for measuring concentrations during the drying of thin films of Polyvinyl acetate (PVAc) and Methanol. Calibration was carried out by differential weighing. The spectra were taken in transmission mode while dried air was blown over the liquid films. The obtained accuracy was +/- (5% + 0,8 g/m²) for small contents of Methanol and +/- (10 % 2 g/m²) for higher Methanol contents. The content of PVAc could be measured with 5% accuracy. The experiments were carried out at room temperature; the examined films had a thickness of about 30 to 60 microns when completely dry.