Transfer of contaminant during the processing of thick bi-layer food packages made of recycled and virgin polymer layers

A new route of recycling old polymers consists of using them as new food packages. Because of the potential contamination of the old polymer resulting from its previous use, the new packages are made of the old polymer layer bound to a virgin polymer layer. As it takes some time for the contaminant to diffuse through the bi-layer packaging, the food is protected over a period of time. The process of binding the two polymer layers is studied, when the two layers are heated at around the melted temperature and then cooled down at room temperature. Heat transfer by conduction through the polymer and the mould during the heating stage is considered as well as the cooling period in air. During this heating and cooling period, the process of contaminant diffusion through the two polymer layers is evaluated by considering a temperature-dependent diffusivity. The results are expressed in terms of profiles of temperature and of profiles of concentration of contaminant developed through the polymer layers. The kinetics of contaminant transfer from the recycled layer to the virgin polymer layer are also determined, for various thicknesses of the package. Dimensionless numbers are used, as well as various thicknesses of the package.     

Characterization of molecular linkages placed between zeolite microcrystal monolayers and a substrate with X-ray reflectivity

We prepared silicalite-1 microcrystal (MC) monolayers on a Si wafer using two different types of molecular linkages, namely, through chloropropyl (CP) groups and through CP/polyethylene imine/CP groups. Whereas the scanning electron microscope images of the two MC monolayers look very much alike but hardly give any information on the nature of molecular linkage between the monolayers and the substrate, their reflectivity curves are distinctively different, despite the fact that the thicknesses of the molecular linkage layers ( approximately 10-20 A) are negligibly small compared to the thicknesses of MC monolayers, ( approximately 3200 A). On the basis of the atomic force microscopic images of the MC surfaces, a rough surface layer with the thickness of approximately 160 A was introduced onto the surface of each MC to conduct a meaningful simulation of the curves with the recursive Parratt formalism. The obtained thickness, roughness, and density of each layer were reasonable, indicating that X-ray reflectivity is a very useful tool for the characterization of very thin layers of molecular linkages existing between much thicker MC monolayers and the substrate.     

X-ray photoelectron spectroscopy studies of polyethylene-aluminium laminates

X-ray photoelectron spectroscopy was used to examine the effects of extrusion temperature, antioxidants and ozone pre-treatment on the oxidation of polyethylene. The oxidation levels are related to the adhesion between polyethylene and aluminium. The relevance of weak boundary layers is discussed.     

X-ray small-angle scattering of bulk polyethylene

Summary A previously described method for evaluating X-ray small-angle scattering curves was applied to a number of well-characterized polyethylene samples. The average thicknesses of the crystalline and amorphous layers were estimated by this method; furthermore, the mean square of the density fluctuations within the samples was determined from the integral small-angle scattering. From these data, combined with the overall densities of the samples, the densities of the crystalline and amorphous layers were calculated; these densities compare well with the figures generally assumed for a two-phase structure.The effects of molecular weight and cooling rate on the thicknesses of the crystalline and amorphous layers are noted, and the thicknesses of the crystalline layers are compared with the melting points of the samples.Finally, a discussion is given of the errors which may be involved ifBragg's law is applied to small-angle scattering curves.

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Zusammenfassung Eine bereits früher beschriebene Methode zur Bewertung von Röntgen-Kleinwinkelstreuungskurven wird auf eine Anzahl genau charakterisierter Polyäthylenproben angewandt. An Hand dieser Methode wird die mittlere Dicke der kristallinen und amorphen Schichten geschätzt; ferner wird an Hand der Integral-Kleinwinkelstreuung das mittlere Quadrat der Dichteschwankungen in den Proben bestimmt. Aus den so erhaltenen Unterlagen und Gesamtdichten der Proben werden die Dichten der kristallinen und amorphen Schichten berechnet; diese Werte entsprechen durchaus den im allgemeinen für eine Zweiphasenstruktur angenommenen Zahlen.Es wird der Einfluß von Molekulargewicht und Kühlgeschwindigkeit auf die Dicke der kristallinen und amorphen Schichten angegeben; außerdem werden die Dicken der kristallinen Schichten mit den Schmelzpunkten der Proben verglichen. Schließlich werden die Fehler erörtert, welche sich bei Anwendung desBragg-schen Gesetzes auf Kleinwinkelstreuungskurven ergeben.

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With 6 figures in 7 details and 2 tables     

Formation and characterization of Cu<Subscript>x</Subscript>S layers on polyethylene film using the solutions of sulfur in carbon disulfide

Results of the formation of copper sulfide layers using the solutions of elemental sulfur in carbon disulfide as precursor for sulfurization are presented. Low density polyethylene film can be effectively sulfurized in the solutions of rhombic (α) sulfur in carbon disulfide. The concentration of sulfur in polyethylene increases with the increase of the temperature and concentration of sulfur solution in carbon disulfide and it little depends on the duration of sulfurization. Electrically conductive copper sulfide layers on polyethylene film were formed when sulfurized polyethylene was treated with the solution of copper (II/I) salts. Cu_xS layer with the lowest sheet resistance (11.2 Ω cm⁻²) was formed when sulfurized polyethylene was treated with copper salts solution at 80°C. All samples with formed Cu_xS layers were characterized by X-ray photoelectron spectroscopy. XPS analysis of obtained layers showed that on the layer’s surface and in the etched surface various compounds of copper, sulfur and oxygen are present: Cu₂S, CuS, CuO, S₈, CuSO₄, Cu(OH)₂ and water. The biggest amounts of CuSO₄ and Cu(OH)₂ are present on the layer’s surface. Significantly more copper sulfides are found in the etched layers.     

Structure and Properties of Self-reinforced Material Made from Ultra-high Molecular Weight Polyethylene-montmorillonite Nanocomposite

High-strength and high-modulus ultra-high molecular weight polyethylene (UHMWPE), named self-re-inforced material, was obtained by the elongation of UHMWPE-montmorillonite nanocomposite at melting temperature. According to the scanning electron microscope (SEM) analysis, a great deal of fibrillar texture formed in the direction of elongation, and the tensile fractured surface was similar to that of highly oriented fiber. The transmission electron microscope (TEM) and selective area electron diffraction (SAED) analyses reveal that the reinforced phase of the self-reinforced material is an extended chain crystal and its size is about 50--200 nm wide and several microns long, and the montmorillonite layers are broken up to pieces in the size from 100 to 10 nm. The broken layers which have a huge surface area interacting strongly with macro-molecules reduces the entanglement density of UHMWPE and induces the chain orientation in flow field. It is supposed that the astriction of montmorillonite layers to polyethylene chains is not only end-tethered but also side-tethered. The differential scan calorimetry(DSC) analysis shows that there are two endothermal peaks for the self-reinforced material, of which the peak at a higher temperature(136.4℃) is ascribed to the melt-ing of the reinforced phase.     

Percolative multiphonon mechanism of electrical conductivity in ion-implanted polymeric films

The temperature dependence of the conductivity of ion-implanted layers of high-pressure polyethylene, polyethylene terephthalate, polyproproylene, and polyimide was studied. It was shown that the predominant charge transfer mechanism over a wide temperature range in these layers is movement of charge carriers in a percolation cluster, the multiphonon mode of energy relaxation being taken into account.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, Nos. 5–6, pp. 454–457, September–December, 1992.The authors wish to express their deep gratitude to Academician V. D. Pokhodenko of the Ukrainian Academy of Sciences for his helpful discussions.     

Changes in row structure of extruded polyethylene film on grafting with styrene. I. Distribution of polystyrene and crystalline reorientation

Extruded films of linear polyethylene were grafted with styrene in a 1:2 styrene---methanol solution and pure styrene. The reaction was induced by simultaneous γ irradiation. Crystallinity of polyethylene was hardly affected by a polystyrene-to-polyethylene ratio as high as 13.5. From the anisotropy of film growth and small-angle x-ray diffraction it was concluded that polystyrene incorporated both into intercrystalline layers and newly formed domains alongside the stacks of lamellae. The proportion of polystyrene in interlamellar layers depends on the length of grafted chains; that is, on grafting conditions. A higher than expected proportion of occluded homopolystyrene was found in films grafted in methanol solution. The glass transition temperature of polystyrene decreased with grafting yield. Grafting in methanol solution produced changes in the x-ray orientation pattern of polyethylene. This was ascribed to untwisting and straightening crystalline lamellae in the row nucleated cylindrites.     

Deformation of oriented polyethylene

The deformation of polyethylene in terms of structural processes has been investigated by low-and wide-angle x-ray diffraction in the case of low-density and, to a lesser extent, high-density polyethylene. The samples possessed a range of simple textures which enabled the deformation processes to be identified. The results are interpreted in terms of a model of stacks of lamellae which have axes along the original draw direction and which deform by lamellar slip, chain slip, and lamellar separation. In most cases these processes accounted for the macroscopic strain but in some cases discrepancies were observed which could be accounted for by inhomogeneous deformation or by the effects of a distribution of lamellar thicknesses. Attempts were made to identify fibrillar slip, without success. The relative contributions of the various deformation processes are examined as a function of temperature and sample treatment by defining a compliance constant for each process. Below room temperature, the results are consistent with expectations based on the α and β mechanical relaxations, whereas the unusual effects at high temperatures are attributed to gradual melting. The compliance constants are also found to depend on the annealing temperature of the sample, and are used to predict the mechanical anisotropy. The volume changes accompanying lamellar separation are examined. They were less than expected in low-density polyethylene, but satisfactory agreement was obtained in high-density polyethylene. A general relation is suggested between volume changes and the lateral development of the lamellae. Hence in narrow lamellae the interlamellar layer can contract laterally whereas the greater constraints imposed by wide lamellae lead to void formation. Other effects examined include the reversibility of the processes which is most marked in the case of chain slip and which is explained by the presence of restoring forces in the amorphous regions including the fold surface. Finally, the differences between low- and highdensity polyethylene are highlighted, emphasizing the part played in the deformation by the amorphous component.     

A raman LAM study of lamellar thickness of virgin polyethylene powder

The lamellar thickness of polyethylene virgin reactor powder has been successfully measured using the Raman longitudinal acoustic mode (LAM). Relatively high lamellar thicknesses have been found. These values change with polymerization temperature in an unusual way, with lamellar thickness being larger for lower polymerization temperature, i.e., at higher undercooling for crystallization. Agreement within an experimental error of 10% has been obtained between values from LAM and those calculated by the Thompson—Gibbs equation from the melting point measured by differential scanning calorimetry.     

Ionic conductivity and activation energy for oxygen ion transport in superlattices--the semicoherent multilayer system YSZ (ZrO2 + 9.5 mol% Y2O3)/Y2O3

The oxygen ion conductivity of YSZ (ZrO(2) + 9.5 mol% Y(2)O(3))/Y(2)O(3) multilayer systems is measured parallel to the interfaces as a function of temperature between 350 and 700 degrees C. The multilayer samples are prepared by pulsed laser deposition (PLD). The film thicknesses, the crystallinity, the texture and the microstructure are investigated by SEM, XRD, HRTEM and SAED. To separate the interface contribution of the total conductivity from the bulk contribution the thickness of the YSZ and Y(2)O(3) layers is varied systematically. The total conductivity of the YSZ films increases when their thickness is decreased from 0.53 microm to 24 nm. It depends linearly on the reciprocal thickness of the individual layers, thus on the number of YSZ/Y(2)O(3) interfaces. This behaviour results from the parallel connection between individual conduction paths in the bulk and the interfacial regions. The activation energy for the ionic conductivity decreases from 1.13 to 0.99 kJ mol(-1) by decreasing the thicknesses of the individual YSZ layers. HRTEM studies show that the YSZ/Y(2)O(3) interfaces are semicoherent. The correlation between interface structure and ionic conduction is discussed.     

Time-resolved spatially offset Raman spectroscopy for depth analysis of diffusely scattering layers

The objective of this study is to use time-resolved (TR) Raman spectroscopy, spatially offset Raman spectroscopy (SORS), and a combination of these approaches to obtain high quality Raman spectra from materials hidden underneath an opaque layer. Both TR Raman and SORS are advanced techniques that allow for an increased relative selectivity of photons from deeper layers within a sample. Time-resolved detection reduces fluorescence background, and the selectivity for the second layer is improved. By combining this with spatially offset excitation we additionally increased selectivity for deeper layers. Test samples were opaque white polymer blocks of several mm thicknesses. Excitation was carried out with a frequency-doubled Ti:sapphire laser at 460 nm, 3 ps pulse width and 76 MHz repetition rate. Detection was either with a continuous-wave CCD camera or in time-resolved mode using an intensified CCD camera with a 250 ps gate width. The Raman photons were collected in backscatter mode, with or without lateral offset. By measuring the delay of the Raman signal from the second layer (polyethylene terephthalate/PET/Arnite), the net photon migration speeds through Teflon, polythene, Delrin and Nylon were determined. Raman spectra could be obtained from a second layer of PET through Teflon layers up to 7 mm of thickness. The ability to obtain chemical information through layers of diffusely scattering materials has powerful potential for biomedical applications.     

An x-ray diffraction study of nonlinear polyethylene. I. Room-temperature observations

In this investigation on samples of high- and low-density polyethylene and ethylene-vinyl acetate copolymers, crystallinities ?_W and crystalline densities ρ_cW were obtained with the aid of wide-angle x-ray scattering (WAXS) methods. From small-angle x-ray scattering (SAXS) the following characteristics were obtained either directly or by combination with the WAXS data: values, or limiting values, of the crystallinity ?_S; crystal densities ρ_cS; thicknesses of the diffuse boundary layer; number-average thicknesses of the crystalline and amorphous layers; and both number and weight averages of the long periods. It was shown that a discrepancy between ?_S and ?_W cannot be attributed to the occurrence of large amorphous regions outside the regular stacks of lamellae; the data were reconciled by assuming that the WAXS crystallinities pertain to the cores of the crystalline lamellae, whereas part of the diffuse boundary layers is comprised in the values of ?_S. The ρ_cW and ρ_cS data of the nonlinear samples show systematic differences, which were attributed to partial incorporation of side groups in the crystalline regions at a concentration estimated to be of the order of 20–40% of the overall concentration. With increasing side-group concentration, the thickness of the core of the crystalline lamellae was found to approach the average length of the linear chain segments between side groups. On the basis of these observations a scheme for the crystallization of nonlinear polyethylene is proposed according to which a number of side groups is encapsulated by the growing crystal. The data can be explained by assuming that all chains, offered at a crystal face where growth takes place, crystallize directly, irrespective of whether the crystallizing stem carries a side group. Further crystallization would then proceed by chain folding at both ends of the first stem, until a noncrystallizable unit is met. In this scheme, allowance is made for about half the stems in the crystals to be connected by folds; this is required in view of the “overcrowding” effect. Finally, the effect of cooling rate and molecular weight on the thicknesses of the crystalline and amorphous layers is discussed, and differences between the amorphous densities of high-and low-density polyethylene are noted.     

Micromechanical modeling of the elastic properties of semicrystalline polymers: A three‐phase approach

The mechanical performance of semicrystalline polymers is strongly dependent on their underlying microstructure, consisting of crystallographic lamellae and amorphous layers. In line with that, semicrystalline polymers have previously been modeled as two and three‐phase composites, consisting of a crystalline and an amorphous phase and, in case of the three‐phase composite, a rigid‐amorphous phase between the other two, having a somewhat ordered structure and a constant thickness. In this work, the ability of two‐phase and three‐phase composite models to predict the elastic modulus of semicrystalline polymers is investigated. The three‐phase model incorporates an internal length scale through crystalline lamellar and interphase thicknesses, whereas no length scales are included in the two‐phase model. Using linear elastic behavior for the constituent phases, a closed form solution for the average stiffness of the inclusion is obtained. A hybrid inclusion interaction model has been used to compute the effective elastic properties of polyethylene. The model results are compared with experimental data to assess the capabilities of the two‐ or three‐phase composite inclusion model. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Sampling depth in infrared diffuse reflection spectroscopy of undiluted samples

Diffuse reflectance of strongly absorbing sample layers is calculated in dependence of their thicknesses from the Kubelka-Munk theory. The results are compared to experimental ones from varnish layers on reflecting metal substrates.     

Measurement of the thickness of U-30MES-5NT and VGM-L sealing compound layers in aircraft products using the ultrasonic nondestructive testing method

A method for measuring the thickness of sealant layers between glass-fiber reinforced plastic and metallic parts of airframes accessible only from one side is proposed. The method is based on use of general-purpose ultrasonic flaw detectors and special-purpose laser-acoustic equipment. It is shown that the developed method allows for measurement of sealant layers with thicknesses less than the ultrasonic wave length.     

Effect of the Cathode Catalyst Layer Thickness on the Performance in Direct Methanol Fuel Cells

Catalyst deposition control is one of the overlooked areas of fuel cell fabrication and research that can affect the overall performance and cost of the fuel cell to manufacture for mass production. The effect of the different individual catalyst layer thicknesses and loadings of the cathode compartment of a direct methanol fuel cell (DMFC) was investigated. The drawdown method was performed at thicknesses varying from 1 mil to 8 mils with platinum loadings ranging from 0.25 mg cm^?2 to 2.0 mg cm^?2. The membrane electrode assemblies (MEAs) with thicker individual layers (8 mil and 4 mil) performed better overall compared to the ones prepared with thinner individual layers (1 mil). The power density maxima for the different loading levels followed an exponential decrease of platinum utilization at the higher loading levels. The painted MEAs tended to display the similar performance characteristics as the drawdown MEA layers closest to the thickness at the respective loadings.     

Cleavage of branched polyethylene by chemical filling

Branched polyethylene, melt-crystallized in commercial fabrication processes, cleaves into two layers when exposed to a prolonged “chemical filling” treatment (i.e., formation of filler in situ by interdiffusion of two reactive permeants). Cleavage has been observed in film and blown bottles. With film, progressive changes in experimental conditions from one sample to another, shifted the cleavage plane from near the surface to deeper lying planes. Separation of a thin surface layer requires more filler deposit than does separation into layers of more equal thickness. These observations suggest that a well defined layer structure may exist in branched polyethylene and that cohesive bonding is stronger between layers near the surface of the film than it is between deeper lying layers. Linear polyethylene showed slight layer separation after prolonged chemical filling, but clean cut separation of large areas was not achieved. This behavior may indicate that the cohesive bonding between layers is much stronger in linear polyethylene than in branched polyethylene.     

Coagulation and flocculation measurements by photon correlation spectroscopy — colloidal SiO2 bare and covered by polyethylene oxide

With photon correlation spectrometry (PCS) the diffusion coefficients, average diameters and polydispersities of colloidal particles can be determined in dilute aqueous suspensions. In this study PCS is used to follow the coagulation and flocculation of silica particles. Electrolyte solution added to suspensions of bare particles and of particles covered with adsorbed polyethylene oxide layers induces aggregation. The rate constants of aggregation are evaluated by the second-order Smoluchowski theory with the assumptions of spherical aggregated particles and volume proportional light-scattering amplitude. Adsorbed PEO layers of molar mass lower thanM _w=160000 decrease the critical flocculation concentration and the flocculation states and rate constants for bare and covered particles are the same at high electrolyte concentrations. Polymer layers of high molar mass (M _w=325000, 900000) reducved at full coverage the rate constants and stabilize the suspensions even at high electrolyte concentrations. At low coverage adsorption of high molar mass polymers results in the same values as of low molar mass PEO. The correlation between rate constants and hydrodynamic PEO layer thicknesses demonstrates the steric influence of the tails of the adsorbed macromolecules on stability and flocculation.Dedicated to Prof. Dr. Joachim Klein on the occasion of his 60th birthday     

聚甲基丙烯酸β羟乙酯在聚乙烯膜上辐射接枝物的形态结构

本文用透射电子显微镜(TEM),光学显微镜(OM),小角X射线散射(SAXS)等方法研究了聚甲基丙烯酸β羟乙酯(HEMA)在聚乙烯(PE)膜上辐射接枝物的形态结构.观察了微相结构随接枝条件变化规律.HEMA为支链的接枝共聚物的基本形态是高度分散的HEMA微区(约几百A)存在于PE连续相中的两相体系.随接枝量增加,微区形态发生变化.SAXS结果进一步证实了接枝共聚物相分离的形态结构,并利用Tsvankin-Buchanan公式计算了共聚物的长周期、无定形层厚及一维结晶度.