bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoplastic bonding to metals via injection molding for macro‐composite manufacture
Authors: Ramani Karthik , Moriarty Brendan
Published: April 2004

In this work, we explore a new method of in‐situ joining of polymers to metals in injection molding to allow direct bonding between thermoplastic and metal parts. Such a method can integrate several downstream steps in product manufacture, allow optimal design of products and joints, and avoid adhesive application, assembly, and associated difficlties. A variety of process parameters and their effects upon the interface tensile strengths were examined. A full factorial experiment was conducted involving four of the critical process parameters identified. The effects upon tensile strength at break of the following process parameters were studied: (1) adherend surface temperature, (2) screw linear velocity, (3) bondline thickness, and (4) pack and hold pressure. The fracture surfaces and the thermoplastic metal interfaces were analyzed. The bonds fabricated with higher adherend surface temperatures have increased mean tensile strength and less adhesive failure. This increase in mean bond tensile strength and less adhesive failure was due to increased polymer penetration of the adherend surface roughness, at the micrometer level, as shown in the analysis of the polymer‐metal interface by a scanning electron microscope (SEM).
Identification of off‐flavor compounds in high‐density polyethylene (HDPE) with different amounts of abscents
Authors: Villberg Kirsi , Veijanen Anja , Gustafsson Irma
Published: April 2004

The use of synthetic pipes for drinking water distribution has increased. High desnity polyethylene (HPDE) is preferred because of its favorable mechanical properties, ease of handling during manufacturing, and low permeability to external contaminants. Off‐flavor drinking water is a problem with plastic pipes. The compounds causing off‐flavors are mainly carbonyl compounds. A combined zeolite called Abscents is used to eliminate odors and to remove odor‐causing compounds. In this study, four different amounts of Abscents were added to raw HDPE pellets, and the influence on the off‐flavor properties were analyzed. When the maximum amount of Abscents was added, almost all the carbonyl compounds disappeared, and the intensities of odors also decreased. The use of Abscents notably increased the acceptability of HDPE pipes. The system used for analysis of volatile organic compounds was a gas chromatographic/mass spectrometric/sniffing system. Purge and trap techniques were used to introduce the volatile, off‐flavor components into the gas chromatograph.
Influence of design on dispersive mixing performance in an axial discharge continuous mixer—LCMAX 40
Authors: Yao Chih‐Hsiang , Manas‐Zloczower Ica
Published: April 2004

The axial discharge continuous mixer combines the features of a continuous mixer and a twin screw extruder, expanding the flexibility of this compounding machine. In this work we analyzed the influence of rotor design on the dispersive mixing performance of a LCMAX 40 unit. Specifically we looked at various arrangements for the pushing and counter pushing units in the design of the LCMAX 40. A fluid dynamics analysis package—FIDAP, based on the finite element method, was used to model the flow behavior of a power law model fluid under different pressurization conditions. Dispersive mixing efficiency was quantified in terms of shear stresses and elongational flow components generated in the flow field. We found that the counter‐pushing unit generally contributes more in building up high shear stresses. However, the generation of elongational flow components, which is beneficial for dispersive mixing, is not solely dependent upon the pushing–counter pushing configuration but rather on the overall rotor geometry. We found that the maximum number of counter‐pushing units in the rotor design of the LCMAX 40 should not exceed two in order to provide adequate material pumping. Rotor designs with alternating arrangements of pushing and counter‐pushing units provide overall better dispersive mixing conditions.
Heat transfer coefficient in a high pressure tubular reactor for ethylene polymerization
Authors: Lacunza Marta H. , Ugrin Pedro E. , Brandolin Adriana , Capiati Numa J.
Published: April 2004

Heat transfer in tubular reactors for the high pressure polymerization of ethylene is very complex, since these tubular reactors are usually divided into several zones that exhibit different flow patterns and critical fouling behavior. The correct estimation of the overall heat transfer coefficient along the reactor axial distance is a major issue when assessing the predictive capabilities of a mathematical model for the process. In general, previous models employed either constant heat transfer coefficients or the usual correlations for the Nusselt number. Neither of these two approaches is accurate enough to allow a correct prediction of the reactor behavior with respect to temperature profiles and product molecular properties. The present work performs a more comprehensive estimation of the heat transfer coefficient in these reactors. At a first stage the overall heat transfer coefficients were estimated by using approapriate energy balances and a good set of experimental data. Then, a predictive model was proposed for the overall heat transfer coefficient. All flow regimes, as well as fouling effects, were taken into account, and the parameter estimation was based on temperature profiles obtained from an industrial reactor. The temperature profiles, conversions, pressures and molecular properties calculated by means of the experimentally fitted heat transfer coefficients or with the predictive model showed good agreement with plant data.
Assessment of lifetime of hot‐water polyethylene pipes based on oxidation induction time data
Authors: Viebke J. , Gedde U. W.
Published: April 2004

A method is presented for assessment of lifetime of polyethylene pipes undergoing thermal oxidation (Stage III failure) based on oxidation induction time (OIT) data obtained by DSC. The method requires pressure testing for limited time periods, sampling from unexposed and exposed pipes, the establishment of a linear relationship between the OIT and the antioxidant concentration, and the taking of OIT profiles through the pipe wall. The method is not applicable to pipes with improper dispersion of the antioxidant. A mathematical procedure based on a model for the migration and chemical consumption of the antioxidant system is used to extrapolate short‐term OIT profiles to obtain the OIT profiles after extended exposure. The lifetime prediction is also based on the empirical establishment of a criterion, a critical OIT value, for the onset of thermal oxidation of the polymer (Regime C). The total lifetime is then obtained under the assumption that the time period of Regime C constitutes 10% of the total lifetime. The pressure testing time required to obtain adequate data for modeling is only a fraction (20% to 70%) of the failure times of the pipes studied. The average difference between the actual and predicted times was 15% for the MDPE pipes studied.
Bulk moduli from physical aging and stress relaxation data
Authors: Kubát M. J. , Vernel J. , Rychwalski R. W. , Kubát J.
Published: April 2004

The process of physical aging is accompanied by a gradual change in a number of physical parameters of the solid under study. In this paper we show that by correlating the excess enthalpy with the excess volume, bulk modulus, K, data of reasonable magnitude are obtained for polystyrene, PS, and poly(vinyl acetate), PVAc. The underlying reasoning is based on standard equilibrium thermodynamics. For PVAc the time dependence of K during the aging process is discussed in terms of corresponding data calculated from dynamic mechanical measurements at varying frequency. Examples are also given of calculations of K from uniaxial stress relaxation data obtained with polyethylene samples where both the volume and the con comitant stress changes were determined. The calculation of K was based on the usual formula relating pressure (1/3rd of the uniaxial stress) to the corresponding volume change. The K data obtained were somewhat lower than those normally reported, an effect likely to be related to the time scale involved.
Microstructure and stiffness analysis of a new ternary melamine‐formaldehyde composite
Authors: Hagstrand P.‐O. , Rychwalski R. W. , Klason C.
Published: April 2004

A new ternary planar random fiber composite manufactured under the name RMC (Reinforced Melamine Compound) is studied. Microstructure and stiffness of the random glass fiber‐reinforced and particulate‐filled melamine‐formaldehyde composite processed by compression molding from RMC molding compounds are analyzed. Glass fiber bundles in a mixture of melamine‐formaldehyde resin with various size of filler particulates outside the bundle space, and small size particulates inside the bundle space are found from scanning electron microscopy (SEM) and optical micrographs. The tensile modulus of the particulate‐filled matrix is modeled using equations of Halpin and Tsai, and Lewis and Nielsen. The tensile modulus of the resin/filler/fiber composite is calculated using the Halpin‐Tsai equation followed by a randomization procedure employing the averaging concept of Nielsen and Chen. Fiber bundles rather than single fibers are assumed as the reinforcing unit. Parameter ϵ representing the reinforcing efficiency is discussed for the case of stiffness in the direction transverse to the bundles orientation. Predicted values of the tensile modulus are in good agreement with experimental results for various compositions. Different resin/filler/fiber compositions are characterized using the calculated tensile modulus values together with merit indices introduced for the purpose of tailoring the composite toward minimized weight and material cost.
Process studies in precision injection molding. I: Process parameters and precision
Authors: Liu C. , Manzione L. T.
Published: April 2004

Precision injection molding is an important technology for improving productivity and lowering costs in fields such as electronics, photonics, and medical plastics by allowing the substitution of molded plastics for more expensive metals and ceramic parts. This work is part of an effort to develop a molding technology that can deliver the micron‐level precision required for these applications. Two engineering thermoplastics with glass and/or mineral fillers, poly(etherimide) (PEI) and poly(benzoate‐naphthoate) liquid crystal polymer (LCP), were studied. Precision was defined as the standard deviation of part mass and part dimensions as measured on a coordinate measuring machine. Robust design, or design of experiments (DOE), principles were used to determine optimal injection molding parameters. The results showed that ram position and hydraulic pressure were the most effective injection phase cut‐off control methods of those studied. With regard to process parameters, those that increase melt fluidity had the greatest effect on improved precision with PEI. For LCP, the effect of process parameters was far more complicated. The cross‐sectional morphology of the liquid crystal parts was investigated in the second phase of the study to assess the influence of morphology on part precision.
Izod impact fracture morphology of rubber‐toughened polysulfone and poly(phenylene sulfide) blends
Authors: Cheung M.‐F. , Plummer H. K.
Published: April 2004

Blends of polysulfone (PSF) and poly‐phenylene sulfide (PPS) exhibit ductile behavior, below 35% by weight PPS, under tensile loading conditions. However, the blends are notch sensitive to Izod impact. The use of a core‐shell type rubber‐modifier effectively toughens the blends. Notched Izod impact strength rises, from ∼ 50 J/m to about 900 j/m, by increasing rubber content from 0% to 10–15%. It remains constant at a rubber content > 10–15%. Scanning electron microscopy (SEM) is used to study the morphology of the fracture surfaces. At low modifier content (5%), smooth or mesa‐like fracture surfaces are observed. Voids and interfacial debonding are revealed. With a higher concentration of toughening agent (> 10%), some crazing is evidence but not consistent. However, matrix yielding and extensive plastic flow of the PSF/PPS matrix are seen throughout, with a higher level of rubber modifier.
Extrusion of polypropylene. Part II: Process analysis of the metering zone
Authors: Lekakou C. , Brandao J.
Published: April 2004

This is a study of the extrusion of thermoplastics with special focus on the extrusion of polypropylene. A multidimensional numerical model is presented for computational simulations of the extrusion in the metering zone. The model contains a non‐isothermal analysis of the extrusion of non‐Newtonian melts in single‐screw extruders. The computer code developed is tested against an analytical solution and against literature data for the case of a high density polyethylene. Computer simulations are carried out for the extrusion of two grades of polypropylene at two different screw rotation speeds. Special attention is paid to the evaluation of variables of practical interest, such as residence times and measures of mixing quality.
Estimating liquid transport properties by a free volume method
Authors: Guo C. J. , De Kee D.
Published: April 2004

A reduced free volume has been used to represent the viscosities as well as the self‐diffusion coefficients of different hydrocarbon liquids with viscosity less than 1 × 10−3 Pa.s at 298K by a master curve. Such correlations allow for the estimation of liquid viscosities as well as the self‐diffusion coefficients of a binary liquid mixture at infinite dilution using only density and occupied volume data of the liquids.
Fracture toughness and mechanical properties of poly(n‐pentyl‐n‐alkylsilanes)
Authors: Klemann Bruce M. , DeVilbiss Tad , Koutsky James A.
Published: April 2004

The mechanical properties and fracture toughness of thin films of a series of poly(n‐pentyl‐n‐alkylsilanes) were investigated. Poly(n‐butyl‐n‐pentylsilane) is the strongest of these polymers with an elastic modulus of 2.96 × 108Pa and a fracture strain of 85% at 25°C. The hexagonal mesophases of these polymers generally show elastic moduli on the order of 107Pa and are often quite extensible. AJ‐integral analysis of the ductile tearing of thin films of poly(n‐butyl‐n‐pentylsilane) and poly(n‐propyl‐n‐pentylsilane) using an Instron tensile testing machine and specimens in the single edge notch (SEN) geometry yielded plane stressJ1c(critical value ofJfor fracture initiation) of 1745 J/m2and 205 J/m2, respectively. Both values are significantly higher than the plane stressG1c(critical energy release rate) value of 109 J/m2obtained for poly(di‐n‐hexylsilane) with a residual stress analysis using the same apparatus and testing procedure.
Fracture behavior of high‐impact polystyrene under an aggressive environment
Authors: Corleto Carlos R. , Sosa Jose , Bradley Walter L. , Hurtado Jose , Daumerie Michael
Published: April 2004

The fracture behavior of three high‐impact polystyrene (HIPS) materials has been investigated using constant load at 1/2 h interval tests of margarine‐exposed compact tension fracture mechanics specimens. Scanning electron microscopy has also been done on the fracture surfaces to correlate the micromechanics of fracture to the fracture test results. The results indicate that the proposed tests provide a useful approach to study the environmental fracture resistance (EFR) of HIPS under the influence of an aggressive environment. It was found that the EFR of HIPS under margarine, with comparable rubber content, improves with decreasing rubber particle size and increasing molecular weight.
Computer simulation and molecular theory of self‐organization and mechanical properties of polymers
Authors: Melker A. I. , Vorobyeva T. V.
Published: April 2004

In this contribution, we report on a study of the self‐organization of extended linear polymer chains into condensed globules using molecular dynamics methods. We have found that condensed chains (globules) are amorphous or crystalline depending on the interaction potential between constituents. Any structure is formed in several stages. The structures obtained were used in further computer simulations to investigate such processes as compression, decompression, fracture, and flow. We have found that there are different types of fracture and plastic behavior with their own energy, fluctuation, and defect characteristics. On the basis of the computer simulation results obtained, the equation of motion is derived for the system of chain macromolecules slipping relative to each other. The equation takes into account the relaxation and friction in the system. The solution obtained gives the general law that connects stress, strain rate, molecular mass, potential relief, and temperature. It also gives sound physical grounds for some empirical relations that are used in polymer technology.
Synthesis and characterization of glycoside non‐ionic surfactants
Authors: Ricardo Nágila M. P. S. , Glendinning Andrew , Price Colin
Published: April 2004

We report on the synthesis of non‐ionic surfactants via the Koenigs‐Knorr reaction with chemical structures GOR and GOPOG, where GO(H) is glucose, R is n‐decyl or n‐dodecyl, and P is polyoxypropylene or polycaprolactone. Surface properties were studied using a Cenco‐du‐Nouy tensiometer. Light and transmission electron microscopy were used to investigate the phase behavior of the surfactants over a range of concentrations. AOR surfactants, where A is the product of amylose degradation and R is decyl, were synthesized by an alcohol exchange procedure.
Synthesis and characterization of bulky side chain methacrylate polymers
Authors: Radić Deodato , Martínez Francisco , Gargallo Ligia , Hamidi Nasrollah
Published: April 2004

The synthesis, and dilute solution behavior of poly(2,4‐dimethylphenyl methacrylate) (2,4DMP), poly(2,5‐dimethylphenyl methacrylate) (2,5DMP), and poly(3,5‐dimethylphenyl methacrylate) (3,5DMP) is described. Comparison is made with results reported for other bulky side chain polymers. The Kuhn‐Mark‐Houwink‐Sakurada (KMHS) relationships were established. The unperturbed dimensions 〈r2〉, the rigidity factor σ, the characteristic ratio C∞, and the thermodynamic parameters were determined, using the Stockmayer‐Fixman equation, from viscometric data in good solvents. The high rigidity observed for these polymers is explained assuming that these polymers behave as kinked‐chains.
Mechanics of failure of plastics by thermal imaging examination of a thermoplastic polypropylene + EPDM blend
Authors: Anne D'Souza Nandika , Brostow Witold , Ramamurthy A. C. , Wang Yingxia , Thomas Robert L. , Favro Lawrence D.
Published: April 2004

Thermal wave imaging combined with stress pattern analysis by measurement of thermal emission (SPATE) is used to study the failure behavior of a polypropylene (PP) + ethylene propylene diene (EPDM) polymer blend. Images corresponding to a propagating crack in a single edge‐notched specimen were measured at three rates of testing: 4 mm/min, 8 mm/min, and 20 mm/min. Conversion to stress values is made through use of a thermoelastic function. It is found that in a 4 mm/min test the crack tip radii blunt rather than propagate with little initiation. Large‐scale necking precedes fracture. At 8 mm/min, some blunting occurs, followed by fast crack propagation. At 20 mm/min, fast crack propagation occurs. The images are digitized to obtain the values of the temperatures at every point in the sample. Data corresponding to the plane of the propagating crack over the span of the test are presented.
Dynamic mechanical behavior of poly(aryl ether ether ketone) in the −150°C to +100°C temperature range: Influence of the nature of sorbed solvents
Authors: Bas C. , Alberola N. D.
Published: April 2004

The dynamic mechanical behavior of poly(aryl ether ether ketone) (PEEK) films submitted to various treatments, i.e. physical aging, crystallization, and immersion in various solvents (water and some alcohols), has been investigated at low temperatures in order to give new insights on the origin of the subglass transitions. Two processes, i.e., the simple thermorheological component at lower temperatures and the cooperative component at higher temperatures, are overlapped in the β relaxation of dry PEEK. Sorbtion of such solvent molecules as water, ethanol, methanol, and isopropanol gives rise to new relaxations.
Effect of added β‐cyclodextrin on the biostability of polyurethane
Authors: Sreenivasan K.
Published: April 2004

Blending of β‐cyclodextrin (BCD) was found to accelerate the biodegradation of polyurethane under biotic environmental exposure. The enhanced degradation induced by BCD has been demonstrated by gel permeation chromatographic and scanning electron microscopic analysis.
Polyethylene exposed to liquid propane: Sorption and permeation kinetics and mechanical properties
Authors: Hedenqvist M. , Johnsson G. , Tränkner T. , Gedde U. W.
Published: April 2004

Data obtained by sorption and permeation measurements of liquid propane in medium‐density polyethylene were analyzed with an analytical diffusion model, assuming a constant diffusion coefficient, and a numerical model, based on the free volume theory of Fujita. The stress‐strain properties of propane‐swollen medium‐density polyethylene were recorded in an Instron tensile tester. The sigmoid sorption curves (modeled here for the first time) were adequately described using nonstationary boundary conditions. The numerical model was capable of representing sorption, desorption, and permeation data, whereas the analytical technique gave satisfactory results only for sorption/desorption data in the initial, transient stage. The difference between diffusion coefficients determined from sorption and desorption measurements and the time dependence of the modulus‐solute concentration relationship can be explained by assuming a relaxation of constrained amorphous chain segments. The penetrant‐induced structure rearrangement is, according to differential scanning calorimetry measurements, confined to the amorphous phase.
Effect of zinc stearate on the rheology of ionic elastomer based on carboxylated nitrile rubber
Authors: Mandal U. K. , Tripathy D. K. , De S. K.
Published: April 2004

Monsanto rheometry, melt viscometry, differential scanning calorimetry, and dynamic mechanical spectroscopy have been used to study the effects of zinc stearate on the rheological behavior of ionomer based on carboxylated nitrile rubber (XNBR) ‐ zinc oxide (ZnO) system. At temperatures below its melting point, zinc stearate functions as a reinforcing agent for ionomer formation. Above its melting point, it acts as a plasticizer for the ionic domains, thereby facilitating easy processing of the ionomer.
Solidification of thermoviscoelastic melts. Part 3: Effects of mold surface temperature differences on warpage and residual stresses
Authors: Bushko Wit C. , Stokes Vijay K.
Published: April 2004

The solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part warpage in the injection‐molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification so that this model can be used to assess packing‐pressure effects in injection molding. Parametric results are presented on the effects of the mold temperatures and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in‐plane and through‐thickness shrinkages, on warpage, and on residual stresses in plaque‐like geometries. The packing pressure is shown to have a significant effect on part warpage. While the results are presented in terms of normalized variables based on the properties of bisphenol‐A polycarbonate, they can be interpreted for other amorphous thermoplastics, such as modified polyphenylene oxide, polyetherimide, and acrylonitrile‐butadiene‐styrene.
On‐Line measurement of parison geometry during blow molding: Parison swelling for three high‐density polyethylenes with different molecular weights and molecular weight distributions
Authors: Eggen Svein , Sommerfeldt Arne
Published: April 2004

An image analysis technique has been developed to measure diameter and thickness distribution of a parison during the extrusion stage in blow molding. The system operates on‐line during extrusion on any commercial blow‐molding machine. The system has been developed to help development of new blow‐molding resins by increasing our understanding of the connection between polymer structure and parison shape. The system can also be used for die design during optimization of a production process. The combined use of experimental design and multivariate projection techniques makes this an efficient tool for the practical processing engineer. Experiments done on three high‐density polyethylene blow‐molding resins show the importance of measuring the time dependence of the diameter and thickness distribution under different extrusion conditions for a given polymer. Our results show that many of the swell and sag related properties we see cannot be directly inferred from standard laboratory swell‐experiments.
Effect of processing on the recyclability of nylon 66/poly(2,6 dimethyl‐1,4 phenylene oxide) (PPO) alloys
Authors: Laverty John J. , Ellis Thomas , O'Gara John , Kim Sooho
Published: April 2004

The recyclability of two commercial nylon 66/PPO [poly(phenylene oxide)] alloys has been investigated by examining the effects of multiple and abusive melt processes upon the impact strength. The loss of performance associated with these exposures has been correlated, in one instance, with the thermal degradation of polybutadiene‐based impact modifier. The degradation of the rubber has been quantified using an indirect measurement of rubber mobility obtained from the NMR free induction decay of mobile and rigid protons in the material. Substitution of the unsaturated rubber modifier with a saturated hydrocarbon resulted in improved recyclability. Both formulations provide evidence of changes in morphology related to instability of the dispersed PPO phase. The coalescence of PPO particles, evident in later stages of prolonged thermal exposure, appears to cause further loss of impact strength. Currently the chemical and/or physical changes responsible for the increase in average PPO particle size are not known. It is probable that the thermal stability of the compatibilizer, formed during the reactive extrusion manufacturing process, may be insufficient to provide a durable morphology for repeated recycling of these alloys.
Extrusion of non‐newtonian fluids in a single‐screw extruder with pressure back flow
Authors: Chiruvella Raman V. , Jaluria Y. , Sernas V. , Esseghir M.
Published: April 2004

The transport phenomena underlying the extrusion of non‐Newtonian fluids in single‐screw extruders is investigated numerically and experimentally. The viscosity of the investigated fluids is a strong function of the temperature and, for the non‐Newtonian case, of the shear rate. Therefore, the governing equations of motion are coupled to the energy equation through the viscosity. The velocity in the down channel direction of the screw extruder is a result of both shear and pressure driven transport. The pressure acts in a direction opposite to that of the drag flow, and comparatively high pressures arise at the die in typical extruders. When a narrow die is used in the screw extruder, the pressure gradient in the down‐channel direction becomes so large that the down‐channel velocity near the screw root becomes negative in terms of the coordinate system fixed to the screw. The conventional marching schemes fail to simulate the fluid flow when the down‐channel velocity becomes negative, since the downstream conditions are not known. Two different numerical schemes used to simulate the fluid flow in a single‐screw extruder for this circumstance, which often arises when dies with high flow resistance are used and which is termed as pressure back flow in the literature, have been discussed. One scheme is based on including the down‐channel thermal diffusion, making the problem elliptic, and the other scheme uses a different coordinate system. Both formulations are found to yield results that are fairly close. Experiments were also carried out to measure the pressures at three different locations in a single‐screw extruder. The computed results were found to be in good agreement with the experimental results. The pressures at the die obtained numerically by treating the flow as isothermal are found to be lower than those obtained when the flow is treated as nonisothermal, indicating the strong influence of thermal transport in this problem.
Computer simulation of viscoelastic flow at the entry region
Authors: Loh K. W. L. , Teoh S. H. , Tay A. A. O.
Published: April 2004

Non‐Newtonian flow has a nonlinear constitutive relationship with an advective nature. It was found that in highly advective (convective) problems, the Galerkin formulation “under‐diffused,” resulting in divergence at low elastic numbers. The use of the Streamline‐Upwinding (SU) method improved the solution, especially when used with the Phan‐Thien‐Tanner (PTT) model. At the boundary discontinuity, however, the stress gradient did not necessarily flow along the streamline direction, and oscillations still remained at the corner. The Discontinuity‐Capturing (DC) method resolved this problem by applying control in the direction of the stress gradient rather than the stream line direction, and a smoother solution at the corner region was achieved.
Characterization of photocurable coatings using fluorescence probes
Authors: Song J. C. , Neckers D. C.
Published: April 2004

In this paper, we describe a novel method for monitoring the degree of cure and coating thickness of photocurable resins using intramolecular charge transfer (ICT) fluorescence probes such as 5‐dimethylaminonaphthalene‐1‐sulfonyl‐n‐butylamide (DASB) and 6‐propionyl‐2‐(dimethylamino)‐naphthalene (PRODAN). As the curing reaction proceeded, the fluorescence emission spectra of the ICT probes were found to exhibit hypsochromic spectral shifts because of the increase in matrix microviscosity, which made it more difficult for the excited molecule to relax to its twisted charge transfer state. The spectral changes of the probes as a function of the degree of the cure were monitored using a fluorescence intensity ratio method, which enabled an internal calibration of fluctuations in lamp intensity and sample thickness. It was found that the ratios of the fluorescence emission intensities at two different wavelengths were correlated linearly with the degree of polymerization for different types of acrylic or unsaturated polyester resins using either UV or visible (VIS) initiators. The coating thickness of photopolymers was measured based upon the nascent fluorescence from the coating substrate by virtue of an emission (from the substrate) and adsorption (by the coating) mechanism. The thicker the coating, the less the nascent fluorescence emission that can be observed. So the intensity of the nascent fluorescence from the substrate can be correlated to the coating thickness.
Effect of casting solvents on the morphology and properties of styrene‐butadiene‐styrene triblock copolymer membranes
Authors: Yang Jen‐Ming , Hsiue Ging‐Ho , Chen Hsin‐Lung
Published: April 2004

The effect of the casting solvents on the morphology and properties of styrene‐butadiene‐styrene (SBS) triblock copolymer membranes has been investigated. The SBS membranes were prepared by both dry and wet processes. The stress relaxation of the membranes prepared by the dry process was studied. It was found that the stress relaxation of the membrane prepared from tetrahydrofuran (THF) proceeded faster than that of the membrane prepared from the mixed solvent of THF and heptane. This phenomenon could be ascribed to the different membrane morphologies created by the two solvent systems. Three different SBS membrane structures were obtained from three different casting solvents. The results were interpreted based on the miscibility between the solvent and the nonsolvent.
Control of a chaotic polymerization reactor: A neural network based model predictive approach
Authors: De Souza Maurício B. , Pinto José Carlos , Lima Enrique L.
Published: April 2004

Continuous polymerization processes may be very sensitive to small changes of the operation conditions. Continuous VA (vinyl acetate) solution homopolymerization reactors may present multiple steady‐states and oscillatory behavior. A predictive control scheme that uses an internal model of the process is employed to stabilize such reactors and make them less sensitive to disturbances while subject to “hard” control action constraints. An ANN (artificial neural network) is used as the internal model, leading to fairly good predictions of the reactor behavior, including its multiplicities. The performance of the resulting control algorithm is compared to that of a “well‐tuned” conventional proportional‐integral‐derivative (PID) controller.
Degradation of polyolefin pipes in hot water applications: Simulation of the degradation process
Authors: Viebke J. , Elble E. , Gedde U. W.
Published: April 2004

A program was developed that yields the number of chain scission and crosslinking events representing the best fit of a simulated molar mass distribution to a molar mass distribution determined by size exclusion chromatography. The program was applied to molar mass distributions of samples taken from pressure‐tested pipes of an unstabilized medium‐density polyethylene. Good fits were obtained after various exposure times at different temperatures and at different positions in the pipe wall. The ratio of the number of chain scission to crosslinking events generally decreased with increasing exposure time and with decreasing accessibility to oxygen in the pipe wall. Correction for long‐chain branching effects led to significant changes in the optimum chain scission and crosslinking values obtained. The broad and asymmetric shape of the molar mass distributions, typical of degraded material from originally stabilized medium‐density pipes, was shown to arise from a combination of a uniformly degraded and a nondegraded component. The program was also successfully applied to the molar mass distribution of a sample taken from a degraded commercial polybutylene‐1 pipe.
A novel method to prepare high‐resistivity polymer composites
Authors: Chan C.‐M.
Published: April 2004

A novel method was developed for the preparation of high‐resistivity conductive polymer composites reproducibly. The conventional method which involves the simple mixing of a conductive filler and a polymer usually produces a conductive polymer composite having a loading curve with a region in which the resistivity changes rapidly as the filler concentration changes. Hence, it is very difficult to obtain reproducible materials in that region. This newly developed method involves the preparation of a conventional conductive polymer composite, which is prepared by the simple mixing of carbon black and a polymer as the first step. The resulting compound, which is crosslinked by either electron‐beam radiation or a chemical‐crosslinking agent, is ground into a fine powder (composite filler) with the particle size less than 250 microns. The composite filler is mixed with another polymer to form a conductive particulate composite which has a loading curve showing a more gradual change of resistivity as a function of filler concentration. The modification of the loading curve is controlled by the resistivity, the shape, and the size of the composite filler.
The recycling of thermoplastics: Prediction of the properties of mixtures of virgin and reprocessed polyolefins
Authors: Bernardo C. A. , Cunha A. M. , Oliveira M. J.
Published: April 2004

A theoretical basis for the prediction of the properties of mixtures of virgin and reprocessed polymers is presented. The concept is developed using equations that describe the loss of polymer properties as a function of processing cycles. These equations correspond to properties that are important in characterization and quality control, such as melt flow index and tensile and impact strengths. Experimental data were determined and used to test the models derived. For glass‐fiber‐reinforced thermoplastics, the data on the degradation of fiber lengths and mechanical properties can help to understand the effect of reprocessing on the fiber‐matrix interaction.
Effect of intramolecular interactions on the miscibility windows of PVC blends with modified SAN copolymers
Authors: Kim Chul‐Hwan , Park Jung‐Ki , Hwang Taek‐Sung
Published: April 2004

We investigated the miscibility windows in the blends of poly(vinyl chloride) (PVC) with chemically modified styrene/acrylonitrile (SAN) copolymers such as α‐methyl styrene/acrylonitrile (α SAN), α‐methyl styrene/methacrylonitrile (MSMAN). The blends of PVC with α SAN were found to have the broader miscibility window. This enhanced miscibility was interpreted in terms of intramolecular repulsion that originates from unfavorable interaction between counits of the copolymers and also intramolecular association of AN units. The intramolecular interactions were studied by using Fourier transform infrared (FT‐IR) spectroscopy. These interactions were reflected by a peak broadening in the nitrile stretching band in the acrylonitrile segments. The intermolecular interactions governing the miscibility in the blends of PVC with the series of copolymers were also discussed.
Mechanical behavior of a ductile polyamide 12 during impact
Authors: Schang O. , Billon N. , Muracciole J. M. , Fernagut F.
Published: April 2004

The mechanical behavior of a polyamide 12 is characterized using a viscoplastic law taking into account viscoelastic deformation. Experimental determinations are performed at constant and very low strain‐rates in isothermal conditions during tensile tests. A finite elements code, based on this behavior, enables us to reproduce tensile tests even at different strain rates (up to 0.5 s−1) provided that heat power dissipation due to deformation is taken into account. The same model partially reproduces multiaxial impact tests. Strain hardening is generally over‐estimated by the calculation. It is pointed out that mechanical behavior should be characterized in ways closer to impact loading conditions than tensile tests to be more efficient because of the difference in microstructural evolutions during drawing.
Cure monitoring of photosensitive resins by photo‐dynamic mechanical analysis
Authors: Renault Thierry , Ogale Amod A. , Drews Mike J.
Published: April 2004

A new technique, photo‐dynamic mechanical analysis, was developed to monitor the cure of photosensitive resins. In this technique, the resin is dispensed on a low modulus substrate and the force needed to maintain a prescribed elongation on the sample is measured while the sample is exposed to an ultraviolet source. The force increases with the extent of cure and reaches a plateau when the resin is fully cured. Photo‐dynamic mechanical analysis was found to be a rapid, continuous, and reliable technique to monitor the extent of cure of photopolymerizable resins. A finite element analysis was developed to calculate the resin modulus from the experimental force data. Thus, it was possible to monitor the resin modulus from the liquid state to the solid state.
A field equation for the distribution of striation thickness from impingement mixers
Authors: May H.‐O.
Published: April 2004

The striation thickness distribution for an impingement mixer is calculated applying the methods of computational fluid dynamics (CFD). The description is based on the three‐dimensional flow field equations together with a two‐equation turbulence model so that no assumption of the residence time distribution is necessary. A field equation is derived in order to describe the striation thickness where the stretching velocity is calculated using the statistical theory of turbulent diffusion. The distribution of striation thickness follows from the solution of this field equation.
The effect of cure cycle of unsaturated polyester resin on the temperature and conversion profiles
Authors: Alperstein D. , Narkis M. , Siegmann A.
Published: April 2004

Temperature and conversion profiles during hot curing of an unsaturated polyester resin were studied. It was found, unexpectedly, that the reaction exotherm was largest in the outer layer close to the hot mold surface and least in the center core. The opposite was true for room temperature curing with a different initiator system. Comparison of the experimental results with heat transfer calculations has led to the conclusion that the kinetic character of cure across the polyester slab thickness was location‐dependent. The variation with location was interpreted in terms of diffusion of the initiator components from the core towards the surface owing to their faster depletion close to the hot surface and the imposition of a temperature profile. Simulation of the experimental results was possible by combining the heat transfer equation with a kinetic equation accounting for an inhibitor induction time and a modified Arrhenius equation containing a location‐dependent activation energy.
Mechanical properties of rotationally molded nyrim
Authors: Harkin‐Jones E. , Crawford R. J.
Published: April 2004

Rotational molding is used primarily for the manufacture of products from powdered plastics. However, there are many advantages to be gained from the use of a liquid plastic feedstock. This paper describes the results of an investigation to study the effect of process variables, such as mold temperature, on the morphology and mechanical properties of parts manufactured by the rotational molding of a reactive liquid nylon, caprolactam plus a diol. Initial mold temperature has a significant effect on the degree of crystallinity, levels drop off sharply at mold temperatures in excess of 140°C, while spherulite size increases after this point. Flexural properties improve with increasing degree of crystallinity while impact strength decreases. A similar trend is observed in moldings containing fillers. A brief study of water uptake and dimensional stability of molded parts is also described.
The effects of powder morphology on the processing of auxetic polypropylene (PP of negative poisson's ratio)
Authors: Pickles A. P. , Alderson K. L. , Evans K. E.
Published: April 2004

With the use of a three‐stage thermal processing route, similar to that used previously for the production of ultra high molecular weight polyethylene possessing a negative Poisson's ratio (i.e. displaying auxetic behavior), an auxetic form of polyethylene has been fabricated. The polypropylene is processed by the compaction, sintering, and extrusion of a powder. The importance of powder morphology on the ability of polypropylene to achieve auxetic behavior has been examined, revealing that particle shape, size, and surface roughness are critical variables for successful processing. Negative Poisson's ratios of up to −0.22 at 1.6% strain have been obtained. The data have been successfully interpreted by use of a simple geometric model based on the polymer microstructure. These suggest that, by further optimizing the processing conditions, much larger negative Poisson's ratios should be achievable.
Devolatilization: A critical sequential operation for in situ compatibilization of immiscible polymer blends by one‐step reactive extrusion
Authors: Hu Guo‐Hua , Sun Yi‐Jun , Lambla Morand
Published: April 2004

The main objective of this study was to show that an efficient removal of residual monomers is very important for in situ compatibilization of immiscible polymer blends by one step reactive extrusion. One‐step reactive extrusion means that when compatibilizing two immiscible polymers with one polymer containing potential functional groups and the other being chemically inert with respect to these functional groups, functionalization of the chemically inert polymer and its subsequent interfacial reaction with the functional polymer are accomplished in a single extrusion process. Two model blend systems were chosen: polypropylene/poly(butylene terephthalate) (PP/PBT) and high density polyethylene/polyamide 6 (HDPE/PA6). A co‐rotating intermeshing twin screw extruder was used to process these blends. Glycidyl methacrylate (GMA) and maleic anhydride (MA) were used to functionalize PP and HDPE, respectively. Results showed that the mechanical properties of both blends in terms of elongation at break and impact strength were improved to a much greater extent with up‐stream devolatilization compared with down‐stream devolatilization.
Competition between textural transitions and pressure effects on the viscosity of thermotropic liquid‐crystal polymers
Authors: Izu Pilar , Eugenia Muñoz M. , Peña Juan José , Santamaría Anton
Published: April 2004

Steady measurements in capillary and slit dies and transient experiments in a cone‐plate system are presented for two thermotropic copolyesters, X7G® and Vectra A950, and a thermotropic copolyesteramide, Vectra B950. The wide shear rate range covered, from 10−2 to 104 s−1, allows us to observe the three regions defined by Onogi and Asada (1). However, the copolyesters on one hand, and the copolyesteramide on the other, show different rheological behavior that can be summarized as follows: For X7G® and Vectra A950: i. higher viscosities in slit than in capillary die flow; ii. upward‐concave pressure profiles in slit die flow; iii. overshoot peaks in transient experiments at a shear strain γM = 2. For Vectra B950: i. lower viscosities in slit than in capillary die flows; ii. linear or slightly convex pressure profiles in slit die flow; iii. overshoot peaks in transient experiments at a shear strain of γM = 180. These seemingly contradictory results are explained by the competition between the texture changes along the flow (a transition from a worm texture to a flow‐aligned region) and the pressure effect on viscosity.
A temperature rising elution fractionation study of short chain branching behavior in ultra low density polyethylene
Authors: Karoglanian Serop A. , Harrison Ian R.
Published: April 2004

The properties of ultralow‐density polyethylenes (ULDPE) have been studied using temperature rising elution fractionation (TREF) as both an analytical and preparative process. TREF was employed to determine the short chain branch distribution and to fractionate the polymer into fractions that enabled further properties studies, including carbon‐13 nuclear magnetic resonance, differential scanning calorimetry, dynamic mechanical thermal analysis, density gradient studies, gel permeation chromatography, analytical TREF, and some simple tensile tests. The results of these studies are reported here.