Properties of a mechanically processed polymeric material

A semicrystalline polymer, polyamide, was processed using a new technique. The technique is that of mechanically grinding the material using large inputs of energy at temperatures below the glass-transition temperature and then later reconstituting the material by applying pressure and holding at a temperature below its melting point for a period of time. This technique is normally known as mechanical alloying and only very recently has been applied to polymeric materials. The mechanical properties of strength, ductility, toughness, and hardness of polyamide material processed by this technique are investigated and compared with those of polyamide material processed by other techniques. The results indicate that altered mechanical properties occur with specific enhancements. This means that useful structural components can be made from polymers using this processing technique. The analysis of x-ray diffraction, nuclear magnetic resonace, scanning electron and optical microscopy suggests that this process has resulted in considerable alteration of both crystal structure and microstructure of this polymeric material. © 1994 John Wiley & Sons, Inc.     

In‐line monitoring of the injection molding process by dielectric spectroscopy

In recent years, electrical techniques like microdielectrometry have increasingly been utilized for their ability to continuously monitor, in a nondestructive way, the advancement of the reaction of thermoset resins under cure. This paper discusses an extension of this technique for the “in‐situ” monitoring of the crystallization of thermoplastics applied during an injection molding process. Electric sensors were positioned at the walls of the mold cavity so that an analysis of the volume dielectric properties of material during the filling, the post‐filling, and the cooling steps could be carried out. Poly(vinylidene fluoride) was chosen for this study. A correlation between the evolution of the dielectric parameters and the succession of the steps in this process was undertaken. The dielectric response was sufficiently sensitive to identify the steps of the closing of the mold, filling, post‐filling, cooling, and ejection of the part. In addition, information concerning the crystallization phenomenon near the wall or in the middle of the sample was collected. The gradual filling of the cavity of the mold was also identified by dielectric measurements. The temperature dependence of dielectric properties of the sample was beneficial in evaluating the increase of the temperature of the mold with the succession of injection cycles. The influence of the packing pressure has been clearly identified and confirms the usefulness of the dielectric method as a probe for detecting the shrinkage of the part during the optimization phase of the machine parameters. The dielectric method detailed herein provides a new non‐invasive technique and could be applied to a closed‐loop control of the injection molding process.     

Nanomaterials for Heterogeneous Combustion

Nanophase materials and nanocomposites, characterized by an ultra fine grain size (less than 100 nm) have attracted wide spread interest in recent years by virtue of their unusual mechanical, electrical, optical, magnetic, and energetic properties. Studies have shown that the thermal behavior of nano‐scaled materials is quite different from micron‐sized powders. Nanosized metallic and explosive powders have been used as solid propellant and explosive mixtures to increase efficiency. At the same time recent studies reveal that the presence of nanosized metals in propellants does not necessary translate into an increased burning rate and burning temperature. The reasons of this effect are far from being clear. This paper presents a new approach to the production of nanocomposites of some energetic materials – ammonium nitrite, cyclotrimethylene trinitramine (RDX), and aluminum – by the vacuum co‐deposition technique. The thermal behavior of the synthesized nanopowder and nanocomposites is investigated. A substantial difference in burning rate of RDX nanopowder has been found in comparison to micron‐sized material. Experimental results allow investigating the effects of nanosized materials on the combustion characteristics.     

The evolution of enzymatic interesterification in the oils and fats industry

Immobilised lipases have now become accepted as a mainstream technology for fat modification. This paper presents the development of this technology in particular for the production of trans‐free fats. One of the factors influencing this development has been concern for health, which has made trans fats a major issue for food manufacturers and consumers. Enzymatic interesterification is a relatively new method for producing trans‐free alternatives for fats used in conventional margarines and shortenings. The development of this technology is examined from the perspective of an eventual industrial application rather than operation only at the laboratory scale. This paper also covers the practical means of operating immobilised enzyme columns and gives examples of how formulations can be adapted to match existing specifications. There are environmental benefits when choosing enzyme technology in comparison with chemical‐based routes. Life cycle assessments have been used to quantify the differences in environmental impact of this new technology. The final process is both capable of providing fats with the correct melting properties but without trans fats and of reducing the environmental impact of fat processing. Finally, the future developments that are anticipated in the applications of this technology are considered.     

A thermally stimulated depolarization current study of polymers in the glass transition region

The low‐frequency dielectric properties of a number of polymers, composites and blends have been studied using a thermally stimulated depolarization current (TSDC) apparatus that was designed and constructed in‐house. The TSDC technique can be used to determine the glass transition of a polymer sample. This TSDC glass transition temperature has been shown to be very similar to that obtained from differential scanning calorimetry (DSC). The actual difference between these two values depends on the heating rates used with each technique, however. TSDC data can also be combined with AC dielectric data to produce a data set, which possesses a very wide frequency range. Finally, individual TSDC relaxation peaks can be fit with the Williams‐Walts distribution function to obtain an estimate of their distributions. This is especially useful when studying polymer blends, but could also be utilized in the study of other systems.     

Interface porosity in multilayered all‐conducting polymer electrodes

Multilayered films made with at least two different electroactive polymers, in which the least conducting one acts as a dielectric and separates the layers made with the other, behave as efficient electrodes for electrochemical supercapacitors. In this work, we present a simple strategy to develop improved multilayered electrodes with structured interfaces by enhancing the porosity of the dielectric. This has been achieved by growing sodium chloride crystals onto a conducting polymer layer and, after generation of all required layers using the layer‐by‐layer electrodeposition technique, salt crystals have been eliminated by water etching. Results from morphological and topographical studies on single‐layered poly(3,4‐ethylenedioxythiophene) (PEDOT), poly(N‐methylpyrrole) (PNMPy), and poly(3,4‐ethylenedioxythiophene‐co‐N‐methylpyrrole) (COP), as well as electrochemical investigations on bi‐layered films with enhanced porosity at the interface between the two layers, have been used to design new four‐layered electrodes. These consist in two layers of PEDOT separated by two layers of nanosegregated COP with a porous interface in the middle. Although the properties of the new four‐layered electrodes improve due to the porous interface, the highest specific capacitance corresponds to the two‐layered electrode in which two PEDOT layers are separated by an ultra‐porous interface. POLYM. ENG. SCI., 59:1624–1635 2019. © 2019 Society of Plastics Engineers     

Orthotropic elastic constants for polyimide film

The orthotropic constants of polyimide film have been characterized using the theory of elasticity of an anisotropic material. Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 shear moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vibrational holographic interferom‐etry is used to determine the orthotropic axes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions. It is also used to evaluate the 2 in‐plane Poisson's ratios by measuring residual stresses in 2‐D and 1‐D square membranes. Using other instruments such as a high pressure gas dilatometry apparatus, a tensile tester, a pressure‐volume‐temperature apparatus, a thermornechanical analyzer, and a torsion pendulum, the 7 other orthotropic constants and the 3 coefficients of thermal expansion are determined.     

A kinetics study in CSTR using simultaneous temperature scanning and composition modulation: The alkaline hydrolysis of ethyl acetate

This work presents a new technique for reaction kinetic studies of liquid phase reactions in a CSTR. By simultaneously varying the reaction temperature (temperature scanning—TS) and reactant feed concentration (composition modulation—CM) while recording the output concentration, the technique allows, through the least‐square fitting of computer‐generated model data to the experimental time‐series, to obtain from a single experiment the reaction orders as well as both Arrhenius parameters. The alkaline hydrolysis of ethyl acetate was chosen to illustrate the technique, assuming a rate law in the form of a simple power law. The set of parameters that resulted in the minimum sum of squared errors was selected. These values were very close to those reported in literature. The technique saves much time and experimental resources.     

A new method for the measurement of dynamic shear mechanical properties of materials with a rheovibron viscoelastometer

The Rheovibron viscoelastometer is useful for obtaining dynamic tensile mechanical properties of films and fibers over a wide temperature range. Numerous studies of dynamic tensile mechanical properties have been made in the temperature range of ?160°C to 250°C in an atmosphere at 0% relative humidity. However, no studies exist which show the measurement of dynamic shear mechanical properties of materials using the Vibron instrument. A new shear grip and procedure was developed for measuring dynamic mechanical properties of material in the shear mode using the Rheovibron instrument. The dynamic shear properties on a polyurethane elastomer and polyester film are presented. This technique will be useful in studies on the dynamic shear characterization of materials in conjunction with end use performance.     

An apparatus for the measurement of dynamic mechanical properties of polymers in a gas medium with the vibron viscoelastometer

The Vibron Viscoelastometer is useful for obtaining dynamic mechanical properties of film and fibers in atmospheres at 0 and 100% relative humidity. No apparatus has previously been available for obtaining dynamic mechanical properties in a gas medium; however an apparatus and procedure have been developed for measuring these dynamic properties in a gas medium using the Vibron instrument. This technique will be useful in studies on the effects of different gases on polymers in the process and on the effects of gas treatments on materials. A new gas cell which is adaptable for other mechanical testing instruments such as the Instron, Tensometer, and Torsion Pendulum is also discussed.     

Characterizing residence times of powder samples on sieves

Recently developed in the author's laboratory, particle chromatography is the most powerful technique in existence both for characterizing and separation particles in the 1 μ to 1 cm size range. Operating on the principle that for a given size seive, a particle of a given shape has a fixed residence time, cascading the particles through n identical sieves separates particles on the basis of shape. The first of a family of instruments, using this new technique, is called the Sieve Cascadograph, and is specifically designed to characterize naturally occurring and manufactured powders such as abrasives and comminuted material, food grains such as wheat and corn, and naturally occurring materials such as sand and soils. Capable of separating particles with subtle differences in shape, the Sieve Cascadograph is a good laboratory or quality control instrument for quantitative differentiation between similar powder samples.     

Yield modeling of an aliphatic polyketone terpolymer in multiaxial stress states

A continuum yield model for pressure dependent anisotropic materials that accounts for the stress state has been combined with a thermally activated model to account for the temperature and rate dependence of yield stress. The resulting model has been applied to describe the yield behavior of a semicrystalline aliphatic polyketone terpolymer. Utilizing biaxial data from this thermoplastic, best‐fit values for loading along principal directions were determined. With these principal values, predictions for the yield strength under biaxial loading conditions were made. These predictions have been compared to experimental data obtained from the material at four different temperatures and three different strain rates. The experimental and theoretical results appear to compare quite well with each other.     

Studies of IR‐Screening Smoke Clouds

This paper contains some results of research on the IR‐screening capability of smoke clouds generated during the combustion process of varied pyrotechnic formulations. The smoke compositions were made from some oxygen or oxygen‐free mixtures containing metal and chloroorganic compounds or mixtures based on red phosphorus. The camouflage effectiveness of clouds generated by these formulations was investigated under laboratory conditions with an infrared camera. The technique employed enables determination of radiant temperature distributions in a smoke cloud treated as an energy equivalent of a grey body emission. The results of the analysis of thermographs from the camera were the basis on which the mixtures producing screens of the highest countermeasure for thermal imaging systems have been chosen.     

An ignition criterion for combustible solids integrating surface temperature and heating rate

Surface ignition temperature has been widely used as an ignition criterion for the piloted ignition of common combustible solids. However, experimental observations have shown that the surface temperature of a solid at ignition varies with external heat flux. In addition, if the external heat flux is smaller than the critical heat flux for ignition, the solid will not ignite while the actual surface temperature may be higher than the defined surface ignition temperature. To overcome these limitations and maintain the simplicity of the surface ignition temperature criterion, a new ignition criterion integrating heating rate and surface temperature is proposed, developed, and validated. Predictions based on the new criterion compare well with experimental results on piloted ignition of a thermoplastic material (black PMMA), a thermoset composite material (E‐glass fiber reinforced polyester composite) and a cellulosic material (Red Oak) subjected to different heat flux levels. Potential factors affecting the accuracy and predictive capability of the new heating rate‐related ignition temperature criterion are discussed. The method and associated procedures to construct the heating rate‐related temperature ignition criterion can be used to obtain the same ignition criterion for other combustible solids. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermochromic core–shell nanofibers fabricated by melt coaxial electrospinning

Microcapsule/nanocapsule and encapsulation techniques have great potential for devices of functional materials. Also, electrospinning has attracted great attention for the fabrication of microstructures and nanostructures. The fluidity after melting limits the application of phase‐transformation thermochromic materials. In this study, with the melt coaxial electrospinning technique, a phase‐transformation thermochromic material was encapsulated in poly(methyl methacrylate) nanofibers. A device of this phase‐transformation thermochromic material was realized. With a poly(methyl methacrylate) shell with good optical transmission and a thermoresponsive core made of crystal violet lactone, bisphenol A, and 1‐tetradecanol core, the fibers had good thermal energy management, fluorescent thermochromism, and reversibility. The fabrication of thermochromic core–shell nanofibers has further potential in the preparation of temperature sensors with good fluorescence signals and body‐temperature calefactive materials with intelligent thermal energy absorption, retention, and release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The application of a new DTA technique to the measurement of the heats of fusion of bulk crystallized polyethylenes and polyethylene single crystals

DTA has been widely used for many years and it has always been assumed that the technique is intrinsically secondary in that the determination of enthalpy changes requires calibration of the equipment. Recently the present authors have shown that this is not so, and under certain conditions DTA becomes an absolute method. A modification of the new technique has now been applied to a polymer and the results are presented here. The heats of dissolution and hence of fusion of various polyethylene samples have been measured, together with their densities. The results are shown to be consistent with those of other workers. No special accuracy or importance is claimed for the actual results, however, because the purpose of the paper is to introduce a new technique in a familiar polymer context. There is scope for improvement and extension of the procedures described here, and the status of DTA in polymer science will be increased in consequence. The use of a liquid system greatly facilitates the preparation and handling of the material under test.     

采用2.25Cr-1Mo-V-Cb-Ca钢的加氢反应器的制造

2.25Cr-1Mo-V-Cb-Ca和3Cr-1Mo-V-Cb-Ca钢已经作为高温高压加氢反应器的材料被发展起来了,这些Cr-Mo-V-Cb-Ca钢由于加了V在高温下有着很高的强度,同时附加的大约0.25％的V还能显著提高高温下抗氢蚀和抗氢脆的能力,附加的Ca也是这种材料独有的特征,它能有效降低焊件热影响区产生再热裂纹的可能性,另外通过附加的V还能减少焊件再热裂纹的灵敏度。虽然采用3Cr-1Mo-V-Cb-Ca钢的加氢反应器已经制造成功了,但本文讨论的是第一次采用2.25Cr-1Mo-V-Cb-Ca钢来制造加氢反应器,而且和ASME规范实例2098比较,我们还取得了这种材料的大量的性能数据。另外,对于传统的探伤技术,我们引荐了一种飞行时间衍射(Time-of-Flight Diffraction)(TOFD)技术来对焊件进行超声波探伤,进一步保证了检测手段的可靠性。     

Review of instrumental inter‐agreement study of spectral and colorimetric data of commercial multiangle spectrophotometers

Several different instruments have been introduced into the market to obtain good color characterization for different measurement configurations. These commercial instruments have different optical and working configurations, however, the measurement data provided by each instrument should be similar to have good consistency when comparing them to each other measuring the same sample material. Therefore, the purpose of this work was to apply an inter‐model agreement study of spectral and colorimetric data of three instruments (CM‐M6, BYK‐mac‐I, and MA98). Two different statistical tests were applied following ASTM recommendations. In general, the measurement geometries close to the specular direction and the flop direction showed greater deviations. In addition, the partial color differences calculated for the comparison of MA98 versus CM‐M6 were larger than the BYK‐mac‐i versus CM‐M6 comparison. Finally, it can be concluded that most of the measurement geometries were statistically significantly different from each other which means that these differences were due to systematic or bias errors and not exclusively to random errors.     

Improved Sensitivity in the Thermal Investigation of Polymeric Nanophases by Measuring the Resonance Frequency Shift using an Atomic Force Microscope

A novel technique has been developed to measure thermal transitions of polymers with the atomic force microscope (AFM) in the non‐contact mode. The resonance frequency of the AFM cantilever is measured as a function of the temperature, and thermal transitions of a polymer are clearly visible as changes in the resonance frequency/temperature response curve. Using the AFM in this mode allows the determination of the thermal properties of a material at a specific spot on the sample, on a macromolecular scale. This adds a new dimension to the standard thermal analysis techniques, rendering it possible to resolve the individual thermal transitions of different polymer phases, for example in structured multiphase polymers.