Rheological,thermal, and mechanical properties of poly(ethylene naphthalate)/poly(ethylene terephthalate) blends

Structural, Theological, thermal, and mechanical properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) obtained by melt blending were investigated using capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) observation, tensile testing. X-ray diffraction, and ¹H nuclear magnetic resonance (NMR) measurements. The melt Theological behavior of the PEN/PET blends was very similar to that of the two parent polymers. The melt viscosity of the blends was between that of PEN and that of PET. Thermal properties and NMR measurement of the blends revealed that PEN is partially miscible with PET in the as molded blends, indicating that an interchange reaction occurs to some extent on melt processing. The blend of 50/50 PEN/PET was more difficult to crystallize compared with blends of other PEN/PET ratios. The blends, once melted during DSC measurements, almost never showed cold crystallization and subsequent melting and definitely exhibited a single glass transition temperature between those of PEN and PET during a reheating run. Improvement of the miscibility between PEN and PET with melting is mostly due to an increase in transesterification. The tensile modulus of the PEN/PET blend strands had a low value, reflecting amorphous structures of the blends, while tensile strength at the yield point increased linearly with increasing PEN content.     

Transmission Electron Microscopic Investigation of the Morphology of High-Speed Spun Poly(Ethylene Terephthalate) Fibers

Permanganic etching was performed on high-speed spun (HSS) and regular fibers of poly(ethylene terephthalate) (PET), and their surface morphologies were investigated via the two-stage carbon replica method using a transmission electron microscope (TEM). The HSS PET fibers, with disordered amorphous regions, showed peculiar surface morphology; many small warts corresponding to the pits of etched disordered amorphous regions were observed. Such unevenness, however, was hardly observed on the surface of the permanganic-etched regular PET fibers, with well-oriented amorphous regions, or on the surface of alkali-etched HSS PET fibers. The permanganic etchant removed the disordered amorphous regions more preferentially compared with the alkali etchant.     

Effect of temperature on the intrinsic viscosity of poly(ethylene glycol) in water/dimethyl sulfoxide solutions

In this work, the intrinsic viscosities of poly(ethylene glycol) with molar mass of 20 kg mol^− 1 were measured in water/dimethyl sulfoxide solutions from (298.15 to 318.15) K. The expansion factors of the polymer chains were calculated from the intrinsic viscosity data. The expansion factor were decreased by increasing temperature; therefore the chain of PEG shrinks and the end-to-end distance become smaller by increasing temperature. Perhaps the interactions of segment-segment are favored toward segment-solvent by increasing temperature; therefore the hydrodynamic volumes of the polymer coils become smaller by increasing temperature. The thermodynamic parameters (entropy of dilution parameter, the heat of dilution parameter, theta temperature and polymer-solvent interaction parameter) were derived by the temperature dependence of the polymer chain expansion factor. The thermodynamic parameters indicate that the interactions of segment-segment were increased by increasing temperature.     

Effect of intercalation on electrical and mechanical properties of C/C composites

The work is concerned with modification of C/C composites by intercalation of copper chloride. The samples of composites were made from graphite fibres and carbon matrix derived from mesophase pitch and from phenol-formaldehyde resin. The samples were prepared by impregnating graphite fibres with a liquid pitch or polymer solution to obtain unidirectional laminates. The laminates were used to prepare the composites which were then subjected to carbonization and graphitization up to 2150 °C. The work discusses the problem relevant to the effect of intercalation on mechanical and electrical properties of composites. The studies indicated that both mesophase pitch-based composites and phenolic-derived carbon-carbon composites changed their electrical and mechanical properties upon intercalation with copper chloride. Electrical conductivity of both types of composites decreased as a result of the damages formed during intercalation.     

Effect of Dispersion of Carbon Black on Electrical and Thermal Properties of Poly(Ethylene Terephthalate)/Carbon Black Composites

A type of grafted carbon black (GCB), prepared with a low molecular weight antioxidant compound by in-situ reaction, was dispersed in poly(ethylene terephthalate) (PET) by a melt-blending process. Dispersion of fillers, volume resistivity, and thermal properties were investigated using scanning electron microscopy, a high-resistance meter, differential scanning calorimetry, and thermogravimetric analysis, respectively. The results show that, compared with carbon black (CB) particles, GCB particles dispersed better in the PET matrix, whereas the conductivity percolation threshold of PET/GCB was higher than that of PET/CB. The addition of GCB or CB elevated the cold crystallization temperature of PET, reflecting the effectiveness of carbon fillers as nucleating agents. But carbon fillers decreased the crystallization enthalpy of PET during both heating and cooling process. Both CB and GCB elevated the starting temperature of thermal degradation of PET and increased the amount of residues for the composites over that of neat PET.     

On the molecular mechanism of the crystal transformation (tetragonal-hexagonal) in polybutene-1

The phase transformation from the tetragonal to the hexagonal crystal modification in highly oriented lamellae of poly-butene-1 has been followed by transmission electron microscopy (TEM). It is found that the reaction-controlling step is the nucleation process. No lattice orientation relationship (besides the [001]-direction, which is parallel in both crystal modifications) exists between non-transformed and transformed crystals. The nucleation is strongly enhanced by thermal or external stresses. Crystal growth, nucleated by external stresses, was observed at temperatures as low as — 150°C. The molecular mechanisms of the transformation are discussed.     

Electroless plating of nickel–phosphorous on surface-modified poly(ethylene terephthalate) films

Chemical surface preparation for Ni–P electroless metallization of poly(ethylene terephthalate) (PET) films without using Chromium-based chemicals, was studied. The applicability of this method was verified by a subsequent metallization process. Thermal analysis was conducted to observe the main thermal transitions and stability of the polymer and metallized films. Contact angle analysis was performed to assess the surface hydrophilicity so as to optimize the substrate preparation process. X-ray diffraction, EDAX and SEM analysis were used to understand the composition and morphology of the polymeric substrate and Ni–P coat growing process. Adherence strength, contact sheet resistivity and optical diffuse reflection were measured on the metallized films. The time of chemical etching affects the polymer surface hydrophilicity, polymer/metal adherence strength, surface resistance and optical diffuse reflection, while Ni coating morphology is controlled by the pH of the electroless bath. High wettability of the polymer surface, adherence strength of 800 N cm⁻², high optical diffuse reflection and low surface resistivity of the Ni coating, were found for films etched for 60 min. Metallizations performed at pH 7.5 produce Ni–P coatings with 12.0 wt.% phosphorous content, which were amorphous and flexible. The contact sheet resistivity of the plated films is sensitive to roughness variations of the substrate. The method proposed in this work allows the production of metallized films appropriate for the fabrication of flexible circuits.     

In-situ SAXS study on PET/ PMMT composites during tensile tests

The nanostructures during the tensile drawing of poly(ethylene terephthalate)(PET)/hexadecyl triphenyl phosphonium bromide montmorillonite(PMMT) nanocomposites were studied by in-situ small angle x-ray scattering. For strain higher than the yield point, the scattering intensity increases dramatically due to the nucleation and growth of nanovoids and crystals. The nanovoids and crystals are significantly dependent on the heating temperature. The effective filling of PMMT in the PET matrix provokes a strong restriction to the long period. The peaks of the long period disappear gradually with the deformation strain increasing from 0% to 34%.     

Sono-assisted preparation of bio-nanocomposite for removal of Pb2+ ions: Study of morphology,thermal and wettability properties

Multi-walled carbon nanotubes (MWCNT) loaded poly(ethylene terephthalate) (PET) composites, with different CNT contents, were fabricated through an ultrasound assisted method as a fast and green way. Then, the obtained composites were fully characterized via FT-IR, UV–Vis, XRD, TGA, FE-SEM and TEM, etc. For this purpose, PET bottle was recycled and applied as matrix of nanocomposites (NC)s. Then, we dispersed the covalent functionalization of MWCNTs with a protein dispersant and obtained a powder of protein-functionalized CNTs. Bio-functionalized MWCNTs showed higher Pb²⁺ removal efficiency compared to MWCNT-COOH as ascertained via batch equilibrium adsorption experiments. Also, the results indicated the novel NCs presents a high affinity for Pb²⁺ heavy metal owing to the presence of several good sites. The contact angle results indicated that the addition of MWCNT-BSA increased significantly the contact angle compared to the pure PET. It was concluded that inflame retarding feature of NC was higher than pure polymer.     

Dielectric study of polyaniline/poly (methylmethacrylate) composite films below the percolation threshold

We report results of dielectric relaxation studies of polyaniline/poly(methylmethacrylate) composites with polyaniline amount less than the percolation threshold in the frequency range of 0.1 Hz to 1 MHz and temperature range of 10 °C–170 °C. We find a significant dependence of the glass transition temperature Tg on the polyaniline amount in the composite. α and β relaxation processes relative to the PMMA matrix are also affected by the presence of polyaniline inclusion. We identify a relaxation process due to ionic conductivity and another process attributed to residual solvent. The characteristic relaxation frequency of each process and the activation energy depend on the polyaniline amount in the composite. The ac conductivity in the high frequency range is fitted to the universal power law of Jonscher characteristic of disordered materials.     

Epitaxial crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene

Crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene (PTFE) was studied. Further, cold-drawn polyethylene (PE) was heat treated in contact with drawn PTFE, holding their drawing axes at right angles to each other, and then the morphological change of PE at the interface was studied. Molecular orientation in the surface layer of the PE was examined by observing the molecular orientation of polycaprolactone (PCLn) crystallized on the PE surface.

It was found that PE, PCLn, and nascent nylon 6 crystallize epitaxially on drawn PTFE, which is well known as a polymer having a low energy surface. Intermolecular interaction between PTFE and the overgrown crystalline polymers was explained on the basis of their crystal structures. The molecular orientation of PE in the interfacial region changes from the drawing direction of PE to the drawing direction of PTFE during annealing. It is proposed that PE partially melts during annealing, and nuclei of PE with their c-axis parallel to the molecular axis of PTFE are formed at the interface. Consequently, PE lamellar crystals with their c-axis perpendicular to the original drawing direction grow in the interfacial region between PE and PTFE.     

Effect of viscosity on the magnetic permeability of Sendust-filled polymer composites

A flake-shaped Sendust/acryl suspension is tape cast and the effect of the viscosity of the suspension on the magnetic permeability of the resulting composite is investigated. The real part of the permeability of the composite is inversely proportional to the viscosity of the suspension, indicating that the lower the viscosity of the suspension, the higher the permeability of the composite. The viscosity of the suspension is controlled by adding a small amount of surfactant; an anionic surfactant is most effective for lowering the viscosity at a given concentration range. It is thought that using a suspension with a relatively low viscosity improves the permeability of the resulting composite due to the easy alignment of the flake-shaped filler with the plain direction of the sheet.     

Mechanical Behavior of Bulk Poly(Ethylene Terephthalate) Subjected to Simple Shear

Abstract

Mechanical behavior of bulk semicrystalline poly(ethylene terephthalate) (PET) processed through simple shear is investigated. The equal channel angular extrusion (ECAE) process was used to achieve the simple shear condition. The PET samples were processed in one and two ECAE passes in the same direction, with the sample rotated 180° about the extrusion axis for the second pass. Microstructural features at the nanometer and micrometer scales were studied by small‐angle x‐ray scattering (SAXS) and scanning electron microscopy (SEM). SAXS results showed that at the nanometer scale, two types of lamellar orientations are induced in both samples, but with different extents of orientation. In the ECAE‐oriented PET structures on the micrometer scale, as revealed by SEM, are well‐defined macrofibrils. However, the fibrillar structures in the sample extruded once are more oriented than those in the sample extruded twice. Fractography investigations suggest that the ECAE‐induced fibrillar structure and stretched amorphous chains are responsible for the change in mechanical properties.     

Model calculation of ion collection in the presence of sputtering

This paper presents a zero order approximation of ion collection during sputtering. Neglecting diffusion, range shortening and knock-on effects and assuming a constant sputtering yield general analytical results are developed which allow a comparison with experimental data. The accumulation of implantation profiles and the build-up of surface concentrations and collected quantities are described in detail for Gaussian range distributions. A thorough discussion of available experimental results indicates that the model is suitable for a variety of projectile-target combinations, in particular for medium mass noble gas atoms collected in high melting point targets. Application to sputtering experiments presents further evidence of a strong fluence dependence of the silicon sputtering yield. Some comments are devoted to recently reported analytical and numerical treatments of ion collection during sputtering.     

Fibrillar crystals of isotactic polystyrene. I. Morphological aspects

Fibrillar crystals have been prepared by the crystallization of isotactic polystyrene from stirred solutions in 1,3,5-trimethylben-zene and cyclohexanol. Similar microfibrils have been prepared in the nascent state by the polymerization of styrene in 1,3,5-trimethyl-benzene with a heterogeneous Ziegler-Natta catalyst. The microfibrils varied in width between 140 and 250 Å and were characterized by periodic lamellar overgrowths which were believed to give rise to a discrete X-ray reflection having a d-spacing of 90 A. Thermal analysis suggested that high growth temperatures favored greater crystal perfection. During crystallization from stirred cyclohexanol solutions, a fractionation of high molecular weight chains occurred which was more efficient at higher crystallization temperatures. In comparison to crystallizations under quiescent conditions, a marked facility of the crystallization process was observed in the formation of stirrer-crystallized and Ziegler-Natta polystyrene. The ease of crystallization of the shear-regenerated and nascent microfibrils has been related to a reduction in the free energy of nucleation. Mechanisms have been proposed to account for a favored nucleation process.     

高直流电场下PET薄膜的电致发光及其可靠性

用自制电致发光(Electrolum inescence-EL)测量装置测试了直流高电场下聚对苯二甲酸乙二酯[poly(ethylene terephthalate)-PET]薄膜EL的光强和光谱。实验表明:PET的发光光强随所加电场而增大,在4.00MV/cm附近发生预击穿。EL光谱在300~400nm、400~460nm、500~600nm和680nm附近存在发射峰,其中500~600nm峰带相对较强,预击穿信号出现后680nm附近的峰带增加很快。为了评价PET的介电性能,本文对实验数据用双参数Weibull分布解析法计算,得出了该薄膜在(24±1)℃,阶跃加压条件下的寿命和击穿电场的累积失效概率和可靠度方程,Weibull假设检验结果表明,实验结果服从Weibull分布。     

Void effect on mechanical properties of copper nanosheets under biaxial tension by molecular dynamics method

The relationship between void size/location and mechanical behavior under biaxial loading of copper nanosheets containing voids are investigated by molecular dynamics method. The void location and the void radius on the model are discussed in the paper. The main reason of break is discovered by the congruent relationship between the shear stress and its dislocations. Dislocations are nucleated at the corner of system and approached to the center of void with increased deformation. Here, a higher stress is required to fail the voided sheets when smaller voids are utilized. The void radius influences the time of destruction. The larger the void radius is, the lower the shear stress and the earlier the model breaks. The void location impacts the dislocation distribution.     

Investigation of the optical anisotropy of PET and PEN films by VIS-FUV to IR spectroscopic ellipsometry

In the last years, a significant amount of research is being performed in the field of polymer research for novel applications, such as flexible electronic devices, photovoltaic cells, high performance optics, data storage, etc. Toward this direction, in this work, the optical anisotropy of biaxially stretched poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) films has been extensively investigated. The optical properties of the films have been studied in terms of their optical, electronic and vibrational response, by Fourier transform IR spectroscopic ellipsometry (FTIRSE) (900-3500 cm⁻¹) and Vis-fUV variable angle SE (1.5-6.5 eV) techniques. The films optical anisotropy is the result of the stretching procedure during their fabrication, which results to the structural rearrangement of the macromolecular chains parallel to the stretching direction and to a higher structural symmetry. During the SE spectra analysis, the films have been approximated as uniaxial materials with their optic axis parallel to the sample/ambient interface leading to the accurate determination of the principal components ?_||(ω) and ?_⊥(ω) of the dielectric function ?(ω). The detailed study of the electronic transitions has been performed in the Vis-fUV region, where the characteristic features corresponding to the n → π* electronic transitions of the carbonyl -CO group and the ¹A_1g → ¹B_1u transition due to the π → π* excitation of the π-electron structures have been identified and analysed. Furthermore, the FTIRSE spectra allowed the accurate identification and assignment of the features of ?(ω) to the vibrational modes of the various bonding structures characteristic of the PET and PEN macromolecular chains.     

Combined meso-scale modeling and experimental investigation of the effect of mechanical damage on the transport properties of cementitious composites

The transport properties of cementitious composites such as concrete are important indicators of their durability, and are known to be heavily influenced by mechanical loading. In the current work, we use meso-scale hygro-mechanical modeling with a morphological 3D two phase mortar-aggregate model, in conjunction with experimentally obtained properties, to investigate the coupling between mechanical loading and damage and the permeability of the composite. The increase in permeability of a cylindrical test specimen at 28% aggregate fraction during a uniaxial displacement-controlled compression test at 85% of the peak load was measured using a gas permeameter. The mortar's mechanical behavior is assumed to follow the well-known compression damaged plasticity (CDP) model with isotropic damage, at varying thresholds, and obtained from different envelope curves. The damaged intrinsic permeability of the mortar evolves according to a logarithmic matching law with progressive loading. We fit the matching law parameters to the experimental result for the test specimen by inverse identification using our meso-scale model. We then subject a series of virtual composite specimens to quasi-static uniaxial compressive loading with varying boundary conditions to obtain the simulated damage and strain evolutions, and use the damage data and the previously identified parameters to determine the evolution of the macroscopic permeability tensor for the specimens, using a network model. We conduct a full parameter study by varying aggregate volume fraction, granulometric distribution, loading/boundary conditions and “matching law” parameters, as well as for different strain–damage thresholds and uniaxial loading envelope curves. Based on this study, we propose Avrami equation-based upper and lower bounds for the evolution of the damaged permeability of the composite.