bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure‐property correlations in stretched LLDPE films using oblique incidence small‐angle X‐ray scattering
Authors: Hu Ruizhong , Lambert W. Scott , Barnes John D. 
Published: April 2004

AbstractThis paper demonstrates the use of oblique incidence small‐angle X‐ray scattering (SAXS) to characterize microstructure in linear low‐density polyethylene films subjected to biaxial deformation in a TM Long stretcher. Differences in tear strength and impact properties were found when two different deformation temperatures were used. SAXS was used to characterize the nanometer scale microstructure of these films. Since the microstructure was expected to be anisotropic, SAXS data were collected in normal incidence, T (transverse) oblique incidence and M (reference direction) oblique incidence. The sections through the three‐dimensional SAXS pattern collected in these three orientations are combined to provide clues to the nature of the complete 3‐D SAXS pattern, which can be interpreted to characterize the changes wrought by deformation.
Morphology of syndiotactic polystyrene as examined by small‐angle X‐ray scattering
Authors: Barnes John D. , McKenna Gregory B. , Landes Brian G. , Bubeck Robert A. , Bank David 
Published: April 2004

AbstractSmall Angle X‐Ray scattering (SAXS) studies have been carried out on injection molded syndiotactic polystyrene (SPS) at room temperature and at elevated temperatures up to 290°C. Features indicating lamellar crystallinity were weak or entirely absent at room temperature, becoming increasingly intense above the glass transition temperature (Tg) for this material. A background scattering whose intensity was roughly proportional to q−2, where q is the scattering momentum transfer, was present throughout the temperature range. We suggest that these results indicate that SPS materials formed in this way are three‐phase systems, with an amorphous phase, a crystalline phase, and a grain boundary phase.
Applications of molecular dynamics to the study of thermal degradation in aromatic polymers. I: Polystyrene
Authors: Nyden Marc R. , Coley Terry R. , Mumby Stephen 
Published: April 2004

AbstractThis paper reports recent progress in the development of a generic molecular dynamics model that accounts for the major chemical reactions involved in the thermal degradation of polymers. The strategy employed in the design of the most recent version of this model was to interface our code for performing reactive dynamics on simple vinyl polymers with a commercial molecular dynamics package (Discover 95). The expanded range of applicability of the integrated model is illustrated by applying it to the study of thermal degradation in atactic polystyrene.
Stability of blends of thermotropic liquid crystalline polymers with thermoplastic polymers
Authors: Machiels A. G. C. , Van Dam J. , De Boer A. Posthuma , Norder B. 
Published: April 2004

AbstractBreakup of fibers of a thermotropic liquid crystalline polymer (TLCP) above the melting temperature in various ordinary polymers has been studied by capillary instability experiments on single TLCP fibers and by annealing experiments on extruded TLCP/thermoplast blends. The TLCP was an aromatic copolyester, Vectra A900, the matrix polymers were PP, PS, PC, PEL PES, and PEBT. Both types of experiments show that the fiber/matrix morphology is, in general, highly unstable in the molten state. The TLCP fibers break up into droplets by a combination of Rayleigh distortions, end‐pinching and retraction, depending on the system and shape of the fiber. Fibers of a thickness of ∼1 μm can break up in a few seconds. Breakup times of fibrous blends and individual fibers are in agreement provided size effects are accounted for. Rayleigh distortions develop exponentially in time up to relative distortions of 0.5 to 0.6. Breakup occurs within a range of wave numbers rather than at one distinct dominant wave number, which is shown to be the consequence of relatively large initial distortions. Apparent values for the interfacial tensions calculated with Tomotika's theory turned out to be of the correct order of magnitude, ranging from 7 mN/m for Vectra/PES to 24 mN/m for Vectra/PP and to yield correct values of the interfacial tensions of PP/PS, PP/PC, and PS/PC using Antonow's rule.
Crystallization and microstructure in quenched slabs of various molecular weight polypropylenes
Authors: Isayev A. I. , Catignani B. F. 
Published: April 2004

AbstractThe purpose of this study was to accumulate material data for use in a simulation of morphology and crystallization in quenched slabs of isotactic polypropylenes (i‐PP's). The molecular weight effect on the crystallization kinetics of various i‐PP's were studied using isothermal and nonisothermal experiments. An experimental setup was constructed to measure the spherulite growth rate of i‐PP's using isothermal and nonisothermal melt crystallization experiments. The molecular weight effect on spherulite growth rate of i‐PP's was determined. Molecular weight effect on nuclei concentrations as a function of temperature was determined from growth and crystallization rate constants. The morphology and crystallization in quenched slabs of i‐PP's were determined from experiments and compared to computer simulations. The molecular weight effect on the degree of crystallinity and morphology was determined for i‐PP during quenching.
Comparative measurements of interfacial tension in a model polymer blend
Authors: Sigillo I. , di Santo L. , Guido S. , Grizzuti N. 
Published: April 2004

AbstractThis work shows the application of several experimental methods to the measurement of the interfacial tension, σ, between two immiscible polymers. A quantitative knowledge of the interfacial tension is important in view of the crucial role that this parameter plays in polymer blend processing. Common to all methods presented here are two main points. The first is that σ is obtained from experiments where the shape of the interface between the liquids is directly observed by means of optical microscopy techniques. The second point is that the interface geometry is controlled by a balance between the interfacial force and the viscous stresses generated by some flow applied to the system. Measurements have been carried out on a model polymer blend, whose constituents are a poly‐isobutylene and a poly‐dimethylsiloxane. both transparent and liquid at room temperature. When compared with each other, the values of interfacial tension obtained from the different methods show a good quantitative agreement. Excellent agreement is also found with results for the same system previously published in the literature.
Creep and physical aging of injection molded, fiber reinforced polypropylene
Authors: Read B. E. , Tomlins P. E. 
Published: April 2004

AbstractTensile creep data have been obtained at 23°C as a function of physical age from test pieces of glass fiber reinforced polypropylene cut from injection molded square plaques in directions parallel and transverse to the flow direction. Smaller compliances were measured for loading parallel to the flow than for loading in the perpendicular direction, reflecting the preferential alignment of the fibers with the flow. Two creep functions have been used to model the creep behavior over both a limited timescale where the age of the test piece remains effectively constant and a wider timescale where significant further aging of the material occurs. The results of these analyses reveal significant differences between modeling injection molded polypropylene and compression molded material.
Conjugate transport in polymer melt flow through extrusion dies
Authors: Lin P. , Jaluria Y. 
Published: April 2004

AbstractA numerical study is carried out on the conjugate thermal transport in polymer and food melts flowing through extrusion dies. The simulation is performed to determine the influence of conduction through the die wall and of the thermal boundary conditions on the transport in the fluid and on the conditions at the outlet. An extrusion die with a uniform temperature or heat transfer coefficient specified at the outer surface is considered. It is found that, because of conduction in the solid wall, important physical variables such as centerline velocity, pressure drop, bulk temperature of the fluid and shear experienced by the fluid are strongly affected by the boundary conditions, as well as by the wall thermal conductivity and thickness. Channels of different geometries are used for the study. The flow in a circular straight tube with constant wall thickness is studied first. Flow and thermal transport in different, constricted, channels are studied next. Different wall materials are also considered. Comparisons with some experimental results are presented, indicating good agreement. The fluids considered in this study are highly viscous, polymer melts. Due to high viscous dissipation and temperature‐dependent viscosity, the flow and heat transfer are coupled and the problem is quite complicated. The results show that, for some operating conditions, the bulk temperature can be high enough to cause significant heat transfer from the fluid to the wall. The downstream variation in the pressure and temperature are calculated. The thermal boundary conditions are found to have a strong influence on the temperature field and thus on the flow. The general dependence of pressure drop on temperature, flow rate, and geometry is investigated. Several other basic aspects of this problem are also discussed.
Viscoelastic behavior of poly(cyanate epoxy)
Authors: Ponteins P. , Medda B. , Demont P. , Chatain D. , Lacabanne C. 
Published: April 2004

AbstractThe viscoelastic behavior of poly(cyanate epoxy) has been investigated by dynamic mechanical analysis and thermostimulated creep. First, the coherence of both sets of data has been shown. The analysis of the fine structure of the low temperature retardation mode has revealed the existence of four cooperative sub modes. The high temperature retardation mode corresponds to the anelastic manifestation of the glass transition. The elementary processes constituting this mode are characterized by retardation times following a compensation law with a compensation temperature Tc ∼ Tg + 60°. The broad range of activation enthalpies reveals that cooperative movements are highly delocalized. The compensation parameters together with the range of activation enthalpy define the microstructure of poly(cyanate epoxy) and allow us to follow its relationship with the viscoelastic behavior.
On the plastic and viscoelastic behavior of methylmethacrylate‐based random copolymers
Authors: Tordjeman P. , Teze L. , Halary J. L. , Monnerie L. 
Published: April 2004

AbstractBoth plastic and Viscoelastic properties were investigated on neat polymethyl‐methacrylate (PMMA) and methylmethacrylatc‐based random copolymers including N‐substituted maleimide units. A strong coupling was evidenced between the glass transition motions and the secondary transition motions for PMMA samples rapidly quenched from the molten state. This coupling was shown to diminish markedly in the case of aged PMMA and to disappear almost completely in the case of MMA‐maleimide copolymers having a maleimide content as small as 5 mol%. Thus, it strongly suggests tnat a greater compacity of the glassy PMMA matrix and (or) the presence of stiff maleimide units in the copolymers are sufficient to hinder the early occurrence of large scale conformational motions in the secondary transition region. In addition, it was shown that the strain softening that follows the yield point is also important for aged PMMA and maleimide‐rich copolymers, but tends to vanish in the other samples. Therefore, the probable origin, at least in this series of materials, of the strain softening would be the different nature of the molecular motions that occur in the secondary relaxation region and in the glass transition region.
The role of anelasticity in high stress mechanical response and physical properties of glassy polymers
Authors: David L. , Quinson R. , Gauthier C. , Perez J. 
Published: April 2004

AbstractNon‐elastic deformation of amorphous polymers is studied from strain recovery tests. In particular, a strain recovery master curve is built. It allows one to estimate recovery times necessary to recover the whole non‐elastic deformation. On such a curve, two non‐elastic deformations, namely anelastic (nonlinear) and plastic deformations, are distinguished by their range of recovery times. The evolution of these two components is followed during a constant strain rate test. This clearly shows the importance of the anelastic deformation for the understanding of the nonlinear response of glassy polymers. Moreover, the structural modifications induced by non‐elastic strain of glassy polymers were studied by mechanical spectroscopy, differential scanning calorimetry and density measurements. These modifications appear to result from the anelastic part of the strain. Lastly, a consistent description of the mechanical response of amorphous solid polymers, and subsequent recovery processes, is proposed. The polymers tested were poly(methyl methacrylate). atactic polystyrene, and polycarbonate.
A physical model of the pressure dependence and biaxial mechanical properties of solid polymers
Authors: Escaig B. 
Published: April 2004

AbstractWe give here a model for the pressure dependent, biaxial mechanical behavior of glassy polymers based on the thermally activated growth of deformation zones (Somigliana dislocation loops). The Coulomb criterion of plasticity, σc = S − mσn, is found as the critical threshold needed to propagate Somigliana loops, in the same way as yield in crystals is found as the stress to move Volterra dislocation loops. While S is the shear strength, it is proposed that m follows basically from chain spacing fluctuations in the polymer glass; the temperature dependences of both parameters are derived. Application to tensile and compressive tests under a confinement pressure P is developed, with the aim to derive the pressure dependent (biaxial) strain‐rate law. In particular, the pressure effect on dislocation density, that is, on plasticity defect nucleation, is shown to have a definite role in the plasticity of these solids. It introduces in the strain‐rate law a normal stress dependent term (exp Dσn), which may have a decisive importance in a number of situations like multiaxial solicitations, solid state polymer shaping, second phase effects in polymer blends, and so on. Finally, a set of constant strain rate experiments is presented on an unsaturated polyester resin crosslinked with styrene. Measurements fit reasonably well with the predictions of the above model up to ∼50 K below the glass transition, at which collective molecular motions invalidate its basic assumptions. The fit includes: (i) the Coulomb Criterion and its temperature dependence; and (ii) the dilative and shear apparent activation volumes at yield at all pressures.
On the plastic behavior of homogeneous ethylene copolymers compared with heterogeneous copolymers
Authors: Gaucher‐miri Valérie , Elkoun Saïd , Séguéla Roland 
Published: April 2004

AbstractThe plastic behavior of homogeneous ethylene‐octene copolymers and heterogeneous ethylene‐butene copolymers has been compared on uniaxial tensile draw. True‐stress‐strain curves have been determined for various draw temperatures and strain‐rates. Significant differences in yield behavior and strain‐hardening have been revealed between the two types of materials, at equivalent crystallinity. In parallel, thermal analysis gave an indication that homogeneous copolymers have much narrow distributions of lamellae thicknesses together with lower values of the most probable thickness. Quantitative data from small‐angle X‐ray scattering support the latter point. An estimation of the surface free energy has revealed a more disordered chain‐folding topology for the homogeneous copolymers. Interpretation of the mechanical behavior is based on the framework of a previous model for the plastic deformation of polyethylene involving competition of homogeneous and heterogeneous crystal slip processes. The former process governs the ability of the material to develop macroscopically homogeneous plastic deformation; the second process is a precursor to necking. It is proposed that the nucleation of dislocations, which is the basic mechanism of the homogeneous crystal slip, is favored for homogeneous copolymers, owing to the lower value of the most probable lamellae thickness. More tie molecules and chain entanglements in the disordered amorphous phase may also favor stable homogeneous plastic deformation in the case of homogeneous copolymers.
Crystallization temperature effect on the solid‐state rheology of a high‐density polyethylene under compression
Authors: Monasse B. , Ferrandez P. , Delamare F. , Montmitonnet P. , Haudin J. M. 
Published: April 2004

AbstractThe plane‐strain compression test provides quantitative data on the polymer rheology in homonogeneous large deformation at constant strain‐rate, and on the friction shear stress between the film and the dies. Thin HDPE films with a homogeneous morphology were formed by quenching or isothermal crystallization. The structure was modified by varying the crystallization temperature over a wide range: 118°C ⩽ Tc ⩽ 130°C. A mechanical model with a pressure‐dependent rheology and two friction laws was tested. The rheological parameters are different in tension and in compression. The occurrence of brittle fracture under compression depends on the crystallization temperature, but the rheological parameters are almost independent of the crystallization conditions.
Microstructure transformation and stress‐strain behavior of isotactic polypropylene under large plastic deformation
Authors: G'sell C. , Favier V. , Hiver J. M. , Dahoun A. , Philippe M. J. , Canova G. R. 
Published: April 2004

AbstractThe macroscopic stress‐strain behavior of monoclinic polypropylene samples was investigated at 70°C under uniaxial tension and simple shear by means of a special videometric testing system that gives access to the constitutive equation of plastic behavior at constant strain rate up to large deformation. At several levels of plastic strain, the microstructural evolution of the material was characterized by means of X‐ray scattering, densitometry and viscoelastic analysis. It appears that the strain hardening is high in tension, whereas it is nearly zero in shear. This behavior is associated with the development of a fiber texture in tension, which differs drastically from the planar crystalline texture developed in shear. Furthermore, it is shown that structural damage takes place as the plastic deformation proceeds in tension, while only little damage is recorded in shear. A viscoplastic model has been developed that specifically tales into account the various slip systems activated in the polypropylene crystallites and the elastic interactions of the lamellae through a self‐consistent scheme. Simulations based on this model reproduce correctly the contrasting strain‐hardening in tension and in shear and the different crystalline textures induced for these two loading paths.
Mechanical percolation in cellulose whisker nanocomposites
Authors: Favier V. , Cavaille J. Y. , Canova G. R. , Shrivastava S. C. 
Published: April 2004

AbstractNanocomposites obtained by casting a mixture of a latex and an aqueous suspension of cellulose whiskers have been studied. Their mechanical properties (e.g. shear modulus) are found to increase by more than three orders of magnitude in the rubbery state of the polymer matrix, when the whisker content is 6 wt%. This large and unusual effect is discussed on the basis of different types of mechanical models, including semi‐phenomenological and numerical finite element calculations. It is concluded that cellulose whiskers form a rigid network linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.
Study of mechanical damage in rubber‐toughened poly(methyl methacrylate) by single and multiple scattering of light
Authors: Schirrer R. , Lenke R. , Boudouaz J. 
Published: April 2004

AbstractAs glassy polymers are usually somewhat brittle, several blending techniques are used to toughen these materials and to increase their impact strength. The microstructures of toughened polymers are complicated, as are their mechanical damage mechanisms. Moreover, these materials are mostly opalescent or even opaque, which renders difficult any optical investigation of the damage process. The scale of the damage generally ranges from nanometers to several micrometers, thus requiring a large panel of experimental techniques to investigate its microstructural evolution. When illuminated with a light beam, any non‐perfectly transparent body will scatter light with a scattering pattern depending on the size, shape, and location of the microscopic light scatterers it contains. If the body is highly opaque, an incident light beam, if not absorbed, is scattered successively by several scatterers before emerging again at the front surface of the body. It has recently been shown that there is a coherent interference enhancement of the randomly multiple scattered light in a small angle range around the exact reverse direction of the incident light. This so‐called coherent backscattering cone can be analyzed in terms of the size, shape and density of the scatterers. In this work, this technique is applied to a rubber‐toughened PMMA containing core‐shell (hard core) particles, an initially transparent material that becomes progressively opaque during mechanical damage under stress. The damage mechanism within the rubber particles is compared with the size and shape of the light scatterers inferred from coherent backscattering and light transmission measurements.
Evolution of the microstructure and mechanical properties of polyamide 6 during impact
Authors: Billon N. , Haudin J. M. 
Published: April 2004

AbstractLow‐energy impact tests were performed on a polyamide 6 using a dart test technique with a 20‐mm‐diameter hemispherical striker. Partial penetrations at controlled and increasing energies allowed to visualize the different steps of the deformation. The evolution of the deformation is described, taking into account the shape and the thickness of the samples, the crystalline orientation, the microstructure and the resulting mechanical properties of the polymer. The deformation results from several steps, which are revealed by the evolution of the force measured on the striker. The deformation induces important and inhomogeneous changes in the microstructure and the orientation of the polymer. Variations may be abrupt. The resulting mechanical behavior is strongly dependent on this evolution and, as a consequence, depends on the location in the sample. These observations confirm that it is impossible to predict such a complex behavior using data from simple tensile tests.