The barrier properties of polyethylene terephthalate to mixtures of oxygen, carbon dioxide and nitrogen

The diffusion and solubility of oxygen, nitrogen and carbon dioxide have been studied in amorphous and biaxially oriented films of polyethylene terephthalate (PET). To measure the sorption and desorption of each gas simultaneously in cases where mixtures of gases were studied, a mass spectrometer was used as a detector. It was found that the solubility and diffusion of nitrogen in PET were markedly affected by the presence of the other gases, oxygen and carbon dioxide with differences in detail between results for the amorphous and biaxially oriented films. It is of particular interest that the presence of oxygen reduces the solubility and increases the diffusivity of nitrogen.     

Morphological interpretation of n-hexane diffusion in polyethylene

The diffusion of small-molecule penetrants in polyethylene is retarded by the detour caused by the crystals and by the segmental constraints imposed by the crystals on the penetrable phase. The earlier reported n-hexane diffusivity data for a series of homogeneous poly(ethylene-co-octene)s showed unexpectedly that the detour was greatest in the low crystallinity polymers. The crystal width-to-thickness ratio and the crystallinity were assessed by electron microscopy and differential scanning calorimetry and used in the Fricke model. The calculations showed that the geometrical impedance factor followed the same trend with increasing crystallinity as the data obtained from n-hexane desorption. The high geometrical impedance factor shown by the low crystallinity samples was due to the presence of crystals with an unusually high crystal width-to-thickness ratio. A unified relationship, including data for both linear and branched polyethylene was found between the fractional free volume and the phase composition of the penetrable phase including the liquid-like, interfacial liquid and the interfacial crystal core.     

聚乙烯可降解薄膜研究进展

聚乙烯(PE)是目前应用生产薄膜最大的塑料品种之一,为了避免"白色污染",利用淀粉和无机填料改性聚乙烯制得可降解薄膜是目前最主要的两种手段。本文探讨了淀粉改性聚乙烯的工艺、机理和改性后薄膜的性能;同时讨论了不同无机填料改性聚乙烯的工艺、机理。     

IR transition moment orientational analysis on semi-crystalline polyethylene films

The recently developed approach of Transition Moment Orientation Analysis is employed to determine the three dimensional orientation and order of the different molecular moieties in semi-crystalline polyolefins. Based on IR transmission spectra for varying polarisation and inclination the quadratically averaged orientation distribution of the different IR transition moments is deduced. By that, the full order parameter tensor and its orientation with respect to the sample coordinate system is obtained.     

Electrical conductivity and self-temperature-control heating properties of carbon nanotubes filled polyethylene films

Electrical properties of polyethylene and carbon nanotube composite films were investigated, when the composite films were set in heating box or under electric field at constant voltage. The composite films were prepared by gelation/crystallization from dilute solution. The mixture of ultra-high molecular weight polyethylene (UHMWPE) and branched low molecular weight polyethylene (LMWPE) was used as matrix, and multi-walled carbon nanotubes (MWNTs) were used as fillers. The filler content was chosen to be 10 wt% (ca. 5.25 vol%) which is a relatively higher loading than the percolation threshold to ensure to act as heating element in plane heater of composite film. The focus was concentrated on the temperature dependences of electric conductivity by external heating and by exothermic effect concerning self-temperature-control heating properties which were measured for the three kinds of UHMWPE-LMWPE composites with the same content of MWNTs in the composites. When a certain voltage was applied to the composite, the surface temperature of film reaches the equilibrium value within less than 100 s. The maximum surface temperature as the equilibrium state of the resultant composite film can be easily controlled by adjusting the composite ratio represented as UHMWPE/LMWPE. The high efficiency of heating and wide adjustability of stable temperature suggested its good application in high efficient plane heater.     

Multiple hydrophilic polymer ultra-thin layers covalently anchored to polyethylene films

A novel procedure has been developed to covalently graft multiple hydrophilic polymer ultra-thin layers to functionalized polyethylene surface. Polyethylene films have been functionalized by two methods, chromic acid oxidation and maleic anhydride grafting, to produce surfaces containing reactive groups, carboxylic acid and anhydride, respectively. The reactive groups formed in the functionalization were used to anchor a poly(vinyl alcohol) (PVA) ultra-thin layer by thermal esterification. After anchoring PVA, a second ultra-thin layer, constituted of poly(acrylic acid) (PAA), was also anchored. The second layer was anchored by thermal esterification between PVA hydroxyl groups and PAA carboxylic acid groups. The procedure presented in this work allows the formation of an ultra-thin layer. The macromolecule anchoring reactions occur only at the interfaces, consequently, only the macromolecules in contact with the interface are anchored. The formation of the ultra-thin layer and the surface characteristics have been analyzed through XPS, ATR-FTIR, SEM, and AFM data.     

Surface photografting of low-density polyethylene films and its relevance to photolamination

Surface modifications of pristine and ozone-pretreated low-density polyethylene (LDPE) films were carried out via UV-induced graft copolymerization with a photoinitiator-containing, epoxy-based commercial monomer (DuPont Somos? 6100 for solid imaging and optical lithography) and also with the photoinitiator-free acrylic acid (AAc). The chemical composition and microstructure of the graft copolymerized surfaces were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). The concentration of surface grafted polymer increased with the UV illumination time and the monomer concentration. For LDPE films graft copolymerized with the epoxy-based monomer, surface chain rearrangement was not observed or was less well pronounced, due to the partial crosslinking of the grafted chains. Simultaneous photografting and photolamination between two LDPE films, or between a LDPE film and a poly(ethylene terephthalate) (PET) film, in the presence of either monomer system, were also investigated. The photolamination rates and strengths depend on the ozone pretreatment time, the UV illumination time, and the UV wavelength, as well as on the nature of the substrate materials. A shear adhesion strength approaching 150 N/cm² could be achieved with either monomer system, provided that the polymer films were pretreated with ozone. The failure mode of the photolaminated surfaces was cohesive in nature in the case of the photoinitiator-containing epoxy monomer, but was either cohesive or adhesional in nature (depending on the substrate assembly) in the case of the photoinitiator-free AAc monomer.     

9-Anthryl and 1-pyrenyl groups as reporters of local environments and diffusion of two N,N-dialkylanilines in polyethylene films. Excited state lifetimes determine spatial information

Changes in the static and dynamic fluorescence from two covalently attached lumophores, 1-pyrenyl and 9-anthrylmethyl, induced by the diffusion of two N,N-dialkylanilines, N,N-dimethylaniline and N,N-dioctadecylaniline, within polyethylene films of 42% crystallinity have been examined. The longer lived excited singlet state of 1-pyrenyl is found to report on events occurring within a larger surrounding volume than the much shorter lived excited singlet state of 9-anthylmethyl. In addition, diffusion of N,N-dioctadecylaniline is found to be more rapid than expected on the basis of simple molecular volume considerations and to occur through two parallel pathways. The results suggest that lumophore lifetimes can be ‘tuned’ to interrogate different volumes of host space in polymers.     

Effects of preparation conditions on the morphology and gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films

In this study, the effect of film preparation conditions on the gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films (containing 18 and 28 wt% vinyl acetate) was investigated. Film blowing and phase inversion methods were applied in the production of PE and EVA films, respectively. The permeation of pure oxygen and carbon dioxide gases was measured at room temperature. The results indicated that with the increase of PE film thickness, permeability and solubility of O₂ and CO₂ in these films decreased; but the diffusivities of gases through PE films increased. In addition, in the case of EVA copolymers, by increasing the content of vinyl acetate, the permeability of CO₂ increased. The rate of increase in CO₂ permeability was different for samples having different preparation conditions. For example, the samples prepared using chloroform as the solvent instead of THF, showed lower CO₂ permeability. Also, the morphological studying of film structure indicated that the higher CO₂ permeability for the samples made from THF solvent is due to the existing of higher porosity in the under layer polymer area. Also scanning electron microscopy (SEM) micrographs showed that with the usage of phase inversion method, there will be a thin dense layer near to the glass substrate.     

Physical aging of thin glassy polymer films monitored by gas permeability

The physical aging at 35 °C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O₂, N₂, and CH₄, for over 200 days. Several techniques were used to accurately determine the thickness of films (∼400 nm-62 μm) in order to obtain absolute permeability coefficients and to study the effects of film thickness on the rate of physical aging. Each film was heated above the polymer T_g to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free volume, was observed at temperatures more than 150 °C below T_g for thin films of each polymer compared to what is observed for the bulk polymers. The films with thicknesses of approximately 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O₂/N₂ selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on physical aging were examined briefly.     

Surface modification of low density polyethylene films by homogeneous catalytic ozonation

Low density polyethylene films were treated by ozone to generate peroxides on the surfaces. The peroxides generated are capable of initiating radical graft polymerization of hydrophilic vinyl monomers onto the polymers, resulting in hydrophilic surfaces. Results of ozonation revealed that molecular ozone instead of hydroxyl radicals was the main oxidant for peroxide generation. A novel approach, aqueous ozonation with the addition of a soluble transitional metal salt, FeCl₃, as a homogeneous catalyst, was proposed and proved to be successful in this study. The addition of FeCl₃ could increase peroxide generation by 22.7%, compared to its non-catalyzed counterpart. An optimum catalyst concentration, 0.04 g/L, was determined. Also, the effects of pH, ozonation time and applied ozone dose on peroxide generation were investigated. The loss in tensile strength of the films would be 15% or less if the applied ozone dose was not over 2 wt.%. The functional groups generated on the film surfaces were characterized by FTIR, the contact angle and surface roughness of the film were also examined before and after ozonation.     

Two-phase modeling of a gas phase polyethylene fluidized bed reactor

A two-phase model is proposed for describing the behavior of a fluidized bed reactor used for polyethylene production. In the proposed model, the bed is divided into several sequential sections where flow of the gas is considered to be plug flow through the bubbles and perfectly mixed through the emulsion phase. Polymerization reactions occur not only in the emulsion phase but also in the bubble phase. Voidages of the emulsion and bubble phases are estimated from the dynamic two phase structure hydrodynamic model. The kinetic model employed in this study is based on the moment equations. The hydrodynamic and kinetic models are combined in order to develop a comprehensive model for gas-phase polyethylene reactor. The results of the model are compared with the experimental data in terms of molecular weight distribution and polydispersity of the produced polymer. A good agreement is observed between the model predictions and actual plant data. It has been shown that about 20% of the polymer is produced inside the bubble phase and as such cannot be neglected in modeling such reactors.     

Graphene/polyethylene nanocomposites: Effect of polyethylene functionalization and blending methods

Since its recent successful isolation, graphene has attracted an enormous amount of scientific interest due to its exceptional physical properties. Graphene incorporation can improve electrical and mechanical properties of polymers including polyethylene (PE). However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-fillers difficult without compatibilization. Graphene was derived from graphite oxide (GO) via rapid thermal exfoliation and reduction. This thermally reduced graphene oxide (TRG) was blended via melt and solvent blending with linear low density PE (LLDPE) and its functionalized analogs (amine, nitrile and isocyanate) produced using a ring-opening metathesis polymerization (ROMP) strategy. TRG was well exfoliated in functionalized LLDPE while phase separated morphology was observed in the un-modified LLDPE. Transmission electron micrographs showed that solvent based blending more effectively dispersed these exfoliated carbon sheets than did melt compounding. Tensile modulus was higher for composites with functionalized polyethylenes when solvent blending was used. However, at less than 3 wt.% of TRG, electrical conductivity of the un-modified LLDPE was higher than that of the functionalized ones. This may be due to phase segregation between graphene and PE, and electrical percolation within the continuous filler-rich phase.     

Yielding of polyethylene through propagation of chain twist defects: Temperature, stem length and strain-rate dependence

The temperature, the stem length and the strain-rate dependence of the yield stress of polyethylene (PE) is investigated via a modified crystal plasticity approach. Yielding is considered in terms of nucleation and propagation of [001] screw dislocations with Burgers vector c/2 due to migration of 180° chain twist defects. The stress-induced twist motion within the dislocation cores is modeled as an Eyring activated rate process. This gives an inelastic contribution to the dislocation core energy depending on the stem length and the strain rate and results in improved predictions of the crystal plasticity approach. The model is compared to available experimental data as well as to the predictions of the modified crystal plasticity approach proposed by Brooks and Mukhtar.     

Enhancement of the performance of gas hydrate kinetic inhibitors with polyethylene oxide

Inclusion of polyethylene oxide into a kinetic inhibitor solution was found to enhance the performance of the inhibitor. Polyethylene oxide is a commercially available high molecular weight polymer that is not a kinetic inhibitor by itself. The hydrate formation experiments in the presence of the various inhibitor solutions were conducted in a vessel in a semi-batch manner at constant pressure and using methane and methane-ethane gas mixtures. In some experiments a non-aqueous liquid phase (n-heptane) was also present. The induction time, the gas uptake and the temperature were measured. It was found that the induction time is prolonged in the presence of the additive by an order of magnitude in some cases compared to the inhibitor only.     

Blown films of nanocomposites prepared from low density polyethylene and a sodium ionomer of poly(ethylene-co-methacrylic acid)

A detailed study of the performance of blown films prepared from nanocomposites based on LDPE and a sodium ionomer of poly(ethylene-co-methacrylic acid) is reported. The organoclay content and film blowing conditions were varied to determine the effect of platelet concentration, exfoliation and orientation on film properties. Mechanical properties including stiffness, puncture resistance, and resistance to tear propagation were evaluated and compared to corresponding properties of unfilled polymer films. Permeability of the films to moisture and common atmospheric gases like oxygen, nitrogen, and carbon dioxide was also measured using standard testing methods.In general, films prepared from nanocomposites based on the ionomer exhibited greater improvements in mechanical and barrier properties over unfilled polymer compared to similar films prepared from nanocomposites based on LDPE. This is due to the greater degree of organoclay exfoliation achieved in the ionomer compared to LDPE. The addition of 3 wt% MMT to the ionomer increased the tensile modulus of blown films by an average of 50% without sacrificing much tear strength, puncture resistance or film extensibility. Gas permeability in these films was lowered by 40% and moisture transmission rate was reduced by 60%.     

聚乙烯塑料管的设计选择

概略介绍了聚乙烯塑料管的材料性能规格、作为压力管线的设计选择,以及管子安装的要求。     

聚乙烯催化剂的进展

叙述了聚乙烯催化剂的进展 ,着重介绍了高密度聚乙烯催化剂、茂金属聚乙烯催化剂和非茂有机金属聚乙烯催化剂。     

高分子量的单端氨基聚乙二醇的合成与表征

通过改进的Gabriel反应制备了单端氨基聚乙二醇(MPEG-NH2),用红外、1HNMR对MPEG-NH2的结构进行了表征。结果表明:制备出了高分子量的单端氨基聚乙二醇(MPEG-NH2),并且转氨率较高,在45%左右。     

Evaluation of the tear properties of polyethylene blown films using the essential work of fracture concept

In the case of very thin materials such as blown films, the applied stress state in front of the crack tip is normally a plane stress condition, and the deformation around the crack tip due to the remote stress is very large. However, current standard test methods for quantifying the fracture toughness of thin films, such as the Elmendorf tear test, cannot explain or represent the tear characteristics accurately. The common way of interpreting the test results from the Elmendorf tear test is to develop an empirical correlation and then compare the average values. In this paper, essential work of fracture (EWF) tests for five commercial polyethylene (PE) blown films have been conducted, and the fundamentals of their tear properties based on fracture mechanics have been studied. The results from the EWF test are interpreted based on two important parameters, i.e., the essential work of fracture (W_e) and the non-essential work of fracture (W_p). Further, the relationship between these parameters and the current standard Elmendorf tear test is shown.