An experimental study on the effect of polymer viscoelasticity on layer rearrangement in coextruded structures

Previous work on the layer thickness uniformity of coextruded structures has centered primarily on the effects of differing polymer viscosities in the individual layers. These differences in viscosities result in a phenomenon known as “viscous encapsulation” in which the less viscous layer tends to encapsulate the more viscous layer producing nonuniform layer thicknesses. In this study, the effect of polymer viscoelasticity on the layer thickness uniformity of multilayer coextruded structures was investigated by coextruding multilayer structures through die channels of different cross-sectional shapes and observing the location of the interface. In order to minimize the viscosity effects, the coextrusion experiments were conducted with identical materials in each layer that were pigmented to allow observation of the layer interface. It was shown experimentally that coextruding identical polymers through channels of various geometries can cause the layers to rearrange. This layer rearrangement appears to be caused by secondary flows that occur in different channel geometries due to the viscoelastic characteristics of the polymer. Layer rearrangement of identical polymers implies that even resins with viscosities well matched for coextrusion may experience nonuniform layer thicknesses when coextruded through large dies.     

LLDPE‐based mono‐ and multilayer blown films: Property enhancement through coextrusion

In this study we investigated the performance of multilayer coextruded linear low‐density polyethylene (LLDPE) blown films. Five‐layer films were compared with monolayer dry‐blended films, and the effects of layer composition and layout on the end‐use properties of the coextruded films were highlighted. Three different LLDPEs were used: a conventional Ziegler‐Natta LLDPE gas phase butene copolymer, an advanced Ziegler‐Natta LLDPE solution octene copolymer, and a single‐site LLDPE solution octene copolymer. Numerous five‐layer coextruded structures comprising the single‐site resin and the other two Ziegler‐Natta resins were produced. The coextruded structures composed of the LLDPE butene and the single‐site resin yielded improved end‐use properties relative to the monolayer‐blended films. This result was ascribed to the presence of interfacial transcrystalline layers. Also, blends of the single‐site LLDPE and the advanced Ziegler‐Natta LLDPE octene resins within selected layers of coextruded films showed slightly enhanced tear resistance. Finally, it was found that haze was significantly reduced when the outside layers were composed of the single‐site resin. POLYM. ENG. SCI., 45:1222–1230, 2005. © 2005 Society of Plastics Engineers     

Direct and Indirect Electron Microscopy of Encapsulated Nanocrystals

The structures of nanocrystalline solids encapsulated within single-walled carbon nantubes (SWNTs) are reviewed together with the methods used for their structural characterisation. The atomically thin channels formed within SWNTs allow their internal van der Waals surfaces to regulate the growth behaviour of encapsulated materials in a precise fashion. Crystalline growth is therefore atomically regulated and nanoscale crystals with precise integral layer architectures are formed that often show either deviations from the bulk or entirely novel structures. In order to characterise these materials extensive use has been made of electron microscopy, energy loss spectroscopy and image reconstruction. In particular the indirect recovery of the wave function at the exit plane of the specimen has enabled the detailed structures of these materials to be determined with improved accuracy.     

Oriented structure of PP/LLDPE multilayer and blends films

Polypropylene/linear low-density polyethylene (PP/LLDPE) multilayer and blends blown films are investigated in terms of crystalline morphology and orientation. The crystalline structures were probed using microscopy, infrared trichroism and X-ray pole figures. Two different PPs were used, one was a homopolymer and the other was a copolymer. Similar orientation characteristics were observed for both PP components in the blends and multilayer films, the PE component, however, showed very different structure, especially for the crystalline a- and b-axes orientation. The row-nucleated structure, epitaxial crystallization and transcrystallization observed in the films are discussed.     

Photodegradation of multilayer films based on PET copolymers

An investigation was conducted on the effects of photodegradation of multilayer films based on PET copolymers. The films were composed by different layers with PET, PET/PEN, and PET/PEI copolymers with a total thickness of 23 μm. The films produced by coextrusion followed by a biaxial orientation in an industrial equipment were exposed to the ultraviolet radiation in the laboratory for periods of up to 600 h. The samples were investigated by FTIR‐ATR, UV/visible spectroscopy, fluorescence spectroscopy, size exclusion chromatography, mechanical properties, and scanning electron microscopy. The results showed that the photooxidation is concentrated at the surface layers and that coextruded films were more sensitive to the UV radiation effects. The deterioration in mechanical properties with exposure and the fracture behavior were shown to be consistent with the amount of degradation that occurred in the films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Performance of polyethylene/ethylene-vinyl alcohol copolymer/polyethylene multilayer films using maleated polyethylene blends

Blends of linear low density polyethylene (LLDPE) and linear low density polyethylene grafted with maleic anhydride (LLDPE-gMA) were used to promote adhesion between LLDPE and ethylene-vinyl alcohol copolymer (EVOH) in a coextruded three layer flat film, trying to avoid the use of a tie layer. These particular films could be an option when the equipment for a five layer system is not available. The effect of the modified polymer on the surface of cast films was characterized through contact angle measurements. T-peel strength, and oxygen and water vapor transmission rate of the multilayer films were measured as a function of LLDPE-gMA content. Compressed films with 0%, 0.03%, and 0.08% of maleic anhydride (MA) were also analyzed by infrared spectroscopy (FTIR). The increased T-peel strength observed when using MA contents higher than 0.08% suggests a good interfacial adhesion between layers. This increase could be associated with specific interactions between the LLDPE-gMA and the EVOH, as the development of covalent bonds through the reaction of the anhydride with the EVOH hydroxyl groups across the interface. This was proved by the FTIR analysis that showed an increase in the ester band absorbance with an increase on the maleated polymer content and bonding time indicating that a chemical reaction occurred, at the interface. The observed changes on the oxygen and water vapor barrier properties of the films were not significant.     

Surface modification of polymers and practical adhesion

The, nature of polymer surfaces has received increasing attention as the use of these materials, in a variety of forms, increases yearly. Modifications of polymer surfaces for adhesion, friction, and diffusion oriented appiications have necessitated a careful analysis of the surfade region morphology (surface physics) and chemical properties of the surface layer (surface chemistry). The behavior of composite structures has involved the discipline of classical fracture mechanics. The orientation of polymeric species or additives which migrate to the interface may modify the wetting characteristics and, most certainly, the frictional properties in addition to the diffusion of penetrant species beyond the boundary layer. The above topics are discussed within the framework of recent analytical and theoretical developments in surface science. The findings of these recent studies have facilitated many exciting technological advances.     

Performance of multilayer films using maleated linear low-density polyethylene blends

Blends of linear low-density polyethylene (LLDPE) and linear low-density polyethylene grafted maleic anhydride (LLDPE-gMA) were prepared by melt mixing and then coextruded as external layers, with a central layer of polyamide (PA) on three-layer coextruded flat films. Blends with contents of 0% to 55 wt% of maleated LLDPE, on the external layers, were analyzed. The T-peel strength and oxygen and water vapor transmission rate of the films were measured. The surfaces of the peeled films were characterized using attenuated total reflection infrared spectroscopy (FTIR-ATR) and scanning electron microscopy (SEM). The observed increase in T-peel strength of the films with 10% and higher levels of maleated LLDPE in the blend suggests good interfacial adhesion between layers. This sharp increase in peel strength appears to be associated, besides interdiffusion, with specific interactions between polymers, as the bond formation between maleic anhydride and the polyamide end groups by in situ block copolymer formation across the interface. No significant modifications in oxygen barrier properties of the films were observed; however, the use of higher contents of LLDPEgMA, even though it increases the adhesion performance, also increases the water vapor transmission rate by a reduction in the degree of crystallinity.     

The effect of confined crystallization on high-density poly(ethylene) lamellar morphology

High-density polyethylene (HDPE) was co-extruded against high glassy transition temperature (Tg) polycarbonate (PC) to fabricate multilayer films. Melt and recrystallization experiments were conducted on these extruded films to study the effects of isothermal recrystallization temperature and layer thickness on HDPE lamellae orientation. WAXS and AFM were used to demonstrate lamellar morphology of HDPE layers. We report that HDPE lamellae show twisted morphology in 30 nm thin layers after confined crystallization at a high temperature (128 °C). It may be the first time that anyone has created such twisted lamellar morphology with HDPE in such a thin layer. Similar twisted morphology of HDPE was also observed when HDPE was coextruded with another high Tg glassy polymer, polysulfone (PSF). Interestingly, the twisted HDPE lamellar morphology associated with an increased crystallinity improves both the oxygen and water vapor barrier properties of the multilayer films.     

Cold sintering and co‐firing of a multilayer device with thermoelectric materials

Cold‐sintered ZnO and Ca₃Co₄O₉ polycrystalline materials were shown to have thermoelectric properties comparable to those of conventionally sintered ceramics. Extending these processing conditions into a cold sintering co‐fired ceramic (CSCC) technology, we integrated n‐type and p‐type thermoelectric oxides and a separating insulating layer to demonstrate functional multilayer thermoelectric generator devices. A co‐fired structure with an insulating 8 mol% yttria‐stabilized zirconia (8YSZ) layer enabled multilayer thermoelectric generators (TEG) to be fabricated with a 5 n‐p junction device (20 layers). A transmission electron microscopy analysis of the interfaces between the various materials under the co‐firing cold sintering showed some interdiffusion of chemical constitutes in a 2.0 μm interface region between the respective ceramic phases. The co‐firing of multilayer ceramic and polymer structures were also shown to be possible using insulation layers of polytetrafluoroethylene (PTFE) thermoplastic layers. This demonstrated the feasibility of a single‐step process for new structures with both ceramics and polymers, opening up new directions for many new device designs.     

Functional barriers in PET recycled bottles. Part II. Diffusion of pollutants during processing

Recycled plastics may be polluted by various chemicals available to consumers. When such materials are used to manufacture packaging materials intended to be in direct contact with food, these pollutants may migrate into food. The use of multilayer structures with a virgin polymer layer as a functional barrier may prevent such migration. This work deals with the possible diffusion of pollutants into and through the virgin layer during processing at high temperatures. A test is designed to measure diffusion coefficients in elastomeric and glassy polymers, in their molten state; 2.5‐dimethoxyacetophenone was used as a surrogate pollutant, and its concentration profiles are monitored by UV microscopy. Based on diffusion coefficients and on activation energies, glassy polymers appear to be much better barriers than polyolefins, even in their molten state. We then focus on poly(ethylene terephthalate) (PET) bottle preforms, processed by injection molding. In a first approach, a worst case situation was simulated by numerical analysis, using both overestimated diffusion coefficient values and very low values of activation energy. It appears that migration into foodstuffs through functional barriers can only be observed with unrealistic high diffusion coefficients and low activation energies. These results were confirmed by experimental determination of the concentration gradients of model pollutants in multilayer structures. It appears that little diffusion occurs, despite at a very high temperature. The effects of temperature and thickness of the functional barrier are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2859–2870, 2004     

Influence of vibrations on interface delamination in metal–polymer composites

The main objective of this work was the study of vibration effects on the viscoelastic coating protecting the steel layer in a metal–polymer composite, with simulated conditions of the transportation of food containers. Mechanical resonance tests in metal–polymer [electrolytic chromium-coated steel–poly(ethylene terephthalate) (PET)] sheets were performed to generate vibration conditions to induce structural modifications in the viscoelastic layer covering the surface of the plates. Consequently, schematic representations of the areas affected by these modifications were made. The modified structures were later analyzed by electron microscopy to detect and evaluate alterations in the morphology of the material. In addition, vibrational Raman spectroscopy analyses were performed to assess the chemical and structural changes on the protective PET at the metal–polymer interface level. The results of this study are expected to provide basic information on the mechanisms and nature of the delamination processes taking place in metal–polymer laminates employed in food-container applications. These damages have previously been detected in some food containers made of PET materials. The study of these damages can lead to the improvement of current composites or the development of higher quality materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

HDPE／PA6共混物层状挤出过程的数值分析

以ＨＤＰＥ／ＰＡ６在挤出机中共混并层状挤出的机理进行了数值分析。提出的ＨＤＰＥ／ＰＡ６／ＨＤＰＥ三层混合模型能处理熔体粘度随剪切速率和温度 二元共混物的层流混全,预测熔体的形变。数值计算的结果与选择工艺条件、得到合格的层状阻隔制品具有一定的指导意义。     

Hydrothermal syntheses of ETS-10 like vanadosilicates using chiral organic molecules. Part I

Vanadosilicates with the structures of ETS-10 and AM-6 microporous materials have been hydrothermally synthesized using organic directing structures agent (SDAs) derivatives of decahydroquinoline, 3,5-dimethyl-piperidine, 2,6-dimethyl-piperidine and (S)-Sparteine. Derivatives of these chiral amines have not been explored before in the sol gel chemistry of vanadosilicates. Physicochemical characterization of the obtained vanadosilicate materials with these different chiral templates was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and infrared (IR) spectroscopy, solid-state NMR spectroscopy, and differential thermogravimetric analysis (DTA)/thermogravimetric analysis (TGA). The results suggest that the presence of the chiral organic templates have different effects in terms of the final phase of the synthesized materials and their morphology. The products obtained using chiral template derivatives of decahydroquinoline reveal that certain products might be very enriched with chiral polymorph A while others present structures which are similar to other large-porous vanadosilicate such as AM-6 and AM-13. Derivatives of 2,6-dimethyl-piperidine and 3,5-dimethyl-piperidine have not favored any structure that resembles a chiral polymorph A, but only known vanadosilicates such as AM-6, AM-13. Derivatives of (S)-Sparteine, on the other hand, have not only favored the formation of structures enriched with a large amount of chiral polymorph A, but also their use has resulted in other unknown vanadosilicate structures whose physicochemical characterizations are in progress.     

In situ optical studies of metal deposition

The importance of microscopic morphological control to metal electro- and electroless deposition in several emerging technologies is discussed. The use of in situ optical probes of the morphological development of deposits is described. A number of these are reviewed to describe both the potential of each method and the available literature on studies of electro- and electroless deposition. Included are optical probes of the mass transfer boundary layer, X-ray diffractive and spectroscopic methods, ellipsometry, surface-enhanced Raman spectroscopy, infrared absorption spectroscopy, second harmonic generation and electroreflectance.     

Deformation mechanisms in polymer fibres and nanocomposites

This review covers the development of the understanding of the deformation micromechanics of both synthetic and natural polymeric fibres using spectroscopic and X-ray diffraction techniques. The concept of fibres as composites, where hard and stiff phases are combined with softer polymeric materials is also discussed. Starting with the first discoveries on the molecular orientation and morphology of polymeric fibres, the widely used concepts of uniform stress and strain are examined for the analysis of fibre deformation. The use of advanced techniques such as Raman and infrared spectroscopies to follow molecular deformation in both rigid-rod (e.g. PpPTA, PBO, PBT, polyethylene) and natural (e.g. cellulose, collagen, silk, chitin) polymer fibres is presented. A clear distinction between fibres that have structures that are subjected to uniform stress or strain is presented, with the evidence that is detected from the response of the molecules (by Raman spectroscopy) and the crystalline fraction (by X-ray diffraction). It is suggested that natural fibres, such as cellulose, silk and others, may have different types of microstructures that are subjected to a uniform strain, which could have potentially led to incorrect determinations of crystal moduli. It is also demonstrated that the Raman and X-ray techniques have been influential on our development of fibres, and have shown that the morphology plays a critical role in mechanical properties. In addition to this, the use of X-ray diffraction using microfocus synchrotron sources is also reviewed. This approach allows a more complete picture of both molecular and crystalline deformations to be developed, and with the advent of nanocomposites it is shown that a combination of the two techniques will be vital for our understanding of their exploitation in technological applications.     

Orientation distribution and layerlike morphology in extrusion-molded sheets of a liquid crystalline copolyester amide

Fracture surface morphology and orientation distribution in the extrusion-molded sheets of a thermotropic liquid crystalline copolyester amide were investigated by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and polarized Fourier transform infrared (FTIR) microspectroscopy. The layerlike morphology consisting of two outer layers and a central layer between them was observed on the fracture surface. The microscopic orientation functions in the extrusion-molded sheets were evaluated from the polarized FTIR microspectra that were measured in the microscopic domain 40 μm wide using a redundantly apertured infrared microscope. The microscopic orientation function in the outer layer was shown to be higher than that in the central layer. The effects of the draw-down ratio and extrusion temperature on the orientation distribution and the layerlike morphology are discussed. © 1993 John Wiley & Sons, Inc.     

Effects of montmorillonite on structures and properties of injection-molded polypropylene

A nanocomposite of polypropylene with montmorillonite (PP-MMT) was prepared via melt blending. The structures and properties of PP-MMT were studied by differential scanning calorimetry, polarized optical microscopy, transmission electron microscopy (TEM), and wide-angle X-ray diffraction (WAXD). The orientation behaviors of both MMT and PP in an injection-molded specimen were revealed by TEM and WAXD. The results indicate that the specimen displays a multilayer structure: in the inner layer, the long axes of MMT stacks are parallel to the transverse direction (TD) of the specimen and the b-axes of PP crystallites are perpendicular to the TD; whereas in the outer layer, the long axes of MMT are perpendicular to the TD and the b-axes of PP crystallites are parallel to the TD. The orientation of PP crystallites in PP-MMT is much lower than that in pure PP, which results in lower molding shrinkage of PP-MMT. Structure–property relationship of PP-MMT was discussed with a conclusion that a moderate improvement in performances of PP-MMT might be derived from the intercalated dispersion and special orientation of MMT stacks. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47442.     

An Introduction to High-resolution EELS in Transmission Electron Microscopy

The practical advantages of an electron monochromator for electron energy-loss spectroscopy (EELS) in transmission electron microscopy are described. Typical examples from materials and nanoparticle research demonstrate the use of EELS with high energy and spatial resolution. Recent instrumental developments are also reviewed with a discussion of how the technique could be used to study catalyst structures of the future.     

Multifunctional Silver Nanoparticles-Decorated Silica Functionalized with Retinoic Acid with Anti-Proliferative and Antimicrobial Properties

The paper describes a rapid and simple method for preparing a multifunctional biomaterial based on retinoic acid covalently bound on silica@Ag particles. Monodispersed SiO₂ particles were prepared by Stöber method and further used for loading the Ag nanoparticles on their surface. This composite was further functionalized with retinoic acid. Characterization of the hybrid materials was made by UV–Visible spectroscopy, Transmission electron microscopy, Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Thermal analysis. The biological evaluation of the obtained materials revealed their potential use for multiple biomedical applications, from anti-proliferative agents to novel antimicrobial and antibiofilm strategies.