bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rubber toughened and optically transparent blends of cyclic olefin copolymers
Authors: Khanarian G. 
Published: April 2004

AbstractA study is presented of increasing the toughness of Cyclic Olefin Copolymer (COC) while maintaining its optical transparency. The COC consists of a random copolymer of ethylene and norbornene, and the impact modifiers consist of thermoplastic elastomers. It is shown that several requirements must be satisfied, namely: for toughening there is an optimum finite particle size, but in order to minimize light scattering the particles have to be as small as possible. In addition, the refractive index of the elastomer must be closely matched to COC over the visible wavelength range and use temperature. Also for toughening, there are additional requirements of the adhesion of the elastomer to COC and high molecular weight. It is found that styrene butadiene styrene (SBS) is the most effective elastomer in toughening COC while maintaining optical transparency. It is also found that the addition of an index matched styrene‐ethylene‐butylene‐styrene (SEBS) copolymer as a compatibilizer to the SBS elastomer is beneficial in increasing the toughness and lowering the optical haze. Finally, light scattering calculations are presented based on the Rayleigh Debye model to calculate the optical haze and transmission of these blends. These calculations take into account the refractive index of COC and the elastomer, the particle size distribution and volume fraction of the elastomer. It is shown that there is reasonable agreement between calculation and experimental results. It is possible to increase the toughness of COC to greater than 50 J/m (Notched Izod) while keeping the optical haze to below 5% with an elastomer loading of 5% (w/w). We also identify opaque blends of COC with a toughness of greater than 500 J/m with an elastomer loading of 20% (w/w).
Pressure‐volume‐temperature behavior of polylactide, poly(butylene succinate), and poly(butylene succinate‐co‐adipate)
Authors: Sato Yoshiyuki , Inohara Kenzo , Takishima Shigeki , Masuoka Hirokatsu , Imaizumi Mitsuhiro , Yamamoto Hirokazu , Takasugi Masanobu 
Published: April 2004

AbstractPressure‐Volume‐Temperature (PVT) behavior of three biodegradable polymers, Polylactide, poly(butylene succinate), and poly(butylene succinate‐co‐adipate), was measured at temperatures from 313 to 493 K and pressures up to 200 MPa. The PVF data in molten state were compared with predicted values of a group contribution modified cell model equation of state (GCMCM EOS). It was found that the GCMCM EOS coupled with one specific volume datum at atmospheric pressure could predict the PVT of the polymer melts to within 0.46% in an average relative deviation of specific volume.
Control of injection velocity using a fuzzy logic rule‐based controller for thermoplastics injection molding
Authors: Tsoi Hoi‐Pang , Gao Furong 
Published: April 2004

AbstractInjection velocity to a large degree determines the melt injection rate during the injection phase, and it has critical impact on the molded part quality, such as shrinkage, warpage, and impact strength. An injection molding machine operates with different injection velocity profiles, barrel temperatures, molds, and materials. These strongly different molding conditions cause the injection velocity dynamics to very significantly and to make the control performance of the injection velocity poor with a typical PID controller. A real‐time, closed‐loop feedback and feedforward control system based on fuzzy logic has been designed, developed, and implemented to control the injection velocity. The fuzzy logic rules of the controller are optimized by analyzing phase plane characteristics. The controller output membership functions are optimized based on a 2k factorial design technique. The experimental results reveal that the fuzzy logic‐based controller works well with different molds, materials, barrel temperatures, and injection velocity profiles, indicating that the fuzzy logic controller has superior performance over the conventional PID controller in response speed, set‐point tracking ability, noise rejection, and robustness.
The effect of the addition of a low profile additive on the curing shrinkage of an unsaturated polyester resin
Authors: Liu C. J. , Kiasat M. S. , Nijhof A. H. J. , Blokland H. , Marissen R. 
Published: April 2004

AbstractComposites made of glass fibers and unsaturated polyester resins are widely applied for various products. The failure processes of such composites are insufficiently understood. Fracture of the resin often initiates bulk composite fracture. Residual stresses occur during the curing of the resin due to the resin volumetric shrinkage. These unfavorable stresses may enhance resin fracture. Moreover, resin shrinkage may decrease the surface quality of the product. The addition of Low Profile Additives (LPA) to the resin may decrease or even remove these problems. The shrinkage behavior of unsaturated polyester resin with varying amounts of LPA is investigated in this work. The emphasis is on the development of curing shrinkage occurring after the gel point of the resin and on accompanying shirnkage stresses. These stresses can be reduced and even reversed by the addition of LPA.
On a pure finite‐element‐based methodology for resin transfer molds filling simulations
Authors: Mohan R. V. , Ngo N. D. , Tamma K. K. 
Published: April 2004

AbstractA physically accurate and computationally effective pure finite‐element‐based methodology for Resin Transfer Molding (RTM) process simulations is presented. The formulations are developed starting with the time‐dependent mass conservation equation for the resin flow. Darcy's flow approximations are invoked for the velocity field, thereby forming a transient governing equation involving the pressure field and the resin saturation fill factor which tracks the location of the resin front surface. Finite element approximations are then introduced for both the fill factor and the pressure field, and the resulting transient discrete equations are solved in an iterative manner for both the pressures and the fill factors for tracking the progression of the resin front in an Eulerian mold cavity. The formulation involves only a pure finite‐element Eulerian mesh discretization of the mold cavity and does not require specification of control volume regions and has no time increment restrictions that exist as in the traditional explicit finite‐element‐control volume based formulations. The present formulations accurately account for and capture the physical transient nature of the mold‐filling process while maintaining improved numerical and computational attributes. Mold‐filling simulations involving various geometrically complex mold configurations are presented, demonstrating the applicability of the developments for practical manufacturing process simulations.
An unsteady multifluid flow model: Application to sandwich injection molding process
Authors: Schlatter G. , Agassant J. F. , Vincent M. , Davidoff A. 
Published: April 2004

AbstractThe sandwich molding process consists of injecting sequentially a skin and core polymers. The thermomechanical model describing the flow of the two polymers into the mold cavity is based on the lubrication approximations. A transport equation characterizes the displacement of the interface between the two fluids. An experimental study has been performed in order to test the influence of processing parameters (viscosities, flow rates, etc.) on the interface location. Numerical simulations are in agreement with measurements.
Measurements and modeling of PS/supercritical CO2 solution viscosities
Authors: Lee Minhee , Park Chul B. , Tzoganakis Costas 
Published: April 2004

AbstractThis paper presents a technology to determine the melt viscosity of a PS/super‐critical CO2 solution using a linear capillary tube die mounted on a foaming extruder. CO2 was injected into the extrusion barrel and the content of CO2 was varied in the range of O to 4 wt% using a positive displacement pump. Single‐phase PS/CO2 solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO2 solutions was determined. The experimental results indicate that the PS/CO2 solution viscosity is a senstive function of shear rate, temperature, pressure, and CO2 content. A theoretical model based on the generalized Cross‐Carreau model was proposed to describe the shear‐thinning behavior of PS/CO2 solutions at various shear rates. The zero‐shear viscosity was modeled using a generalized Arrhenius equation to accommo‐date the effects of temperature, pressure, and CO2 content. Finally, the solubility of CO2 has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.
Process‐induced residual stresses in compression molded UHMWPE
Authors: Miller Keith , Ramani Karthik 
Published: April 2004

AbstractNon‐isothermal cooling during processing causes the development of residual stresses, which are analyzed for compression molded UHMWPE, and affects the dimensional stability. The development of thermal residual stresses was predicted using an incremental stress analysis that included temperature‐dependent material properties. Strain gauges were used to measure the residual stresses as layers were removed from a molded disk using a Process Simulated Laminate (PSL) approach. The PSL technique has not previously been applied to a compression molded neat polymer. For initial surface cooling rates of ∼ 11°C/min, the model predicted a compressive stress at the bottom surface of 14 MPa and a tensile stress near the center of 2.5 MPa and matched the experimental distribution well. Because the compressive residual stress was 70% of the yield strength (∼20 MPa), a lower cooling rate was also tested (2.6°C/min). The maximum tensile and compressive stresses for this cooling rate were, 0.91 MPa and 2.5 MPa, respectively. The model demonstrated its use for predicting thermal residual stresses in compression molded parts, instead of trial‐and‐error experimentation. UHMWPE is shown to develop residual stresses continually from ∼ 120°C to 23°C.
Water blown free rise polyurethane foams
Authors: Niyogi Debdarsan , Kumar R. , Gandhi K. S. 
Published: April 2004

AbstractA model is developed in this work for predicting the bubble size distribution in polyurethane foams generated by using water as a chemical blowing agent. The model combines equations of energy balance, kinetics of the reactions of isocyanate with water and polyol, and nucleation and growth of CO2 bubbles. It is found that as the water content of the reaction mixture is increased, the mean bubble size decreases and the bubble size distribution become narrower. Exactly the opposite occurs in polyurethanes foamed with a physical blowing agent, e.g., DuPont Freons. This suggests that a combination of physical and chemical blowing agents can be employed to control bubble size distribution.
Experimental study of post‐shear crystallization of polypropylene melts
Authors: Lee O. , Kamal M. R. 
Published: April 2004

AbstractIn order to study the effects of Processing shear stresses on crystallization behavior, a fiber pullout technique was applied in conjunction with polarized light microscopy and a hot stage. The shear apparatus consisted of a single glass fiber sandwiched between two layers of polypropylene films mounted on the hot stage. At the crystallization temperature, shearing was introduced by pulling the fiber at a constant velocity for a fixed period of time. Static crystallization of the polymer then ensued. Computerized data acquisition and image analysis were employed to observe the evolution of crystallinity, morphology, and growth rates of crystallites in various shear and temperature fields. Two distinct morphological zones were produced upon fiber pullout: bulk spherulites and a shear‐induced layer localized within the vicinity of the fiber surface. The two zones displayed similar kinetic behavior despite the difference in appearance. A comparison of growth behavior in the two zones revealed rates independent of the shear rate but strongly dependent on the crystallization temperature. The main influence of the shear appeared to be in producing higher nucleation rates in the shear zone near the fiber.
Effects of solvent‐particle interaction kinetics on microstructure formation during three‐dimensional printing
Authors: Wu Benjamin M. , Cima Michael J. 
Published: April 2004

AbstractLactone‐based absorbable polyesters, such as polylactide‐co‐glycolides, are commonly used for the construction of biomedical devices. Many such devices can be constructed by a novel manufacturing technology known as three dimensional printingTM (3DPTM), which fabricates complex structures by ink‐jet liquid binder onto loose powder in a laminated fashion. The predominant 3DP binding mechanism for lactone based absorbable polyester powder is dissolution‐reprecipitation. The objective of this study is to compare the relative time scales for particle dissolution and solvent evaporation during 3DP processing. An experimental setup was devised to determine the time scale for particle dissolution. This time scale was found to be particle size independent for small particles, but size dependent for larger particles. The time scale for chloroform evaporation from typical 3DP powder beds was determined to be on the same order as the particle dissolution time scale. Dissolution‐evaporation (DE) plots were constructed to illustrate the relationship between evaporation time scale, dissolution time scale, particle size, printing conditions, and external mass transfer conditions. The DE plot provides a good estimate of the necessary printing conditions under which the evaporation time is sufficient for particle dissolution for a given particle dimension. Microstructural analysis of the printed structures demonstrated the importance of the relative time scales of particle dissolution and solvent evaporation. Practical implications of these findings in 3DP are described.
Effect of filler on cure behavior of an epoxy system: Cure modeling
Authors: Lu Mangeng , Shim Mija , Kim Sangwook 
Published: April 2004

AbstractThe effects of filler on the reaction of an epoxy system cured with aromatic diamine have been studied within the temperature range 70 ˜ 130°C using a differential scanning calorimeter. Various kinetic models including homogeneous reaction, diffusion‐controlled reaction, surface reaction and nucleation and growth models have been tested. Kinetic analysis using integral and derivative procedures on the isothermal data indicates that the cure reaction process can be described well with the autocatalytical and surface reaction models. However, it has been found that the catalysis of fillers can be retarded effectively by the curing temperature.
A new approach to analyzing residence time and mixing in a co‐rotating twin screw extruder
Authors: Gasner Glenn E. , Bigio David , Marks Charles , Magnus Fredrick , Kiehl Christopher 
Published: April 2004

AbstractA series of experiments was conducted to determine what correlations exist between an experimental parameter, percent drag flow, and other parameters such as head, tail and mean residence time. Experimentation was carried out on two polymer systems, a model system of near‐Newtonian fluid and a viscoelastic system of polyisoprene with several additives. To aid in the residence time analysis, data from three literature sources were cited and replotted. A family of residence time curves for a partially filled system can be combined into one curve by plotting the number of screw revolutions carrying the tracer to the extruder exit versus the percent drag flow. This method of plotting the data for each screw configuration estimates the mean residence time for any throughput and screw speed once a few data points are taken. In all four sets of experiments, the number of screw revolutions carrying the tracer to the exit decreases with increasing percent drag flow. The filled volume of the extruder was calculated from residence time data to show that percent drag flow is linearly related to extruder filled volume. When percent drag flow increased in the viscoelastic system the following results were recorded: fraction of polymer residence time spent in conveying elements increased, fraction of residence time spent in mixing elements decreased, polymer Mooney viscosity increased, number and weight average molecular weights increased and polydispersivity increased.
Preparation of macromolecular tracers and their use for studying the residence time distribution of polymeric systems
Authors: Hu Guo‐Hua , Kadri Ilham 
Published: April 2004

AbstractIn this study, an easy route was developed to incorporate antracene moieties in polymer chains. It consisted of copolymerizing the monomer of a polymer of interest with 3‐isopropenyl‐α, α'‐dimethylbenzyl isocyanate (TMI) and then reacting the isocyanate‐bearing polymer with 9‐(methylamino‐methyl)anthracene. Such an antracene‐bearing polymer was then used as a tracer (macrotracer) to determine the RTD function of polymers in a twin screw extruder and compared with an antracene as a microtracer. As long as the tracers were well mixed with a polymer of interest and the resulting mixture had the same geometrical form as the polymer before they were charged to the flow stream, the differences between the microtracer and the macrotracer were not reflected in the measured RTD distribution. A variation in the feed rate (Q) or screw speed (N) changes both the RTD and the intensity of axial mixing. On the other hand, for a given but small Q/N, commonly called specific throughput, variations in Q and N change the RTD but not the intensity of axial mixing. When it is small, Q/N can be used as an operating parameter to separate the effect of the residence time from that of mixing for a small Q/N.
Optimized runner systems for multicavity injection molds. Part I: Runner sizing
Authors: Lee Ching‐Chih , Stevenson James F. 
Published: April 2004

AbstractA strategy has been developed for optimizing the design of runners in injection molds with multiple identical cavities. This approach is based on mathematically rigorous derivations using the power‐law viscosity model under conditions where the pressure drop in runners is not significantly influenced by temperature variation. The design rule to minimize runner volume for specified injection pressure and rate is simple: The diameter of any runner downstream from a junction is determined by dividing the diameter of the upstream runner by the cube root of the number of downstream branches at the junction. This rule has been extended to noncircular runners using the hydraulic radius approximation and the requirement of equal velocities in the circular and noncircular runners. Minimum volume cross‐sectional shapes have been determined for U‐shaped and trapezoidal shaped runners. For circular runners a method for estimating the pressure drop for nonisothermal flow quantifies the deviation from the pressure drop for isothermal flow at the melt temperature. As runner size decreases, the trend is for viscous heating to dominate over cooling and for the estimated nonisothermal pressure drop to be lower than the isothermal pressure drop.
Brittle to ductile: Fracture toughness mapping on controlled epoxy networks
Authors: Crawford Emmett D. , Lesser Alan J. 
Published: April 2004

AbstractA series of epoxy networks with controlled molecular weight between crosslinks (Mc) was constructed with a difunctional epoxy resin and a mixture of aliphatic amines. The glass transition and yield strengths decreased as Mc increased, while the elastic properties were independent of Mc. In determining the effect of Mc on fracture toughness, the fracture behavior changed from a brittle fracture to a ductile fracture as Mc increased. The tests and analyses used to evaluate the fracture energy changed from a linear elastic fracture mechanics approach for brittle failures to an elastic‐plastic fracture mechanics approach for ductile failures. The ductile responses also showed an increasing fracture resistance with crack extension. Two popular models were used to describe the fracture energy as a function of yield strength. The analysis showed that a change in fracture energy by a thermally induced change in yield strength was equivalent to a change in fracture energy by a chemically induced change in yield strength. In addition, comparisons between the two models allowed insightful relationships to be drawn.
Rotational isomeric relaxation in poly(ethylene glycols) studied by acoustic spectroscopy
Authors: Striboulevich Anatoly , Sperkach Volodymyr , Sperkach Yaroslav 
Published: April 2004

AbstractAcoustic spectra have been investigated for a series of poly(ethylene glycols) (PEGs) with molecular masses of 200, 400, and 600. Velocity of sound propagation c and sound attenuation αf−2 were measured in the frequency interval from 5 to 2500 MHz and temperature interval from 278 to 343 K. The acoustic spectra of PEGs in the frequency range studied comprise two simple dispersion regions. Characteristic parameters for these regions were calculated. Possible molecular mechanisms of the processes responsible for the regions are considered. It turns out that the low‐frequency dispersion region is caused by conformational restructuring processes in PEG molecules. The main contribution to the sound attenuation was shown to be caused by rotational isomeric relaxation process of the type trans‐trans↔trans‐gause. Thermodynamical and kinetic parameters of the low‐frequency relaxation region are reported.
Controlled release PVC membranes: Influence of phthalate plasticizers on their tensile properties and performance
Authors: Donempudi Shailaja , Yaseen Mohammed 
Published: April 2004

AbstractThe design of controlled release polymer dispensers (CRPD) for effective release of the active ingredients at desired rates requires a careful study and generation of data on several properties of the polymer membranes. Presence of optimum tensile properties is one of the prerequisites for the CRPD in deciding their suitability for application in the fields. Polyvinylchloride (PVC) membranes containing di n‐alkyl phthalate (alkyl= methyl, ethyl, butyl&octyl) with concentrations ranging from 10–30% with an increment of 2.5% were prepared. The tensile strength and percent elongation of these membranes as a function of concentration of the phthalate plasticizers, their size and aging period were performed. An increase in the tensile strength with increasing phthalate content was noticed up to 17.5% phthalate. Then followed a decrease with further increase of phthalate content. In contrast, the percent elongation was observed to increase constantly with increased concentration of the plasticizer. The ambiguous increase in the tensile strength up to 17.5% plasticized films is attributed to the antiplasticization effect of the plasticizer. The properties showed a linear behavior with respect to the size of the alkyl chain length and also the period of aging. The membranes with 17.5% and 20% were found to have optimum tensile properties and good property retention with aging for their application in controlled release of agrochemicals.