bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical analysis of promoted polyester and vinylester reinforced composites in RTM molds
Authors: Yousefi A. , Lafleur P. G. , Gauvin R. 
Published: April 2004

AbstractThis article presents a one‐dimensional simulation of the post‐filling period in the resin transfer molding (RTM) process. In this work, transient heat conduction and kinetic of cure equations were solved simultaneously using the Galerkin finite element method. The kinetic models employed in this study were developed with regard to the effects of additives frequently used in the formulation of composite parts (e.g., promoting agents and reinforcements). These specialized kinetic models enabled us to predict the influence of incorporated reinforcement on the process variables, e.g., gel time and demold time, and on the distributions of temperature and extent of cure in through‐the‐thickness direction of the polyester‐based and vinylester‐based composites. It was shown that in the case of vinylester, the incorporation of glass fibers gave rise to a severe inhibition of the cure reactions at high conversions. The inhibiting effect of glass fibers in polyester‐based formulation was found less significant, and the delay in the exotherm temperature peak was mainly attributed to the thermal effects induced in the presence of glass fibers. The numerical predictions were compared with the experimental data obtained in a heated mold for a reinforced polyester part.
Modeling of imidization kinetics
Authors: Seo Yongsok 
Published: April 2004

AbstractWe investigated the applicability of a new kinetic model to the polyamic acid imidization process, which has been generally represented as involving two steps, fast and slow, with specific rate constants due to the existence of kinetically nonequivalent amic acid states. A time dependent nonlinear function of the form sech(‐at) for the rate expression allowed us to simulate the general features of the imidization process. In the early stage, it is almost a constant, in accordance with the process of imidization of highly active amic acid groups, which is eventually limited by the chemical conversion of amic acid groups into imide rings. In the final stage, the reaction rate decreases exponentially because it is controlled by the conversion rate of amic acid groups from inactive to active states. Overall reaction rate is determined by the change in the rate‐determining stage, and thus eventually exhibits a sharp drop in reaction rate. Comparison showed good agreement with experimental data. Activation energies calculated from the new model were in good agreement with those obtained from the first order model. The applicability of the model was further assessed by modeling a process involving two separate imidization processes. Simulation results showed good quantitative and qualitative correlations with experimental data. The model is also in good agreement with another complicated model.
A study of brittle‐ductile transition in polyethylene
Authors: Kitao Koichi 
Published: April 2004

AbstractThe brittle‐ductile transition temperatures (BDTT) of polyethylenes with different degrees of crystallinity, such as LDPE, LLDPE, MDPE, and HDPE, were evaluated using Charpy impact test. The effect of the specimen cooling condition on the BDTT was a main concern in the study. A rise in the cooling plate temperature (Tp) for high density resins brought about a fall in BDTT and an increase in the Charpy impact value Et. However, embrittlement was observed during a tensile test for HDPE samples with a rise in Tp. A crack shielding effect by microvoid formation is proposed as the toughening mechanism for HDPE.
Molecular degradation of concentrated polystyrene solutions in a fast transient extensional flow
Authors: Clay J. D. , Koelling K. W. 
Published: April 2004

AbstractThe extensional degradation of concentrated polymer solutions is studied. Extensional flows are prevalent in the polymer processing industry, but their effect on polymer degradation is often overlooked. Previous research into dilute solution extensional degradation proved that this type of flow is much more effective than shear flow in causing chain scission. This research extends these dilute solution studies into the concentrated regime, where intermolecular entanglements are expected to affect chain scission. A concentrated polystyrene solution is degraded in an opposed pistons device. This device cycles the solution across a sharp contraction, imposing a strong extensional flow. The flow field is modeled to determine the extension rate along the centerline, and the degradation is quantified by measuring the zero shear viscosity and the molecular weight distribution. The results show that degradation is more significant compared to dilute solutions. The zero shear viscosity drops 30% after a single pass across the orifice at high strain rates. As in a dilute solution, the extensional flow leads to preferential cleavage of the high molecular weight chains. All chains longer than a measured critical molecular weight are ruptured. Multiple passes across the orifice increase chain scission, although degradation is the most significant in the first pass through the high strain rate region.
Pattern‐based closed‐loop quality control for the injection molding process
Authors: Woll Suzanne L. B. , Cooper Douglas J. 
Published: April 2004

AbstractThe basis for a novel pattern‐based closed‐loop control strategy for the injection molding process is presented. The strategy uses artificial neural networks (ANNs) embedded within a cascade design to analyze sensor patterns, identify process character and control part quality. The platform for this work, the injection molding process, is an industrially significant, cyclic manufacturing operation. Final part quality of this process is a nonlinear function of many machine and polymer variables. Part quality control of this process is currently attained via single input–single output machine controls supervised by human operators. Presented here is a method that employs ANN technology to improve upon this approach and provide the basis for closed‐loop part quality control. In the cascade design, machine controller set‐points of an inner loop are updated based on ANN analysis of mold cavity pressure patterns. The controller action maintains the desired pressure pattern set‐point of the outer loop associated with desired part quality. Control strategy details are provided along with set‐point tracking demonstrations that support feasibility of this pattern‐based approach.
Characterization of the interfacial bond in paper‐polypropylene laminates and the effects of aging under service conditions
Authors: Somodi Paul J. , Eby R. K. , Scavuzzo Rudolph J. , Wilson Guy R. 
Published: April 2004

AbstractThis study focused on the behavior of the paper‐polypropylene‐paper (PPP) laminate while aging in hot oil in the absence of voltage stress. The results provide an understanding of both the quality of the interfacial bond and the performance of this bond during service. X‐ray photoelectron spectroscopy performed on two different peeled laminates suggest that the bond failed primarily adhesively. Weibull statistical analysis of the peel strength data obtained on unaged laminates and those aged in polybutene oil at 90°C for 120 hours showed that the strength loss is consistent with one failure mechanism and the failure rate increases with applied stress. For the aged sample, Weibull analysis results are consistent with the prior loss of peel strength due to the aging. Experiments on the solubility of the oil show that lamination reduces the amount of absorption in comparison to the unlaminated composite. Swelling experiments on the individual components show differential swelling between the paper and polypropylene to be the source of the strength loss. The polypropylene swells, and the paper shrinks. Measurements on the laminate show that both paper and polypropylene shrink, indicating that the paper governs the laminate swelling process. During aging, the differential swelling generates internal stresses on the interface. In addition to yielding the magnitudes of these stresses, finite element analysis also predicts plastic deformation and creeping of the polypropylene as well as tensile stresses between the paper and polypropylene at a free edge. Very likely these processes damage the bond and contribute to the loss of bond strength.
Extrusion die design for slowly reacting materials
Authors: Pan Jing‐Pin , Wu Ping‐Yao , Liu Ta‐Jo 
Published: April 2004

AbstractThe flow distribution of slowly reacting polymeric materials inside an extrusion die was analyzed by lubrication theory. The viscosity of the polymeric liquid was assumed to be time‐dependent owing to chemical reaction. Three types of extrusion dies were considered: a T‐die, a linearly tapered coat‐hanger die with a choker bar, and a curvilinearly tapered coat‐hanger die. It was found that the T‐die is not suitable to deliver the polymeric liquid films, whereas the two coat‐hanger dies can deliver the polymeric liquid films with acceptable flow uniformity and residence time distribution.
Gas transport in ring substituted polyanilines
Authors: Chang Min‐Jong , Myerson Allan S. , Kwei T. K. 
Published: April 2004

AbstractThe gas transport properties of polymethoxyaniline (PMANi) and polyethoxyaniline (PEANi), in which the methoxy and ethoxy groups were introduced onto the benzene rings at the ortho position, were studied to determine the effect of substituents. Measurements were carried out at 40 psi from 25°C to 55°C. When compared with polyaniline, the gas permeability increases with the size of substituent because of the increases in the diffusivities while the selectivities remain the same or increase for some gas pairs. Excellent correlations were found between the diffusion coefficients and the molecular diameters of gases and between the solubility coefficients of gases and their boiling points (or critical temperatures).
Optimized cooling and gauge tolerances in blown film extrusion
Authors: Feron B. , Wolf D. , Wortberg J. 
Published: April 2004

AbstractNumerical calculations of the air flow and heat transport processes in film blowing have been made, considering the turbulence of the air flow. The parameters air mass flow, air temperature, air velocity, and angle‐of‐attack have been varied. The results have shown that the air massflow has the strongest influence on cooling in the processing window examined. So the massflow is a very efficient actuator of a film thickness control system. Moreover, the angle‐of‐attack together with the bubble shape is responsible for the occurrence of vortices. Such vortices can be the reason for unstable behavior in the bubble forming zone and hence for increased thickness tolerances of the film.
Mechanical and dielectric properties of bulky side chain poly(methacrylates). Analysis of the low frequency phenomena. 1: Poly(5‐indanyl methacrylate)
Authors: Calleja Ricardo Diaz , Jaime's Catherine , Sanchis‐Sanchez M. J. , Martinez‐Piña Francisco , Gargallo Ligia , Radic Deodato 
Published: April 2004

AbstractThis paper composes the dynamic mechanical and dielectric relaxation properties for Poly (5‐indanyl methacrylate) (P51M), a polymer with a bulky side chain. Measurements were carried out from about −100°C to near 250°C. A secondary loss peak was observed in dielectric measurements at room temperature (20°C at 0.1 Hz.), whereas nothing was resolved in the mechanical spectrum. A prominent α relaxation associated with the glass transition was also observed near 107°C at 0.1 Hz. in the dielectric and the mechanical spectra. Dipolar dielectric loss overlapped with conductivity at high temperatures and low frequencies. A new method to split the conductive, interfacial, and dipolar contributions to the spectrum is proposed.
Co‐condensates of resorcinols and methylol compounds for adhesive resins
Authors: Christjanson Peep , Köösel Arne , Siimer Kadri , Suurpere Aime 
Published: April 2004

AbstractA proton magnetic nuclear resonance study was performed on co‐condensation reactions of resorcinol, 5‐methylresorcinol and 2,5‐dimethylresorcinol with methylol compounds, including ortho‐ and para‐methylolphenol, N‐methylol‐caprolactam, methylol‐N,N‐diethylurea, methylolurea and N,N′‐dimethylolurea. Spectral assignments, reaction kinetics and composition of products are discussed. The reaction in melt (120°C) with methylolphenols occurs as co‐condensation in the presence of all catalysts studied. In resorcinols C4C6 substitution is favored. The rate constants of methylol disappearance clearly indicate the preferable influence of acid and alkaline catalyst (not zinc acetate) on para‐methylol. The reaction with N‐containing methylol compound does not give any co‐condensate in the presence of alkaline catalyst. The optimum conditions for co‐condensation mainly depend on reactivity of co‐reagents with formaldehyde and stability of methylol compound. The quantitative amount of co‐condensate with methylolcaprolactam can be obtained in melt‐condensation (70°C) in the presence of acid catalyst. Because of the higher reactivity of urea, the reaction in melt (100°C) in the presence of acid catalyst does not lead to quantitative co‐condensation. The condensation of methylol compound or resorcinols with formaldehyde can be avoided substantially by performing the reaction in aqueous solution at lower temperature.
Synthesis and properties of new esters of cellulose and inorganic polyacids containing phosphorus, molybdenum, tungsten and vanadium
Authors: Luneva N. K. , Oputina A. G. 
Published: April 2004

AbstractWe studied the mechanism of cellulose esterification by inorganic polyacids and established the parameters for cellulose modification that allow the phosphorylation to primary alcohol groups of polymer upon introducing pyro‐ and tripolyphosphates into the ester groups. The product obtained is an ionite with an exchange capacity of about 6 mmol/g. We obtained derivatives of cellulose by introducing the residues of phosphorus‐containing heteropolyacids into ester groups by the sorption of ammonium molybdate and sodium tungstate. The materials are effective sorbents for purification of technogene waters containing radionuclides and are active components of sorption membranes for the separation of alkaline metals.
Long‐term water absorption and swelling of glass‐bead filled plastics
Authors: Kochetkov V. A. , Maksimov R. D. 
Published: April 2004

AbstractThe results of experimental and theoretical investigation of epoxy EDT‐ 10/glass‐bead plastics at long‐term (10 years) exposure in water are presented. The curves of water absorption and swelling are determined. It was expected that the addition of hollow glass spheres (beads) must substantially reduce the sorptional capacity of a material, because of reduction of the volume content of the matrix, and therefore, because of reduction of the volume where the molecules of water can diffuse. However, the water absorption process in glass‐bead filled plastics was found to continue during the total term of the experiments without a tendency to stop. After ten years the equilibrium state was not achieved and the concentration of water in the composite specimens became more than the equilibrium concentration of water in unfilled EDT‐10 epoxy. The swelling coefficient was found to be a non‐linear function of water content. It was found that the initial parts of experimental curves of water absorption and swelling (during the first year of exposure) show an agreement with calculated data, good enough for engineering applications. Subsequently the discrepancy between the experimental results and calculated data increased. The possible reasons for such a discrepancy are discussed.
Dynamic mechanical properties of polyolefin foams studied by DMA techniques
Authors: Rodríguez‐Pérez M. A. , Rodríguez‐Llorente S. , De Saja J. A. 
Published: April 2004

AbstractIn this work a preliminary study on the viscoelastic behavior of polyolefinic foam sheets with different chemical (polyethylene and polypropylene) and cellular structure by means of Dynamical Mechanical Analysis (DMA), in the low frequency and low compression ranges, is presented. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) are also used to determine the morphological parameters of the samples. A connection between the morphological parameters (apparent degree of crystallinity, type of cellular structure, homogeneity, cell size and shape, cell‐wall thickness) and the viscoelastic behavior, a basic key for the development of mechanical and insulating applications, has been established.
Molecular packing density in the crystalline state of semi‐rigid chain polymers. I: Polyimides
Authors: Privalko Valery P. , Pedosenko Alexey V. 
Published: April 2004

AbstractPublished data on crystal lattice unit cell parameters were used to calculate molecular packing density coefficients (Kc) in the crystalline state for a series of polyimides. The values of Kc were shown to decrease, the larger the chain cross‐section thickness, and the lower the ratio of chain persistence length to chain thickness.
Modeling droplet deformation in melt spinning of polymer blends
Authors: Padsalgikar A. D. , Ellison M. S. 
Published: April 2004

AbstractWe report the results of a study of droplet deformation in uniaxial elongational flow under nonisothermal conditions. A mathematical model is developed that simulates deformation conditions in fiber spinning. To test our model, a blend of polypropylene and polystyrene was spun into fibers. The blend morphology of the fibers is accurately predicted by the proposed model. Morphological studies have shown that immiscible additives remain dispersed in the matrix as suspended droplets and that the droplets are elongated into fibrils under the action of shear or extensional forces during processing.
A study on multiple melting of isotactic polypropylene
Authors: Kim Y. C. , Ahn W. , Kim C. Y. 
Published: April 2004

AbstractMultiple melting characteristics of a highly isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC). Double melting characteristics were observed on melting iPP crystallized isothermally at temperatures ranging from 110 to 140°C. iPP crystallized below and above 125°C exhibited different double melting characteristics from each other. For iPP crystallized below 125°C, the single melting peak split into two peaks during slow DSC heating scans without changing the total crystallinity in the polymer. On the other hand, the double melting endotherm of iPP crystallized above 125°C seemed to come from two preexisting crystal fractions having different Tm. There existed an optimum annealing temperature range where the five‐minute annealing of iPP raised Tm of the polymer significantly. The treatment also increased the crystallinity of iPP crystallized isothermally at 110°C by 12%.
Dynamic fracture toughness of polypropylene reinforced with cellulose fiber
Authors: Clemons Craig M. , Giacomin A. Jeffrey , Koutsky James A. 
Published: April 2004

AbstractTo better understand mechanisms of fracture under impact loading in cellulose‐reinforced polypropylene, dynamic fracture analysis was performed based on linear elastic fracture mechanics. Dynamic critical energy release rates and dynamic critical stress intensity factors were deduced from instrumented Charpy impact test measurements. Dynamic fracture toughness increased with cellulose content. However, the assumption of linear elasticity began to break down for cellulose fiber contents exceeding 40% by weight. Scanning electron microscopy showed considerable fiber curl in the composites, especially at low fiber contents; at high fiber contents, composites developed a three‐layer structure.
Determination of the fracture toughness of thermoformed polypropylene cups by the essential work method
Authors: Pegoretti A. , Marchi A. , Riccò T. 
Published: April 2004

AbstractIn this work the anisotropic fracture behavior of neat and rubber‐modified polypropylene cups induced by a vacuum thermoforming process is studied. The effect of different draw‐ratios is also examined. An elasto‐plastic fracture mechanics approach, based on the method of the essential work of fracture, is applied to samples cut from the thermoformed cups both longitudinally and transversally to the drawing direction. For all the products examined a strong anisotropy in the fracture behavior is observed. The fracture resistance for cracks propagating along the drawing direction is lower than in the transverse direction, this fracture anisotropy being enhanced at higher draw‐ratio. The presence of the rubber particles results in an increase in the fracture toughness for cracks running transversally to the drawing direction, but, at the same time, it seriously reduces the fracture resistance for cracks propagating along the drawing direction. In order to better understand the dependence of the fracture behavior upon the processing conditions and material structure, dynamic mechanical thermal analysis, transmission electron microscopy, and X‐ray diffraction measurements are also carried out.
Manufacture and use of pulverized flexible polyester polyurethane foam particles
Authors: Sims G. L. A. , Angus M. W. , Crosley I. 
Published: April 2004

AbstractCrucial process modifications were shown necessary to improve the economics of cryogenic grinding of flexible polyurethane (PU) foam. It is concluded that foam densification prior to cryogenic processing was essential to reduce insulation effects. In comparative studies of foam and densified foam, increasing the density to ∼800 kg/m3 resulted in dramatically reduced cryogen use and vastly improved output. Results indicated that cryogenic pulverization presents a significantly more economic solution than previously recognized. Particles produced by this method were added to foam formulations and effects of particle size and structure on compression properties and cell structure of resultant foams were studied. Particle sizes <100 μm gave similar compression properties and cell size to virgin foam at up to 10 parts by weight on 100 parts of polyol, but cell structure and compressive properties showed increasing divergence as particle size and addition concentration increased. Studies of alternative uses showed that the PU particles showed promise as fillers in rigid PU foam formulations and suggested an extending or reinforcing action in natural rubber vulcanizates.
A study on the pan‐milling process and the pulverizing efficiency of pan‐mill type equipment
Authors: Wang Qi , Cao Jizhuang , Huang Jingui , Xu Xi 
Published: April 2004

AbstractIn this paper, the pan‐milling process and the pulverizing mechanism and efficiency of pan‐mill type equipment, which was designed and manufactured in our lab for pulverization, mixing, and stress reactions of polymers, have been studied. The effects of load and rotation speed of the equipment on the pulverizing of polystyrene was investigated by means of quantitative operation, particle size, and distribution measurement as well as theoretical analysis using the Rosin‐Rammler Function and the logarithmic normal distribution function. The results demonstrate that lower rotation and higher load are favorable to higher pulverizing efficiency and to the mode of surface pulverizing. As a result of the quite strong forces during pan‐milling, mechanochemical degradation takes place, which is a first‐order reaction.