bluuebunny/crossref_metadata_2025_split huggingface dataset:
Orientation in polypropylene sheets produced by die‐drawing and rolling
Authors: Chaffey Charles E. , Taraiya Ajay K. , Ward Ian M. 
Published: April 2004

AbstractTwo 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

AbstractThe 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

AbstractIn 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

AbstractOrientation 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

AbstractThe 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

AbstractThe 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

AbstractUltrasonics 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

AbstractHighly 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

AbstractDifferential 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

AbstractCavity 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

AbstractCavity 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

AbstractAn 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

AbstractIsotaclic 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

AbstractElectrically 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

AbstractA 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

AbstractTwo 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

AbstractA 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

AbstractAn 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

AbstractFluorine‐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