Hydrostatic extrusion of linear polyethylene: Effects of extrusion temperature and polymer grade

The hydrostatic extrusion behavior of linear polyethylene has been examined for two homopolymers of very different molecular weight characteristics and for a copolymer. Good unflawed extrudates could be obtained in all cases, and the extrusion behavior at a fixed temperature correlated well with the melt flow index. Although the maximum values of axial Young's modulus obtainable from the higher molecular weight homopolymer and the copolymer were lower than those possible for the lower molecular weight homopolymer, such materials do show improvements in creep behavior which could be advantageous. The effect of temperature on the extrusion behavior is discussed; the results suggest that for each grade of polymer there is an optimum temperature for effective extrusion, i.e., extrusion which gives optimum modulus enhancement. Finally, the melting behavior and the temperature dependence of the axial Young's moduli of the extrudates are considered in terms of our present knowledge of the structure of these high modulus materials.     

A strip resonance technique for measuring the ultrasonic viscoelastic parameters of polymeric sheets with application to cellulose

An acoustic strip resonance apparatus that measures the viscoelastic response of polymeric sheets over the temperature range of 100–400°K and at frequencies from 20 to 100 kHz is described. This is a computer-controlled instrument which uses the resonant frequency and the quality factor of standing waves in strips to calculate the ratio of complex Young's modulus to density. Results are presented for cellophane and paper samples. These are consistent with measurements reported by others at lower frequencies. That is, (1) a single predominant secondary relaxation process which corresponds to the γ relaxation occurring at 200°K and 1 Hz is found in dry samples at 260°K and 60 kHz; (2) as moisture is added, the γ relaxation weakens and a higher temperature, β, relaxation appears; and (3) at low temperature, moisture addition initially increases the mass specific Young's modulus. The effects of methanol on the viscoelastic parameters of cellulose were also measured and found to be similar to those of water.     

Effect of Zinc Oxide on Morphology and Mechanical Properties of Polyoxymethylene/Zinc Oxide Composites

This paper studies the effects of zinc oxide (ZnO) on morphology and mechanical properties of pure polyoxymethylene (POM) and POM/ZnO composites. POM/ZnO composites with varying concentration of ZnO were prepared by melt mixing technique in a twin screw extruder. The dispersion of ZnO particles on POM composites was studied by scanning electron microscope (SEM). It is observed that the dispersion of ZnO particles is relatively good. The mechanical properties of the composites such as tensile strength, stress at break, Young's modulus and impact strength were measured. Increasing content of ZnO up to 4.0 wt% increases the impact strength of POM. Addition of ZnO beyond 4.0 wt% decreases the impact strength. The composites containing ZnO content greater than 2.0 wt% show increased Young's Modulus. The tensile strength and stress at break decrease with increasing ZnO content. This may be due to the compatibility between ZnO and POM.     

Effects of humidity on Young's modulus in poly(methyl methacrylate)

Tensile tests on poly (methyl methacrylate) (PMMA) were conducted to clarify the effects of humidity and strain rate on tensile properties, particularly Young's modulus. Prior to the tensile tests, specimens were kept under various humidity conditions at 293 K, which were the same as the test conditions, for a few months to adjust the sorbed water content in the specimens. The tensile tests were performed under each humidity condition at three different strain rates (approximately 1.4 × 10^?3, 1.4 × 10^?4, and 1.4 × 10^?5 s^?1). Stress‐strain curves changed with humidity and strain rate. Young's moduli were also measured at small applied stresses (below 6.7 MPa) under various humidity conditions at 293 K. Young's modulus decreases linearly with increasing humidity and a decreasing logarithm of strain rate. These results suggest that Young's modulus of PMMA can be expressed as a function of two independent parameters that are humidity and strain rate. A constitutive equation for Young's modulus of PMMA was proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 460–465, 2002; DOI 10.1002/polb.10107     

Dynamic mechanical and crystal-strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus

Dynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range ?150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room-temperature value.     

Rheo-optical studies of high polymers. XIV. Study of the deformation mechanism in polymer blends of polypropylene with ethylene–propylene rubber

To clarify the deformation mechanism in polyblends of polypropylene with ethylene–propylene rubber having different compositions, simultaneous measurements of the infrared dichroism with stress and strain under a constant rate of strain of 1.64%/min have been carried out. The orientation function of the crystallographic c axis of polypropylene in the blends has been obtained as a function of strain ranging from 0 to 20% and of polypropylene content ranging from 0.3 to 1.0. These results have been compared with the temperature dependences of the dynamic Young's modulus and of the loss modulus, as well as of stress–strain curves for the same blends. The modulus data analyzed by Kerner's equation reveal the occurrence of phase inversion at polypropylene contents higher than about 0.5, and this is supported by the infrared dichroism data. The strong effect of quenching on crystalline structure and mechanical properties of pure polypropylene has also been elucidated.     

Characterization of the matrix of polybutene-1 films containing needle crystals

The microstructure and the mechanical properties of polybutene-1 films containing needle crystals are described. AboveT _g, the Young's modulus is nearly temperature independent over a temperature range of 100 °C. Mechanical and thermal measurements indicate that the end and side surfaces of the needle crystals act as physical tie points for the amorphous molecules.     

Fabrication of Bioactive Polyoxymethylene Nanocomposites for Bone Tissue Replacement

Summary: Stearic acid modified nano hydroxyapatite (n-SHA) filled polyoxymethylene (POM) nanocomposites were prepared by melt mixing method for bone tissue replacement and regeneration applications. Contact angle measurements of POM nanocomposites were carried out to understand the effect of n-SHA addition on the hydrophobicity of nanocomposites. The mechanical properties like tensile strength, Young's modulus and elongation at break were found to be increased significantly by the incorporation of n-SHA into the POM matrix. The bone-bonding ability of the nanocomposites was evaluated by examining the apatite formation on their surface after soaking in simulated body fluid (SBF) and apatite formation was studied by atomic force microscopy (AFM). The protein adhesion studies revealed the enhanced biocompatibility of the nanocomposites due to the presence of n-SHA nanofillers on the surface and it provides favorable binding sites for protein adsorption. The significant improvement in the biocompatibility as well as mechanical, thermal and hydrophobic properties of the POM nanocomposites makes it a potential future material for bone implantation.     

Effects of water freezing on the mechanical properties of nafion membranes

Most of the research efforts on Nafion have been devoted to the study of the perfluorinated ionomer membranes at optimal conditions for the desired applications, such as high temperature and low relative humidity for polymer electrolyte membrane fuel cells (PEM FC). In view of the possible changes induced by the freezing of water in the structure of Nafion and considering that in cold start conditions of a PEM FC device, Nafion needs to work also below 273 K, we measured the Young's modulus (Y) and the elastic energy dissipation (tan δ) in the temperature range between 90 and 470 K and the stress–strain curves between 300 and 173 K. The measurements reported here indicate that the mechanical properties of wet Nafion membrane change dramatically with temperature, that is, from a rubber‐like behavior at room temperature to a brittle behavior below 180 K. Moreover, we observed that the freezing of the nanoconfined water is complete only below 180 K, as indicated by a large increase of the Young's modulus. Between 180 and 300 K, the large values of tan δ suggest the occurrence of friction between the liquid water bound to the walls of the hydrophilic domains and the solid ice residing in the center of channels. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Thermo-mechanical characterisation of in-plane properties for CSM E-glass epoxy polymer composite materials – Part 2: Young's modulus

The in-plane Young's modulus of a CSM E-glass/epoxy material is characterised through the use of dynamic mechanical analysis (DMA). The measured data is used to generate material models which describe the property behaviour as a function of conversion and temperature. Gelation of the epoxy resin plays a major role in the modulus development and is measured directly on the glass/epoxy material. The Young's modulus is described through a bi-functional model including the liquid/solid transition of the material. The evolution of Young's modulus is modelled by decoupling modulus increments caused by time and temperature, and is graphically illustrated through a Modulus-Temperature-Transformation (MTT) diagram. Based on the established material models presented in this paper and models in Part-1, it is feasible to assess residual stresses and shape distortions of composite parts made from this glass/epoxy material.     

Dynamic bulk and shear relaxation in glassy polymers. I. Experimental techniques and results on PMMA

In this paper the authors describe in detail the experimental techniques for the simultaneous measurement of the dynamic Young's modulus and the dynamic Poisson's ratio, from which the dynamic bulk and shear moduli can be calculated. Experimental results are presented on the effects of temperature, frequency, and tensile strain on these properties of poly(methyl methacrylate) (PMMA). The temperature and frequency effects indicate that the β relaxation in PMMA is not a purely internal motion but is coupled to the bulk.     

Effect of the comonomer content on the mechanical parameters and microhardness values in poly(ethylene‐co‐1‐octadecene) synthesized by a metallocene catalyst

Stress–strain and microhardness measurements were carried out on a series of copolymers of ethylene and 1‐octadecene with different comonomer contents in the corresponding homopolymer of ethylene, synthesized with a metallocene catalyst. The different mechanical properties, deduced from the stress–strain curves (Young's modulus, yield stress, deformation at break, and energy to break) are interpreted in terms of the crystallinity and molecular weight of the samples because these two characteristics show considerable variations with the comonomer content. The microhardness values are explained in terms of these properties, and they are also correlated with Young's moduli and yield stresses deduced from the stress–strain curves. Linear relations are found between microhardness and yield stress and between the logarithm of the microhardness and the logarithm of the elastic modulus. The properties deduced from these lines are compared with literature values. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 277–285, 2001     

Tensile properties of ultradrawn polyethylene

High-density polyethylene filaments prepared by a solid-state deformation in an Instron capillary rheometer show unusually high crystal orientation, chain extension, axial modulus, and ultimate tensile strength. The Young's modulus and ultimate tensile strength have been determined from stress–strain curves. Gripping of this high modulus polyethylene has been a problem heretofore, but the measurement of ultimate tensile strength has now been made feasible by a special gripping procedure. Tensile moduli show an increase with sample preparation temperature and pressure. Values as high as 6.7 × 10¹¹ dyne/cm² are obtained from samples extruded at 134°C and 2400 atm and tested at a strain rate of 3.3 × 10^?4 sec^?1. The effect of strain rate and frequency on modulus has also been evaluated by a combination of stress–strain data and dynamic tension plus sonic measurements over nine decades of time.     

The dynamic mechanical behavior of ultra-high modulus linear polyethylenes

The dynamic mechanical properties of a number of ultra-highly drawn polyethylenes have been studied over a wide range of temperature. It is shown that the materials possess low temperature Young's moduli as high as 1.6 Mbar, a figure which approaches the theoretical and experimental values for the c-axis crystalline modulus of this polymer. The α and γ relaxation processes are still clearly discernible even at highest drawn ratios (ca. 35) and a quantitative analysis of the results, using structural data obtained from broad line nuclear magnetic resonance (NMR) measurements, suggests that the data are consistent with a modified series model.     

Preparation and characterization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites for long‐term bone implants

In this work, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for long‐term bone implants have been obtained via extrusion and injection molding processes and characterized by differential scanning calorimetry (DSC), temperature‐modulated DSC (TMDSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and tensile mechanical and in vitro stability tests. Based on the DSC results, it was found that the degree of crystallinity increases for POM/0.5% HAp sample and decreases for POM/1.0% HAp and POM/2.5% HAp. SEM and TEM observations for POM/HAp nanocomposites indicated that the dispersion of HAp in the polymer matrix was uniform and the diameter of the HAp particles was less than 100 nm for most of them. Young's modulus increases with increasing HAp concentration, whereby elongation at break decreases. On the contrary, HAp concentration does not have a significant influence on the tensile strength. TG results show that for POM/0.5% HAp, POM/1.0% HAp, and POM/2.5% HAp, thermal stability slightly increases in comparison to pure POM, whereas for POM/5.0 HAp and POM/10.0% HAp, lower thermal stability was observed. In vitro data reveal that with an increase of HAp content, bioactivity of nanocomposites increases; a good in vitro chemical stability of POM and POM nanocomposites was confirmed. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermodynamic properties of phenol–formaldehyde resin

Characterization measurements of a commercial phenol-formaldehyde resin prepared from constituents including phenol and formaldehyde in the molar ratio 1:1.33 are reported. The measurements consist of (1) the linear thermal expansion coefficient between approximately 85 and 270°K; (2) the specific heat capacity between approximately 6 and 100°K; (3) the Young's modulus at room temperature. A critical examination of the data reveals that: (1) the vibrational behavior is predominantly that of a three-dimensional assembly; (2) as far as data available from other sources permit an assessment to be made, the principle of additivity appears to be applicable to the specific heat capacity between approximately 50 and 100°K; and (3) the data lie near the limit of an empirical relationship observed between the Young's modulus and linear thermal expansion coefficient of other polymers.     

On the nonlinear evolution of the Poisson's ratio under quasi-static loading for a carbon fabric-reinforced thermoplastic. Part II: Analytical explanation

When observing or describing the damage state in a composite material, often only Young's modulus or residual deformation are considered. Generally, however, the Poisson's ratio is more sensitive to damage than those properties. Rather than observing the Poisson's ratio as function of crack density, the evolution of the Poisson's ratio as function of the longitudinal strain was studied in part I of this research, where a peculiar shape of the evolution was observed and proven to be entirely due to the material itself, rather than the sensors used for the strain measurement.In this article, a theoretical explanation for the peculiar evolution of the Poisson's ratio as function of the longitudinal strain is presented. Based on this explanation, extra experiments were conducted for validation purposes.The material used for this study is a carbon fabric-reinforced PPS.     

Elastic modulus and thermal conductivity of ultradrawn polyethylene

The axial and transverse Young's modulus and thermal conductivity of gel and single crystal mat polyethylene with draw ratios λ = 1–350 have been measured from 160 to 360 K. The axial Young's modulus increases sharply with increasing λ, whereas the transverse modulus shows a slight decrease. The thermal conductivity exhibits a similar behavior. At λ = 350, the axial Young's modulus and thermal conductivity are, respectively, 20% and three times higher than those of steel. For this ultradrawn material both the magnitude and the temperature dependence of the axial Young's modulus are close to those of polyethylene crystal. The high values of the axial Young's modulus and thermal conductivity arise from the presence of a large percentage (∼85%) of long needle crystals. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3359–3367, 1999     

Inorganic-Macroion-Induced Formation of Bicontinuous Block Copolymer Nanocomposites with Enhanced Conductivity and Modulus

A facile and electrostatically driven approach has been developed to prepare bicontinuous polymer nanocomposites that is based on the polyoxometalate (POM) macroion induced phase transition of PS-b-P2VP from an initial lamellar phase to a stable bicontinuous phase. The multi-charged POMs can electrostatically cross-link P2VP blocks and give rise to bicontinuous phases in which the POM hybrid conductive domains occupy a large volume fraction of more than 50 %. Furthermore, the POMs can give rise to high proton conductivity and serve as nanoenhancers, endowing the bicontinuous nanocomposites with a conductivity of 0.1 mS cm⁻¹ and a Young's modulus of 7.4 GPa at room temperature; these values are greater than those of pristine PS-b-P2VP by two orders of magnitude and a factor of 1.8, respectively. This approach can provide a new concept based on electrostatic control to design functional bicontinuous polymer materials.     

The structural,electronic, elastic,vibration and thermodynamic properties of GdMg

We have investigated the structural, elastic, electronic, vibration and thermodynamic properties of GdMg alloy using the methods of density functional theory within the generalized gradient approximation (GGA) for the exchange-correlation functional. We have presented the results on the basic physical parameters, such as the lattice constant, bulk modulus, pressure derivative of bulk modulus with and without spin-polarization (SP), second-order elastic constants, Zener anisotropy factor, Poisson's ratio, Young's modulus, and isotropic shear modulus. The thermodynamic properties of the considered compound are obtained through the quasi-harmonic Debye model. In order to obtain further information, we have also studied the pressure and temperature-dependent behavior of the volume, bulk modulus, thermal expansion coefficient, heat capacity, and Debye temperature in a wide temperature range of 0–1200 K. We have also calculated phonon frequencies and one-phonon density of states for B2 structure of GdMg compound. The temperature-dependent behavior of heat capacity and entropy obtained from phonon density of states for GdMg compound in B2 phase is also presented.