bluuebunny/crossref_metadata_2025_split huggingface dataset:
A barometer of crystallization rates of polymeric materials
Authors: Khanna Y. P. 
Published: May 2005

AbstractA crystallization rate coefficient (CRC) parameter is introduced which has allowed a direct comparison of the crystallization rates of various polymers on a single scale for the first time. Basically, CRC represents a change in cooling rate required to bring about 1°C change in the supercooling of the polymer melt. For the polymers studied, this value varies between 35 h−1 (polyethylene terephthalate) and 155 h−1 (poly(tetrafluoroethylene)) and jumps to 295 h−1 for indium metal; the precision being better than ±5 percent. The reliability of CRC has been tested against the established trends e.g., (i) a large decrease in the crystallization rate of polyethylene terephthalate with increase in molecular weight, (ii) a lower crystallization rate of the “virgin” nylon 6 as compared to the processed nylon 6 resin, (iii) an increase in the crystallization rate of nylon 6 in the presence of nucleating agents, and (iv) a dramatic increase in crystallization rate as we go from poly(ethylene terephthalate) to poly(tetrafluoroethylene) and then from poly(tetrafluoroethylene) to the metals. The significance of the CRC barometer is discussed in the light of prior difficulties in directly comparing the crystallization rates of polymers.
Knit line fractures in injection molded liquid crystalline polymers
Authors: Engberg K. , Knutsson A. , Werner P.‐E. , Gedde U. W. 
Published: May 2005

AbstractThe microstructure and fracture behavior of Injection molded samples of unfilled and filled grades of liquid crystalline polymers (Vectra® and Ultrax®) containing cold and warm knit lines have been studied by scanning electron microscopy, X‐ray scattering, and Instron tensile tests. Four process parameters—melt temperature, mold temperature, injection time, and holding pressure—have been varied in accordance with a 24 factorial design experiment. In cold knit lines a 200 µm thick region with transverse orientation with Hermans orientation function f ≈ 0.12–0.18 is formed on both sides on the weld area. The strength of the cold knit lines is very low, 9.0–19.8 MPa corresponding to 15–20% of the full strength of the material. The strength of the warm knit lines increases markedly with increasing distance from the insert and is generally significantly greater (40–45 MPa, 48 mm from the insert) than in the cold welds. Annealing at 260–300°C of samples containing cold knit lines causes first a partial healing of the knit line and later extensive chemical degradation of the polymer.
Mechanical properties and mechanism of the degradation process of 316°C isothermally aged graphite fiber/PMR‐15 composites
Authors: Scola D. A. , Vontell J. H. 
Published: May 2005

AbstractA series of graphite fiber/PMR‐15 polyimide composites, isothermally aged at 316°C in flowing air (100 cc/min) for time periods up to 2000 h, were investigated for mechanical property changes, fiber/resin interface changes, overall dimensional changes, and weight loss. The mechanism of the degradation process is suggested based on shear and flexural property measurements at room temperature and 316°C, optical micrographs of composite cross sections, and SEM analysis of fractured surfaces. The fiber materials investigated in composite form were Celion 6000 unsized and epoxy sized. G40‐700 unsized and epoxy sized, and T40R and IM6 both unsized.
Interpenetrating polymer network approach to tough and microcracking resistant high temperature polymers. Part III. LaRC‐RP71
Authors: Pater Ruth H. 
Published: May 2005

AbstractA high performance semi‐interpenetrating polymer network (semi‐IPN) has been synthesized from Thermid‐600 and LARC‐TPI. Notable improvements in resin fracture toughness and graphite fiber reinforced composite microcracking resistance over the unmodified Thermid‐600 neat resin and composite have been realized. The chemistry, processing, physical and mechanical properties, and phase morphology of the neat resin and composite reinforced with graphite fibers are presented.
Vibration based non‐destructive evaluation of polymer composites
Authors: Shelby M. D. , Tai H. J. , Jang B. Z. 
Published: May 2005

AbstractA feasibility study on the use of vibration spectrum analysis as a tool for nondestructive evaluation (NDE) of polymer composites was conducted. Material integrity of polymer composite samples was determined from the vibrational measurements by analyzing the resonant frequency and damping information. A number of important “states” in the composites tested could be characterized by this analysis. The vibration tehnique was found to be sensitive to physical flawing (fiber breakage, delamination, and matrix cracking). Vibrational NDE has many potential advantages that make it very attractive for composite applications. These include the ability to make global measurements of large structures in real‐time, no geometry restrictions, and high sensitivity to a wide variety of damage states.
Crystallization kinetics of poly(ethylene terephthalate). Part I: Kinetic equation with variable growth rate
Authors: Kim S. P. , Kim S. C. 
Published: May 2005

AbstractA new crystallization kinetic equation has been derived considering the decrease in growth rate. The average linear growth rate of spherulite was assumed to be proportional to the m‐th order of the uncrystallized fraction of the crystallizing material. A modified Avrami equation, 1 − Vc = exp[‐Kf(t)n], was used where f(t) is the integral of the growth function, (1 − Vc)m. The validity of the equation was tested by analyzing the isothermal crystallization kinetic data of poly(ethylene terephthalate) from the melt using differential scanning calorimetry.
Models for the compressibility of layered polymeric sponges
Authors: Swyngedau S. , Nussinovitch A. , Peleg M. 
Published: May 2005

AbstractThe characteristic sigmoid compressive stress‐strain relationships of sponges and their layered arrays are described by two kinds of mathematical models having three experimentally determined parameters. Since sponge compression is not accompanied by a significant cross‐sectional area expansion, it was assumed that the stress in a multilayered array is the same in each layer. This enables prediction of the array's stress‐strain relationship from the parameters of the individual layers and their known thickness. The applicability of the method is demonstrated with experimental data of two kinds of double‐layered arrays of polyurethane sponges. It is shown that the arrays' compressive behavior can be satisfactorily predicted irrespective of the mathematical form of the model and whether the strain is expressed as engineering strain or Hencky's.
Study of rubber‐modified brittle epoxy systems. Part I: Fracture toughness measurements using the double‐notch four‐point‐bend method
Authors: Sue Hung‐Jue 
Published: May 2005

AbstractThe double‐notch four‐point‐bend (DN‐4PB) technique is known to produce fruitful information revealing the toughening mechanisms around the sub‐critically propagated crack tip. In this study, correlations among the single‐edge‐notch three‐point‐bend (SEN‐3PB), the single‐edge‐notch four‐point‐bend (SEN‐4PB), and the DN‐4PB toughness measurement techniques have been conducted using various modified‐epoxy systems. The toughnesses of both the neat and rubber‐toughened epoxy systems are found to be independent of the testing techniques used. Specifically, when the peak load is plotted against B. W1/2/Y (B: thickness, W : width, and Y: correction factor), the data obtained from SEN‐3PB, SEN‐4PB, and DN‐4PB all fall on the same line. The slope of this line is defined as the stress intensity factor. These results imply that with a single DN‐4PB test, it is possible to gain the information needed to describe both the toughening mechanisms and the fracture toughness value of relatively brittle (KIC ≤ 1.2 MPa. M1/2) polymeric materials.
Morphology and strength of polycarbonate to poly(butylene terephthalate) vibration‐welded butt joints
Authors: Hobbs S. Y. , Stokes V. K. 
Published: May 2005

AbstractUnder the right conditions, the strength of vibration‐welded butt joints of amorphous polycarbonate (PC) to semicrystalline poly(butylene terephthalate) (PBT) are shown to be as high as the strength of PBT, the weaker of the two materials. Optical, scanning and transmission electron microscopy are used to examine the morphology of the weld zone. Acoustic microscopy is used to visualize poorly bonded regions. The effects of the weld parameters on weld strength and weld morphology are considered in detail.
Strength of glass‐filled modified polyphenylene oxide vibration‐welded butt joints
Authors: Stokes Vijay K. 
Published: May 2005

AbstractThe strengths of glass‐filled modified polyphenylene oxide (GF‐MPPO) welds relative to the strengths of GF‐MPPO are shown to depend on specimen thickness. (Modified polyphenylene oxide is a blend of poly (2,6‐dimethyl‐1,4‐phenylene ether) and high‐impact polystyrene.) Relative strengths on the order of 70 and 87 percent can be achieved in 6.1 and 3.18‐mm‐thick specimens, respectively. Welds of GF‐MPPO to modified polyphenylene oxide (MPPO) can easily attain the strength of MPPO, the weaker of the two materials. In contrast to MPPO, in which weld strength decreases with increased weld pressure, the strengths of GF‐MPPO to GF‐MPPO welds and GF‐MPPO to MPPO welds, are not affected by weld pressure.
Quality assurance of computer controlled hot‐tool welding for mass production
Authors: Potente H. , Natrop J. 
Published: May 2005

AbstractThe hot‐tool welding process is commonly used for welding plastics, but high seam quality can be obtained only by optimizing weld parameters. Because of demand for better quality, the importance of quality control is increasing. At present, quality control is mainly performed by inspecting the end product, resulting in high scrap rates. An effective quality control system must therefore be able to recognize errors as they occur during the manufacturing process. For this, an FMEA (Failure Mode Effect Analysis) should be performed prior to mass production, and statistical quality control should be implemented during and after the process. This paper describes a quality control system for computer controlled hot‐tool welding that is based on an understanding of the physics of the process.
Dual polymer bonding of thermoplastic composite structures
Authors: Smiley A. J. , Halbritter A. , Cogswell F. N. , Meakin P. J. 
Published: May 2005

AbstractThis paper describes a process that facilitates fusion bonding of thermoplastic composite components without the need for complex fixtures and without disrupting the fiber alignment in the component laminates. The dual polymer bonding process, Thermabond, requires that an interlayer polymer be fused to the surface of each laminate prior to bonding. The characteristics of the interlayer polymer allow for joining of the components at a temperature below the softening/melting point of the reinforced polymer in the composite laminates. This leads to significant processing advantages without significant loss in mechanical performance. Discussions of resin compatibility, the effect of process conditions on mechanical performance, and the application of the APC‐2/PEI Thermabond system to various structural components are included.
Orientation studies of poly(vinyl chloride). Part I: Intrinsic birefringence
Authors: Jabarin Saleh A. 
Published: May 2005

AbstractThe intrinsic birefringence of rigid poly(vinyl chloride), PVC, was obtained from measurement of birefringence and infrared dichroism. Rigid PVC samples were stretched at temperatures above the glass‐transition temperature, Tg, to various stretch ratios. The measured intrinsic birefringence obtained in this study is consistent with theoretically calculated and previously measured values using other techniques and samples. From the intrinsic birefringence, the principal polarizability differences of the PVC monomer were also calculated, and the results are comparable with those estimated from flow birefringence measurements of PVC dilute solutions.
Study of birefringence character of injection‐ and compression‐molded polycarbonate and its interpretation
Authors: Wu Jong‐Pyo , White James L. 
Published: May 2005

AbstractBirefringence development in molded polycarbonate is of great importance in the manufacture of optical discs. It is important in characterizing birefringence to realize that we are dealing not with a scalar but with the anisotropy of the refractive index tensor–and with the orientation and shape of the refractive index ellipsoid. This usually varies heterogeneously; i.e., point‐to‐point through the thickness of molded parts. We present here an experimental study of the shapes and orientations of refractive index ellipsoids in injection‐ and compression‐molded polycarbonate parts. We consider the variations in ellipsoid character as a function of molding conditions such as injection rate and quench. In injection‐molded parts, the refractive index ellipsoid is coaxial with the flow direction in the center of the parts, but varies with position in the direction of the mold walls. In some cases, the extinction angle reaches a maximum at the mold wall and in other cases, there is an intermediate maximum. In the central “flow‐thickness” direction plane, the transverse axis of the refractive index ellipsoid is perpendicular to this plane. The birefringence (in principal axis coordinates) in the flow‐thickness direction plane exhibits an intermediate maximum whose position and magnitude vary with molding conditions. In some cases, multiple maxima exist. In compression‐molded parts, a principal axis is normal to the mold wall. The results are interpreted in terms of the Rheo‐Optical Law using flow‐induced orientation and residual stress mechanisms. If the contribution of the residual stress to the birefringence can be subtracted, we may compute biaxial orientation factors. We do this for a case that has low residual quench stresses.
Theory of crystallization in high‐speed spinning
Authors: Schultz J. M. 
Published: May 2005

AbstractRemoval of the heat of fusion during steady‐state crystallization in a high‐speed spinline places restrictions on the morphology of the crystallites. An appropriate model is that of a thermal dendrite. It is shown that for this case there exists at each temperature along the threadline a limiting growth velocity, beyond which heat cannot be conducted away fast enough to permit growth. It is suggested that crystallization occurs when a fluid element reaches a temperature at which heat can just be conducted away rapidly enough. Comparison of dendrite theory predictions with experimental values of crystallite diameter and crystallization temperature shows satisfactory agreement. Poly(ethylene terephthalate) has been taken as the example.
Phase behavior and mechanical properties of poly‐p‐phenylene terephthalamide/amorphous nylon molecular composites
Authors: Yang Jen‐Chang , Fukai Tomohiro , Kyu Thein 
Published: May 2005

AbstractPoly(p‐phenylene terephthalamide) (PPTA)/amorphous nylon (AN) molecular composites were prepared from sulfuric acid solution by rapidly coagulating in distilled water. The regenerated films appear homogeneous and transparent. However, the rod‐like and flexible macromolecules are probably entrapped in a single phase during rapid coagulation, thus thermodynamically unstable and undergoing phase segregation upon thermal treatment. The miscibility between PPTA/AN was identified by a dielectric relaxation method. Phase behavior and kinetics of phase separation in PPTA/AN mixtures were thoroughly investigated by time‐resolved light scattering as well as optical microscope. A pseudo phase diagram reminiscent of a lower critical solution temperature (LCST) was established by a cloud point measurement. Several temperature‐jump experiments were undertaken from ambient to a two‐phase temperature region. The low PPTA content molecular composites were prepared by coagulating in a non‐solvent, then by compression molding below the phase separation temperatures. The 30 wt% PPTA molecular composite exhibits over three‐fold increase in tensile modulus relative to that of the neat AN, however, there is little or no improvement in the tensile strength. On the other hand, by a slight addition of AN into PPTA, the tensile and compressive failures of spun fibers may be improved.
Parison swell—A new measurement method and the effect of molecular weight distribution for a high density polyethylene
Authors: Swan P. L. , Dealy J. M. , Garcia‐Rejon A. , Derdouri A. 
Published: May 2005

AbstractThe measurement of parison swell is difficult because swell is a time‐dependent phenomenon and because, for a parison, two independent swell ratios must be determined. A new technique has been developed that makes use of a video camera focused on the end of the parison. Unlike previous techniques designed to measure time‐dependent swell, no oil bath is required. The new technique was used to study the effect of molecular weight parameters on the parison swell of high density polyethylene. For a series of blends of two resins having significantly different weight‐average molecular weights, the blends exhibited larger swell ratios than the base resins.
Crystallization kinetics during polymer processing—Analysis of available approaches for process modeling
Authors: Patel Rajen M. , Spruiell Joseph E. 
Published: May 2005

AbstractAn analysis of available methods of dealing with polymer crystallization for process modeling is presented. Problems encountered in using isothermal data to predict nonisothermal results are discussed and illustrated using experimental data for nylon 6. A half‐time analysis is used to evaluate and extrapolate the isothermal crystallization rates. It is concluded that none of the available models are entirely satisfactory for computing nonisothermal crystallization from isothermal data, though the Nakamura model is shown to be more satisfactory for process modeling than other models discussed in the literature. A nonlinear regression method is presented for directly fitting nonisothermal crystallinity data using the Nakamura model to obtain crystallization rate equation parameters. Two empirical methods for including amorphous orientation effects are also considered and evaluated by comparing predicted results to online experimental data for melt spinning of nylon 6.
Rheological and morphological characterization of selected poly(organo)phosphazenes
Authors: Mujumdar A. N. , Kojima M. , Young S. G. , Chan E. K. , Magill J. H. 
Published: May 2005

AbstractRheological properties of selected poly(organo)phosphazenes have been studied using capillary rheometry. Melt viscosities of polymers were calculated as a function of shear stress and shear rate. Thermal stability was also studied. In the range of shear rate studied, all polyphosphazenes showed shear thinning behavior. The power law model was fitted to the data to get the power law index and the consistency index. Poly[bis(phenoxy)phosphazene] showed a Newtonian plateau at low shear rates whereas poly[bis(trifluoroethoxy)phosphazene] and poly[bis(p‐phenylphenoxy)phosphazene] which exhibited liquid crystalline character were shear thinning even at low shear rates. Solid state capillary extrusion of polyphosphazenes was found to be more successful in fiber formation than other “state‐of‐the‐art” processes, such as gel‐spinning. The molecular weights of all polyphosphazenes synthesized were found to be too low for, Couette fiber spinning. Chemical, physical, and morphological studies were made on all fibers prepared. Many investigative techniques, such as X‐ray diffraction, differential scanning calorimetry (DSC), density measurements, scanning electron microscopy (SEM), optical microscopy, solution nuclear magnetic resonance (NMR) spectroscopy, and gel permeation chromatography (GPC) analysis are featured in this paper as characterization tools.
An ultraviolet method for the determination of the residence time distribution in a twin screw extruder
Authors: Cassagnau P. , Mijangos C. , Michel A. 
Published: May 2005

AbstractThe stereoselective substitution of chlorine atoms was used to graft anthracene and phenyl groups onto the poly(vinyl chloride) (PVC) backbone as ultraviolet (UV) tracers for the assessment of the residence time distribution (R.T.D) of PVC chains during the extrusion of rigid and plasticized PVC. The residence time distribution obtained using these‐grafted tracers was compared with that obtained using a free UV tracer (anthracene). The polymeric tracer had a narrower R.T.D and a shorter mean residence time. This difference of behavior between a free and grafted tracers was attributed to the compatibility of these tracers with the PVC.
Mechanical modeling of initiation of localized yielding under plane stress conditions in rigid‐rigid polymer alloys
Authors: Sue H. J. , Pearson R. A. , Yee A. F. 
Published: May 2005

AbstractTwo‐dimensional Finite Element Method simulations, which involve consideration of the nonlinearity of a material, have been conducted to gain understanding about the rigid‐rigid polymer toughening concept we proposed. The simulation results for the plane stress condition indicate that as long as the inclusion phase possesses (i) a 60% difference in the tangent modulus from that of the matrix at any given strain level prior to failure or (ii) smaller yield or craze stain than the yield strain of the matrix, then, localized shear yielding will occur around the inclusion. A toughened rigid‐rigid polymer alloy system can then be obtained. The plain strain case is also discussed with an implementation of the rigid‐rigid polymer toughening concept.
A study on the performance of barrier‐screw extruders
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C. 
Published: May 2005

AbstractAn experimental and theoretical study was conducted on the performance of barrier‐screw extruders. For the experimental study, an extruder (D = 63.5 mm and L/D of 24) with a Davis‐Standard barrier screw was used to extrude a low‐density polyethylene. The extruder had nine pressure transducers which were mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel, so that we could measure axial pressure profiles during extrusion. Also conducted were tracer experiments (i.e., screw ‘pushout’ experiments), which enabled us to examine the profiles of melt film thickness in the solid channel. For the theoretical study, the analysis of Elbirli, et at, was extended by making the following modifications: (a) the flow through the barrier flight clearance was treated separately from the flow of melt film above the solid bed; (b) the melt films surrounding the solid bed were assumed to circulate around the solid bed; and, (c) convective heat transfer was included in the energy equations for the melt channel and melt films surrounding the solid bed. Prediction of axial pressure profile was found to be in reasonable agreement with experiment. Predictions are presented of the effects of extrusion conditions on the thicknesses of the upper and lower films, and on the solid‐bed velocity. Practical implications of these results are discussed from the view of designing barrier screws and selenting barrier‐screw extruders.