bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon fiber‐reinforced composites: Effect of fiber surface on polymer properties
Authors: Ko Yoon Suk , Forsman William C. , Dziemianowicz Theodore S.
Published: December 2004

Dynamic mechanical measurements in a torsional (shear) mode have been used to characterize an unfilled epoxy (Epon 828/m‐phenylene diamine) and A series of uniaxial graphite fiber (Hercules types A and HM) composites. In unfilled resins containing an excess of the epoxy component, Mc—the average molecular weight between crosslinks—decreases with increasing temperature and duration of cure, suggesting a temperature‐dependent side reaction. In fiber‐reinforced composites, the dynamic mechanical response is sensitive to fiber type and curing schedule; elevation of Tg by as much as 45°C has been observed. Comparison of the dynamic data with properties predicted by micromechanical models shows only a fair agreement at room temperature, which rapidly worsens at higher temperatures. Surface treatment of type A fibers gives enhanced interlaminar shear strength (ILSS), both at ambient conditions and after hydrothermal aging. Dynamic data for surface‐treated systems during hydrothermal aging show a sharper drop in G′ and increase in tan δ. The dynamic data and ILSS results are interpreted in terms of a balance of polymer‐fiber interactions, a weak but widespread preferential adsorption of epoxy oligomers on the graphite basal planes at the fiber surface, and a low concentration of covalent bonds between polymer and fiber‐surface‐functional groups.
Computational scheme for the calculation of molecular weight distributions for nylon 6 polymerization in homogeneous, continuous‐flow stirred‐tank reactors with continuous removal of water
Authors: Ramagopal A. , Kumar Anil , Gupta Santosh K.
Published: December 2004

An efficient computational scheme has been established for obtaining the molecular‐weight distributions (MWDs) for Nylon 6 polymerization in homogeneous, continuous‐flow stirred‐tank reactors (HCSTRs) with water vaporization. A three‐step procedure is used: the moment equations are solved by a sequential application of Brown's algorithm, the moments so calculated are used to give an empirical Flory‐Schultz distribution and, finally, this empirical distribution is used as a starting guess in Brown's algorithm applied to species mass‐balance equations to give the exact MWD. The moment‐closure approximations normally used for hutch reactors have been found to work equally well with HCSTRs for residence times of industrial significance.
Effect of sub‐Tg relaxations on the gas transport properties of polyesters
Authors: Light R. R. , Seymour R. W.
Published: December 2004

The relationship was determined between sub‐Tg molecular motions and the transport of O2 and CO2 in amorphous polyesters and copolyesters based on poly(ethylene terephthalate) [PET] and poly(1,4‐cyclohexylenedimethylene terephthalate) [PCDT], Modifications of the polyester with certain acid co‐monomers restricted the molecular motions that occurred in the β‐relaxation region and in turn decreased the O2 diffusion coefficient. The solubility coefficient was unchanged by those modifications. Modification of PET with 1,4‐cyclohex‐anedimethanol increased the magnitude of the β‐relaxation and both the diffusion and solubility coefficients of O2. Similar relationships between the β‐relaxation magnitude and CO2 permeability were also found. The temperature dependence of O2 permeability followed an Arrhenius relationship, with different activation energies (Ep) above and below the β‐relaxation. The activation energy was smaller below the β‐relaxation. Values of Ep above and below the β‐relaxation did not depend on the chemical structure of the polymer.
The effect of temperature and humidity on the long‐term performance of poly(butylene terephthalate) compounds
Authors: Borman W. F. H.
Published: December 2004

A model was developed that closely fits new and previously published test data for the aging of poly(1,4‐butylene terephthalate) (PBT) compounds under conditions of elevated temperature and high relative humidity. The model equation, stated in terms of absolute temperature and water vapor partial pressure, allows extrapolation of accelerated aging data to ambient conditions that prevail in realistic applications of the materials. For practical reasons, the water vapor partial pressure is preferred as a model variable over relative humidity, although it is shown that both variables are equivalent in a formal sense.
Observation of molecular chain scission during crazing of polystyrene
Authors: Popli R. , Roylance D.
Published: December 2004

A series of gel permeation chromatographic (GPC) separations has been performed on polystyrene specimens in an attempt to discern whether or not mechanical crazing is accompanied by significant covalent bond scission. It was found that the extent of scission is not large but is indeed present in concentrations that are detectable by GPC. This suggests that molecular‐slippage‐only models of the crazing process are perhaps overly idealized and that crazing cannot take place in highly entangled polymer solids without some bond rupture.
Economics of polymer blends
Authors: Utracki L. A.
Published: December 2004

Economic, technological, and regulatory pressures gradually narrow the chemical variety of polymers: in 1975, the market share of polyethylene was 40 percent, poly(vinyl chloride), 23 percent, polystyrene, 12 percent, and polypropylene, 11 percent, adding up to 86 percent of all thermoplastics (1‐3). The same pressures compel the plastics processor to diversify formulations and production methods. He must resort to new materials (e.g., polymer blends, polymer alloys, and composites) and new methods of manufacture. In this work, the economics of blending will be discussed.

There are five reasons to employ polymer blends:

higher performance at a reasonable price,

modification of performance as a market develops,

extending the performance of expensive resins,

re‐use of plastics scrap,

generation of a unique material as far as its processabilitv and/or performance are concerned.

In Canada, the cost of blending varies from 8 to about 20 ¢/lb, depending primarily on the volume and the kind of material. The cost effectiveness depends on the total technical and economic environment in which the manufacturer operates; it has to be computed for each case separately. In the text, guidelines and examples are provided.
Finite element analysis of wire coating
Authors: Mitsoulis E.
Published: December 2004

A general‐purpose finite element program has been used to simulate the flow of polymers through wire‐coating dies. The analysis includes Newtonian and power‐law fluids. The effect of normal stresses was examined through a simple viscoelastic constitutive equation, Nonisothermal wire coating was studied to obtain the temperature field within the melt. The effect of a slip condition at the solid boundaries was also examined. The determination of the coating melt free surface was carried out through an iterative procedure. The finite element solution provides details about the existence and extent of recirculation regions, about hot spots due to viscous dissipation, and also captures the stress singularities present at the impact of the melt with the wire and at the exit from the die. Pressure distribution, maximum temperature rise, haul‐off wire tension, maximum wire tension, and stresses at the wire surface and die wall are also presented.
A study of the dynamics of foam growth: Simplified analysis and experimental results for bulk density in structural foam molding
Authors: Amon Moris , Denson Costel D.
Published: December 2004

A cell model describing the diffusion‐induced growth of closely spaced single bubbles developed in an earlier publication is now used as the microscopic building block of an analysis of low‐pressure structural foam molding. Heat transfer, solidification, and bulk flow of the foam in the mold cavity are included in this macroscopic analysis. An experimental method is described whereby the bulk density of an expanding thermoplastic polymeric foam is measured as a function of time when the expanding foam is prepared by the short shot injection molding process. Instantaneous and final bulk foam density data obtained for various values of the controlling process parameters are compared with the predictions of the model. These predictions are found to be in qualitative agreement with the experimental measurements reported here. However, quantitative differences exist between the two. These differences are explained mainly by the omission of melt elasticity and bubble coalescence in the model.
Enthalpy recovery and physical aging of polymer‐diluent binary systems: A network epoxy and water
Authors: Ellis T. S. , Kahasz F. E.
Published: December 2004

Physical aging of a network epoxy resin in both the dry and water plasticized state has been investigated using calorimetric methods. Enthalpic retardation (recovery) towards equilibrium below the glass transition temperature (TK) has been qualitatively and quantitatively evaluated over a wide temperature range by following the enthalpy recovered (Er) on re‐heating through to and beyond the glass transition. Results indicate that water, acting as a plasticizer, accelerates aging at any given temperature. However, by using the respective Tg as a point of reference, a simple comparison of the kinetics of aging in the dry and plasticized state suggests that in the temperature range studied there are no significant differences. These observations, together with observed dilational and relaxational effects of water which appears to erase all accumulated aging effects in dry aged material, are commented upon and their importance in the' context of transport‐phenomena and moisture sorption‐desorption cycles are discussed.
A non‐destructive technique of measuring residual stresses in circular rods of transparent polymers
Authors: Mittal R. K. , Rasitmt V.
Published: December 2004

Residual stresses, generally present in solid polymers, arise as a result of temperature gradients during solidification. These stresses influence the mechanical behavior of polymers and therefore it is important to measure them; most conventional methods are destructive. In the present work, a non‐destructive photoelastic technique is discussed and applied to circular rods of poly(methyl methacrylate) (PMMA). This technique involves the measurement of the distribution of total birefringence across a diameter; the residual stress distribution is obtained numerically from the birefringence distribution. The influence of the birefringence caused by molecular orientation is also investigated. This technique is also applied to a glass rod, in which case the molecular birefringence is minimum. It is seen that the residual stresses obtained in this case are consistent with equilibrium considerations.
Time‐dependent behavior of nylon‐6 under uniaxial and biaxial loadings at constant rate
Authors: Mittal R. K. , Singh I. P.
Published: December 2004

The large deformation behavior of nylon‐6 when subjected to constant loading rate tests has been investigated experimentally. Three types of loadings—tension, torsion, and combined tension‐torsion—have been used and the strain histories for each type analyzed. It is shown that a piecewise power law in time can adequately describe the strain histories up to equivalent strains as high as 30 percent for all cases. This piecewise power law shows well‐defined transitions from one mode to the other while each mode is characterized by a power law exponent valid for all types of loading. On the basis of experimental results, it is also possible to establish the functional form of various kernels involved in the Green‐Rivlin representation of the non‐linear viscoelastic behavior of nylon‐6. This method of finding kernels is much simpler than the conventional method of carrying out a large number of multi‐step creep tests. A comparison is also made between the results of the present work and the well‐known Findley equation, particularly with respect to the instantaneous strain response of materials.
Continuous extrusion of reacting polyurethane foam
Authors: Jerard Robert B. , Ravens Thomas R.
Published: December 2004

This paper explores the concept of continuously extruding reacting polyurethane foams. The control of the process is hampered by the fact that the state of the conversion of the extrudate is not directly observable. We present the general concept, describe an experimental apparatus, present a mathematical model of the process, and report on some initial experimentation. In the experimental work, low density (0.5 g/cc) polyurethane foam was extruded in a cylindrical cross section at a rate of 250 g/min. Maximum run time was thirty minutes. In all cases, the experiment had to be stopped due to problems in the process. Problems requiring further investigation were identified: channelling of uncured liquid foam around the solid cured foam, poor skin quality due to adhesion of the foam to the wall, and the general lack of observability of the conversion field.
Monitoring of laminate cure with microdielectrometry
Authors: Bidstrup Wayne W. , Sheppard Norman F. , Senturia Stephen D.
Published: December 2004

We report the use of microdielectrometry for monitoring the cure of the matrix resins in epoxy‐glass and epoxy‐graphite composites. The multi‐ply laminates are cured in a press using ramped temperatures. The microdielectrometer sensor is embedded in a cavity made by cutting a hole in each of the inner plies. For a brominated‐epoxy glass‐reinforced prepreg ramped to final cure temperatures as high as 200°C and at pressures up to 60 psi, a reproducible pattern of cure events is observed beginning with the flow of resin onto the sensor electrodes and ending with the characteristic stabilizing of the loss factor late in cure. The apparent dielectric properties (permittivity and loss factor) show good reproducibility for identically prepared samples, but their characteristics differ from those observed in neat resin. A ten‐fold increase in resin conductivity is noted when cures of glass‐reinforced prepreg are compared to cures of neat resin flaked off the prepreg. Special techniques are required in sample preparation when monitoring the cure of prepregs containing conductive fibers such as graphite.
The use of microdielectrometry in monitoring the cure of resins and composites
Authors: Sanjana Z. N.
Published: December 2004

As thermosetting resins and composites made from them begin to be used in critical applications, it becomes necessary to monitor and analyze the cure of the resin within the confines of the processing equipment. Such measurements have been carried out using a dielectric technique called dielectrometry or dielectric analysis. Conventional dielectrometry has certain limitations associated with the use of parallel plate geometry for electrodes. For in situ measurement of cure, intrusiveness of electrodes is a problem which may require placement of electrodes in non‐strategic areas. Since electrode spacing changes during cure, it is difficult to deduce permittivity and loss factor from the data. At lower frequencies the capacitive currents are small and signal‐to‐noise ratios are small, therefore, measurement at low frequencies (>100 Hz) typically require large electrode sizes. One approach to overcome the problems described above is the development of microdielectrometry. A solid state integrated circuit chip, 2 by 4 mm in size, is used as the sensor. The miniature sensor can measure the properties of a dielectric on its surface, therefore it need not intrude into the composite part. Transistors which are built into the integrated circuit are used to amplify the signal to make low frequency (>1 Hz) measurements feasible. The electrode geometry does not change, therefore loss factor and permittivity data can be deduced in real‐time. During cure of the resin or composite material, permittivity and loss factor are measured continuously at a series of preselected frequencies. Real‐time‐data is plotted on a strip chart and is also stored in a cassette for later analysis. Temperature of the curing material is measured either by a diode on the sensor or by externally placed thermocouples. Results on an aromatic amine cured epoxy resin and a dicyandiamide cured epoxy resin prepreg are presented in this report. The data obtained by microdielectrometry is compared and correlated to results obtained using differential scanning calorimetry, infrared analysis, and dynamic mechanical analysis. Results show that microdielectrometry can be used to follow the cure of epoxy resins and absolute measurements of permittivity and loss factor can be made to provide information on the mechanisms that produce the observed changes. Data at 1 Hz can be obtained but for certain lossy systems at typical cure temperatures, the data is often out of range of the instrument, thus restricting use to 10 Hz and higher frequencies. At very high loss factors (>100) a “blocking” phenomenon is observed due to charge pile up at electrode surfaces which results in erroneously high permittivity values.
Development of a mathematical model for the pultrusion process
Authors: Han Chang Dae , Lee Dai Soo , Chin Hong Bai
Published: December 2004

A mathematical model has been developed to simulate the pultrusion process, namely the profiles of temperature and the degree of cure in both the axial and radial directions in a pultrusion die of cylindrical shape. For the study, the equations of continuity and energy transport, coupled with a kinetic expression for the curing reaction, were solved numerically, using a finite difference method. For the kinetic expression, we used an empirical expression of the form dα/dt = (k1 + k2αm)(1 − α)n to describe the curing behavior of both unsaturated polyester and epoxy resins. Differential scanning calorimetry (DSC) was used to investigate the curing behavior of the following systems: unsaturated polyester resin/glass fiber, epoxy resin/glass fiber, and epoxy resin/carbon fiber. The results of DSC runs were used to determine the kinetic parameters, which enabled us to predict the effects on the pultrusion characteristics of the following variables: (1) the type of initiator; (2) the type of fiber reinforcement; (3) the type of resin; and (4) the pulling speed and hence the residence time.
Effect of water absorption on physical properties of high nitrile barrier polymers
Authors: Jabarin S. A. , Lofgren E. A.
Published: December 2004

Water absorption studies were made on a series of high nitrile barrier polymers, as a function of polymer composition, rubber content, temperature, orientation and relative humidity. Results indicate that absorbed water has a great influence on both mechanical and thermal properties of the polymer. Absorbed water in high nitrile polymers causes a large decrease in the glass transition temperature and yield stress. These effects are found to depend on polymer composition, amount of absorbed water, and degree of orientation. The significance of these results is discussed in relation to end‐use properties of the polymer.
Viscoelastic properties of highly loaded ferrite‐filled polymeric systems
Authors: Saini D. R. , Shenoy A. V.
Published: December 2004

Viscoelastic properties in terms of complex viscosity |η*| and storage modulus G' have been studied for highly filled polymer composites. The viscous response and elastic response to changes in the frequency of dynamic oscillations have been fitted through an appropriate Theological model. A relationship between |η*| and G' is shown to exist, and the model parameters determined through the correlation have been shown to be useful in estimating the viscoelastic properties of commercially important ferrite‐filled polymeric systems with loading in the range of 87–94 weight‐percent.
Finite element simulation of fountain flow in injection molding
Authors: Mavridis H. , Hrymak A. N. , Vlachopoulos J.
Published: December 2004

Fountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. The use of a general purpose finite element program for the appropriate boundary conditions made possible the detailed flow description behind an advancing liquid front moving at constant speed inside two‐dimensional channels and tubes. The results were qualitatively the same for both Newtonian and shear‐thinning fluids.
Injection molding: The effect of fill time on properties
Authors: Cox Howard W. , Mentzer Charles C.
Published: December 2004

The effect of fill time on the mechanical properties, surface appearance, and part dimensions of several polymers was determined. Two crystalline materials, polypropylene and nylon 6,6, and an amorphous material, acrylonitrile‐butadiene‐styrene (ABS), were used. In addition, the effect of the presence of glass fibers was examined using glass fiber reinforced nylon 6,6. The fill time was varied from 0.8 to 20 sec which included both the viscous flow controlled region (short fill times) where laboratory samples are ordinarily molded and the heat transfer controlled region (long fill times) where production parts arc commonly molded. No large variations in tensile properties were observed for polypropylene or nylon, but a 10 percent increase in peak tensile stress and strain for ABS did indicate that molecular orientation increased with increasing fill time. However, significant differences did occur in the properties of glass reinforced nylon. Peak tensile stress increased 15 percent and flexural strength decreased 10 percent as the fill time was increased. Although no change in the flexural modulus was observed, the scatter in the modulus decreased with increasing fill time. These property variations can be attributed to differences in the glass fiber orientation of the skin and core regions of the part. The measurement of molded tensile bar dimensions indicated there was little effect of fill time on the shrinkage of the various polymers except for shrinkage in the length direction for polypropylene. The shrinkage increased from 13 to 15.4 mm/m over the fill time range, a great enough difference to affect the fit of large parts. The most dramatic change with fill time was the surface appearance of the glass reinforced nylon. The surface of samples molded at short fill times had a dark uniform color and smooth appearance while samples molded at long fill times had a lighter color and a porous surface. This surface porosity is due to crystallization prior to complete pressurization of the mold. Therefore, in addition to affecting surface appearance, other surface related properties such as aging and the ability to plate plastic parts could also be affected.
An experimental investigation of capillary extrudate swell in relation to parison swell behavior in blow molding
Authors: Kalyon Dilhan M. , Kamal Musa R.
Published: December 2004

An experimental study was carried out to study and characterize the capillary extrudate swell and parison swell behavior in extrusion blow molding of two commercial blow molding grade high density polyethylene resins. The capillary extrudate swell behavior of these resins were determined employing a capillary rheometer and a special thermostatting chamber. Parison swell behavior was determined using an Impco A13‐R12 reciprocating screw blow molding machine in conjunction with cinematography and pinch‐off. The experimental conditions under which capillary extrudate and parison swell data can be related are elucidated. Excellent agreement is found between the area swell values determined on the basis of capillary and parison swell experiments.
Microstructural influences on volumetric properties of styrene‐butadiene‐styrene block copolymers
Authors: Diamant Joram , Williams Michael C.
Published: December 2004

A water‐displacement method was used to measure the specific volume of three styrene‐butadiene‐styrene (SBS) block copolymers over the temperature range 4°C to 65°C. The polymers contained 0.268. 0.293, and 0.482 weight fraction polystyrene, varied in molecular weight, and are known to be phase‐separated at these temperatures. Coefficients of thermal expansion were also obtained and found to be constant over this temperature range. Results are compared with various models of composite behavior, the most successful of which is the linear mixing rule which gives good predictions over this composition range. Deviations for specific volume are negative, and for expansion coefficient positive, from the linear rules. More complex behavior is suggested, however, and this is interpreted in terms of microstructural characteristics. Some apparent contradictions in data reported by other workers are explained. Results are presented also for samples stretched uniaxially up to 300 percent strain; only slight evidence of dilation is seen at 22°C. but increase of the expansion coefficient is more apparent.
Residence time distribution in a commercial twin‐screw extruder
Authors: Wolf D. , Holin N. , White D. H.
Published: December 2004

The residence time distribution of poly(vinyl chloride) (PVC) polymers in a counterrotating twin screw commercial extruder was determined and analyzed. The experimental technique involved the use of manganese dioxide as a tracer after being neutron activated and was injected into the extruder during normal operation without interrupting the poly(vinyl chloride) compound production. The experimental results enabled us to better understand the flow and mixing conditions in the extruder.
High‐TG base‐soluble copolymers as novolac replacements for positive photoresists
Authors: Turner S. Richard , Arcus Robert A. , Houle Conrad G. , Schleigh William R.
Published: December 2004

Several high‐Tg, phenolic copolymers based on N‐(p‐hy‐droxyphenyl)maleimide with various comonomers were prepared, and the properties of a number of these copolymers were studied. The copolymers were 1:1 in composition and were predominantly alternating. The thermal properties of these copolymers were investigated by differential scanning calorimetry and thermal gravimetric analyses. The chain‐stiffening effect of the maleimide group was responsible for Tg's of 200°C and above. Tg was a function of composition and molecular weight. Dissolution rates of thin films of these copolymers were investigated by laser interferometry. The dissolution rates were sensitive to copolymer molecular weight and to the functionality, i. e., the type of phenolic OH groups and the concentration of OH groups present. When these copolymers were used as binders for NDS (diazonaphthoquinone sulfonate) photochemistry, high‐resolution positive images were obtained that were resistant to thermal deformation at 200°C and above.
The fracture behavior of surface embrittled polymers
Authors: So Paul K. , Broutman L. J.
Published: December 2004

Normally ductile polymers may exhibit unexpected brittle fractures because of a phenomenon termed surface embrittlement. The problem may arise whenever a thin brittle layer is present on the surface, which may result from the application of brittle paint or, more commonly, from surface degradation caused by exposure to elevated temperatures, ultra‐violet radiation, and stress‐cracking agents. In rubber‐modified polymers such as acrylonitrile‐butadiene‐styrene and high‐impact polystyrene, exposure to the outdoor environment inevitably results in the formation of a thin surface layer containing cross‐linked rubber particles in a matrix of reduced molecular weight. Although the depth of material adversely affected is typically small compared to the bulk, a drastic reduction in ductility nonetheless has been observed. To better understand the mechanism of embrittlement, this paper examines the criterion for embrittlement by considering the mechanism for enhanced energy absorption of rubber‐toughened plastics and elementary concepts of fracture mechanics. It has been shown that a critical coating thickness exists when multiple crazing is essentially inoperative and the deformation is localized, to the tip of a fast moving sharp crack restricting strain energy dissipation to a relatively small region.
Sorption equilibria and kinetics of ethanol in miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blends
Authors: Chiou J. S. , Paul D. R.
Published: December 2004

At 35°C miscible blends of poly(vinylidene fluoride) (PVF2), and poly(methyl methacrylate) (PMMA), may be semicrystalline or wholly amorphous and rubbery or glassy depending on composition and prior history. Ethanol is rather soluble in PMMA and plasticizes it, while sorption into PVF2 is rather small. The equilibrium sorption of ethanol into these blends decreases in a well defined manner as the PVF2 content increases and is only slightly affected by prior history of the sample. On the other hand, the kinetics of ethanol sorption varies in a complex manner with composition, ranging from Case II kinetics for glassy blends to Fickian diffusion for rubbery ones, and is a strong function of prior history. Quantitative descriptions are given and discussed in terms of the various mechanistic processes known to occur.
Small angle x‐ray studies of siloxane‐urea segmented copolymers
Authors: Tyagi D. , McGrath J. E. , Wilkes G. L.
Published: December 2004

Novel segmented copolymers were synthesized using aminopropyl terminated linear poly(dimethylsiloxane) oligomers as the soft component and various diisocyanates as the hard segments. As a result of the large differences in the cohesive energy density (solubility parameter) between the two components, phase separation occurs to form a microdomain structure at relatively low oligomer molecular weights. Since chain extenders were not employed during the synthesis, the “hard” segments are strictly related to the length of the diisocyanate moiety utilized in the reaction, In this paper we utilize these copolymers as reasonable models for investigating the various methods available for determining the interfacial layer thickness between the hard and soft phase. Specifically, in these systems there is no hard segment length distribution as is the usual case for segmented urethanes. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers. The degree of positive and negative character was found to be dependent upon copolymer composition. Negative deviations were accounted for in terms of a finite interfacial thickness, which turned out to be relatively small as anticipated, while the positive deviations were assigned to isolated hard segments that reside within the soft segment matrix, i.e., concentration fluctuations. In calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. Cautionary comments are also provided for researchers who apply less complete small angle x‐ray scattering (SAXS) analysis to related block or segmented copolymers with regard to phase separation behavior.
Forced in‐plane flow of an epoxy resin in fibrous networks
Authors: Adams Kurt L. , Miller Bernard , Rebenfeld Ludwig
Published: December 2004

A method to study the forced in‐plane flow of an epoxy resin into fibrous networks is presented. A radial in‐plane flow apparatus has been developed which allows strict control of all important experimental variables as well as visual observation of the experiment. From the position and shape of the advancing resin front as a function of time, effective directional permeabilities are obtained and used to compare structurally different fibrous networks. Test results for an initial series of woven and nonwoven fabrics reinforce the method of data analysis and demonstrate the effects of pore structure, weave type, weave balance, fabric layering, fiber orientation, and compressibility.
The process of cavity filling including the fountain flow in injection molding
Authors: Gogos Costas G. , Huang Chieh‐Fong , Schmidt Larry R.
Published: December 2004

This work deals with the simulation of the filling of a cavity utilizing the Marker‐and‐Cell numerical technique in solving the transient problem involved. The cavity is confined by two parallel plates, and is “end fed.” The flow was assumed isothermal and the fluid incompressible, obeying the power law model. Special attention was given to the flow region near the advancing melt front, in order to obtain a better insight of the “fountain effect,” during which the fluid flows from the center to the walls of the cavity. The results of the simulation of the front flow region are supported by and in qualitative agreement with experimental results involving “tracer resins” during cavity filling. Although the flows considered were slow and isothermal, this study has significant practical ramifications on industrial mold filling during injection molding.
Polycarbonate/phenoxy blends: Physical behavior and development of interchange reactions in melt‐processing conditions
Authors: Mondragón I. , Gaztelumendi M. , Nazábal J.
Published: December 2004

The miscibility of the polycarbonate of bisphenol A with the polyhydroxyether of bisphenol A was analyzed using differential scanning calorimetry and the, results are compared with the torque data obtained using a Brabender Plasticorder. The possibility of interchange reactions was analyzed by means of the observation of the melt‐viscosity variation versus processing time in the mixer‐bowl. These reactions form graft‐copolymers that develop into crosslinked copolymers at higher residence times. It was also shown that the speed of these reactions depends on the processing temperature. The variation produced on the glass‐transition temperature because of branching was also analyzed.
The melt compatibility of blends of polypropylene and ethylene‐propylene copolymers
Authors: Lohse David J.
Published: December 2004

Blends of polypropylene with ethylene‐propylene copolymers of various compositions have been studied by small angle neutron scattering with regard to their compatibility at room temperature and in the melt. It has long been known that such blends separate into distinct phases at lower temperatures due to the crystallinity of the isotactic polypropylene, The work described herein has shown that these blends are also immiscible in the melt, even where the ethylene content of the copolymer is as low as 8 percent. Moreover, the separated phase domains grew rapidly at melt temperatures. Blends of atactic polypropylene with isotactic polypropylene did become miscible upon melting.
Hydroxyl group determination in prepolymers by 1H NMR spectroscopy
Authors: Goldwasser J. M. , Adolph H. G.
Published: December 2004

A fast and specific method has been developed for the determination of hydroxyl content in prepolymers that contain hydroxymethylene functional groups. This method involves reaction of the sample with either trifluoroacetic anhydride or hexafluoroacetone to separate the terminal oxymethylene signals in the 1H NMR spectrum from those of the repeating unit and integration against an internal trinitrobenzene standard. This procedure generally requires less than 50 mg of polymer and has been employed in the analysis of prepolymers with number average molecular weights ranging up to 10000. The analysis has been tested using several different prepolymers. Precision of analysis was determined to be within 2.7 percent using a Varian XL‐200 spectrometer.
Characterization of epoxy thermosetting systems by differential scanning calorimetry
Authors: Galy Jocelyne , Sabra Abed , Pascault Jean‐Pieirre
Published: December 2004

Differential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non‐catalyzed diamine‐epoxy systems, the reaction enthalpy ΔH and the glass transition temperature Tg are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine‐to‐epoxy ratio r on Tg is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of Tg is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.
Montmorillonite polymer concrete: Zero‐shrinkage and expanding polymer concrete with enhanced strength
Authors: Haque E. , Armeniades C. D.
Published: December 2004

Conventional polymer concrete (PC) suffers from setting stresses, generated during the cure of the resin binder, when polymerization shrinkage is hindered by the close packing of filler and aggregate particles. Setting stresses impair significantly the strength of the cured PC. Current zero‐shrinkage and expanding PC formulations achieve these properties with a sacrifice in strength. Here we present a novel method for producing zero‐shrinkage and expanding PC systems with concomitant enhancement in strength. This is achieved by dispersing small amounts of the mineral montmorillonite (MMT) into the resin. As the system cures, the resin interacts with the hydrated mineral: at temperatures above 100°C some of the hydration water is released, creating expansion forces, which counteract resin shrinkage. MMT contents of 0.2 percent or less give rise to zero‐shrinkage polyester PC systems with flexural strength 30 percent greater than the corresponding conventional PC; higher MMT contents create PC systems that expand upon curing or generate hydrostatic pressure during constant‐volume cure. We discuss the effects of MMT content and cure temperature on the volume change and strength of the resulting PC. We then propose a mechanism for the action of MMT as a highstrength expansion agent, based on differential scanning calorimetry and thermomechanical analysis of these systems.
Deformation and fracture characterization of inelastic composite materials using potentials
Authors: Schapery R. A.
Published: December 2004

An approach using strain energy‐like potentials to characterize deformation and fracture of inelastic, nonlinear composite materials is described. The inelasticity may be due to various causes, including microcracking, microslipping, and rate processes responsible for fading memory (viscoelasticity). The concept of work potentials is introduced first, and then arguments are given for their existence for inelastic materials. Emphasis in the paper is on elastic composite materials with changing or constant states of distributed damage. Experimental results on polymeric composites are subsequently presented to illustrate this approach to deformation and fracture characterization. Finally, extension to viscoelastic behavior is discussed.
Volume change and the nonlinearly thermo‐viscoelastic constitution of polymers
Authors: Knauss W. G. , Emri I.
Published: December 2004

The time‐dependent behavior of linearly viscoelastic materials is known to be very sensitive to changes in temperature and in solvent (water) concentration. Following an investigation by the authors of this sensitivity in terms of the associated small volume changes, a nonlinearly viscoelastic model of constitutive behavior was formulated earlier in terms of the free volume concept and evaluated in terms of experiments on poly(vinyl acetate). Following a brief presentation of the earlier results these concepts are expanded and refined in the present paper to deal with transient deformation histories under pressure. In this connection, model computations explore the effect of simultaneous pressurization and straining. In addition the effect of “ageing” the polymer under pressures of various magnitudes and for different lengths of time are investigated. It becomes clear that the yield phenomenon depends sensitively on pressure and on the ageing time. In addition, the volume change under transient thermal histories in the glass transition range is explored, largely in terms of Kovacs' experimental data and attendant computations. These considerations are presented from a unified point of view of nonlinear thermoviscoelastic constitutive behavior, principally with phenomenological material description in mind. These computations provide guidance to the design of experiments for the proper determination of the relevant material functions and seem to indicate a need for the reevaluation of certain experimental procedures in the time histories of thermal material characterization.
The nonlinear viscoelastic characterization of graphite/epoxy composites
Authors: Dillard D. A. , Straight M. R. , Brinson H. F.
Published: December 2004

Fiber reinforced plastics offer many structural advantages for a variety of designs. Before these material systems can achieve more widespread usage, however, some of the unanswered questions regarding the long‐term behavior and durability of these materials must be answered. Nonlinear compliance data is presented for T300/934 and T300/5208 graphite/epoxy composites. Several nonlinear viscoelastic techniques are compared for modeling the response. Comments for applying nonlinear models to orthotropic materials are given. A procedure for predicting long term laminate response from short term unidirectional data is reviewed.
Multiaxial nonlinear viscoelasticity of solid polymers
Authors: Buckley C. P.
Published: December 2004

A scheme is presented for characterizing multiaxial nonlinear viscoelasticity of solid polymers in a manner suitable for application to the prediction of deformation of polymeric parts. The basis of the scheme is the systematic exploitation of simplifications resulting from: (1) restrictions on the class of stress histories considered, (2) material symmetry (e.g., isotropy), and (3) the nature of viscoelastic nonlinearity in any given material. Several classes of stress history are considered. In the special case of inplane response of an isotropic material to a two‐dimensional proportional loading history, it is shown that the nonlinearity can be expressed through the dependences of compressibility B and shear compliance J on two invariants of the stress history: I1 and I2′, which separately characterize the magnitudes of hydrostatic and deviatoric components of the stress tensor. When this approach is applied to the description of biaxial creep and recovery of isotropic polypropylene, it is found that for strains up to 0.012, B is independent of I1 and I2′, while J is linearly related to I1 and I2′. These results are used to predict axial strain and hoop strain in the wall of a pressurized pipe, and the predictions compared with those obtained with three approximate procedures.
Flow distribution in spiral mandrel dies
Authors: Rauwendaal Chris
Published: December 2004

An analysis of flow of a power law fluid in a spiral mandrel die is presented. The analysis is applied to study the effect of various die design parameters on the flow distribution at the end of the spiral mandrel section. Three variables that have a very strong effect on the flow distribution are the number of grooves, the initial clearance, and the groove helix angle. The distribution is improved by increasing the number of grooves, by using a non‐zero initial clearance, and a relatively small helix angle. Two more variables that have a significant effect on the flow distribution are the taper angle and the initial groove depth. The optimum taper angle was found to be between 1 and 3 degrees. The distribution uniformity improves with the initial groove depth, while the pressure drop reduces at the same time.
Effects of mixing on morphology, rheology, and mechanical properties of blends of ultra‐high molecular weight polyethylene with linear low‐density polyethylene
Authors: Vadhar Parimal , Kyu Thein
Published: December 2004

Various blends of ultra‐high molecular weight polyethylene (UHMWPE) with linear low‐density polyethylene (LLDPE) were prepared in an internal (Banbury type) mixer, a static mixer, and by solvent blending. Two mixing techniques, namely simultaneous and sequential loading methods, were employed with the internal mixer. In the former case, the two polymer components were simultaneously loaded at 180°C and mixed. The latter method allowed the UHMWPE component to diffuse at 250°C and cooled it down to 180°C, then the LLDPE component was added subsequently and mixed. Rheological and mechanical properties of these blends are profoundly affected by the mixing techniques used. Rheological results shows yield characteristics of UHMWPE/LLDPE blends, in particular in blends of high UHMWPE contents. Tensile properties of sequentially loaded blends vary more or less linearly with blend compositions. However, negative or positive deviations are seen in the simultaneously prepared blends. Differential scanning calorimetry (DSC) studies indicate that co‐crystallization takes place between UHMWPE and LLDPE components in sequentially mixed blends. DSC and small‐angle light scattering (SALS) studies show that separate crystallization takes place in simultaneously blended compounds as a result of poor mixing. It seems that the sequential loading method provides more homogeneous compounds than those of simultaneous blending.
Influence of casting and curing conditions on gas sorption and transport in polyimide films
Authors: O'Brien K. C. , Koros W. J. , Husk G. R.
Published: December 2004

Carbon dioxide and methane gas permeabilities, solubilities and diffusivities for poly [N, N′‐(phenoxyphenyl)‐pyromellitimide] films synthesized in our laboratory are contrasted with values measured for a chemically identical commercial polyimide film, Kapton H. The synthesized samples exhibited greater permeabilities, solubilities, and diffusivitles than those of the commercial sample. At the same time, the higher carbon dioxide permeability is associated with only a moderate reduction in permselectivity for the CO2/CH4 system. The increased sorption and transport coefficients for the synthesized sample are attributed to a lower degree of aggregation and orientation of this film as compared to the Kapton H sample.
Polymers based on divalent metal salts of mono(hydroxyethyl) phthalate—a review
Authors: Matsuda Hideaki
Published: December 2004

Divalent metal salts of mono(hydroxyethyl) phthalate are useful starting materials for synthesis of ionic polymers into which metal is firmly incorporated. This article surveys a series of polymers that have been synthesized by using metal salts. The salts can react with compounds having functional groups capable of reacting with hydroxyl groups. By polyaddition reactions of the salt‐diol with diisocyanates in dimethylformamide, metal‐containing polyurethanes, polyurethane‐ureas, and isocyanurate‐type crosslinked polyurethanes are obtained. In polycondensation reactions of the salt‐diols with anhydrides, some systems give unsaturated polyesters soluble in styrene. Meanwhile, polyaddition reactions of systems of the salt‐anhydride‐epoxide give metal‐containing polyesters containing ionic links in the main chain. The metal carboxylate groups of the salts catalyze the reactions in this case. The reactions have offered a commercially favorable synthetic route. Through the proper selection of components, various types of metal‐containing unsaturated polyesters, cured resins, and cured rubbers are obtained. The effect of introducing metal on their physical and other properties results, and, in addition, generally Mg is more effective than Ca in improving the properties of the polymers.