bluuebunny/crossref_metadata_2025 huggingface dataset:
Confined parison inflation behavior of a high‐density polyethylene
Authors: Dutta A. , Ryan M. E.
Published: May 2005

An analysis of the confined parison inflation step associated with the extrusion blowmolding of a high‐density polyethylene is presented. Based upon simple geometrical considerations and material conservation principles, relationships describing the wall thickness variation have been obtained for various mold configurations. The experimentally measured part thickness distribution is found to be in good qualitative agreement and reasonable quantitative correspondence with the theoretical predictions. Furthermore, the expressions for the thickness variation have been utilized in order to estimate the confined inflation time for the case of a power‐law constitutive equation. In addition, a brief discussion of some practical mold design considerations is given based upon the theoretical analysis.
Analysis of void formation in extruded bars
Authors: Titomanlio G. , Piccarolo S. , Marrucci G.
Published: May 2005

In extruding thick polymeric objects such as bars, voids may form as a consequence of fast cooling. As is well known, this phenomenon is due to volume contraction of the inner zone which takes place when the external “shell” is already solidified. Recent experimental results on this effect show the influence of various parameters such as polymer melt viscosity, bar diameter, and operating pressure upon a critical extrusion velocity above which voids are detected. A detailed analysis of the phenomena which are thought to be relevant is presented and compared with the experimental results.
Crazing in polypropylene
Authors: Jang B. Z. , Uhlmann D. R. , Vander Sande J. B.
Published: May 2005

The subject of crazing in crystalline polymers is reviewed and specific consideration given to crazing in polypropylene (PP). Tensile tests conducted over a wide spectrum of temperatures and strain rates indicate that, for a given test temperature, there exists a critical strain rate above which crazing is the dominant deformation mode of PP. Similarly, for a given strain rate, there exists a critical temperature which demarcates crazing from shear yielding as the characteristic process of deformation. High deformation rates and low temperatures favor crazing, while low rates and high temperatures favor shear yielding. Crazes in crystalline PP were found to be morphologically similar to those in glassy polymers: high reflectivity, large area‐to‐thickness ratio, and planarity. They have a higher tendency to bifurcate than those in glassy polymers. Two types of craze fibrils could be identified: those parallel to σ11, and the randomly oriented interconnecting fibrils. It is demonstrated that microtome‐trimming at low temperature followed by suitable chemical treatment is an effective technique of sample preparation for SEM examination of craze morphology in crystalline polymers. Further evidence has been provided that crazes in spherulitic polymers do not in general follow an interspherulitie path, but propagate through spherulites. The length of a craze in PP is not restricted to one spherulite diameter, nor does it grow radially.
Craze initiation, crack growth, and lifetime trends in fatigue of poly(vinylchloride)
Authors: Mandell J. F. , Chevaillier J.‐P. F.
Published: May 2005

The fatigue behavior of pure poly (vinylchloride) (PVC) and a PVC pipe compound has been investigated. Unnotched S‐N lifetime, fatigue‐crack growth, and craze/crack‐initiation data are presented. The data trends, coupled with direct‐microscopic observation, suggest that the unnotched‐specimen lifetime in fatigue is dominated by the craze/crack‐initiation process. This differs from the observed consistency of crack propagation and specimen‐lifetime trends in several other polymers, whose failure can be traced to the initiation and growth to instability of a single dominant craze/crack.
The creep of kevlar‐29 fibers
Authors: Lafitte M. H. , Bunsell A. R.
Published: May 2005

Single Kevlar‐29 fibers have been subjected to creep loading over a temperature range of 23 to 400°C for which the applied load was 50 percent that of tensile strength at each temperature considered and also subjected to a range of loads at 23°C. It has been shown that strain expressed as a logarithmic function of time describes the experimental results obtained. Up to 70 percent of breaking load, a primary creep mechanism dominates and at higher loads a secondary creep process becomes increasingly important.
Capillary extrusion of elastomeric emulsion crosslinked interpenetrating networks
Authors: Silverstein M. S. , Narkis M.
Published: May 2005

The rheological properties of an elastomeric emulsion thermosetting (EMSET) interpenetrating network (IPN) of poly(ethyl acrylate) (70 percent) and polystyrene (30 percent) were studied using a capillary rheometer to test if the submicron thermoset particles, persumably the flow units, could flow as a thermoplastic matrix. The IPN exhibited power law behavior over a wide range of shear rates (0.05 to 500 s−1), with a power law exponent of approximately 0.18 over a large range of temperatures (80 to 200°C), without a yield stress or a Newtonian plateau evident. The flow activation energies were found to be comparable with most processable thermoplastic materials at 4 kcal/mole for constant shear rates, and 20 kcal/ mole for constant shear stresses. The effect of a roll mill shear modification step prior to extrusion indicated stability of the flow units. The pervasive rippling melt fracture and the significant slip velocity at the wall emphasized the importance of slip in the flow mechanism of this elastomeric EMSET IPN.
Errors that result from thermal degradation during shear measurements on some molten polymers
Authors: Gregory D. R. , Wampler F. C.
Published: May 2005

Shear sensitivities of molten polymers may be determined from measurements made on individual samples subjected in one test to a series of either increasing or decreasing shear rates. Many polymers, including polyesters, degrade when molten. If the effect of degradation is significant, and is ignored during data analysis, a significant error could result. The magnitude of the error depends directly on the magnitude of the reaction rate constant for degradation, which differs from polymer to polymer and which increases as temperature increases. In rheological characterization of molten polymers, one should know or determine the degradation behavior of the polymer being investigated and then account for it in the data analysis. Experimental results for poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are presented and discussed. Ways to account for degradation in shear sensitivity measurements are also presented.
Effect of the cross‐channel flow on the melting performance of a single‐screw extruder
Authors: Lindt J. T. , Elbirli B.
Published: May 2005

A new comprehensive mathematical model has been developed for the melting zone of a single‐screw extruder processing a (semi) crystalline polymer. It has been demonstrated that the cross‐channel flow plays an important role in the melting mechanism. When incorporated into a non‐Newtonian fluid model combined with the rigid solid bed concept, the present analysis leads to significantly improved predictions of the melting rate and axial pressure profile. This conclusion is supported by experimental data and by a quantitative examination of the flow and thermal patterns prevailing in the melting zone.

It is suggested that under the constraints of the commonly accepted assumptions concerning the physico‐chemical properties of the polymeric system the transport analysis of the Maddock mechanism is virtually complete.
Continuous reactive processing I: Reactive coating
Authors: Schmidt M. J. , Castro J. M.
Published: May 2005

The big success of the reaction injection molding (RIM) process has brought about a marked interest in reacting polymer processing. In the present work, we study the technical feasibility of a continuous process to coat metallic conductors using reacting polymers. In the envisioned system, RIM type reactants are mixed and then injected into a tubular reactor through the center of which we pass the cable to be coated. The predictions of the mathematical model developed show that a feasible process can be designed by adequate control of the heat transfer phenomena. The process needs in general, a low reactor temperature and a high cable temperature.
Crystallinity as a selection criterion for engineering properties of high density polyethylene
Authors: Hoffman D. Mark , McKinley Barbara M.
Published: May 2005

The Differential Scanning Calorimeter (DSC) was used to discriminate among 25 commercial high density polyethylenes (HDPE) on the basis of their degree of crystallinity and melting temperature. The area under the melting endotherm correlated directly with density and inversely with creep and thermal expansion measurements. Since high crystallinity was related to the design required properties of density, creep, and thermal expansion, DSC studies readily identified eight of the more promising polymers from the group of 25. The overall crystallization kinetics of polyethylenes with 75 percent crystallinity were analyzed by the Avrami and Fischer‐Turnbull equations. Results indicate small disk‐like spherulites (Avrami n = 2) following nucleation‐controlled growth kinetics. These conclusions are in reasonable agreement with polarizing microscope observations. An equilibrium melting temperature between 141 and 142°C was estimated from Hoffman‐Weeks plots. Processing thick parts from highly crystalline polyethylene is difficult because of the 14 percent volume change on crystallization. Higher degrees of crystallinity are associated with moderate molecular weight, so the viscosity range of these polyethylenes is not especially suited for processing by extrusion. These caveates necessitate tradeoffs between optimal design properties and processing requirements for HDPE parts.
Flexible microcellular foam from polymethylpentene/cyclohexane
Authors: Williams Joel M. , Moore Joyce E.
Published: May 2005

Rapid freezing of a polymethylpentene (PMP)/cyclohexane solution to −80°C gives a tough, flexible foam, in marked contrast to the weak, friable foams obtained by phase‐separation of PMP from other solvents. X‐ray diffraction and differential scanning calorimetry (DSC) data indicate that the isotactic PMP is in an amorphous state. The production of a flexible, robust foam tube from PMP/cyclohexane implies that this material could find applications as replacement parts for arteries and veins or as filter devices. In sheet form, this material seems ideally suited for use as light‐weight insulation for clothing because its open, microcellular structure permits moisture to escape as vapors, but retards air flow. This study demonstrates that process parameters, such as solvent composition, play an important role in determining the various microstructures and physical properties that can be obtained from a single polymer.
Enhancing adhesion by ion beam‐induced atomic mixing at the interface between copper film and polyimide substrate
Authors: Koh S. K. , Pae K. D. , Stoffel N. G. , Hart D. L.
Published: May 2005

Ion beam mixing was used to improve the adhesion between deposited Cu film (400 Å) and polyimide (PI) substrate. Ar+ ion with the energy levels between 180 and 200 keV, and the dose between 1014 to 4 × 1016 ions/cm2 were used. The surface analyses were carried out by Rutherford Backscattering Spectroscopy (SEM). RBS analysis, using 2 MeV He+ ions, showed mixing of Cu and FI and the mixing depended on the Ar+ energy and dose. The X‐ray study showed a very broad halo for deposited Cu film but the (111) peak appeared after the Ar+ implantation and the peak increased with Ar+ ion dose. Optical micrographs showed that Cu film formed circular bubbles after many thermal cycles when adhesion was poor and fracture cracks when adhesion was good.
Process parameters estimation for structural reaction injection molding and resin transfer molding
Authors: González‐Romero V. M. , Macosko C. W.
Published: May 2005

Some design strategies for structural reaction injection molding (S‐RIM) and resin transfer molding (RTM) are presented. Our approach makes use of moldability diagrams to define the parameters necessary to meet the process requirements. Moldability diagrams are presented for the filling and curing steps. The criterion for selecting the amount of fiber reinforcement, injection time, catalyst level, and process temperatures in order to optimize properties and demold time is described.
Mechanical and thermal properties of epoxy resins with reversible crosslinks
Authors: Engelberg P. I. , Tesoro G. C.
Published: May 2005

The tensile properties: Young's modulus, ultimate tensile strength, ultimate elongation, the glass transition temperature, and the dynamic mechanical properties (dynamic shear modulus (G'), loss tangent (Tan δ)), of three epoxy resins (Epon 828, Epon 836, Epon HPT 1071) cured with the disulfide‐containing crosslinking agent—4.4‐dithiodianilme (DTDA) have been characterized. The results show that DTDA is a satisfactory crosslinking agent for the epoxide resins that have been studied as compared to the well‐known curing agent methylene dianiline (MDA). There are no significant differences between the properties of Epon 828 cured with DTDA at stoichiometric ratio (2:1) and Epon 828 cured with DTDA at small amine excess ratio (1.75:1). The glass transition temperature of the cured tetrafunctional epoxy resin Epon HPT 1971 (235°C) is significantly higher than that of difunctional epoxy resins such as Epon 828 (Tg–175°C), but the product is too brittle to be used without plasticizer.
A comparison of torsional and capillary rheometry for polymer melts: The Cox‐Merz rule revisited
Authors: Venkatraman S. , Okano M.
Published: May 2005

Rheological properties of high and low density polyethylene melts (HOPE and LDPE) were measured under two different deformation modes: sinusoidal strain (“dynamic”) and constant rate‐of‐strain (“steady‐state”). For the sinusoidal measurements, a torsional geometry was used, whereas the “steady‐state” measurements were carried out in both torsional and capillary flow. The complex and “viscous” components of the “dynamic” viscosity were compared with the “steady‐state” viscosities, corrected for both non‐Newtonian and end effects. For the HDPEs, the Cox‐Merz rule was found to be not valid. The corrected viscosity is closer in magnitude to the “viscous” component, and not to the complex viscosity. However, for the LDPEs, the corrected viscosity is equivalent to the complex viscosity. These results are compared to other correlations found by various authors.
Binary blends of nylons with ethylene vinyl alcohol copolymers: Morphological, thermal, rheological, and mechanical behavior
Authors: Ahn Tae Oan , Kim Chang Kee , Kim Byung Kyu , Jeong Han Mo , Huh Jung Do
Published: May 2005

Binary blends of ethylene vinyl alcohol copolymers, containing 62 (EVOH‐62) and 71 (EVOH‐71) mole percent vinyl alcohols, with nylons (nylon‐6, nylon‐6/12, and nylon‐12) have been prepared from melt mixing in a twin screw compounding machine. Morphological, thermal, rheological, and mechanical properties were determined. EVOH‐62/nylon‐6 and EVOH‐71/nylon‐6 blends showed homogeneous phase morphologies in the nylon‐6‐rich region, and fine phase separations (c.a. 2 × 10−7 m) in the EVOH‐rich region. Melting point depression, positive deviations in viscosity and flexural modulus, and negative deviation in impact strength from the simple additive rule were generally observed. And the results were possibly interpreted in terms of compatibility and increased nylon/EVOH interactions over the nylon/nylon interactions. On the contrary, clean phase separations in large domains were observed from EVOH‐71/nylon‐6/12 and EVOH‐71 /nylon‐12 blends. Fibrillation was also obtained from EVOH rich blends. Probably due to the incompatible nature of these blends, yield at low rate of shear and a mechanical property drop were also observed.
Crystallization kinetics and nucleating agents for enhancing the crystallization of poly(p‐phenylene sulfide)
Authors: Song Sang S. , White James L. , Cakmak Mukerrem
Published: May 2005

An experimental study of crystallization kinetics and the influence of nucleating agents on the solidification of poly(p‐phenylene sulfide) (PPS) is described. The effect of molecular weight is considered by investigating PPS samples having different viscosity levels. We studied the effect of a range of nucleating agents including aluminum oxide, calcium oxide, silicon dioxide, titanium dioxide, kaolin, and talc. All of these compounds were found to enhance the rate of crystallization; in particular, silicon dioxide, kaolin, and talc were the most effective nucleating agents. An effort to study particle size effects of the silicon dioxide showed that the nucleation was very sensitive to the source of the material. These studies did, however, show that nucleation rates tended to increase with decreasing particle size and increasing loading of silicon dioxide. Comparison of PPS crystallization rates with those of other polymers indicates that it crystallizes much more slowly than polyethylene or isotactic polypropylene and is slower than polyetherether‐ketone, when comparisons are made on an equivalent basis. PPS crystallizes at similar rates to polyethylene terephthalate (PET). However, our nucleated PPS does not crystallize as rapidly as nucleated PET.
The role of repulsive interactions in polyamide blends
Authors: Ellis T. S.
Published: May 2005

Phase phenomena in mixtures containing any combination of aliphatic and aromatic polyamides can be formulated by the application of a mean‐field binary interaction model. This has been achieved by the quantitative analysis of the solubility of an aromatic polyamide, denoted as nylon 3Me6T, in a homologous series of aliphatic polyamides. A critical feature of this development required an estimation of the upper and lower bound concentration of methylene units of the latter for which the aromatic polyamide moved from a miscible to immiscible condition. The fabrication of random copolyamides of caprolactam‐laurolactam and 2‐pyrrolidinone‐caprolactam, respectively, has allowed an accurate determination of these critical limits. A survey of the behavior of polyamide blends will be discussed in light of this improved quantitative definition of the model. A principal feature of these analyses is the exclusion of a role for hydrogen bonding interactions. Details concerning the nature of interactions in these systems and how they are influenced by chemical structure are discussed.
Poly(Phenylene oxide)/polyamide blends via reactive extrusion
Authors: Campbell J. R. , Hobbs S. Y. , Shea T. J. , Watkins V. H.
Published: May 2005

Reactive extrusion of functionalized polymers provides a convenient, commercially attractive route for the preparation of copolymers useful in compatibilization of polymer blends. In the current study, the grafting chemistry of maleic anhydride to poly(phenylene oxide) in the absence of a radical initiator is contrasted to that of efficient quinone‐methide trapping agents such as maleimides. In the case of maleic anhydride, functionalization is shown to occur randomly along the polymer backbone whereas maleimides react to give both main chain and end‐group derivatives. Use of this anhydride‐functionalized polyfphenylene oxide and an end‐group functionalized analog in blends with polyamide‐6,6 affords high levels of graft and diblock copolymers respectively, sufficient for the preparation of highly ductile materials. The properties of these polyamide blends are found to depend on the amount of copolymer formed during extrusion with final copolymer levels being in turn returned to the degree of anhydride functionalization. The properties and morphology of blends containing graft or diblock copolymers derived from main‐chain and end‐group functionality respectively, are rationalized in terms of the relative effectiveness of different copolymer structures in blend compatibilization.
Enhanced spherulite growth rates of isotactic polypropylene in incompatible blends
Authors: St‐Jean G. , Barreto M. C. , Brown G. R.
Published: May 2005

Isothermal radial growth rates (G) of isotactic polypropylene (iPP) spherulites in immiscible blends with a polyethylene based ionomer (1) partially neutralized with Zn+2, (2) completely acidified, and (3) completely esterified have been determined at crystallization temperatures between 118 and 124°C by time‐lapse photomicroscopy. In these blends iPP spherulites grow with increased G as compared to that of pure iPP. This behavior is attributed to increases in the rate of transport, due to limited miscibility induced by mechanical mixing. However, subtle differences in the melting behavior suggest that changes in Spherulite morphology may also be a contributing factor.
Experimental analysis of inertial effects in the impact testing of polymers
Authors: Zanichelli C. , Rink M. , Pavan A. , Ricco T.
Published: May 2005

Inertial effects occurring In the impact testing of polymers were experimentally probed by measuring the force versus time response of various materials with two different instrumented impact testers, both with and without anvil. The analysis focused on the first force peak, which was modeled using a mass‐spring analog to account for machine‐specimen interaction.
Phenolic triazine (PT) resins. II: Cure characterization by dynamic melt rheology and its comparison to DSC
Authors: Khanna Y. P. , Kumar R. , Das S.
Published: May 2005

A new approach involving dynamic melt rheology i.e. dynamic mechanical analysis in a molten inert matrix, is presented for studying the cure of thermoset resins. The degree of cure by dynamic melt rheology has been correlated with that from differential scanning calorimetry, DSC (correlation coefficient = 0.87) and the lack of an excellent correlation is attributed to the uncertainties with the DSC method at higher cure levels. A kinetic expression with appropriate constants, “E, A, and n” from our new approach is presented for predicting the time‐temperature dependence of the degree of cure. Advantages of dynamic melt rheology are discussed in relationship to conventional dynamic mechanical and DSC methods.
A double bubble tubular film process to produce biaxially oriented poly(p‐phenylene sulfide) (PPS) film
Authors: Rang Ho Jong , White James L.
Published: May 2005

A double bubble tubular film process to produce biaxially oriented poly(p‐phenylene sulfide) (PPS) film is described. Operating windows were developed for stable operation of both the first and second bubbles. Films produced from single bubble tubular film extrusion were largely amorphous having only seven to nine percent crystallinity. Double bubble PPS tubular film had up to 20 percent crystallinity which was increased to 30 percent by further annealing. The first and second bubble films had surface roughness standard deviation heights of 0.01 to 0.04 μm. Orientation was characterized by birefringence and wide angle X‐ray diffraction pole figures of the 110 and 112 reflections. Biaxial orientation factors were computed. The double bubble films had higher Young's modulus and tensile strength but lower elongation to break than the single bubble films. Annealing further increases Young's modulus and tensile strength but decreases elongation to break. Double bubble and annealed films with roughly equal second bubble drawdown ratio and second blow up ratio tend to have balanced properties in the plane of the film.
The elastic properties of woven polymeric fabric
Authors: Warren William E.
Published: May 2005

The in‐plane linear elastic constants of woven fabric are determined in terms of the specific fabric microstructure. The fabric Is assumed to be a spatially periodic interlaced network of orthogonal yarns and the Individual yarns are modeled as extensible elastica. These results indicate that a significant coupling of bending and stretching effects occurs during deformation. Results of this theoretical analysis compare favorably with measured in‐plane elastic constants for Vincel yarn fabrics.
Image reversal in a negative deep UV resist
Authors: Hargreaves John S.
Published: May 2005

A negative deep UV resist, XP 8843 (Shipley Co.),

Since this paper was written the name of this resist has been changed from XP 8843 to SNR 248‐10.

has been made positive by the addition of 1,2,4‐triazole. This is achieved by exposing the resist in the presence of the additive thereby inhibiting the crosslinking reaction. After exposure the additive is removed by heating under a vacuum. Unexposed areas of the resist may then be exposed and the resist crosslinked under normal processing conditions.
Methanol‐Induced crack healing in poly(methyl methacrylate)
Authors: Lin C. B. , Lee Sanboh , Liu K. S.
Published: May 2005

Crack healing in poly(methyl methacrylate) (PMMA) by methanol treatment at 40°C–60°C has been investigated. It is found that the methanol treatment reduces the glass transition temperature in PMMA. Crack healing only occurs at an operating temperature higher than the effective glass transition temperature. There are two distinctive stages for crack healing based on the recovery of mechanical strength. The first stage corresponds to the progressive healing due to wetting, which has a constant crack closure rate at a given temperature. Immediately following the first stage, the second stage corresponding to diffusion enhances the quality of healing behavior. The surface morphologies obtained during healing and after fracture tests confirm these two stages. By comparing the fracture stress with the fractography, the fracture surface for stage I of crack healing is coplanar to the original crack surface. On the other hand, the original crack surface is destroyed in stage II of crack healing. It occurs in the region incorporating the original healed surface and appears to be like the Virgin fracture surface. It is also found that the tensile fracture stress of PMMA treated by methanol can recover to that of the virgin material. In addition, it is interesting to find that after sustained methanol treatment, the “snake bone” phenomenon on the fracture surface emerges.
Strength development at incompatible semicrystalline polymer interfaces
Authors: Yuan B.‐L. , Wool Richard P.
Published: May 2005

The structure of an interface that develops from laminating polypropylene/polyethylene (PP/PE) by hot compression‐molding was analyzed by optical and electron microscopy. The interface strength was measured by means of a butt‐joint specimen. For the laminate formed by isothermal crystallization above the PE melting temperature, it was found that the interface strength increased with time due to the formation of PE influxes between the PP spherulites. The inter‐spherulitic influxes broke up the sharp PP/PE interface plane and provided considerable strength by mechanical interlocking. Intra‐spherulitic entanglements were also noted for PP spherulites nucleated near the interface. Fast crystallization prevents the formal/on of influxes and results in a weak interface. For the hon‐iscthennal crystallization case during cooling at 10°C/min, the interface morphology of PP/HDPE was found to be different from that of PP/LLDPE. The difference in crystallization temperatures and growth rates between PP and HDPE during rapid cooling permitted the HDPE to crystallize first which prevented the formation of influxes. With PP/LLDPE, the PP crystallized first allowing some influxes to develop. Normally the interface between PE and PP is very weak. However, to obtain good mechanical properties for a given PP/PE couple, one can control the processing thermal history to optimize the development of influxes and mechanical strength at the interface.
Phase morphology coarsening and quantitative morphological characterization of a 60/40 blend of polycarbonate of bisphenol a (pc) and poly(styrene‐bco‐acrylonitrile) (san)
Authors: Quintens D. , Groeninckx G. , Guest M. , Aerts L.
Published: May 2005

A 60/40 polymer blend of polycarbonate of bisphenol A (PC) with a styrene‐co‐acrylonitrile (SAN) copolymer was prepared by melt compounding. Injection molded sheets of this, blend were annealed at 200°C as a function of time. The phase morphology of these sheets, studied using transmission and scanning electron microscopy, was found to coarsen as a function of the annealing time. Using the Chalkey procedure, the microstructure of the annealed blends was quantified. Initial tensile stress‐strain data highlight the influence of microstructure on ductility for these co‐continuous blends.
Morphology of unsaturated polyester resin‐additive blends
Authors: Suspene Laurent , Gerard Jean‐François , Pascault Jean‐Pierre
Published: May 2005

The morphologies and impact behavior of blends based on an unsaturated polyester matrix and different added rubbers were studied by scanning electron microscopy (SEM). These rubbers were prepared from a carboxy‐terminated acrylonitrile‐butadiene copolymer (CTBN). The introduction of an epoxy‐terminated triblock copolymer (ETON) by exchanging 10% by weight of the CTBN rubber compatibilizes the initial blend by reducing the interfacial tension between the components. Consequently, the morphology of dispersed phase was modified: decreasing of the particle size and reducing the number of large particles. For a blend with 5 phr of rubber, Charpy impact behavior was enhanced and the number of catastrophic failures was reduced. This study displays the existence of relationships between the interfacial tension between components and the morphology of the resulting materials.
Adaptation of photoacoustic fourier transform infrared spectroscopy for studying the thermal oxidation of nylon 66 at 150°c correlated to mechanical properties
Authors: Murty E. M. , Yehl T. W.
Published: May 2005

Oven aged tensile bars of heat stabilized, glass reinforced nylon 66 material were studied by Fourier transform infrared (FTIR) spectroscopy using a photoacoustic detector. Flat weighed scrapings were removed from tensile bars whose tensile strength, elongation, impact, molecular weight, and thermal properties had previously been measured. Using the amide I band of nylon 66 as an internal standard, the thermal oxidation of nylon was followed using a commercially available photoacoustic detector. The infrared absorbance spectra demonstrate the formation of carbonyl stretching vibrations due to the thermal oxidation of nylon with a band center at 1713 cm−1 whose width at half height is 40 cm−1. The difference infrared spectra support reaction mechanisms dealing with an Initial increase in the degree of polymerization followed by transamidation reactions with subsequent formation of an α, β unsaturated carbonyl species and chain scissioning. By using data related to the percent retention of certain physical properties which had also been measured on these tensile bars, subtractive infrared spectroscopy yielded additional fundamental information regarding nylon 66 degradation. Consequently, nylon products being used in underhood automotive applications are currently being investigated for thermal oxidative degradation using this rapid and relatively non‐destructive photoacoustic FTIR technique for durability considerations.
In‐situ monitoring of the resin transfer molding impregnation and cure process
Authors: Kranbuehl D. , Eichinger D. , Hamilton T. , Clark R.
Published: May 2005

Resin transfer molding (RTM) of advanced fiber architecture materials promises to be a cost effective process for obtaining composite parts with exceptional strength. However there are a larger number of material processing parameters that must be observed, known, and/or controlled during the resin transfer molding process. These include the viscosity both during impregnation and cure. In‐situ sensors which can observe these processing properties within the RTM tool during the fabrication process are essential. This paper will discuss recent work on the use of frequency dependent electromagnetic sensing (FDMS) techniques to monitor these properties in the RTM tool. Our objective is to use these sensing techniques to address problems of RTM scaleup for large complex parts and to develop a closed loop, intelligent, sensor controlled RTM fabrication process.
Dynamic mechanical response of a thermoplastic sheet molding compound‐glass fiber composite
Authors: Otaigbe J. U.
Published: May 2005

The dynamic mechanical properties of nylon 6/continuous glass fiber composites at four levels of fiber volume content were studied between ‐180 and 130°C using a free resonance torsion pendulum. The composites were produced by anionically polymerizing caprolactam monomer within a swirl type glass fiber mat using a vacuum injection technique. In addition to the expected strong dependence of shear storage modulus on fiber volume content, the glass transition temperature of the nylon 6 was observed to increase slightly and the mechanical damping decrease with fiber volume fraction. Introduction of about 7 weight percent water (i.e., equilibrium hygroscopic state) into the composite led to a considerable broadening of the transition peaks and a much lower plasticizing action of water in the composite relative to the pure nylon 6 matrix.
A unified simulation of the filling and postfilling stages in injection molding. Part II: Experimental verification
Authors: Chiang H. H. , Hieber C. A. , Wang K. K.
Published: May 2005

The unified numerical simulation of the filling/postfilling stages of the injection‐molding process described in Part I is compared in the present paper with experimental results obtained with instrumented test molds. Flush‐mounted pressure traces in the delivery system as well as in the cavity are favorably compared with corresponding predictions for both an amorphous and a semicrystalline polymer. It is demonstrated that the present unified formulation is well suited to handle complicated molds where compressibility effects can become important even during the filling stage, as portions of the cavity fill and undergo a packing behavior even when other regions of the cavity are still only partially filled.
Microwave joining and repair of composite materials
Authors: Varadan Vijay K. , Varadan Vasundara V.
Published: May 2005

A novel technique that uses microwave power for joining and repair of thermoplastic and thermoset composites and ceramics is discussed. Enhanced microwave heating resulting from the use of conducting polymers and chiral microinclusions shows considerable promise for joining and repair of composites. The method is attractive because it produces clean and reliable interfacial joints, it is fast, it does not entail alteration of the bulk materials, and it does not result in volumetric heating. System details, including magnetron, waveguides, circulators, coupling iris, and the applicator for delivering microwave power, are described. Material requirements for the efficient absorption of microwave power are discussed. Microwave heating can be increased by doping the components to be joined or by the use of microwave adhesive films. Recent developments in electromagnetic chirality for microwave absorption are introduced and the design of composite materials for enhanced absorptivity is discussed. Results are presented for the welding and repair of thermoplastic, thermoset, and ceramic components.
Effect of physical aging on the fracture behavior of crosslinked epoxies
Authors: Truong V.‐T. , Ennis B. C.
Published: May 2005

The effect of physical aging on the fracture behavior, crack opening displacement, and plastic deformation zone of unmodified and rubber‐modified epoxies was determined at two aging temperatures and different displacement rates. The strain energy release rate decreases to between 40 and 50% (for rubber modified and unmodified samples, respectively) of the unaged values after 35 days aging. Systematic dependence of the decrease in fracture toughness by aging on the rubber content is not apparent. The increased yield stress after physical aging is the main factor contributing to the reduction in fracture toughness, crack opening displacement, and plastic deformation zone. Physical aging suppresses the crack blunting mechanisms in epoxies.
The application of size‐exclusion chromatography to study molecular‐weight changes of flame‐retardant fiber‐reinforced polyesters
Authors: Miller R. L. , Seymour R. W. , Branscome L. W.
Published: May 2005

Reinforced plastics based on poly(cyclohexanedimethylene terephthalate) (PCT) are excellent for electrical and electronic applications, particularly in the manufacture of electrical connectors. PCT offers a high heat deflection temperature, low cost, and relative ease of processing. For the injection molding process, stability of the melt is an important consideration, especially for materials with high melting points such as PCT. The combination of the polyester resin with flame retardant additives, processing aids, and thermal stabilizers results in a number of competing reactions which can change the molecular weight and molecular‐weight distribution (MWD) of the base polymer in the composite. Typical analytical techniques such as melt or dilute solution viscosity do not give adequate means of monitoring these changes so as to allow the polymer chemist to determine the effects of various additives on MWD. Size‐exclusion chromatography (SEC), by virtue of providing information on the entire MWD, was found suitable to study molecular‐weight changes in the melt due to both branching and chain cleavage, even when both phenomena occur simultaneously. Changes in the MWD over time at processing temperatures can be used to determine kinetic parameters and have been used to optimize PCT additive formulations for best processability and mechanical property retention.
Optimization of a tubular nylon 6 reactor with radial gradients
Authors: Srivastava D. , Gupta Santosh K.
Published: May 2005

Optimal jacket‐fluid temperature profiles for tubular Nylon 6 reactors (in the presence of radial gradients of temperature and concentration) have been obtained using an algorithm based on the continuous minimum principle developed for a distributed parameter system. A gradient search technique has been devised and implemented for obtaining these optimal profiles. The optimal temperature profiles are found to be at the maximum permissible temperature, Tmax, at the beginning of the reactor and then slowly decrease to the minimum permissible temperature, Tmin, near the end of the reactor. The effect of varying several parameters is also studied. The desired value of the chain length and the reaction time are found to be the parameters which effect the optimal profiles most significantly.
Crystallization kinetics of poly(phenylene sulfide) (PPS) and PPS/carbon fiber composites
Authors: Kenny J. M. , Maffezzoli A.
Published: May 2005

The evolution of crystallinity of neat PPS and of the carbon fiber reinforced polymer under different processing conditions is studied. Crystallization from the amorphous state at low temperatures (cold crystallization), crystallization from the melt during cooling, and crystal melting processes are analyzed using calorimetric techniques under both isothermal and nonisothermal conditions. Cold and melt crystallization kinetics are described using an Avrami equation and an Arrhenius expression for the temperature dependence of the kinetic constant. Also, the melting kinetics of the, reinforced and of the unreinforced polymer are studied in this work. The effect of carbon fibers on the crystallization kinetics of PPS is analyzed, and a comparison of the crystallization behavior of PPS and other semicrystalline thermoplastic matrices, such as poly(etheretherketone) (PEEK), is presented.
Viscoelastic response of model epoxy networks in the glass transition region
Authors: Gerard J. F. , Galy J. , Pascault J. P. , Cukierman S. , Halary J. L.
Published: May 2005

Six epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition Tg on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients Cg1 and C which are related to some free volume characteristics on the molecular scale. Cg1, related to the free volume fraction available at Tg depends mainly on crosslink density, even though the product Cg1C, related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.
RIM‐pultrusion of nylon‐6 and rubber‐toughened nylon‐6 composites
Authors: Ning Xin , Ishida Hatsuo
Published: May 2005

Unidirectionally reinforced thermoplastic composites of Nylon‐6 and polypropylene oxide‐Nylon‐6 block copolymers have been prepared by the reaction injection molding (RIM)‐pultrusion process. This process takes advantage of both the RIM and the pultrusion techniques, while avoiding their inherent shortcomings. It also represents a novel way of incorporating toughening rubber domains into a thermoplastic composite. The composites produced exhibit excellent mechanical integrity with essentially zero void content. The chemical and physical states of the composites produced by the process were probed in terms of mechanical relaxation behavior using a dynamic mechanical spectrometer. Due to the simultaneous occurrence of both polymerization and crystallization processes in the reacting system, the resulting material is in a thermodynamically nonequilibrium state. An annealing effect is shown to correspond structurally to an increase in matrix crystallinity and the degree of phase separation, Izod impact tests were used to compare Nylon‐6 and rubber‐toughened Nylon‐6 RIM‐pultruded composites. The potential of secondary processing was, demonstrated by compression molding of the RIM‐pultruded composite rods.
A study on the mold filling process in resin transfer molding
Authors: Um Moon‐Kwang , Lee Woo Il
Published: May 2005

A numerical simulation of the mold filling process during resin transfer molding (RTM) was performed using the boundary element method (BEM). Experimental verification was also done. Darcy's law for anisotropic porous media was employed along with mass conservation to construct the governing differential equation. The resulting potential problem was solved with the boundary element technique. As the calculation domain changed due to the proceeding resin front, boundary nodes were rearranged for each time step. The node which goes out of the calculation domain as time progresses was relocated at the intersection between the solid boundary and the line drawn between the node at previous and at current time steps. Results showed good agreement with data for a rectangular mold. To evaluate further the validity of the model, the area velocity of the resin‐impregnated region during mold filling was calculated. The area velocity thus calculated was compared with the corresponding resin inlet velocity to check the mass conservation. A close agreement was observed, which renders confidence in the resin front proceeding algorithm. Numerical calculations were also performed for complicated geometries to illustrate the effectiveness of the current method.
Experiments and modeling of flow of elastomers in an internal mixer with intermeshing rotors
Authors: Min K. , Suh K. G.
Published: May 2005

The direct observation of flow in the internal mixer with various rotor geometries is described. With decreasing distance between two rotors, additional transfer flow was observed in the inter‐rotor area. The FAN (Flow Analysis Network) method with assumption of fully filled, Newtonian fluid and isothermal condition was employed to simulate the flow patterns in the mixer with non‐intermeshing and intermeshing rotors. The distributive mixing capability was considered in terms of the fractional flow in the mixer calculated for various rotor geometries.
A study on the performance of the maddock mixing head in plasticating single‐screw extrusion
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C.
Published: May 2005

An experimental and theoretical study was conducted on the performance of the Maddock mixing head in plasticating single‐screw extrusion. For the experimental study, a low‐density polyethylene was extruded in an extruder that had nine pressure transducers mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel. Two screws with the Maddock mixing head were used, namely: one screw to measure the pressure difference between the entrance and the exit of the mixing head in the down‐channel direction, and the other screw to measure pressure variations in the cross‐channel direction in the middle of the mixing head. Our experimental results showed both pressure decrease and pressure increase in the down‐channel direction of the mixing head, depending upon the extrusion conditions employed. Using the flow analysis network (FAN) method, we predicted pressure variations in both the downchannel and cross‐channel directions of the Maddock mixing head, which agree with experimental results.
Effects of catalyst fragmentation during propylene polymerization. IV: Comparison between gas phase and bulk polymerization processes
Authors: Ferrero Monica A. , Chiovetta Mario G.
Published: May 2005

A comparative study of the effects of catalyst fragmentation in the gas phase and bulk polymerization processes in performed. Typical operating conditions for each process are used for the comparison. The monomer concentration in the bulk process is nearly one order of magnitude larger than that in the gas phase process. The energy transfer conditions between the particle and the fluid phase are better in the liquid phase. The rate of mass transfer within the macroparticle at the initial steps of the polymerization is found to be slower in the bulk process than in the gas phase process. In the liquid phase process, fragmentation takes place more slowly. Temperature excursion values are smaller even though the dimensionless monomer concentrations are, in fact, greater because of the higher monomer concentration available in the liquid phase. The final steady rate of reaction and the ultimate catalyst yield reflect this phenomenon. Although the microparticle nucleus size affects both processes, the diffusion control that occurs when the fragments are large affects the gas phase process more intensely. In the bulk process, even at the lowest value reached by the rate of reaction, this is still sufficiently high so as to produce high yields.
Photoinduced reversible refractive index changes in doped poly(methyl methacrylate) lightguides
Authors: Lückemeyer Th. , Franke H.
Published: May 2005

Planar polymer lightguides of poly(methyl methacrylate)(PMMA) doped with the azo dye, N,N‐dihexyl‐4‐amino‐4′‐nitro‐azobenzene (DHANA) were fabricated on a suitable glass substrate or on one surface of a regular prism. The absorption of this azo dye is strong in the green spectral region. With the red light of a HeNe laser (633 nm) these polymer films may be used as lightguides. However, in this spectral region, the guided light influences the waveguiding properties of the polymer film, making this combination a possible candidate for an all optical device material. The observed refractive index changes are intensity dependent and the response time is of the order of 100ms.