bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimum heating system design for compression molds
Authors: Kwon T. H. , Forcucci S. J. 
Published: December 2004

AbstractCompression molding is a widely used method of forming composite materials where long fibers are necessary for strength requirements. Compression molding involves putting the charge through a specific, material dependent temperature and pressure path to induce thermochemical cure. During cure, certain temperatures are required for a time. Spatial variation of the cavity temperature can lengthen time needed for curing and cause voids and residual stresses in the part. Towards the goal of uniform cavity surface temperature, an interactive graphics based computer aided system for compression mold heating design has been developed. The system employs a boundary element method treating long, thin cylindrical electric heating elements as singular line sources. It is coupled with a CONMIN algorithm, a nonlinear constrained minimization procedure to, optimize the heating system for uniform temperature over the cavity surface. Realistic constraints are featured to insure design feasibility. The problem is also decomposed in such a way to allow easy redesign and a sensitivity study. Through the optimization process, it was found that uniformities can be obtained which are far better than anything that could be achieved through common sense.
Determination of poisson's ratio for polyimide films
Authors: Bauer C. L. , Farris R. J. 
Published: December 2004

AbstractThe Poisson's ratios of polyamic acid and polyimide films were determined using a high pressure gas dilatometer. In this technique, a sample is held at constant length and a hydrostatic pressure is applied to the sample. The resulting change in stress on the sample with applied pressure provides a measure of Poisson's ratio. For fully cured polyimide films based on pyromellitic dianhydride and oxydianiline, Poisson's ratio was measured to be 0.34 at approximately 1% strain. This value increases to 0.48 as the strain is increased to 5%.
The processing and use of organosilicon polymers for photonic applications
Authors: Bagley B. G. , Quinn W. E. , Kurkjian C. R. 
Published: December 2004

AbstractThree potential applications for the “ladder” siloxanes in photonic technologies are discussed. These are: (1) as a silica fiber cladding material for which a silica fiber core‐siloxane cladding index depression (Δn) of 0.04 is observed; (2) as a fiber coating material to provide mechanical and environmental protection for which a siloxane coated silica core fiber is observed to have improved properties over a fiber coated with an epoxy‐acrylate or linear siloxane. Thus, the ladder siloxane can serve a dual coating/cladding function; and (3) as the passive lightguiding element in planar optoelectronics for which the index depression (Δn), as compared to silica, is 0.04 for the cured siloxane. 0.02 for a fenestrated silica obtained by removing the organic component from the siloxane, or values between 0.02 and 0.0 obtained by sintering this fenestrated silica.
Parametric sensitivity of chain polymerization reactors exhibiting the trommsdorff effect
Authors: Kapoor Bir , Gupta Santosh K. , Varma Arvind 
Published: December 2004

AbstractThe recently developed mathematical technique for studying the parametric sensitivity of reactors is extended to include chain polymerization systems exhibiting the gel and glass effects, as well as physical property variations. The sensitivities of the two temperature maxima with respect to various parameters are computed. It is found that, for a sample system, poly(methyl methacrylate), all the sensitivities of the gel effect induced temperature peak attain their maxima at the same conditions—this leads to a generalized temperature sensitivity constraint applicable to reactor design or operation. This sensitivity boundary is associated with high conversions and high molecular weights. The analysis shows that the dimensionless propagation activation energy, ϵp, and the dimensionless initiation activation energy, ϵd, are the two most important parameters governing the system performance. Sensitivities of the gel effect‐induced number average chain length peak with respect to various parameters are also obtained. Again, all of these chain length sensitivities show maxima at the same condition, leading to the concept of a generalized chain length sensitivity criterion of constraint. Most importantly, the temperature and chain length sensitivity boundaries are virtually identical.
Recent developments in hot plate welding of thermoplastics
Authors: Watson M. N. , Murch M. G. 
Published: December 2004

AbstractThis paper considers the hot plate welding process applied to three injection molded thermoplastic materials: polypropylene, high impact polystyrene, and poly(phenylene oxide). Weld quality was assessed by tensile testing. The process was found to be suitable for all three materials, although tolerance to variations in process parameters varied. The parameters in the heating phase, i.e., hot plate temperature and time, were the most important for achieving good welds, whereas parameter variations in the consolidation phase were relatively unimportant.
Grafting of unsaturated acids and silanes to ethylene polymers: A kinetic model
Authors: Motha Kshama , Seppälä Jukka , Bergström Christer 
Published: December 2004

AbstractA general kinetic model was developed to simulate the grafting of monomers such as unsaturated carboxylic acids and silanes to ethylene polymers. The polymers considered were ethylene‐co‐vinyl acetate (EVA), ethylene‐co‐butyl acrylate (EBA), and low‐density polyethylene (LDPE). Grafting was assumed to proceed by a free‐radical mechanism involving chain transfer. Organic peroxides having a strong tendency for hydrogen abstraction were selected as the source of primary radicals. The model simulated the grafting reaction as taking place in a single screw extruder. The residence time distribution in the extruder was experimentally determined by tracer analysis, according to which the extruder was a plug‐flow reactor connected to two mixed reactors in parallel. The model is able to predict the extent of grafting in terms of predefined parameters. Comparison of model predictions with available experimental data showed slight deviations, the possible causes of which are discussed. However, the kinetic behavior expected on the basis of the input parameters was observed, and, as such, the model allowed study of the effect of process variables on grafting kinetics and provided insight into the reaction mechanism.
Effect of processing on uniaxial creep behavior and environmental stress‐crack resistance of a linear low‐density polyethylene
Authors: Crissman J. M. 
Published: December 2004

AbstractThis paper describes characterizations performed on two types of polyethylene T‐Joints as well as the starting resin from which they were manufactured. It was found that the melt flow rate of material taken from the two types of joints differed from that of the starting resin and differed from each other by as much as a factor of two. Investigation of the environmental stress‐crack resistance (ESCR) and uniaxial creep behavior of material from the two joints revealed further significant differences in behavior between the two joints. These observations lead to the conclusion that subtle differences in the processing conditions can result in significant differences in the long‐term mechanical behavior.
Melt immiscibility in crosslinked polyethylene
Authors: Phillips P. J. , Vatansever A. 
Published: December 2004

AbstractLow density polyethylene crosslinked by decomposition of dicumyl peroxide shows evidence for two phases being present in the melt in a narrow temperature range just above the melting point. The effect has been studied in detail using differential scanning calorimetry, transmitted light intensity, and wide angle X‐ray diffraction studies at 107°C. It is believed that the effect is caused by the presence of relatively low molecular weight molecules which remain as an extractable fraction after crosslinking.
Measurement and correlation of mutual diffusion coefficients for styrene‐butadiene rubber (SBR)‐ethylbenzene systems
Authors: Iwai Yoshio , Miyamoto Shinji , Nakano Katsuyuki , Arai Yasuhiko 
Published: December 2004

AbstractThe mutual diffusion coefficients for styrene‐butadiene rubber (SBR)‐ethylbenzene systems were measured using a sorption apparatus with a quartz spring at 100 and 130°C for mass fractions of ethylbenzene ranging from 0 to 0.17. The mutual diffusion coefficients were correlated with good agreement by the free‐volume theory.
Isothermal volume relaxation in aged polycarbonate measured by positron annihilation lifetime spectroscopy
Authors: Hill A. J. , Katz M. , Jones P. L. 
Published: December 2004

AbstractThe positron annihilation lifetime spectroscopy (PALS) technique is used to measure volume relaxation in physically aged glassy polycarbonate. The relaxation times and activation energy calculated for the isothermal relaxations in the aged polycarbonate are greater than those parameters calculated for unaged polycarbonate. The activation energy of 8.2 kcal/mol in the aged polycarbonate is used to identify the phenyl group motion or the cooperative carbonate‐phenyl interaction as the molecular features responsible for the thermally induced open volume relaxations. It is postulated that the open volume relaxation kinetics as measured by PALS can be used as a nondestructive indication of property differences between aged and unaged polycarbonate.
High pressure tubular reactors for ethylene polymerization optimization aspects
Authors: Brandolin A. , Valles E. M. , Farber J. N. 
Published: December 2004

AbstractOptimal policies for operation of high pressure tubular reactors for ethylene polymerization are presented. The work is based on a previously developed model, allowing accurate representation of different configurations and operation conditions of industrial relevance. Several policies based on temperature and initiator concentration as control parameters are evaluated and compared.
Impact resistance performances of polyamide 6 blended with different rubber phases
Authors: Crespy A. , Caze C. , Coupe D. , Dupont P. , Cavrot J. P. 
Published: December 2004

AbstractWe have studied the impact strength, by Charpy and Izod tests, of blends of polyamide 6 with different rubbers, 10 wt% of each, or rubbers and glass fibers (8.5 wt% and 15 wt% respectively). The rubbers are from three different families: (i) a nonreactive cross‐linked terpolymer, methyl methacrylate/butadiene/styrene (17/64.5/18.5); (ii) two block copolymers compatible with the matrix, poly(tetramethylene glycol)/polamide 12 (70/30 or 34/66); and (iii) two polymers containing reactive functionality, a terpolymer ethylene/ethyl acrylate/maleic anhydride (68/30.5/1.5) and a copolymer ethylene/acrylic acid (90/10). The classification of additives in regard to improved impact depends on the procedure used for the impact strength measurement, particularly on whether the samples are notched or unnotched. The results are discussed in relation to the dimensions and the adhesion of the rubber particles. The level of adhesion has been estimated from observations in scanning electron microscopy of cavities due to pullout nodules and of nonextracted rubber after treatment in boiling xylene. Strong variations in the morphologies are found, depending on the chemical nature of the rubber. The crystalline state of the polyamide in the blends has also been evaluated from differential scanning calorimetry.
Fatigue strength of vibration welded thermoplastic butt joints
Authors: Stokes Vijay K. 
Published: December 2004

AbstractFatigue data are presented for the strengths of 120‐Hz vibration‐welded butt joints of four resins: the three amorphous polymers polycarbonate (PC), polyetherimide (PEI), and modified polyphenylene oxide; and the semicrystalline polymer poly(butylene terephthalate). Data are also presented for the fatigue strength of 250‐Hz vibration welds of the high‐temperature polymer PEI. For all the welds, fatigue strength was evaluated through 10‐Hz, tension‐tension, load‐controlled tests at an R value (ratio of minimum stress) of 0.1. Surprisingly, for all the stress levels studied, none of the PC test specimens failed at the welds, indicating that the fatigue strength of PC welds equals that of the base resin. This is not true of the other three resins, except at relatively low stress levels. For each of the four resins, macrographs are used to highlight the differences between the failure surfaces of monolithic specimens and specimens that failed at the welds.
Extension behavior and morphology in polypropylene extended under hydrostatic pressure
Authors: Ariyama Takashi , Takenaga Mitsuru 
Published: December 2004

AbstractThe effect of hydrostatic pressure on molecular deformation of polypropylene extended under hydrostatic pressure is investigated by using internal friction measurements, wide angle X‐ray diffraction, and polarizing microscopy. A homogeneously transparent straight part is obtained by extending samples in the pressure range from 78 to 128 MPa. The overall mechanical properties of a sample extended under P = 102 MPa is significantly different from that of a sample extended under P = 128 MPa. The difference is related to the magnitude of hydrostatic pressure, the extension ratio, and the extent of transparency. The observed results on the β relaxation in the extended samples is found to be related to the morphological reorganization from a coarse spherulitic to a fine spherulitic structure. The cold‐drawn sample at atmospheric pressure has the γ‐peak at around °50°C, while the hydrostatically extruded samples and the extended samples have no γ‐peak. Consequently, the hydrostatic pressure suppresses the formation of the molecular structure relevant to the γ relaxation.
On the solution of fiber orientation in two‐dimensional homogeneous flows
Authors: Akbar Sameer , Altan M. Cengiz 
Published: December 2004

AbstractThis work presents an analytical technique to describe the orientation behavior of short fibers in arbitrary two‐dimensional homogeneous flows. It is shown that the fiber orientation, specified by a unit vector, can be analytically calculated at any instant using any initial orientation and flow kinematics. The rotation of a fiber with the bulk fluid deformation is expressed in terms of orientation vector components by utilizing an equivalent strain tensor calculated from the fluid kinematics. This technique is then used to evaluate the orientation behavior of a large number of fibers starting from different initial orientations, representing an orientation state. The orientation distribution function is generated statistically by considering the frequency distribution curve of the orientation of the large number of fibers. It is shown that using a combination of analytical solutions and statistical methods provides a convenient description of fiber orientation behavior. The accuracy of the generated orientation distribution function is found to be dependent on the number of fibers used in the analytical solution. The statistical orientation distribution function is compared with the exact solutions for certain homogeneous flows and found to be in close agreement.
Studies on poly(vinylchloride)‐based polymer blends intended for medical applications. Part II: Mechanical properties
Authors: Pal S. N. , Ramani A. V. , Subramanian N. 
Published: December 2004

AbstractBinary polyblends of plasticized poly(vinylchloride) (PPVC1) with acrylonitrile‐butadiene rubber (NBR1), compounded graft polymer of vinyl chloride and ethylene‐vinyl acetate copolymer (EVAPVC) and ternary blends of PPVC1, NBR1, and EVAPVC were formulated to study mechanical properties. For the “pure” components, elongation at break was found to be in the order PPVC1 < EVAPVC < NBR1. Addition of both EVAPVC and NBR1 resulted in improvement of ultimate elongation and tensile energy to break. PPVC1‐NBR1 binary blends exhibited synergistic behavior for both ultimate tensile stress and elongation at break, indicating the presence of appreciable specific interactions between the polymers. About 30% replacement of PPVC1 by NBR1 or EVAPVC resulted in marginal fall in modulus and significant improvement in elongation at break. EVAPVC or blends containing EVAPVC had a tendency to creep. A simple generalized equation suggested for various mechanical properties works satisfactorily. The results obtained have practical implications and indicate that PVC‐based polyblends can be investigated further for potential applications in medicine.
Phase transformations in a thermotropic liquid crystalline copolyester and its blends with polyether sulfone
Authors: Zheng Johnny Q. , Kyu Thein 
Published: December 2004

AbstractMesophase transitions in a thermotropic liquid crystalline polymer comprising p‐hydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) in a copolymer ratio of 60/40 were studied by means of optical microscopy, light scattring, and wide‐angle X‐ray diffraction (WAXD). According to time‐resolved light scattering and optical microscopic studies, at about 250°C, a mesophase transition was evident in which Schlieren texture developed with elapsed time. This transition has been identified as a solid crystal‐nematic mesophase transition associated with the melting of PHB‐rich crystals. It is concluded that the copolymer sequence may not be random. An isotropic, amorphous blend of PHB‐PET/polyether sulfone (PES) was prepared by solvent casting from hexafluoro‐2‐propanol solution. However, this homogeneous blend appears to be kinetically entrapped during solvent removal. Thermally induced phase separation takes place upon heating slightly above the glass transition temperature of PES. Morphology development within phase‐separated domains has been qualitatively examined by light scattering and optical microscopy.
Optical waveguiding as a method for characterizing the effect of extended cure and moisture on polyimide films
Authors: Noe Susan C. , Pan Jeffrey Y. , Senturia Stephen D. 
Published: December 2004

AbstractIntegrated optics techniques (i.e., guiding light through a thin film) have been used to study the effects of extended cure and moisture exposure on polyimide films as manifested in changes in the TE (in‐plane) and TM (out‐of‐plane) refractive indices and in their difference (birefringence). Mechanical testing of these films has been done using the load‐deflection technique. Du Pont polyimide Pyralin 2555 and 2556 (benzophenone tetracarboxylic dianhydride‐oxydianiline/metaphenylene diamine), cured repeatedly at 400°C and 375°C respectively, show an increase in refractive index as a function of cure (possibly due to densification), as well as an increase in birefringence (due to increased residual stress). Upon exposure to moisture, the TM and TE refractive indices both increase (absorption of the polar water molecule), but the TE index does not increase as much. Mechanical testing has shown that the residual stress in the polyimide film increases with extended cure and decreases with moisture exposure due to moisture‐induced swelling of the film. A model is proposed which relates the optical results to the mechanical measurements. Based on our data, a preliminary stress‐optic coefficient is reported.
The structure of highly oriented high modulus polyethylene
Authors: Zubov Y. A. , Chvalun S. N. , Selikhova V. I. , Konstantinopolskaya M. B. , Bakeev N. Ph. 
Published: December 2004

AbstractA comparative study of the structure of uniaxially‐oriented bulk samples of linear PE of various molecular weights over a wide range of draw ratios has been carried out by means of small and wide angle X‐ray analysis, NMR‐spectroscopy and DSC. The structure of oriented high molecular weight PE samples, prepared by drawing single crystal mats to draw ratios up to 200, have also been studied. A large number of unfolded tie‐molecules have been found to exist in the trans‐conformation in PE amorphous regions. These tie‐molecules, which connect the adjacent crystallites along the axis of orientation, and are not large crystals, account for the high mechanical properties of these samples. It has been shown that in the course of the orientation process, chain unfolding in the amorphous regions is accompanied by the formation of continuous linear systems consisting of several coherent crystallites and tie‐molecules. These are coherently aligned along the macromolecular axis.
Emulsion copolymerization: Kinetics model and reactor performance
Authors: Quarderer George J. , Katti Sanjeev S. 
Published: December 2004

AbstractThe Dow process for producing perfluorinated ionomeric membranes includes several emulsion copolymerizations involving gaseous tetrafluoroethylene and a second liquid phase monomer. The choice of the organic phase monomer depends on the desired product. The emulsion copolymerization reactor model was developed by extending the Smith‐Ewart‐Gardon theory for emulsion polymerization processes. Population balance techniques and Flory‐Huggins solution theory were applied. The resulting coupled partial differential equations were solved using the method of characteristics. The reactor model, with minimal adjustable parameters, predicts most polymerization results, including molecular weight, reaction rates in the three process stages, latex particle size, polymer composition, and the composition drift as a function of reaction time. The analysis and reactor model is used in the manufacturing process to set process conditions to obtain the desired properties in the polymer product.
Synergism on tensile properties of injection molded polybutene‐1 /polypropylene blends
Authors: Lee Mao‐Song , Chen Show‐An 
Published: December 2004

AbstractBlends of polybutene‐ 1 (PB‐1) and polypropylene (PP) have been injection and compression molded. A synergism appears in the ultimate elongation and the tensile strength for the injection moldings. The maximum point of the synergism at the composition of 25 wt% PB‐1 shifts to 50 wt% PB‐1 after annealing at 145° C for 1 h. A linear relation and negative deviation from the additivity rule for these two properties are observed for the compression moldings with quick cooling and slow cooling, respectively. Thermal analysis, polarized optical microscopy, and scanning electron microscopy (SEM) are used to study the occurrence of the synergism. The mutual interference between the two components on the crystal formation and the plasticization effect of PB‐ 1 on PP result in the synergism. An increased phase separation probably occurs during the compression molding with slow cooling. So, the blends compression‐molded with slow cooling having a higher amount of PP have brittle breaks, similar to pure PP.
Three‐dimensional path line tracking and residence time distribution in fishtail dies
Authors: Huang Chin‐Ching , Tsay Sun‐Yuan , Wang Yeh 
Published: December 2004

AbstractThe flow kinematics of power‐law fluids in fishtail dies is studied. A general isothermal three‐dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super‐elliptical curves, which allows a smooth transition from a circle to a slit. The three‐dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power‐law index does not affect the residence time distribution significantly.