Temperature effects on permeation of modified atmosphere gas mixtures through a low density polyethylene package film

Permeation of CO₂ and O₂ through a low density polyethylene film was studied with CO₂-N₂ mixtures in the temperature range 263-283 K, and with CO₂-O₂-N₂ mixtures in the range 257-313 K. The temperature dependence of the permeabilities of these gases agreed with the Arrhenius expression. The activation energy for carbon dioxide diffusion was between 3.53 × 10⁴ and 3.74 × 10⁴J/mol; the activation energy for oxygen diffusion was 3.13 × 10⁴J/mol. The pre-exponential constant for oxygen was higher than that of carbon dioxide in various mixtures. It was also found that the pre-exponential constant of carbon dioxide decreased with increasing CO₂ concentration in the mixtures.     

Gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene,polyethylene/polyamide,and polyethylene/modified polyamide bottles

An investigation of the gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene, polyethylene (PE)/polyamide (PA), and polyethylene/modified polyamide (MPA) bottles is reported. The gasoline permeation resistance improves dramatically after blending PA and MPA barrier resins in PE matrices during blow‐molding, and the order of barrier improvement corresponds to the order of barrier improvement of the barrier resins added in PE. Somewhat unexpectedly, the gasoline permeation rates of the annealed PE and/or PE/PA bottles annealed at 90°C or higher temperatures increase significantly with the annealing temperature and time. On the contrary, the gasoline permeation resistance of the annealed PE/MPA bottles increase significantly as the annealing temperature and/or time increase. For instance, the gasoline permeation rate of the PE/MPA bottle annealed at 120°C for 32 h is about 190 times slower than that of the as‐blow‐molded PE bottle. Further investigations found that, after blending the MPA and PA barrier resins in PE matrices, the relatively nonpolar hydrocarbon components present in the gasoline fuels were significantly blocked, without permeation during the permeation tests, in which the as‐blow‐molded PE/MPA bottle inhibited the permeation of hydrocarbon components more successfully than did the as‐blow‐molded PE/PA bottle. In contrast, the amounts of polar components that permeated through the as‐blow‐molded PE/PA and PE/MPA bottles were very small and about the same as the amount that permeated through the as‐blow‐molded PE bottle. Possible mechanisms accounting for these interesting behaviors are proposed in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2827–2837, 2001     

Modelling and simulation of hydrogen permeation through supported Pd-alloy membranes with a multicomponent approach

Hydrogen transport in Pd-based supported membranes was described by means of a model considering several elementary steps of the permeation process, improving what done by Ward and Dao [1999. Model of hydrogen permeation behavior in palladium membranes. Journal of Membrane Science 153 (2), 211-231] for self-supported membranes. The model includes the external mass transfer in the multicomponent gaseous phases on both sides of the membrane, described by the Stefan-Maxwell equations. The transport of the multicomponent mixture in the multilayered porous support was also considered and described by means of the dusty gas model, which takes into account Knudsen, Poiseuille and ordinary diffusion. The diffusion in the Pd-alloy layer is modeled by the irreversible thermodynamics theory, taking the hydrogen chemical potential as the driving force of the diffusion in the metallic bulk. The interfacial phenomena (adsorption, desorption, transition from Pd-based surface to Pd-based bulk and vice-versa) were described by the same expressions used by Ward and Dao (1999). Thicknesses of 1 and are considered for the Pd-alloy layer. The asymmetric support consists of five layers, each one characterized by a specific thickness and mean pore diameter. The model separates the permeation steps and consequently their influence, quantifying the relative resistances offered by each of them. Comparison with some experimental data in several conditions in the literature shows a good agreement. The developed tool is able to describe hydrogen transport through a supported Pd-based membrane, recognizing the rate-determining steps (e.g., diffusion in the metallic bulk or in the porous support) involved in the permeation.     

Oxygen permeation resistance of polyethylene,polyethylene/ethylene vinyl alcohol copolymer,polyethylene/modified ethylene vinyl alcohol copolymer,and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer bottles

The oxygen permeation resistance of polyethylene (PE), polyethylene/ethylene vinyl alcohol copolymer (PE/EVOH), polyethylene/modified ethylene vinyl alcohol copolymer (PE/MEVOH), and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer (PE/MPAEVOH) bottles was investigated. The oxygen permeation resistance improved significantly after the blending of ethylene vinyl alcohol copolymer (EVOH) barrier resins in PE matrices during blow molding; less demarcated EVOH laminas were found on the fracture surfaces of the PE/EVOH bottles. Surprisingly, the oxygen permeation resistance of the PE/MEVOH bottles decreased significantly, although more clearly defined modified ethylene vinyl alcohol copolymer (MEVOH) laminas were found for the PE/MEVOH bottles as the compatibilizer precursor contents present in the MEVOH resins increased. In contrast, after the blending of modified polyamide (MPA) in EVOH resins, more demarcated modified polyamide–ethylene vinyl alcohol copolymer (MPAEVOH) laminar structures were observed in the PE/MPAEVOH bottles as the MPA contents present in the MPAEVOH resins increased. In fact, with proper MPAEVOH compositions, the oxygen permeation resistance of the PE/MPAEVOH bottles was even better than that of the PE/EVOH bottles. These interesting oxygen barrier and morphological properties of the PE, PE/EVOH, PE/MEVOH, and PE/MPAEVOH bottles were investigated in terms of the free volumes, barrier properties, and molecular interactions in the amorphous‐phase structures of the barrier resins present in their corresponding bottles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2528–2537, 2004     

Effects of processing conditions on the barrier properties of polyethylene (PE)/modified polyamide (MPA) and modified polyethylene (MPE)/polyamide (PA) blends

Different modified polyamide (MPA) and modified polyethylene (MPE) resins were prepared by reactive extrusion of different contents of a compatibilizer precursor (CP) with either polyamide (PA) or polyethylene (PE). The MPE and MPA resins were then blow‐molded with designed amounts of PA or PE resins to prepare four different sets of MPE/PA and PE/MPA bottles with the same CP, PA, and PE compositions. Somewhat surprisingly, the xylene permeation resistance of the MPE bottles is worse than that of the base PE bottle and decreases consistently as MPE contains more CP. In contrast, the MPE/PA and PE/MPA bottles exhibit much better xylene permeation resistance than that of the base PE bottle, wherein the PE/MPA bottles show significantly better permeation resistance than that of the corresponding MPE/PA bottles prepared at the same blow‐molding conditions. On the other hand, it is worth noting that the xylene permeation rate of each of the MPE/PA and PE/MPA bottles prepared at a fixed extrusion temperature reaches a minimum when prepared with an optimum screw speed near 400 rpm. Similarly, at a fixed screw speed, the highest permeation resistance of each PE/MPA bottle is always obtained when prepared at an optimum extrusion temperature of about 230^oC. However, the xylene permeation resistance of each MPE/PA bottle improves consistently when prepared at the higher extrusion temperatures used in this study. These interesting phenomena were investigated in terms of the morphology, thermal analysis of the PE/MPA and MPE/PA blends, the compatibility between PE (or MPE) and MPA (or PA), and the viscosity ratios of MPA (or PA) to PE (or MPE) during the blow‐molding process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1997–2008, 2000     

Effects of composition of modified polyamide on barrier properties of polyethylene/modified polyamide blends

A systematic study on the effects of types and contents of compatibilizer precursors (CPs) on degrees of crystallinity (W_c), melt shear viscosities (η_s), and permeation barrier properties of modified polyamides (MPAs) and on their corresponding morphology and barrier properties of bottles blow-molded from polyethylene (PE)/MPA blends is reported. Two alkylcarboxyl-substituted polyolefins were selected as CPs to modify PA and to improve its permeation resistance to xylene by the “reactive extrusion” process. The barrier improvements of MPAs prepared in this study depend significantly on the type and content of CP present in the MPA. A maximum improvement in barrier properties of each MPA series samples were found as the contents of CP reached an “optimum” value. On the other hand, it is interesting to note that bottles blow-molded from PE/MPA series samples exhibited better barrier properties because the MPAs used were associated with better permeation resistance to xylene. The melt shear viscosities of MPAs were found to depend on the type of CP used and increase with increasing CP contents. In contrast, the W_c of MPAs decreased with increasing CP contents. Further analysis of the fracture surfaces of bottles blow-molded from PE/MPA blends also indicated that the morphology of MPA laminas depended on the type of CP present in the MPA, and these MPA laminar structures became clearer as the contents of CPs increased. Possible mechanisms accounting for the interesting behaviors described above are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1531–1540, 1997     

Sorption characteristics of binary hydrocarbon mixtures in low density polyethylene

Sorptions of six pure hydrocarbons and five of their binary mixtures in low density polyethylene have been measured. Composition of the binary mixture sorbed has been determined experimentally by a direct method. Selectivity due to sorption has been shown to constitute a major portion of the permselectivity. Correlations have been developed to predict the quantity and composition of the binary mixture sorbed in the polymer at any temperature, when the pure compound sorptions at some temperature are known.     

Modified gas‐translation model for prediction of gas permeation through microporous organosilica membranes

A modified gas‐translation (GT) model was applied for the theoretical analysis of gas permeation through microporous organosilica membranes derived from bis(triethoxysilyl)ethane (BTESE) via a sol–gel method using different water/alkoxide molar ratios. The pore sizes of BTESE‐derived membranes were quantitatively determined by normalized Knudsen‐based permeance analysis, which was based on a modified‐GT model, using experimentally obtained permeances of He, H₂, N₂, C₃H₈, and SF₆. The pore sizes of BTESE‐derived membranes were successfully controlled from 0.65 to 0.46 nm by increasing the H₂O/BTESE ratio from 6 to 240. Furthermore, theoretical correlations of all possible pairs of permeance ratios were calculated based on the modified‐GT model. The experimental data were in good agreement with the theoretical correlation curves, indicating that the modified‐GT model can clearly explain gas permeation mechanisms through microporous membranes, and, thus, can be used to predict the gas permeation properties for these membranes. © 2014 American Institute of Chemical Engineers AIChE J 60: 4199–4210, 2014     

Surface modification of low density polyethylene in a fluorine gas plasma

Low density polyethylene was fluorinated in a glow discharge generated from a dilute mixture of fluorine in helium. The effects of pressure, flow rate, power and time of treatment have been examined. The fluorinated polymers were characterized using e.s.c.a. to identify the species present in the surface layer and to estimate the depth of fluorination. For typical plasma treatment of polyethylene films the fluorination depth was about 40 Å; a competition of ablation and ion-assisted etching processes with chemical reaction was observed. The depth of fluorination was increased to values above 60 Å by carrying out the reaction within a metal screen. The presence of the screen also reduced the reaction rate by about a factor of two. Other features of the treated polyethylene were determined by contact angle measurements, surface infra-red spectroscopy, solvent sorption and differential scanning calorimetry. Some early results of treatment of polyethylene powders in a fluidized bed reactor are also presented.     

Strawberry drying: Development of a closed-cycle modified atmosphere drying system for food products and the performance evaluation of a case study

In the present study, a closed-cycle modified atmosphere drying (CC-MAD) system was developed as an alternative drying technique to facilitate drying processes for agricultural commodities appropriate to highly humid and sunny regions with a better quality. An absorption dehumidifying system was designed for working pseudo-continuously with the most efficient absorbent in terms of moisture absorption, desorption rate, and capacity. The system, assisted by a solar panel for absorbent regeneration, was tested, while its optimum working condition was determined by strawberry drying. This unique process was comparatively carried out using hot-air and freeze-drying techniques in terms of processing time and final product quality. Strawberry slices (5?mm thickness) were dried successfully using CC-MAD. The optimum drying conditions of CC-MAD were determined as drying temperature of 60°C, drying air/gas velocity of 3?m/s and drying medium oxygen level of 9.47%. The loss of ascorbic acid was significantly reduced by CC-MAD technique. These losses were found to be 2.9, 6.9, 27.2, and 23.8% by freeze-drying, CC-MAD, hot-air drying, and hot-air drying combined with CC-MAD, respectively. The total monomeric anthocyanins loss was also significantly reduced by the CC-MAD technique (20.3%), in a similar way to that of freeze-drying (18.1%) in comparison with hot-air drying (40.4%). In addition, CC-MAD (12,446?kJ/kg fresh product at 4?h drying time) is three times more advantageous in terms of energy cost compared with freeze-drying (30492.8?kJ/kg fresh product at 24?h drying time) and six times faster in terms of drying time. This new drying system can be used as an alternative to freeze-drying in the drying of foods, especially in products sensitive to oxidation.     

The permeation of hydrocarbons through a polyethylene membrane

Permeation data of a number of linear, branched and cyclic hydrocarbons have been determined up to a pressure of 70% of the saturation vapour pressure and a temperature range of 30–50°C. The concentration of solvent in the membrane at the liquid site has been determined by desorption. An average diffusion coefficient has been computed assuming the liquid concentration in the membrane at the permeate side to be zero. The activation energy of the permeation has been correlated with molecular structure.     

Dehydration of water–alcohol mixtures by vapor permeation through PVA/clay nanocomposite membrane

An organic/inorganic hybrid nanocomposite membrane, poly(vinyl alcohol)/clay (PVAC), was prepared. The morphology of PVAC nanocomposite membranes were characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), and atomic force microscopy (AFM). The crystallinity and surface roughness increases with an increasing clay content in the PVAC nanocomposite membrane. Compared with the pure poly(vinyl alcohol) (PVA) membrane, the hybrid nanocomposite membrane (PVAC) shows an improvement in the thermal stability and the prevention of the water‐soluble property. The oxygen permeability and the water‐vapor permeation rate decreases with an increasing clay content (1–3 wt %) in the PVAC nanocomposite membranes. In addition, the effects of the clay content on the vapor‐permeation performance of an aqueous ethanol solution through the PVAC nanocomposite membranes was also investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3632–3638, 2003     

Preparation and gas permeation of immobilized fullerene membranes

Fullerene‐dispersed membranes were homogeneously prepared under the conditions in which a 10 wt % polystyrene solution containing 1 wt % fullerene was dried under a reduced pressure of 50 cmHg at room temperature. The fullerene membranes prepared with 1,2‐dichlorobenzene were found to have the darkest color, and showed no evidence of fullerene crystals in their photomicrographs. UV‐visible and infrared absorption spectra of the fullerene membranes showed fullerene bands, which indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of pure nitrogen, oxygen, carbon dioxide, ethane, and ethylene were found to increase significantly in the fullerene membranes compared to those in the polystyrene membranes, although the ideal separation factors for oxygen/nitrogen and ethylene/ethane in the fullerene membranes (i.e., 4.3 and 1.7, respectively) were slightly less than the separation factors in the polystyrene membranes. The permeability increase originated from the increase in diffusion coefficients in the fullerene membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 529–537, 2000     

Modelling of the behaviour of gas-solid two-phase mixtures flowing through packed beds

This work is concerned about gas-solid two-phase mixtures flowing upwards through packed beds. An Eulerian-based two-fluid model coupled with a newly proposed porosity distribution model is used to simulate the flow behaviour. The results are compared with recently published experimental results in terms of both hydrodynamics and solids motion. It is found that the use of the newly proposed porosity model not only gives better agreement with experimental porosity data, but also provides a much better prediction of the pressure drop than other porosity models could do. The results also show that the model predicts very well the dynamic hold-up of suspended particles, and captures the main features of the radial distributions of the suspended solids concentration and the axial solids velocity. A discrepancy occurs, however, at the wall region where the predicted axial solids velocity peak is sharper and higher than the measurements. The work also leads to a new relationship for the pressure drop of dilute gas-solid two-phase mixtures flowing through packed beds, which agrees very well with experiments.     

Selective permeation across a blend film of cellulose acetate and polymer or copolymer of c-(Nε-AcrLys-Sar)

A blend film of cellulose acetate and the homopolymer (PCP) or the copolymer with styrene [P(CP_ST)] or 4-vinylpyridine [P(CP_VP)] of $\text{cyclo(}\text{N}{}^{\mathrm{\epsilon }}\text{-}\text{acryloyl-}\text{l}\text{-lysylsarcosyl}\text{)}$ [c-(N^ε-AcrLys_Sar)], which is a vinyl compound carrying a cyclic dipeptide in the side chain, was prepared and investigated as a selectively permeable film for ions and polar substances. For the permeation of alkali metal chlorides, the solubility coefficient S increased in proportion to the content of PCP in the blend film, whereas the diffusion constant D_s increased up to 20 wt% of PCP content and levelled off beyond it. D_s of Rb⁺ was greatest for any blend film regardless of the composition. It was considered that the hydrophilic PCP forms water channels in the blend film and metal salts diffuse by coordination with cyclic dipeptide ligand groups which are arrayed along the water channels. In this process, the cooperative interaction of the ligand groups with a metal ion along the flexible polymer chain should work most efficiently with Rb⁺, leading to the Rb⁺ selectivity in the permeation. A similar ion selectivity was observed with the blend film of P(CP_ST). For the blend film of P(CP_VP), S increased in proportion to the content of P(CP_VP), where D_s was a minimum at 20 wt% of P(CP_VP) content. The ion selectivity was not observed with either S or D_s. For the permeation of alkali metal salts across the blend film of PCP, D_s and the ion selectivities were compared for chlorides and thiocyanates, and no remarkable difference was observed. D_s for the permeation of alkaline earth metal salts across various blend films were smaller than those for alkali metal salts. A blend film containing 20 wt% of PCP was found to permeate l-phenylalanine about three times as fast as d-phenylalanine. The optical resolution of racemic phenylalanine by the permeation across the blend film was possible. With increasing content of PCP in the blend film, the urea permeability increased but the oxygen permeability decreased.     

Oxygen permeation through films of polypropylene/hydrogenated oligocyclopentadiene blends

Oxygen permeation through films of isotactic polypropylene (iPP)/hydrogenated oligocyclopentadiene (HOCP) blends was studied as a function of the weight fraction of the two components and temperature. Increasing HOCP content lowers oxygen permeability and diffusivity through the films and increases the glass transition temperature of the polymer blends. Activation energies for permeation and diffusion processes were also measured. Annealing for 2 min at 100°C was shown to completely transform the smectic phase in the -crystalline form and to induce a marked increase in oxygen permeability and diffusivity, especially in the blends, and a corresponding decrease in the activation parameters.     

复合硫化物近常温热催化降解低密度聚乙烯薄膜

采用回流法合成新型热敏催化剂,将其与低密度聚乙烯(LDPE)熔融共混制得复合薄膜,并置于近常温黑暗烘箱中热催化降解。通过扫瞄式电子显微镜(SEM)、X射线能量色散光谱分析(EDX)、力学性能、原子力显微镜(AFM)、热重分析(TG)、凝胶渗透色谱(GPC)和傅里叶变换红外光谱(FT-IR)等表征手段对研究复合薄膜的热降解性能进行了研究。结果表明：纯聚乙烯薄膜在黑暗近常温条件下亦能发生热降解,但效果甚微;而复合薄膜的降解效果明显优于纯聚乙烯薄膜。在55℃下热降解45 d后,复合薄膜力学性能明显下降,粗糙度明显增加且周围出现了不同程度的褶皱与鳞片状结构,甚至于剥落现象,热分解温度下降13℃,分子量亦明显减小,同时出现了羧基和羟基等特征吸收峰。     

Artificial ageing of low density polyethylene film containing chemically bound UV - stabilizer

This paper deals with photostabilization of low density polyethylene films (LDPE) grafted with the UV-stabilizer 2-hydroxy-4-(3-methacryloxy-2-hydroxy-propoxy) benzophenone (HMB). The influence of grafting yield and the other grafting conditions upon photostabilization efficiency of LDPE films were then studied. The chemically bound monomer (HMB) was localized mainly near the surface of an LDPE film. The grafted LDPE film was exposed to an ultraviolet radiation source, and the degree of oxidation and other photooxidative changes were determined by transmission IR and ATR IR spectroscopy. Experimental results show that radiation grafting of a UV-stabilizer upon LDPE films is an efficient photostabilization method.     

Micro-morphology of modified and nonmodified blends of polypropylene with linear low density polyethylene

Modified and nonmodified blends of linear low-density polyethylene (PE) and polypropylene (PP) form separated phases of crystalline PP and PE. They form spherulitic crystals in the core, but highly oriented nonspherulitic phases at the skin of injection molded test bars. The dimension of the spherulites decreases with increasing PE content within the blends. Crystallization behavior of both crystalline phases is influenced by the other phase. The crystallization temperature of PP is increased in the presence of the compatibilizer. Transmission electron micrographs of blends modified by poly(styrene-block-ethylene/butylene) (SEBS) and stained by OsO₄ showed co-continuous lamellar structure of the blends with a polypropylene phase containing the majority of the modifier. Smaller portions of the modifier can be found on the surface of the two olefinic phases as dispersed spheres, with an average diameter of 50–90 nm. The lamellar structure is independent of the spherulitic structure, and interpenetrates the spherulites. The conclusion of this study is that this block copolymer, while improving the physical properties of the blends, is not a true compatibilizer of the system according to the conventional terminology of physical chemistry.