Temperature dependency of gas barrier properties of biodegradable PP/PLA/nanoclay films: Experimental analyses with a molecular dynamics simulation approach

Polypropylene (PP)/poly(lactic acid) (PLA)/clay nanocomposite films with various compositions (PP‐rich and PLA‐rich) were prepared. Their structural and barrier properties against CO₂, O₂, and N₂ were investigated. The microstructure of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy, and wide angle X‐ray scattering. The PP‐rich with 75/25 composition revealed the best barrier properties against all the gases which could be justified according to its microstructure. Selectivity of O₂/N₂ and CO₂/N₂ was also measured. It was found that the addition of nanoclay as a gas barrier component reduced the permeability in both systems. The permselectivity was also reduced in the PP‐rich films while it was increased in the PLA‐rich system. Moreover, the temperature dependency of permeability, selectivity, and permselectivity for PP, PLA, and PP/PLA (75/25) samples was examined. The results showed that the temperature dependence of permeability obeyed an Arrhenius equation and order of activation energy of permeability for O₂, CO₂, and N₂ gases was found to be E_P < E_P/PLA < E_PLA. According to solubility measurements, the order of solubility coefficient for gases was as follows: CO₂ > O₂ > N₂. Finally, the molecular dynamics (MD) simulation was performed to estimate the diffusivity coefficients of the gases and showed that solubility increases with increasing temperature, which was in accordance with the experiments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46665.     

Vapor Permeation and Pervaporation of Aqueous 2‐Propanol Solutions through the Torlon® Poly(amide imide) Membrane

Abstract

In the present study, vapor permeation and pervaporation of aqueous 2‐propanol mixtures were investigated using Torlon^® poly(amide imide) as a membrane material. Torlon membranes preferentially permeated H₂O from aqueous 2‐PrOH mixtures both by vapor permeation and pervaporation. Diffusion experiments led to the conclusion that both solubility selectivity and diffusivity selectivity showed a preference for H₂O. Solubility selectivity is by far the dominant factor governing permselectivity, and as a result, Torlon membranes showed permselectivity toward water in vapor permeation and pervaporation. The present study showed that Torlon^® poly(amide imide) is a membrane material potentially applicable to the dehydration of water miscible organics.     

The atomistic simulation of the gas permeability of poly(organophosphazenes). Part 2. Poly[bis(2,2,2-trifluoroethoxy)phosphazene]

Self-diffusion and sorption of seven gases (He, H₂, O₂, N₂, CH₄, CO₂, and Xe) in poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PTFEP) have been investigated by molecular dynamics and Grand Canonical Monte Carlo (GCMC) simulations of two amorphous cells and an α-orthorhombic crystalline supercell. In the case of MD simulation of diffusion coefficients, values obtained for both amorphous and crystalline PTFEP are similar and comparable to experimental values reported for semicrystalline samples. These results indicate that gas diffusion is unrestricted in the crystalline state of PTFEP as has been reported for poly(4-methyl-1-pentene) (PMP) and, more recently, for a crystalline form of syndiotactic polystyrene (sPS).In contrast to both PMP and sPS that have low-density crystalline forms, only He exhibits any solubility in the α-orthorhombic crystalline cells of PTFEP during simulation. In addition, values of the solubility coefficients obtained from simulation of the amorphous cells are three to five times larger than would be expected by extrapolating values reported for semicrystalline samples to 100% amorphous content. These results suggest that while the crystalline domains do not restrict gas diffusivity in PTFEP, they significantly reduce gas solubility in semicrystalline PTFEP through the reduction of amorphous content and through some additional effect of the crystallites on amorphous-phase solubility, possibly through chain immobilization of the amorphous phase. Similar solubility behavior has been suggested for polyethylene on the basis of recent simulation studies.As reported in a prior communication, the solubility of CO₂ in PTFEP is very high compared to other gases due to a weak quadrupole-dipole interaction between CO₂ and the trifluoroethoxy group of PTFEP. As a result, the solubility coefficients of CO₂ obtained from GCMC simulation of the amorphous cells and from permeability measurements of semicrystalline samples are both larger than predicted by a simple correlation of gas solubility coefficients with the Lennard-Jones potential well parameter, ε/k, of other gases as proposed by Teplyakov and others. A modified form of this correlation that includes a Flory interaction term is shown to fit all gas solubility data for this polymer including that of CO₂.     

Effect of micropores diffusion on kinetics of CH4 decomposition over a wood-derived carbon catalyst

In order to optimise hydrogen production from biomass gasification, catalytic conversion of methane contained in a surrogate biomass syngas (CH₄ 14%; CO 19%; CO₂ 14%; H₂ 16%; H₂O 30%; N₂ 7%) is investigated over a fixed bed of porous wood char as a function of temperature (800–1000 °C) and space time (1.6–6.2 min g L⁻¹). Determination of Thiele modulus evidences a change of kinetic regime from chemically- to diffusion-controlled when the temperature increases; this finding is particularly relevant when porous chars having an average pore width of 1 nm are used as catalysts. Mass diffusion transfers are accounted for by a model introducing an internal effectiveness factor. Knudsen diffusion in micropores is shown to limit the conversion rate of methane per unit mass of catalyst, and explains why such a rate is not proportional to the BET surface area, especially when the latter is higher than typically 300 m²/g. It is concluded that diffusion limitations in micropores should be taken into account, otherwise underestimated activation energy and intrinsic kinetic constant are obtained in some experimental conditions.     

电渗强化多孔介质孔内流动及传质

建立了电场中多孔介质孔内流动模型 ,通过计算比较了Poiseuille流和电渗流对孔内流动的贡献 ;提出“有效扩散系数”来定量描述电渗对多孔介质孔内传质过程的强化作用 ;建立了电色谱理论塔板高度模型 ,比较了Poiseuille流和电渗流对色谱理论塔板高度的影响 .计算结果表明采用Poiseuille流强化孔内传质的方法仅适用于孔径大于 5 0 0nm的大孔颗粒 ;而电渗流则可提高不同孔径的介质孔内的传质 ,降低色谱分离理论塔板高度 ;依据Yoshida模型计算了不同的有效扩散系数下的吸附穿透曲线以揭示电场强度对电色谱吸附行为的影响 ,理论预期与实验结果一致     

Osmotic Dehydration of Apple Cylinders: II. Continuous Medium Flow Heating Conditions

Mass transfer of apple cylinders during osmotic dehydration was quantitatively investigated under continuous medium flow conditions. The influences of the main process variables (solution concentration, operation temperature, contact time, and solution flow rate) were determined. A second-order polynomial regression model was used to relate weight reduction (WR), moisture loss (ML), solids gain (SG), and mass diffusivity (D _m and D _s ) to process variables. The conventional diffusion model using a solution of Fick's unsteady state law involving a finite cylinder was applied for moisture diffusivity and solute diffusivity determination. Diffusion coefficients were in the range of 10^?9–10^?10 m²/s, and moisture diffusivity increased with temperature and flow rate, increased with solution concentration (> 50°Brix), and decreased with increasing solution concentration (< 50°Brix), but solids diffusivity increased with temperature and concentration and decreased with increasing flow rate. A continuous-flow osmotic dehydration (CFOD) contactor was developed to be a more efficient process in terms of osmotic dehydration efficiency: time to reach certain weight reduction (T _w ) and moisture loss (T _m ) were shorter than that of conventional osmotic (COD) dehydration processes. Effectiveness evaluation functions used in this study could be widely applied to osmotic dehydration system evaluation.     

The effect of freezing on the hot air and microwave vacuum drying kinetics and texture of whole cranberries

Abstract

The aim of this study was to evaluate the effect of convective and cryogenic freezing, hot air convective drying (HACD) at 60, 70, 80, and 90?°C and microwave vacuum drying (MWVD) at 100, 150, 200, 300, 450, and 500?W on the drying kinetics and texture of whole cranberries. Effective moisture diffusivities and drying rates were higher, whereas drying times were shorter for the samples dried by MWVD compared with the samples processed by HACD. The drying kinetics of cranberries during MWVD was discussed based on the hypothesis postulating that changes in the drying rate of cranberries during MWVD can be explained by and correlated with changes in the pressure gradient on material surface. Cranberries processed by MWVD were characterized by significantly greater hardness, gumminess, and chewiness in comparison with HACD samples. MWVD was found to be an effective method for producing dried snacks characterized by hard and crispy texture and considerable resistance to stress associated with manufacturing, packaging, storage, and delivery. HACD produced brittle fruit that were difficult to store and transport and were not fully suitable for direct consumption. Convective freezing before MWVD improved the overall appearance of cranberries, whereas cryogenic freezing combined with high temperature HACD adversely influenced the drying rate and produced dried cranberries with suboptimal overall appearance.     

An Artificial Neural Network Model for Prediction of Drying Rates

Abstract

Drying rate data were generated for training of an ANN model using a liquid diffusion model for potato slices of different thicknesses using air at different velocities, humidities and temperatures. Moisture content and temperature dependence of the liquid diffusivity as well as the heat of wetting for bound moisture were included in the diffusion model making it a highly nonlinear system. An ANN model was developed for rapid prediction of the drying rates using the Page equation fitted to the drying rate curves. The ANN model is verified to provide accurate interpolation of the drying rates and times within the ranges of parameters investigated.     

Microwave drying of mango ginger (Curcuma amada Roxb): prediction of drying kinetics by mathematical modelling and artificial neural network

Curcuma amada (Mango ginger) was dried at four different power levels ranging 315–800 W to determine the effect of microwave power on moisture content, moisture ratio, drying rate, drying time and effective diffusivity. Among the fifteen thin layer drying models considered for evaluating the drying behaviour, the semi‐empirical Midilli et al., model described the drying kinetics very well with R² > 0.999. Drying rate and effective diffusivity increased as the microwave power output increased. Activation energy was estimated by a modified Arrhenius type equation and found to be 21.6 kW kg^?1. A feed‐forward artificial neural network using back‐propagation algorithm was also employed to predict the moisture content during MW drying and found adequate to predict the drying kinetics with R² of 0.985.     

Real-time estimation of slowest heating point temperature and residual cooking time by coupling multipoint temperature measurement and mathematical modelling: Application to meat cooking automation

In this work, an innovative procedure for real-time heat transfer modelling and dimensional change estimation during meat cooking was presented. By using a multipoint temperature probe, a punctual calculation of slowest heating point (SHP) temperature was obtained at each time from the radial temperature distribution inside the product. Experimental temperature data from the multipoint probe was combined with a mathematical algorithm previously validated to perform a real-time estimation of SHP temperature and residual cooking time on the basis of the data stored at each instant. The developed procedure and algorithm were validated by cooking pork loin and roast beef samples at 180 and 200 °C both under natural and forced convection regimes. Real-time predicted cooking time and SHP endpoint temperature values were very close to those experimentally obtained: at the 85% of the cooking process, the maximum percentage errors for SHP endpoint temperature and cooking time prediction were 1.72 and 1.67%, respectively. In addition, SHP location inside the meat samples was also obtained at each time instant and used to estimate dimensional changes during cooking: calculated final characteristic dimensions were very similar to those experimentally obtained for all cooking trials. The developed approach could be useful for the automatic cooking operations planning in food-service with microbial safety assurance.