bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Breakup 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

The 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

This 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

Tensile 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

A 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

The 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

Both 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

Non‐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

We 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

The 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

The 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

The 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

Nanocomposites 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

As 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

Low‐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.
Orientation in polypropylene sheets produced by die‐drawing and rolling
Authors: Chaffey Charles E. , Taraiya Ajay K. , Ward Ian M.
Published: April 2004

Two orienting techniques for stiffening semicrystalline polymers, rolling and die‐drawing, are compared with respect to the anisotropy they produce in isotactic polypropylene (PP). Billets of PP were either drawn at 145°C through a tapered slotted die in the Leeds large‐scale die‐drawing machine to reduction ratios R of 2.2, 5.1 and 7.6, or rolled between rolls of 65 mm diameter at 120°C to R = 2 to 5. Drawing increased the crystallinity, as estimated from differential scanning calorimetry, density and wide‐angle X‐ray diffraction (WAXD); it thus disrupts the original PP structure, developing an oriented crystalline structure. WAXD pole figures showed that both die‐drawing and rolling oriented the molecular chain axis nearly parallel to the machine direction and the b axis perpendicular to the drawing plane. This approximate uniaxial symmetry was confirmed by ultrasonic measurements of the stiffness matrix. In tensile and falling‐dart impact tests, samples failed by delaminating in the drawing plane. Although stresses are applied to the material in quite different ways in die‐drawing and in rolling, the geometry of deformation in both is similar, close to plane strain.
Study of the molecular structure of PET films obtained by an inverse stretching process. Part I: Constant speed drawing of amorphous films
Authors: Vigny M. , Tassin J. F. , Gibaud A. , Lorentz G.
Published: April 2004

The constant rate stretching of amorphous poly(ethylene terephthalate) films is the first step of the industrial “inverse” process. To study this process, films deformed under uniaxial planar symmetry conditions have been produced on a laboratory stretching machine in order to discuss the influence of macroscopic parameters, such as draw ratio, temperature and melt viscosity of the amorphous film, on the deformation mechanism. The structure of oriented films has been characterized by combining X‐ray diffraction and refractive index measurements. Stress strain curves have been simultaneously recorded. The draw temperature and the molecular weight of the polymer are determining factors controlling the development of molecular orientation and crystalline structure in the stretched films. The major influence of relaxation processes is described and a comparison with constant force drawn films is given.
Studies of post drawing relaxation phenomena in poly(ethylene terephthalate) by infrared spectroscopy
Authors: Pearce R. , Cole K. C. , Ajji A. , Dumoulin M. M.
Published: April 2004

In this paper, we study the relaxation behavior of initially amorphous poly(ethylene terephthalate) (PET) films drawn, at 80°C using a draw rate of 2 cm/min, to a draw ratio (λ) from 1 to 5 and then quenched to room temperature. These films were then heated at different temperatures from 68 to 80°C for different times and their orientation determined. The orientation measurements were performed by transmission infrared spectroscopy and the bands used for the determination of orientation were those at 1340 and 970 cm−1 for the trans conformers, normalized using the 1410 cm−1 benzene ring vibration. The crystallinity was determined by thermal analysis. It is shown that when PET is drawn to λ values up to 2–2.5 (before stress‐induced crystallization), the orientation relaxes rapidly at temperatures close to the glass transition temperature of PET. For λ values of 3 or higher, the orientational relaxation of the amorphous regions is hindered. This effect is ascribed to the development of strain‐induced crystallites, which are believed to act as pseudo‐crosslinks.
Orientation of amorphous poly(ethylene terephthalate) by tensile drawing, roll‐drawing, and die‐drawing
Authors: Ajji A. , Cole K. C. , Dumoulin M. M. , Ward I. M.
Published: April 2004

Orientation of initially amorphous poly(ethylene terephthalate) films and sheets was carried out by means of tensile drawing in a tensile tester, roll‐drawing using a series of four rolling stations, and by die‐drawing. The drawing temperature was 80 and 90°C and drawing rate ranged from 2 to 20 cm/min in the different processes. Crystallinity was observed to increase with draw ratio for all these processes. The onset of crystallinity development depends on the drawing rate. The glass transition temperature was essentially constant and crystallization temperature decreased with increasing draw ratio. The trans conformers content was observed to increase with draw ratio at the expense of the gauche conformers for the three processes. The orientation of the trans conformers increases readily from the beginning of draw and saturates rapidly. The orientation of the gauche conformers was negligible. Some differences are observed for the behavior of the 1020 and 730 cm−1 benzene ring bands, which may be due to differences in the benzene ring configuration at the surface as a result of different deformation mechanisms for the die and roll‐drawing. However, further investigations to elucidate this hypothesis are needed. The mechanical properties obtained in the longitudinal direction increased for all the processes. In the transverse direction, the roll and die‐drawing processes induced a decrease in modulus and strength with increasing draw ratio, similar to that observed for uniaxial orientation. This indicates that these processes are mainly uniaxial, despite the plane strain nature of the deformation.
Novel composites by hot compaction of fibers
Authors: Ward I. M. , Hine P. J.
Published: April 2004

The production of solid section products from highly oriented fibers by a novel compaction procedure is described for melt‐spun and gel‐spun polyethylene fibers, poly(ethylene terephthalate) and polypropylene fibers and Vectran liquid crystalline copolyester fibers. Differential scanning calorimetry and electron microscopy have been used to study the structure of the compacted polymers. For the most successful compaction, selective surface melting of a small fraction of each fiber enables the formation of a fiber composite of high integrity, where the matrix phase is formed by epitaxial crystallization of the melted fraction on the initial fibers, retaining a high proportion of their initial strength and stiffness. A wide range of potential applications is envisaged for the composites produced by hot compaction. In many cases these composites will be produced by thermoforming. In addition to the obvious advantages of high stiffness and strength, in several instances the unrestricted exploitation of unique properties of the fibers such as transparency to microwave radiation or low thermal expansion coefficients offer additional incentives for the use of these hot compacted materials rather than conventional fiber/resin composites.
Crystallization of syndiotactic polystyrene
Authors: Lawrence S. St. , Shinozaki D. M.
Published: April 2004

The crystallization of syndiotactic polystyrene (sPS) was studied over the temperature range from the glass transition (Tg) to the melting point (Tm). Using transmission electron and optical microscopies, the different lamellar and spherulitic microstructures which were formed over this temperature range were correlated with the measured crystallization kinetics. The rate of crystallization was measured isothermally using thin samples in a differential scanning calorimeter. The low temperature transformations were achieved by quenching first to the amorphous state, then reheating. The experimental measurements at both high and low temperatures of transformation could be closely fitted to the predicted rate constant. It was found that to estimate the crystallization parameters most accurately, the data must be fitted simultaneously at high and low temperatures and a relatively high value for the equilibrium melting temperature (561 K) must be used. The non‐isothermal crystallization kinetics have been predicted from the isothermal experiments using Nakamura's model in a manner similar to earlier work on other polymers.
Ultrasonic determination of mechanical moduli of oriented semicrystalline polymers
Authors: Lévesque Daniel , Legros Nathalie , Ajji Abdellah
Published: April 2004

Ultrasonics has been used for the determination of the mechanical properties of oriented semicrystalline polymers through time‐of‐flight measurements of elastic waves propagating in various directions within the material. While being nondestructive, such a method allows one to obtain more mechanical moduli with a better accuracy than the conventional tensile tests, especially regarding the shear properties and the Poisson's coefficients. Until now, the approach used to interpret the data was approximate and not rigorous. We present here a self‐consistent rigorous approach for interpreting time‐of‐flight data based on the group velocity including allowance for lateral displacement of the transmitted beam. Results are presented for roll‐drawn PET with various draw ratios. These samples are considered to have transversely isotropic symmetry. For the Young's moduli, comparisons are made with conventional tensile tests and the differences observed are interpreted in terms of viscoelastic efforts considering both the amorphous and crystalline phases.
Ram extrusion of high‐density polyethylene and polypropylene in solid state: Process conditions and properties
Authors: Legros N. , Ajji A. , Dumoulin M. M.
Published: April 2004

Highly oriented high‐density polyethylene (HDPE) and polypropylene (PP) were obtained by solid state extrusion near, but below, the melting temperature. Draw ratios of 6 and 11 were obtained using properly designed dies, preformed billets and lubrication for different extrusion temperatures. Orientation induced significant changes in properties and morphology that are related to the final draw ratio. The draw ratio was observed to decrease with an increase in extrusion speed due to the molecular relaxation occurring because of local heating during deformation. An increase in the degree of crystallinity was observed for the oriented polymers as well as a large improvement in the tensile modulus. Significant molecular relaxation and elastic recoil were observed during processing. Extrusion speed strongly increases the extent of relaxation, and, consequently, reduces many of the mechanical properties.
Evolution of hot strain induced crystalline texture of poly(ethylene terephthalate) films
Authors: Dargent E. , Grenet J. , Dahoun A.
Published: April 2004

Differential scanning calorimetry, birefringence and X‐ray poles figure analysis were used to characterize the evolution of the strain induced crystalline texture of poly(ethylene terephthalate) films. The films are initially wholly amorphous and drawn above the glass transition temperature. For a critical draw ratio, a crystalline phase appears with a weak crystalline fiber texture. For the highest draw ratio we observe that the texture is better defined, and the drawing tends to align the crystallites with the draw direction and to increase slightly the degree of crystallinity. For the highly drawn sample an extra texture is also observed.
Multi‐cavity pressure control in the filling and packing stages of the injection molding process
Authors: Kazmer David , Barkan Philip
Published: April 2004

Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality plastic parts. Recent developments in injection molding process technology have enabled closed loop control of cavity pressure at one point in the mold. In this paper, a scheme is described that enables the simultaneous control of cavity pressure at multiple locations in both multi‐gated parts and/or multi‐cavity molds. This has been achieved by the addition of dynamic valves in the melt delivery system, each of which can be independently controlled to meter the flow and pressure of the polymeric melt to its portion of the mold. The development and capabilities of the control system are presented, demonstrating the feasibility of simultaneous multi‐cavity pressure control in both the filling and packing stages of the injection molding process. A description of the ability of multi‐cavity pressure control to improve process capability and molded part quality is presented in a companion paper.
The process capability of multi‐cavity pressure control for the injection molding process
Authors: Kazmer David , Barkan Philip
Published: April 2004

Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality thermoplastic parts. This Interest has led to the achievement of closed loop cavity pressure control, but only at one point in the mold cavity. A system has been recently described that extends this capability to provide simultaneous control of cavity pressure at multiple locations in the mold through the addition of dynamic valves in the melt delivery system, each of which can be independently controlled to meter flow and pressure to its portion of the mold. This paper describes the ability of the multi‐cavity pressure control system to improve process capability and molded part quality. Experimental investigation has shown that the technology enables significant process flexibility to arbitrarily balance flow, move knit‐lines, and control multiple part dimensions. In the presence of typical production process disturbances, moreover, closed loop multi‐cavity pressure control was shown to increase the process capability index, Cp, from 0.52 for the conventional injection molding process to 1.5. After these capabilities have been discussed, several limitations of the process are described that lead to promising areas of future research.
Palladium(II) complexes with polyphosphazene
Authors: Das Pronab , Indra Erik M. , Belfiore Laurence A.
Published: April 2004

An allylphenoxy‐substituted polyphosphazene has been modified via inorganic chemical concepts. The transition metal salt is bis(acetonitrile)dichloropalladium(II). The coordination complexes have been characterized using acid‐base solution chemistry, sol‐gel phase transitions, thermomechanical property measurements and infrared spectroscopy. Solid complexes of polyphosphazene and PdCl2 cannot be dissolved in the original solvent (i.e., tetrahydrofuran) used during sample preparation. These polymeric palladium complexes also cannot be disrupted by a stronger base, like triphenylphosphine. There is a monotonic increase in the glass transition temperature at higher concentrations of palladium chloride. Tg of the pure polymer increases by 21°C in the presence of 10 mol% palladium chloride. The increase in high‐strain mechanical properties cannot be explained solely by a “filler effect.” At higher PdCl2 concentrations, there is a direct correlation between the enhancement in Tg, higher mechanical fracture stress, and increased infrared absorbance @ 1092 cm−1 because of the formation of a palladium‐π‐complex with allylic substituents in the phenoxy sidegroup. Palladium chloride relinquishes its acetonitrile ligands after dissolution in THF, and the vacant sites in the first‐shell coordination sphere of the transition metal are occupied by these allylic substituents in the sidegroup. This produces interchain coordination crosslinks, which modify the thermomechanical properties of polyphosphazene/ PdCl2 complexes.
Trans‐ and Dimethyl quinacridone nucleation of isotactic polypropylene
Authors: Sterzynski T. , Calo P. , Lambla M. , Thomas M.
Published: April 2004

Isotaclic polypropylene (iPP) was nucleated specifically for structural and mechanical studies, especially of impact resistance. Nucleation was accomplished by two red pigments: a linear trans‐quinacridone dye (as β‐phase nucleator) and a dimethyl quinacridone resulting in the formalion of a pure α‐phase structure. This procedure allowed the comparison of both the crystal structure and the morphology of the polymer. For the β‐nucleated iPP, by means of the WAXS measurements in the transmission mode, a maximum of the k‐value (fraction of β‐phase) was found for a concentration of 5 × 10−5 wt% of the trans‐quinacridone. By means of polarized light microscopy (PLM), the mold temperature and pigment concentration dependent spherulites distribution on the cross section of the samples was observed. DSC permitted confirmation of the WAXS measurements, giving a characteristic double melting peak for the β polypropylene. By isothermal WAXS measurements the temperature of 135°C as the upper limit of the β phase was detected. For both nucleating agents (linear trans‐quinacridone and dimethyl quinacridone) the dependence of the mechanical properties (modulus of elasticity and brittleness by impact resistance) on the pigment concentration was observed. For the β‐phase iPP the highest ductility by impact testing corresponds to the highest values of the k parameter. The explanation is based on the SEM observations, which permitted the detection of spherulites with cross‐hatched lamellae (for the α‐spherulites) and with simple radial growth lamellae for the β‐spherulites.
Conductive polymer blends prepared by in situ polymerization of pyrrole: A review
Authors: De Jesus M. C. , Fu Y. , Weiss R. A.
Published: April 2004

Electrically conductive polymer blends can be prepared by in situ polymerization of pyrrole within another polymer matrix. This may be accomplished using either electrochemical or chemical oxidative polymerization. This paper reviews the literature on this subject.
Convective and radiant (IR) curing of bulk and waterborne epoxy coatings as thin layers. Part I: Methodology
Authors: Blanc D. , Laurent P. , Andrieu J. , Gérard J. F.
Published: April 2004

A method for studying the curing of 100 μm‐thick epoxy‐based layers coated on steel substrates is described. A simple waterborne epoxy reactive system based on a diglycidylether of bisphenol‐A prepolymer and with a polyether triamine was set up by emulsifying the epoxy resin with the use of an ethoxylated‐nonylphenol emulsifier. The parliculur phenomena involved during the isothermal curing of such an epoxy emulsion were decomposed by considering the same formulation without water and without water + emulsifier. The chemical kinetics were determined by DSC and by size exclusion chromatography. As previously proposed for numerous epoxy‐amine reactive systems, for the three types of coatings, a second‐order autocatalytic law was able to interpret the data. The presence of water delays the gelation characterized by rheological measurements. As a consequence, the epoxy conversion at the gel point increases. This phenomenon can be related to the inhomogeneous polymerization process during which the epoxy groups can be trapped into the initial epoxy particles. In addition, the microdielectrometry technique was used to follow the curing degree of the epoxy reactive system of thin layers during the drying and curing processes under radiant heatings such as infrared curing.
Synthesis and properties of new polymaleimides containing allyl groups
Authors: Guozheng Liang , Aijuan Gu
Published: April 2004

Two new polymaleimides containing allyl groups in their backbone were synthesized and characterized. The synthesis of these polymaleimides was carried out by reacting allyl polyamine with maleic anhydride. The monomers were characterized by infrared spectroscopy (IR), 13C‐NMP, and elemental analysis. Differential Scanning Calorimetry (DSC) of monomers showed that the presence of allyl groups reduces the curing temperature. Thermogravimetric analysis (TGA) revealed that all polymers were stable up to 400°C in air or 500°C in nitrogen atmosphere. Their char yield at 800°C under anaerobic conditions was 58–61%.
A model for the non‐isothermal viscoelastic behavior of polymers
Authors: Drozdov Aleksey D.
Published: April 2004

A new constitutive model is derived for the viscoelastic behavior of polymers under non‐isothermal loading. The model extends the Tobolsky concept of adaptive links (entanglements) between polymeric molecules to thermoviscoelastic media. Employing this model, we calculate residual stresses built up in an epoxy resin plate under cooling from the rubber‐glass transition temperature, analyze the effect of material parameters on residual stresses, and compare results of numerical simulation with experimental data.
Living radical polymerization. II. Improved atom transfer radical polymerization of acrylamide in aqueous glycerol media with a novel pentamethyldiethylenetriamine‐based soluble copper(I) complex catalyst system
Authors: Jewrajka Suresh K. , Mandal Broja M.
Published: April 2004

An improved atom transfer radical polymerization (ATRP) of acrylamide was achieved in a glycerol/water (1:1 v/v) medium with 2‐halopropionamide initiators, CuX (X = Cl or Br) as catalysts, pentamethyldiethylenetriamine (PMDETA) as a ligand, and CuX2 (≥20 mol % CuX) and excess alkali halide (ca. 1 mol/dm3) as additives. The first‐order kinetic plots for the disappearance of the monomer at 130 °C were linear; this was a significant improvement over the results obtained earlier with the bipyridine ligand. However, even under such improved situations, about 7 mol % of the polymer chains were estimated to be formed dead. The polydispersity index was approximately 1.5. At a lower temperature (ca. 90 °C), a lower polydispersity index (1.24) was obtained for the bromide‐based initiating system. Chain‐extension experiments proved the living nature of the polymers. The presence of both extra halide ions and the monomer was necessary to take the CuX–PMDETA complex into solution. It was suggested that the soluble Cu(I) complex was formed with one PMDETA molecule acting as a monodentate ligand and with two halide ions and one acrylamide molecule occupying the other three coordination sites. Some support for the involvement of all three ligands (X−, PMDETA, and acrylamide) in the complex formation was obtained from ultraviolet–visible spectroscopy studies. The better ATRP with the PMDETA ligand was attributed to the better stability and lesser hydrolysis of the 1:1 Cu+2/PMDETA complex with respect the corresponding bipyridine complex. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2483–2494, 2004
Synthesis and properties of fluorine‐containing polyethers with pendant hydroxyl groups by the polyaddition of bis(epoxide)s with diols
Authors: Konno Yousuke , Kudo Hiroto , Kameyama Atsushi , Nishikubo Tadatomi
Published: April 2004

Fluorine‐containing polyethers with pendant hydroxyl groups were synthesized by the polyaddition of fluorine‐containing bis(epoxide)s with certain fluorine‐containing diols with quaternary onium salts as catalysts. When the polyaddition was performed with 2,2′,6,6′‐tetrafluoro‐4,4′‐biphenol diglycidiyl ether and 2,2′,6,6′‐tetrafluoro‐4,4′‐biphenol, the corresponding polyether with pendant hydroxyl groups was successfully obtained in good yield. The polyaddition of certain fluorine‐containing bis(epoxide)s with diols also proceeded in bulk to provide the corresponding fluorine‐containing polyethers with high molecular weights. These polyethers were highly transparent at 157 nm for 0.1 μm thickness, with their transmittance of 14–75% at 157 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2543–2550, 2004
Reaction of carbon dioxide with glycidol: The synthesis of a novel hyperbranched oligomer with a carbonate main chain with a hydroxyl terminal
Authors: Motokucho Suguru , Sudo Atsushi , Sanda Fumio , Endo Takeshi
Published: April 2004

A novel branched polycarbonate with a hydroxyl group at the chain end was synthesized by the copolymerization of glycidol with carbon dioxide (CO2). The copolymerization was carried out with 5 mol % of an alkali metal halide or quaternary ammonium salt as a catalyst under atmospheric CO2. The obtained poly(glycidol‐co‐carbon dioxide) was O‐benzoylated and O‐silylated, and the corresponding polymers were analyzed with IR, size exclusion chromatography, 13C NMR, and 29Si NMR. The IR spectroscopy analysis of the O‐benzoylated polymer revealed that the maximum incorporation degree of the carbonate group was 90% (i.e., the CO2/glycidol composition ratio was 0.9:1.0). The incorporation of CO2 as a carbonate unit was also confirmed by the treatment of this polymer with n‐butylamine, which caused the aminolysis of the carbonate and led to degraded products. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2506–2511, 2004
13Carbon nuclear magnetic resonance of ethylene–propylene–1‐hexene terpolymers
Authors: Escher Fernanda F. Nunes , Galland Griselda Barrera
Published: April 2004

We report the complete 13C NMR characterization of a series of ethylene–propylene–1‐hexene terpolymers obtained with the metallocenic system rac‐ethylene bis‐indenyl zirconium dichloride, with different comonomer ratios. A detailed study of 13C NMR chemical shifts, triad sequence distributions, monomer‐average sequence lengths, and reactivity ratios for these terpolymers is presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2474–2482, 2004
Polyelectrolyte complexes. VI. Polycation structure, polyanion molar mass, and polyion concentration effects on complex nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate)
Authors: Dragan Ecaterina Stela , Schwarz Simona
Published: April 2004

The formation and characterization of some interpolyelectrolyte complex (IPEC) nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate) (NaPAMPS), as a function of the polycation structure, polyanion molar mass, and polyion concentration, were followed in this work. Poly(diallyldimethylammonium chloride) and two polycations (PCs) containing (N,N‐dimethyl‐2‐hydroxypropyleneammonium chloride) units in the backbone (PCA5 and PCA5D1) were used as starting polyions. The complex stoichiometry, (n−/n+)iso, was pointed out by optical density at 500 nm (OD500), polyelectrolyte titration, and dynamic light scattering. IPEC nanoparticle sizes were influenced by the polycation structure and polyanion molar mass only before the complex stoichiometry, which was higher for the more hydrophilic polycations (PCA5 and PCA5D1) and for a higher NaPAMPS molar mass, and were almost independent of these factors after that, at a flow rate of the added polyion of about 0.28 mL × (mL PC)−1 × h−1. The IPEC nanoparticle sizes remained almost constant for more than 2 weeks, both before and after the complex stoichiometry, at low concentrations of polyions. NIPECs as stable colloidal dispersions with positive charges in excess were prepared at a ratio between charges (n−/n+) of 0.7, and their storage colloidal stability, as a function of the polycation structure and polyion concentration (from 0.8 to ca. 7.8 mmol/L), was demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2495–2505, 2004