bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of imidization kinetics
Authors: Seo Yongsok
Published: April 2004

We 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

The 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

The 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

The 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

This 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

The 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

The 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

Numerical 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

This 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

A 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

We 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

The 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

In 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

Published 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

We 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

Multiple 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

To 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

In 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

Crucial 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

In 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.
Measurement of melt viscoelastic properties of polyethylenes and their blends—a comparison of experimental techniques
Authors: Xanthos M. , Tan V. , Ponnusamy A.
Published: April 2004

Two polyethylene resins (LDPE and HDPE) and their blends were characterized for dynamic shear rheology, extrudate swell in a capillary rheometer, and recoverable strain as measured by the Melt Elasticity Indexer in attempts to compare parameters related to the so‐called “melt elasticity” as obtained by different experimental techniques. Such parameters may be useful in screening materials for their melt processability. Data were obtained at equivalent shear rates/frequencies and different temperatures. With respect to the individual blend components, the LDPE resin with the lower Melt Index (MI) had higher storage modulus and Weissenberg number than the HDPE resin. However, by using criteria based on “recoil” and strain recovery, ranking was different with the LDPE resin shown to exhibit lower “melt elasticity.” In this case, extrudate swell data were found to correlate reasonably well with equilibrium recoverable strain data. With respect to blends, complex viscosity and storage modulus versus composition curves showed positive deviations from linearity, similar to those observed in melt heterogeneous blends. Similarities between the short time recoverable strain vs. composition and the storage modulus vs. composition curves suggest that similar morphological states may exist in the melt over the experimental times and conditions applicable to these different experimental techniques.
Electrical properties of polymer composites prepared by sintering a mixture of carbon black and ultra‐high molecular weight polyethylene powder
Authors: Chan Chi‐Ming , Cheng Chi‐Leung , Yuen Matthew M. F.
Published: April 2004

Conductive polymer composites were prepared by sintering a mixture of ultrahigh molecular weight polyethylene (UHMWPE) powder and carbon black. Two processing parameters—time and temperature—were shown to have a notable effect on the resistivity of the composites. The relationships between the processing parameters and morphology were studied using optical microscopy and transmission electron microscopy (TEM). The results of the optical microscopy studies indicate that the carbon black is distributed in the interfacial regions between the UHMWPE particles. The dimension of the carbon black channels increases with the carbon black concentration. TEM micrographs show that a high degree of intermixing between the carbon black and the polymer occurs at higher temperatures and longer processing times, resulting in higher resistivities. A positive temperature coefficient (PTC) effect was observed for these materials. A mechanism for the PTC effect in this system is proposed. The magnitude of the PTC effect is found to be inversely proportional to the dimension of the carbon black channels in the composites. The dimension is directly related to the carbon black concentration. The PTC effect is a result of the polymer volume expansion caused by melting of the crystallites. A large PTC effect is observed for the composites with a low carbon black concentration and vice versa. No negative temperature effect (NTC) is observed at temperatures substantially above the melting point of the polymer.
New model of flow in a Farrel Continuous Mixer
Authors: Bang Dae‐Suk , White James L.
Published: April 2004

A model for flow in a Farrel Continuous Mixer based upon cylindrical coordinate hydrodynamic lubrication theory is presented. Pressure and flux fields over the rotor surface are calculated. The pumping characteristics of the various sections of the machine rotors were calculated. Generally Farrel Continuous Mixers are operated under starved conditions. Calculations are presented for continuous mixers operating under starved conditions. Pressure and fill factor profiles are determined. Fill factors are predicted to be increased by increasing throughput, increasing exit gate pressure and reducing screw speed.
Evaluation of the weld‐line strength of thermoplastics by compact tension test
Authors: Cho Kilwon , Ahn Sunghee , Park Jinbae , Park Chan Eon , An Jeong Ho
Published: April 2004

In order to understand the relationship between processing conditions and the properties of weld‐lines on a molecular level, it is necessary to evaluate the true strength of the weld‐line that is not affected by the V‐shape notch on the surface of the weld‐line zone. In this experiment, the weld‐line strength of several brittle, ductile, or phase‐separated polymers was evaluated using the compact tension test by measuring the critical stress intensity factor, KIC, or the critical J‐value, JIC, and the results were compared with those obtained by tensile testing. For brittle polymers such as poly(methyl methacrylate) (PMMA) or styrene acrylonitrile copolymer (SAN), the value of the weld‐line factor, i.e., the strength ratio between the welded and the non‐welded specimen, is higher than that measured by tensile testing, because of the notch sensitivity of brittle thermoplastics and the notch dependence of tensile strength. On the other hand, in the case of ductile polymers such as polycarbonate (PC), the weld‐line factor is similar for both the tensile and compact tension tests. However, the dependency of the weld‐line factor on melt temperature is more obvious in the compact tension test. From these results, it seems that the compact tension test is more appropriate for measuring the interfacial adhesion strength across the weld‐line, which excludes the notch effect.
Influence of miscibility on the morphology and properties of polycarbonate/(maleic anhydride)‐grafted‐polypropylene blend
Authors: Ning Ping , Ko Tze‐Man
Published: April 2004

Maleic‐anhydride‐grafted polypropylene (MAH‐g‐PP) was added to polycarbonate (PC) as a processing agent. Its influence on the morphological, thermal, rheological, and mechanical properties of PC/MAH‐g‐PP blends was investigated by differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), dynamic contact angle goniometry, and tensile and impact strength experiments. The results indicated that the processability and miscibility of the blends were improved significantly by addition of 5–20 wt% MAH‐g‐PP to PC. The melting temperature of MAH‐g‐PP increased as the relative composition of MAH‐g‐PP in the blends increased mainly because of enlargement of the crystallite size. The DSC, FTIR as well as SEM results strongly suggested that a chemical reaction might have taken place between the PC and MAH‐g‐PP. This chemical reaction could have contributed to the improvement of the mechanical properties of the blends and the miscibility between the PC and MAH‐g‐PP components.
Heat transfer and solidification of polymer melt flow in a channel
Authors: Lin P. , Jaluria Y.
Published: April 2004

A numerical study is carried out on the conjugate thermal transport and solidification in polymer melts flowing through channels. A continuum model with the enthalpy formulation is used for a laminar, two‐dimensional, axisymmetric, incompressible, and steady flow. The influences of axial diffusion, viscous dissipation, and temperature‐dependent viscosity are included. A fully elliptic, control volume, finite difference method is employed to solve the governing equations. Numerical results are analyzed by examining the effects of outer wall temperature, Biot number, and mass flow rate. Isotherms and other results are also presented.
Disordering of crystalline PEEK upon mechanical treatment
Authors: Papkov V. S. , Gerasimov M. V. , Dubovik I. I.
Published: April 2004

It has been established that crystalline PEEK can become completely amorphous upon rolling at room temperature. This effect was verified by data of differential scanning calorimetry. X‐ray diffraction and density measurements. In contrast to quenched amorphous PEEK samples, cold crystallization in rolled amorphous samples is shifted to lower temperatures and starts just with the onset of the glass transition. This shift, along with the decrease in the heat of cold crystallization from 21 J/g (for quenched amorphous sample) to 11 J/g, suggest some retention of paracrystalline structure in rolled amorphous samples.
Powder extrusion: Fundamentals and different applications
Authors: Wolfson S. A. , Nikolskii V. G.
Published: April 2004

We propose a novel polymer extrusion process, known as the solid state shear extrusion pulverization and modification (SSSE process), based on the simultaneous action of shear deformation and pressure at selected temperatures. This process can be used for continuous pulverization and copulverization of various polymers. Including different blends, filled materials, thermoplastics, vulcanized rubbers, crosslinked polymers, polymer composites, and natural polymers. Various aspects of this process are considered, including unusual microstructure and properties of powders, low energy consumption, and mechanochemical effects. Possible applications of SSSE to polymer/rubber recycling and to obtaining advanced polymer powders and modified powders are considered, together with scaling‐up problems of equipment suitable for industrial application.
Debonding and fracture of particulate‐filled isotactic polypropylene
Authors: Dubnikova I. L. , Muravin D. K. , Oshmyan V. G.
Published: April 2004

Experimental data on particulate‐filled polypropylene rupture are presented, with discussion and explanation of the regularities found. The systems studied are characterized by ductile properties of a semi‐crystalline matrix and a low level of interfacial interaction. Polypropylene as a host and aluminum hydroxide particles, without or with anti‐adhesive treatment, were used. Two concentration regions of different debonding micromechanisms were found. At low filler fraction (< 15–20 vol. %) particles debond independently and completely at the initial stages of drawing, and a microhomogeneous flow mechanism takes place. Above a critical filler content, debonding proceeds in a correlated way with the formation of narrow craze‐like deformation zones transverse to the stretching axes. These zones screen new debondings in their neighborhoods, more or less efficiently, dependent upon filler fraction and, hence, the porosity inside crazes and the level of interfacial interaction. Whether microhomogeneous or craze‐like mechanisms occur essentially determines the regularities of further deformation and fracture: localized or macrohomogeneous flow, ductile or quasi‐brittle fracture, the drop or the rise of ultimate strains with increase of particle diameters. A theoretical description of the transition between microhomogeneous and craze‐like mechanisms is proposed.
Rheokinetics of free‐radical polymerization of acrylamide in an aqueous solution
Authors: Kulichikhin S. G. , Malkin A. Ya. , Polushkina O. M. , Kulichikhin V. G.
Published: April 2004

A method of rheokinetic analysis is applied to free‐radical polymerization of acrylamide in a water solution initiated by an oxidizing reducing system. The special feature of this system is the second‐order kinetics of the initiation stage. Theoretical analysis predicts the main effects, such as the time dependence of viscosity and the degree of polymerization, concentration influence of a monomer and an initiator, and the temperature dependence of the viscosity profile at different experimental conditions. Experimental data confirmed the idea about the second‐order reaction of initiation. Observed dependencies were close to theoretical predictions. Rate constants of different individual stages of a reaction and “apparent” values of activation energy were found and compared with published values. The possibility of solving an inverse rheokinetic problem from viscometric data was confirmed.
Crystallization and stress‐strain properties of ultra‐high‐molecular‐weight‐polyethylene gels filled with iron particles
Authors: Kerber M. L. , Ponomarev I. N. , Lapshova O. A. , Grinenko E. S.
Published: April 2004

Crystallization of ultra‐high‐molecular‐weight‐polyethylene (UHMW‐PE) filled solutions and gels was studied by differential scanning calorimetry. It has been found that the structure and properties of the gelating systems depend on solvent type, polymer concentration, and filler. Crystallization rate decreases as the polymer content is increased. The crystallization rate dependence on filler concentration passes through a maximum. The influence of a disperse filler on the structure, the stress‐strain and relaxation properties of UHMW‐PE gels has been studied. The results demonstrate the advantage of using less thermodynamically active solvents (thermodynamic activity means polymer‐solvent interaction). This gel‐technology enables us to obtain UHMW‐PE based materials with a 90‐vol% content of iron particles. Highly loaded fibers based on UHMW‐PE were obtained with a tensile strength of 40–50 MPa and an elastic modulus of 350–400 MPa.
Porous materials from crystallizable polyolefins produced by gel technology
Authors: Andrianova G. P. , Pakhomov S. I.
Published: April 2004

A new method for obtaining porous and porous fiber polymers is presented. This method is based on using gel‐type technology (without previously preparing polymer solutions) for crystallizable polymers, preparing polyethylenes, and including polyethylenes of very high molecular mass and isotactic polypropylene. The method consists in swelling crystalline polymer films at elevated temperatures in a proper solvent with subsequent precipitation with a non‐solvent at different conditions. In this case, simultaneous or consecutive processes of phase separation of amorphous or/and crystalline type occurs; stretching the sample can also accompany this process. Complete phase diagrams of two‐ and three‐component systems (polymer‐solvent and polymer‐solvent precipitator) were constructed. Temperature‐concentration boundaries of amorphous separartion (binodal) and crystallization (liquidus) are reported for the system polyethyleneo‐xylenedimethyl formamide. Phase transitions of both types influence characteristics of the resultant porous structure. They were prepared by simultaneous (precipitation of a gel by dimethyl formamide at 25°C) or consecutive (precipitation with a hot non‐solvent at 138°C and following cooling) phase separation. Studied were the effect of experimental conditions (temperature, times for solvation and precipitation, polymer molecular mass, the thermodynamic quality of solvents and parameters of film stretching) on peculiarities of the structure and quantitative characteristics of final porous and fiber‐porous polyolefins. It has been demonstrated that the method proposed allows us to obtain a crystalline and highly porous polymer with open poros, a bimodal size distribution and with a highly developed inner surface. Further high strength and small shrinkage are characteristic of the fiber‐porous materials. The method under discussion appears to be universal, it does not require a preliminary preparation of polymer solutions and can be realized within a general technology of polymer films and sheet processing. Highly porous polymers obtained by this technology, primarily based on polyethylenes of very high molecular mass, can be used as neutral supports for multi‐functional membranes, polymeric covers, frame systems for implants and other applications.
Thermally stable polyimide binders from aromatic dianhydrides and acetyl derivatives of aromatic diamines: Formation mechanism
Authors: Goykhman M. Ya. , Svetlichnyi V. M. , Kudriavtsev V. V. , Antonov N. G. , Panov Yu. N. , Gribanov A. V. , Yudin V. E.
Published: April 2004

Polyimide resins based on dianhydrides of aromatic tetracarboxylic acids and acetyl derivatives of aromatic diamines have been developed for impregnating carbon fibers and glass cloth. Binder prepolymers are soluble in amide solvents and acetone and also form melts with a viscosity of 0.1–0.3 Pa · s at 250–300°C. The melt lifetime is 20–30 min. An increase in temperature leads to the formation of a crosslinked insoluble system of high thermal stability. The formation of polyimide binders was studied with the aid of IR and NMR spectroscopy. A mechanism of the reaction of aromatic dianhydrides with acylated amines is proposed. On the basis of polyimide binders from dianhydride of 3,3′,4,4′‐benzophenonetetracarboxylic acid and bis‐[4‐acetaminophenyl]‐sulfone, bis‐[4‐acetaminophenyl]‐ether, and N,N‐diacetyl‐p‐phenylene diamine, carbon fiber composites with good physico‐mechanical properties were obtained.
Influence of hydrodynamic stirring on composition of copolymer obtained in continuous reaction systems
Authors: Kuchanov S. I. , Kholostyakov A. G. , Kozlov N. I.
Published: April 2004

A mathematical modeling method is employed to analyze the dependence of the composition of a copolymer prepared under a continuous regime on the level of longitudinal stirring in a reactor. The extent was established to which this factor controls the limits of the alteration range of copolymer composition at various values of the reactivity ratios of monomers and their feed composition.
Mechanical and dynamic mechanical properties of zinc neutralized salts of poly(ethylene co‐acrylic acid) and its blend with epoxidized natural rubber
Authors: Mohanty S. , Vijavan K. , Neelkantan N. R. , Nando Golok B.
Published: April 2004

Mechanical and dynamic mechanical properties of the zinc neutralized salts of poly (ethylene co‐acrylic acid) (PEA) and its blends with epoxidized natural rubber (ENR) have been studied. Improvement in tensile strength, hardness (Shore‐A), and a reduction in elongation at break and tension set with the increase in degree of neutralization of the blend constituents corroborate the existence of hard and rigid domains of ionic clusuters in the non‐hydrocarbon and flexible backbone chain. The occurrence of a new relaxation peak due to ionic aggregates and the disappearance of the crystalline transition indicates the formation of a new ionic cluster phase in the matrix. A shift in the glass transition temperature towards higher temperature supports the existence of ionic crosslinks in the polymer matrix.
A new approach in modeling template polymerization
Authors: Semino Daniele , Polacco Giovanni , Ricciardi Alessandra
Published: April 2004

This work attempts to describe the peculiar kinetics that take place in template polymerization which proceeds according to the zip‐mechanism. The unique situation of the molecules adsorbed on a template chain, which, with respect to the template propagation and termination reactions, are bound to react with the molecules that are positioned on their sides, is characterized. The definition of different species according both to their nature and to the nature of their neighbors leads to the construction of a kinetic model that, despite its analytical complexity, is characterized by a quite limited number of unknown kinetic constants. The model is developed by deriving the dynamic equations that describe the conversion versus time behavior all along the course of the reaction. The model predictions are compared with experimental data referring to the radical polymerization of sodium methacrylate (MAA · Na) in the presence of poly(allylamine) hydrochloride (PAAm · HCl). The good agreement confirms the validity of the model. Moreover, the model offers a significant contribution into understanding the peculiarities of template polymerization systems.
The craze initiation response of a polystyrene and a styrene‐acrylonitrile copolymer during physical aging
Authors: Gusler Gloria M. , McKenna Gregory B.
Published: April 2004

The influence of structural recovery or physical aging on the craze initiation of amorphous polystyrene and a styrene‐acrylonitrile copolymer has been examined in two states of stress/deformation and at different temperatures. Studies of craze initiation in equibiaxial creep were performed using a “bubble” inflation test geometry while uniaxial elongation in stress relaxation conditions was studied by bending the specimen over a variable radius of a curvature test jig. All tests were performed by aging the specimen and testing it at the same temperature subsequent to a quench from above the glass transition to below it. The results are compared with expectations from three craze models: Sternstein and Ongchin (1), Argon (2), and Kambour (3). The results are most consistent with the model of Kambour, but discrepancies arise because, e.g., the impact of aging on the stress for crazing in the equibiaxial tests is different for the polystyrene than for the styrene‐acrylonitrile copolymer. The results also suggest that there are two regimes of behavior for craze initiation under equibiaxial stresses, a behavior not manifested in the uniaxial stress relaxation experiments.
Evolution of phase morphology in compatibilized polymer blends at constant quench depths: Complementary studies by light scattering and transmission electron microscopy
Authors: Jackson C. L. , Sung L. , Han C. C.
Published: April 2004

The effect of added block copolymer on the phase separation and morphology evolution in a partially miscible blend of polystyrene and polybutadiene near the critical composition is studied by temperature jump light scattering (TJLS) and transmission electron microscopy (TEM). As block copolymer is added, the phase boundary is shifted to lower temperatures and the phase separation process is slowed dramatically. Since the quench depth greatly affects the rate of phase separation in any blend system, we have used equivalent quench depths by adjusting for the shift in the phase boundary as block copolymer is added. The morphology evolution of these ternary blends was studied by preparing TEM specimens at equivalent shallow quench depths (ΔT = 1.6°C) and allowing each blend mixture to coarsen for the time required to reach a specific constant size, or q‐value, using the TJLS data on the kinetics of phase separation. The q‐range selected was q ∼ 0.003–0.005 nm−1, which corresponds to a spacing of 1–2 μm in real space. The combination of light scattering and microscopy techniques more rigorously describes the compatibilization process in these complex ternary systems.
Stress relaxation experiments in polycarbonate: A comparison of volume changes for two commercial grades
Authors: Colucci D. M. , O'Connell P. A. , McKenna G. B.
Published: April 2004

Stress relaxation experiments were performed on two grades of polycarbonate at room temperature. The tests were performed in uniaxial extension and compression at deformations from the small strain, linear viscoelastic regime to the highly nonlinear viscoelastic regime just below yield. Simultaneous to the control of axial strain, both stress and lateral strain were measured, the latter providing the volume change for the samples. The volume change measurements in tension show initial dilatation of the samples followed by a volume relaxation that at the largest strains in one grade of polycarbonate leads to densities greater than those of the undeformed sample. In the case of the compression measurements, the volume decreases upon deformation, but, rather than relaxing back towards the undeformed volume, the samples continuously densify. The differences in the tensile dilatation for the two grades of polycarbonate suggest that the volume behavior may be related to the propensity to yield vs. fracture.
Structure‐property correlations in stretched LLDPE films using oblique incidence small‐angle X‐ray scattering
Authors: Hu Ruizhong , Lambert W. Scott , Barnes John D.
Published: April 2004

This paper demonstrates the use of oblique incidence small‐angle X‐ray scattering (SAXS) to characterize microstructure in linear low‐density polyethylene films subjected to biaxial deformation in a TM Long stretcher. Differences in tear strength and impact properties were found when two different deformation temperatures were used. SAXS was used to characterize the nanometer scale microstructure of these films. Since the microstructure was expected to be anisotropic, SAXS data were collected in normal incidence, T (transverse) oblique incidence and M (reference direction) oblique incidence. The sections through the three‐dimensional SAXS pattern collected in these three orientations are combined to provide clues to the nature of the complete 3‐D SAXS pattern, which can be interpreted to characterize the changes wrought by deformation.
Morphology of syndiotactic polystyrene as examined by small‐angle X‐ray scattering
Authors: Barnes John D. , McKenna Gregory B. , Landes Brian G. , Bubeck Robert A. , Bank David
Published: April 2004

Small Angle X‐Ray scattering (SAXS) studies have been carried out on injection molded syndiotactic polystyrene (SPS) at room temperature and at elevated temperatures up to 290°C. Features indicating lamellar crystallinity were weak or entirely absent at room temperature, becoming increasingly intense above the glass transition temperature (Tg) for this material. A background scattering whose intensity was roughly proportional to q−2, where q is the scattering momentum transfer, was present throughout the temperature range. We suggest that these results indicate that SPS materials formed in this way are three‐phase systems, with an amorphous phase, a crystalline phase, and a grain boundary phase.
Applications of molecular dynamics to the study of thermal degradation in aromatic polymers. I: Polystyrene
Authors: Nyden Marc R. , Coley Terry R. , Mumby Stephen
Published: April 2004

This paper reports recent progress in the development of a generic molecular dynamics model that accounts for the major chemical reactions involved in the thermal degradation of polymers. The strategy employed in the design of the most recent version of this model was to interface our code for performing reactive dynamics on simple vinyl polymers with a commercial molecular dynamics package (Discover 95). The expanded range of applicability of the integrated model is illustrated by applying it to the study of thermal degradation in atactic polystyrene.