bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the effect of electrode type and substrate temperature on plasma polymerization of two model compounds: Acrylonitrile and hexamethyldisiloxane
Authors: Akovali G. , Dilsiz N.
Published: December 2004

Polymers were prepared from saturated (HMDS) and unsaturated (AN) monomers in a radio frequency discharge (plasma). The effect of selected parameters such as electrode type (such as Cu, Zn, Ni, Al), reactor type, and substrate temperature (other parameters constant) on chemical structure and the rate of polymer deposition was examined by Fourier transform infrared (FTIR) spectroscopy. Differences in the nature of electrodes and reactor types were found to yield similar plasma products with similar rates of deposition for two monomers. In the tubular reactor used, deposition rates were observed to decrease with increasing substrate temperatures showing different dependencies on temperature for the monomers tested.
Viscoelastic material characterization and modeling for polyethylene
Authors: Popelar C. F. , Popelar C. H. , Kenner V. H.
Published: December 2004

An extensive set of stress relaxation and constant strain rate tests for characterizing the mechanical responses of a medium density polyethylene and a high density polyethylene that are commonly used in natural gas distribution piping is described and analyzed. The development of coherent master curves for the relaxation modulus, maximum stress, and the time‐to‐failure for pressurized pipes through a combination of both horizontal and vertical shifting is presented. The relaxation data are used to develop a nonlinear Viscoelastic material model. The model is assessed by making comparisons of the predicted stress‐strain response with the measured response in the constant strain rate tests.
Thermomechanical properties of 1C molding compounds
Authors: Bair H. E. , Boyle D. J. , Ryan J. T. , Taylor C. R. , Tighe S. C. , Crouthamel D. L.
Published: December 2004

Eight commercial semiconductor grade epoxy compounds that are used to encapsulate 1C (integrated circuit) devices have been evaluated for their ability to minimize the development of thermal stresses which can cause failure during device temperature cycling. Thermal expansion, dynamic modulus and adhesion studies are used to describe the mechanical interaction between the plastic package and the silicon device it surrounds. A “figure of merit” is defined for the development of stress on the 1C device as it is cooled after the packaging process. The stress is shown to be proportional to the product of three terms: (αp‐αs)Ep(Tanch‐T) where αpand αsare the expansion coefficients for the plastic and silicon, respectively,Epis the modulus of the epoxy andTanchis the temperature at which the epoxy becomes anchored to the silicon device during transfer molding. In addition, the importance of good adhesion between the epoxy encapsulant and the silicon device to prevent package cracking has been demonstrated by finite element analysis and a novel adhesion test.
Twin screw extrusion devolatilization: From foam to bubble free mass transfer
Authors: Foster R. W. , Lindt J. T.
Published: December 2004

The present research program, based upon the experimental performance of a 20 mm counter‐rotating, non‐intermeshing twin screw devolatilizer with several polymer/solvent systems has developed theoretical approaches to modeling both the bubble growth dominated mass transfer regime as well as the essentially bubble free regime (1, 2). This work encompasses the area of transition from the bubbling to the non‐bubbling areas. This transition to some degree, probably exists in nearly all real devolatilization processes. The work combines a foam simulation model, which integrates elementary bubble processes, with the mass transfer from single phase liquid films through a penetration theory based model. The modeling is successful at correlating the experimental data and shows realistic effects with regard to residence time, surface area, and average mass transfer coefficient as functions of vent loading.
Influence of solvent and molecular weight on thickness and surface topography of spin‐coated polymer films
Authors: Spangler Lora L. , Torkelson John M. , Royal J. Scot
Published: December 2004

The influence of polymer molecular weight, molecular weight distribution, and polymer‐solvent interactions on the thickness and topography of spin‐coated polymer films was examined. For films prepared from dilute solutions, highly volatile solvents or fair or “poor” solvents for the polymer adversely affect film surfaces causing nonuniformities (waves) to appear. However, if the concentration of these solutions is increased to approximately the concentration at which entanglements are formed, nearly uniform films are produced even if the solvent employed is highly volatile, such as dichloromethane. When toluene is employed as the solvent, which has a relatively low volatility and therefore forms nearly flat film surfaces, films prepared from dilute solution were found to have thicknesses, h, proportional to η Ω−0.49 for polystyrene and η Ω−0.49 for poly(methylmethacrylate) where ηo is the zero‐shear rate solution viscosity and Ω is the rotational speed at which the films were prepared. These results suggest that the exponents associated with ηo and Ω may be nearly independent of the type of polymer used as long as flat films are produced. Finally, the molecular weight parameter most important in controlling final film thickness for films made from dilute solutions is Mv, the viscosity‐average molecular weight.
Composites from compounding wood fibers with recycled high density polyethylene
Authors: Yam Kit L. , Gogoi Binoy K. , Lai Christopher C. , Selke Susan E.
Published: December 2004

The development of composites consisting of wood fibers and recycled plastics offers not only an opportunity to utilize an abundant natural resource but also a means to alleviate the serious plastics disposal problem. In this work, aspen fibers are incorporated into recycled high density polyethylene with a co‐rotating inter‐meshing twin‐screw extruder to study processing‐property relationships. Tensile, impact, and flexural strengths are measured as functions of fiber concentration. The effects of fiber pretreatment, screw configuration, and compounding temperature on the properties of composites are discussed.
Miscibility studies in blends of polybenzimidazoles and poly(4‐vinyl pyridine)
Authors: Makhija S. , Pearce E. M. , Kwei T. K. , Liu F.
Published: December 2004

Poly[2,2'‐(m‐phenylene)‐5,5'‐bibenzimidazole] (PBI) is shown to be miscible with poly(4‐vinyl pyridine) over the entire composition range. Experiments were performed with commercial PBI as well as a lower molecular weight material synthesized by us. Blend miscibility is evidenced by single glass transition temperature intermediate between the pure polymers. Hydrogen bonding between the components was detected by infrared spectroscopy.
The V‐notch at weld lines in polystyrene injection moldings
Authors: Tomari K. , Tonogai S. , Harada T. , Hamada H. , Lee K. , Morii T. , Maekawa Z.
Published: December 2004

A major factor that weakens the weld line in injection moldings is the V‐notch structure. Though the existence of a V‐notch is well known, its depth variation with molding conditions has not been detailed. The aim of this paper is to clarify the V‐notch structure and its effect on the strength of general purpose polystyrene injection moldings. A dog bone type tensile specimen with a weld line was molded under several molding conditions. The surface of the weld line was partially eliminated by cutting with a milling machine to seven levels of cut depth (Dc). As a result, the weld strength increased with Dc to about 50%. The relationship between the weld strength and Dc made it possible to determine the V‐notch depth, which vas defined as the “depth of the weld line.” From these results, a hypothesis is proposed that the V‐notch has a structure with a fine groove on the surface and a poorly bonded inner layer. This study considered the relationships among the weld strength, the depth of the weld line, and molding conditions.
Numerical and experimental studies of bubble growth during the microcellular foaming process
Authors: Ramesh N. S. , Rasmussen Don H. , Campbell Gregory A.
Published: December 2004

A new experimental technique for studying the dynamics of bubble growth in thermoplastics using scanning electron microscopy is developed. The influence of temperature, saturation pressure, molecular weight, and the nature of physical blowing agent are investigated. The experimental results show that, the above, process variables control the growth of foams during processing. The existing Newtonian model for the growth of a single bubble in an infinite amount of polymer has been modified to account for the non‐Newtonian effects by modeling the polymer as a power law fluid. The experimental data has been compared with the appropriate viscoelastic cell model which considers the growth of closely spaced spherical bubbles during the foaming process. The simulation results indicate that the predictions of the cell model are in qualitative agreement with the trends of the experimental data and the quantitative agreement is reasonable. The cell model also gives an equilibrium radius which agrees with the experimental data. Other viscous models do not predict the equilibrium radius of the bubble and underpredict the experimental data.
A non‐isothermal healing model for strength and toughness of fusion bonded joints of amorphous thermoplastics
Authors: Bastien L. J. , Gillespie J. W.
Published: December 2004

A study to investigate the influence of processing on the fusion bonding of graphite (AS4) poly(etheretherketone) (PEEK) thermoplastic composites (BASF commingled PEEK/graphite NCS woven fabric) using a polyetherimide (PEI) film at the interface is presented. Fundamental to all fusion bonding processes is the intermolecular diffusion between surfaces in intimate contact. A model based on the healing theory of amorphous polymers has been proposed to predict strength and toughness as a function of non‐isothermal process history. This model considers two different microscopic failure mechanisms of a healed interface. For the first time, using non‐isothermal data and proper data reduction procedures, it is possible to differentiate between these two mechanisms, which are otherwise indistinguishable from isothermal data. Temperature dependent reptation times representative of the kinetics of chain diffusion in the polymer have been evaluated for both mechanisms over a large range of process temperatures using fracture tests conducted on lap shear specimens manufactured using a hot press. Three alternate and independent techniques to estimate the reptation time in PEI indicate that the model based on the average interpenetration distance is most representative of the physical system. Lap shear strength predictions based on this formulation have been generated for various non‐isothermal conditions measured in the hot press and are within 20% of the experimental data. The model was used to show that in isothermal processes, maximum strength and toughness can be achieved in less than 1 s for temperatures exceeding 290°C. Application of the model to a highly non‐isothermal technique such as resistance welding using amorphous film technology is also presented. Model predictions show that asymptotic strength may be achieved in relatively short process times with appropriate welding conditions.
Effect of morphology, crosslink density, and miscibility on interpenetrating polymer network damping effectiveness
Authors: Fay J. J. , Murphy C. J. , Thomas D. A. , Sperling L. H.
Published: December 2004

The areas under the linear loss modulus versus temperature curves (loss area, LA) and tan δ versus temperature curves (TA) were evaluated for a number of acrylic, methacrylic, styrenic and butadiene based copolymers and interpenetrating polymer networks, IPNs, as a function of crosslink density and comliosition, and were compared with values predicted by group contribution analysis. The LAs of the sequential IPNs, cross‐poly(n‐butyl methacrylate)‐inter‐crosspolystyrene, were found to exhibit up to 30% larger LAs than the poly(n‐butyl metacrylate‐stat‐styrene) copolymers, which had LAs slightly less than the values predicted from the group contribution analysis. At constant chemical composition (50% n‐butyl methacrylate, 50% styrene), LA equals 14.4 GPa K for the IPN, attributed to a synergistic effect resulting from the IPN's microheterogeneous morphology, as compared with 10.7 GPa K for the single phase, miscible copolymer. Increases in the LA with increased concentration of polymer, network II were also observed for cross‐poly(ethyl acrylate)‐inter‐crosspolystyrene and cross‐polybutadiene‐inter‐cross‐polystyrene IPNs. On the other hand, cross‐polybutadiene‐inter‐cross‐poly(methyl methacrylate) IPNs had LAs much lower than were predicted by the group contribution analysis, which were attributed to lower miscibility in this system relative to the other systems evaluated. In general, decreased crosslink densities and lower concentrations of network II increased TA. These findings demonstrate how the morphology of a multiphase polymeric material can affect LA and TA, with significant increases In damping capability over the average of the component polymer values.
Simultaneous acoustic wave propagation and dynamic mechanical analysis of curing of thermoset resins
Authors: Chow Andrea W. , Bellin Jack L.
Published: December 2004

A study of simultaneous acoustic and rheometric (dynamic mechanical) measurements of the epoxy curing process is undertaken to assess the validity of using acoustic cure‐monitoring sensors for process control. Our results demonstrate that the acoustic technique provides a sensitive means for monitoring the cure of neat epoxy over the entire cure cycle. The acoustic modulus calculated from the shear velocity qualitatively tracks the mechanically measured dynamic modulus and correctly ranks the stiffness of two epoxy compositions. When the frequency difference is accounted for, using time‐temperature superposition of the dynamic mechanical measurements, quantitative agreement between the acoustic and mechanical moduli for fully cured epoxy resins is also quite good.
Determination of ejection temperature and cooling time in injection molding
Authors: Yu Chi J. , Sunderland J. E.
Published: December 2004

Estimation of cooling time for a given injection molding part is becoming increasingly important, especially when a large number of parts are produced. In order to calculate the cooling time, the ejection temperature should be known. However, to date, there is no easy way to obtain the ejection temperature even though the material selected and part thickness are known. This study uses a combination of experimental, analytical, and statistical means to establish equations for calculating ejection temperature according to material properties, part thickness, and molding conditions such as injection and mold temperatures. Therefore the cooling time of a given injection molding part can be estimated in its early design stage.
Quantitative measurement of voids formed during liquid impregnation of nonwoven multifilament glass networks using an optical visualization technique
Authors: Mahale Anant D. , Prud'Homme Robert K. , Rebenfeld Ludwig
Published: December 2004

A technique based on matching the refractive index of an invading liquid to that of a fiber mat has been used to study entrapment of air (“voids”) that occurs during forced in‐plane radial flow into nonwoven multifilament glass networks. The usefulness of this technique is demonstrated in quantifying and mapping the air pockets. Experiments with a series of fluids, with surface tensions varying from 28 × 10−3 to 36 × 10−3 N/m, viscosities from 45 × 10−3 to 80 × 10−3 Pa · s, and inlet flow rates from 0.15 × 10−6 to 0.75 × 10−6 m3/s, have shown that void content is a function of the capillary number characterizing the flow process. A critical value of capillary number Ca = 2.5 × 10−3 identifies a zone below which void content increases exponentially with decreasing capillary number. Above this critical value, negligible entrapment of voids is observed.
A local theory of heating in cross‐ply carbon fiber thermoplastic composites by magnetic induction
Authors: Fink Bruce K. , McCullough Roy L. , Gillespie John W.
Published: December 2004

For joining and repair of continuous fiber thermoplastic composites, induction heating has been viewed a strong candidate. Induction heating employs an applied alternating magnetic field, which induces a rotational emf in a grid of conductive carbon fibers, which are then used to carry resulting currents. In continuous carbon fiber crossply composites the available paths for “eddy current” loops are along the network of conductive carbon fibers. For this to occur, an electrical transfer must take place between crossing fibers in adjacent plies. Tests involving variable thicknesses of interply neat film layers have been performed to provide insight into the mechanisms taking place. These tests indicate that the primary mechanism for heating in such laminates is dielectric losses in the polymeric region between fibers in adjacent planes that form the conductive loop. Therefore, heating is not uniform in such composites despite a uniform magnetic flux. Heating patterns were viewed using liquid crystal materials and E‐type thermocouples. Several factors leading to nonhomogeneous thermal distributions have been considered, including current density effects, internal emf cancellation, and rotational field effects. Global and local considerations are addressed, a localized model is proposed, and the corresponding theory is developed qualifying the early results. Additional testing has supported the theory.
Transcrystallinity phenomena in a polypropylene/kevlar fiber system. I: Influence of crystallization conditions
Authors: Avella Maurizio , Della Volpe Gaetano , Martuscelli Ezio , Raimo Maria
Published: December 2004

The isothermal crystallization from the melt of isotactic polypropylene in the presence of Kevlar 49 fibers has been investigated. The nucleating ability of the fibers was demonstrated, and the presence of extensive transcrystalline regions was related to crystallization parameters, such as crystallization temperature, melt precrystallization temperature, and residence time at precrystallization temperature. The results are discussed in terms of the presence of heterogeneities in the bulk and preformed self‐seeded nuclei located in the anfractuosities of fiber surfaces.
A mixing model for multicomponent reactions in twin screw extruders applied to the polymerization of urethanes
Authors: Ganzeveld K. J. , Janssen L. P. B. M.
Published: December 2004

To understand the performance of multicomponent reactions in twin screw extruders the mixing mechanism in the extruder had to be understood. Therefore, two new relevant mixing parameters are defined; the mixing efficiency, which is the average number of passages of material through a high shear region; and the mixing deficiency, which is the fraction of material that does not pass through a high shear region. With these parameters an analysis can be made of the mixing circumstances in the extruder. The new model was applied to the polymerization of urethanes in a counter‐rotating twin screw extruder. The results agreed very well with the theoretical expectations.
Improving adhesion between thin chromium film and polyimide substrate by Ar+ irradiation
Authors: Koh S. K. , Pae K. D. , Caracciolo R.
Published: December 2004

Ar+ irradiation and annealing at an elevated temperature are used to improve the adhesion of deposited Cr thin films by vacuum evaporation onto polyimide (PI) substrates. The Ar+ ions of 50 and 200 keV and various Ar+ doses ranging from 1 × 1013 to 2 × 1016 ions/cm2 are chosen for the experiments, after many preliminary trials. The surface analyses are conducted employing Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared spectrometry (FTIR), X‐ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM). Ar+ irradiation produces an interfacial layer of about 100 Å (10 nm) thick in which Cr particles and PI molecules are physically mixed and chemically bonded. The chemical bonds of CrO and a trace of CrC are observed by XPS and FTIR. Impact‐wear tests are also conducted in order to determine the effects of the Ar+ irradiation on the wear property of a Cr/PI system. A significant increase in the property is observed and the increase appears to be a function of the degree of adhesion of the Cr film to the PI substrate.
Flow birefringence in polymer rheology
Authors: Subramanian R. , Wilson D. R. , Picot J. J. C.
Published: December 2004

Based on a linear stress‐optical relation, off‐center and centerline velocities along with the orientation angle measurements (via the birefringence method) can be used to test constitutive equations for polymeric melts without the need to measure viscosity hood stresses directly. For polydimethylsiloxane (Dow Corning type 200 grade 300 Pa · s) melt in a 60° wedge flow cell (inward flow) at a pressure drop of 70 psi, the orientation angles computed by the Power‐Law model and Goddard‐Miller model with two terms in the Taylor Series and a single relaxation time of 0.005 s were compared with the experimentally measured values. It was found that the Goddard‐Miller model agreed quite well with the measured data. The stress‐optical coefficient (C) was evaluated from the velocity, birefringence, and orientation data. It was calculated to be 1.44 × 10−10 m2/N for combined shear and extension using the two‐term Goddard‐Miller Model. For centerline flow (purely extensional), the zero‐extension‐rate elongational viscosity (η0) was calculated to be 930 Pa · s, slightly greater than three times the zero‐shear‐rate viscosity (η0). The cell can be adapted for transient flow experiments.
CO2 laser welding of polymers
Authors: Duley W. W. , Mueller R. E.
Published: December 2004

Deep penetration welding of polymers can be carried out at high speed with relatively low laser power. This results from an efficient coupling CO2 laser radiation to polymers that leads to volume heating. A brief review of energy coupling and heat transfer effects in polymers under CO2 laser welding conditions is given. Some examples of low power (10 to 100 watt) CO2 welding of polypropylene and polyethylene at depths of up to 1.5 cm are discussed.
Strength model of adhesive‐bonded double‐lap joints under cantilevered bending
Authors: Yang C. , Pang S. S. , Griffin S. A.
Published: December 2004

The objective of this study was to develop mathematical relations for predicting the strength of adhesive‐bonded double‐lap joints under cantilevered bending. Based on the strength of composite materials theory, two models were proposed to predict the stress‐strain distribution and vertical deflection of the laminates and the adhesive under this loading condition. The first model was based on the basic beam theory with the assumption that every cross section in a plane before bending remains plane after the bending load is applied. In the other model, a strain gap between each bonded surface is assumed. Based on the second model and the predicted peel failure mode, the effects of shear modulus of the adhesive, joint length, and adhesive thickness on the joint strength were evaluated. Scotchply composite laminates were used as the adherends of the double‐lap joints in the experimental investigation. An Instron machine fitted with a special apparatus was used for conducting the experiments. By the attachment of strain gages to the adherends and through the use of a dial indicator, the theoretical models were verified experimentally.
Molecular structure, morphology, and antioxidant consumption in medium density polyethylene pipes in hot‐water applications
Authors: Karlsson K. , Smith G. D. , Gedde U. W.
Published: December 2004

Changes in polymer structure and antioxidant concentration have been systematically studied as functions of temperature, hoop stress, exposure time, and location in pipe wall on pressure tested pipes of medium density polyethylene. The pressure tests have been performed with water as the internal medium and air as the external medium at temperatures in the range 80 to 105°. Infrared spectroscopy shows that oxidation is initiated at the inner wall surface just prior to the onset of the so‐called stage III fracture. X‐ray diffraction and size exclusion chromatography show that oxidation involves only the amorphous phase and results in a significant molar mass reduction. The near‐inner‐wall material exhibits a 10% reduction in mass average molar mass before the onset of stage III fracture and thereafter a more dramatic decrease. Oxidation induction time measurements by differential scanning calorimetry show that the antioxidant concentration is almost twice as high in the center of the wall as in the near‐inner‐wall and outer‐wall material of the unexposed pipe, that the loss of antioxidant is anomalously rapid at the beginning of the high temperature exposure, and that the antioxidant concentration profile gradually becomes more skewed towards the outer wall on prolonged exposure. The data presented in this paper are used in a parallel paper for modeling purposes.
Dynamic mechanical analysis of polypropylene composites based on surface‐treated sepiolite
Authors: Morales E. , Ojeda M. C. , Linares A. , Acosta J. L.
Published: December 2004

The dynamic mechanical properties in terms of the storage modulus G′, loss modulus G″, and loss tangent δ have been studied for polypropylene‐sepiolite composites. The effect of surface treatment on the relaxation spectra has been elucidated, and quantitative values indicating the extent of polymer‐filler interaction have been given. Analysis of the results show that the addition of sepiolite leads to an increase in the values of the modulus, a value of the glass transition temperature lower than that of unfilled polypropylene, and displacement towards higher temperatures of the αc relaxation associated with the crystalline regions. Surface treatment of the sepiolite, by esterification with organic acids of different chain length, does not have a marked effect on the relaxation spectra of the composites, even though the polymer‐filler interaction parameter decreases with respect to untreated sepiolite.
Effects of compatibilizers on the properties of polyamide/polypropylene blends
Authors: Holsti‐Miettinen R. , Seppälä J. , Ikkala O. T.
Published: December 2004

Compatibilization of polyamide 6/isotactic polypropylene blends was investigated by mechanical, morphological, thermal, and rheometrical methods. The primary objective was to obtain blends combining the desirable properties of the two components. Four compatibilizers including maleic anhydride, fumaric acid, or glycidyl functionalities were applied at two concentrations (5 and 10%). Maleic anhydride grafted styrene‐ethylene‐butylene‐styrene block copolymer (SEBS‐g‐MAH) was observed to give excellent mechanical properties, especially at high polyamide/polypropylene ratios. The correlation between morphology and mechanical and rheological properties is discussed, and the interesting effect of blending on the kinetics of crystallization is noted.
Morphological, thermal, and rheological properties of nylon/acrylonitrile‐butadiene‐styrene alloys
Authors: Aoki Yuji , Watanabe Makoto
Published: December 2004

Melt blends of nylon‐6/modified ABS (acrylonitrile‐butadiene‐styrene terpolymer) have been prepared using a single screw extruder. Electron microscopic observations revealed that the rubber particles are as finely dispersed as in ABS. Both the heat of fusion and the dynamic storage modulus of the blends were linear functions of the blend composition. The melting point of nylon crystallites and glass transition temperatures of poly(acrylonitrile‐co‐styrene) (AS) and the rubber phase in ABS and the amorphous phase in nylon were almost independent of the composition. Very high Izod impact strength was achieved over a broad compositional range. These facts suggest that the nylon and the modified ABS are not mixed on a molecular level although there must be sufficient interaction between them. The melt viscosities were increased with an increase in the ABS component. In the region of less than 65% ABS, the viscosities bend off to the zero‐shear viscosity at low shear rates. Above 65% ABS, the viscosity curves were expressed by a power law fluid. The power law index decreased with an increase in the ABS content. The activation energy of flow vs. composition curve indicated a discontinuous point between 60% and 70% ABS. The phase inversion takes place at about 65% ABS, judging from the rheological point of view.
Blends of polycarbonate with poly(methyl methacrylate): Miscibility, phase continuity, and interfacial adhesion
Authors: Kolarik Jan , Lednicky Frantisek , Pukanszky Bela , Pegoraro Mario
Published: December 2004

Dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) concurrently show that polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends have a two‐phase structure. The differences between the Tgs of parent polymers and the Tgs of conjugate phases, determined by both DMTA and DSC, indicate a limited miscibility of components and allow the approximate composition of conjugate phases to be calculated. The Flory‐Huggins interaction parameter calculated by using these data assumes values about 0.035 ± 0.010. Phase inversion occurs in an interval close to the 50/50 composition, though the molar masses and melt viscosities of the polymers were rather different. Partial miscibility of components ensures interfacial adhesion capable of sustaining the stress transfer between phases up to fracture. Yield stress of the blends is very close to values foreseen by the rule of mixtures. A specific feature of the blends studied is that the addition of 10 to 20 vol% of PMMA to PC increases the strain at break and work to fracture, which are rather low for the PC used. The enhanced capability of the blends to absorb mechanical energy is probably linked to plastic deformation of the dispersed PMMA.
Shear‐rate‐dependence modeling of polymer melt viscosity
Authors: Hieber C. A. , Chiang H. H.
Published: December 2004

Steady‐shear‐viscosity data sets for commercial‐grade acrylonitrile‐butadiene‐styrene terpolymer, nylon, polycarbonate, poly(methylmethacrylate), and polystyrence are fitted in terms of a generalized Cross/Carreau modeling for the shear‐rate dependence. Based upon extensive data sets from the open literature as well as in‐house measurements, it is shown that the shear‐rate dependence can be more accurately described in terms of the Cross rather than Carreau model. Although the resulting viscosity fits based upon these two models might differ by 20% or more for the same well‐characterized data set, the resulting effect upon simulating the injection‐molding process is found to be much smaller since such predictions reflect a range of shear stresses (varying linearly from centerline to wall of cavity) over which the two models alternate in relative magnitude. This is demonstrated by detailed representative numerical predictions which are presented for both the filling and post‐filling stages.
Effects of polyethylene molecular structure on peroxide crosslinking of low density polyethylene
Authors: Bremner T. , Rudin A. , Haridoss S.
Published: December 2004

The effects of molecular structure on the dicumyl peroxide crosslinking of two low density polyethylenes have been studied. Peroxide efficiency was determined largely by the content of terminal vinyls in the two polymers. Differences in molecular weight distribution and branch content had comparatively little influence on the gel content but hot creep resistance of the vulcanized materials was affected. Scorching was affected, also, by the presence of vinyl unsaturations in the polymer.
Structure and mechanical properties of highly oriented poly(ethylene terephthalate) films
Authors: Evstatiev M. , Fakirov S. , Apostolov A. , Hristov H. , Schultz J. M.
Published: December 2004

The relationships between the supermolecular structure of poly(ethylene terephthalate) films subjected to cold drawing and subsequent zone annealing and their mechanical properties are investigated. The effectiveness of zone annealing is compared to that of annealing with fixed ends. Microstructural changes occurring during heat treatment and zone annealing are monitored using wide angle X‐ray scattering, small angle X‐ray scattering, infrared spectroscopy, differential scanning calorimetry, and static mechanical tests. The very high modulus and strength of the zone‐annealed films are directly attributed to the large number of the molecules connecting the crystallites.
The effect of strain rate on the deformation and relaxation behavior of 6/6 nylon at room temperature
Authors: Bordonaro C. M. , Krempl E.
Published: December 2004

The influence of strain rate changes in the range from 10−3 to 10−6 1/s on the zero‐to‐tension loading and unloading behavior as well as short term relaxation properties is investigated using cylindrical specimens of circular cross section. A clip‐on extensometer measures and controls the axial strain in an MTS servohydraulic, computer‐controlled mechanical testing machine. Strains do not exceed twenty percent and all deformation is macroscopically homogeneous. An increase in strain rate causes an increase in stress level. Surprisingly, the total stress drop in a 20 min relaxation period increases with prior strain rate. When the relaxation test is started in the inelastic region with low tangent modulus the total stress drop is nearly independent of the stress and strain at which relaxation commences. Unloading to zero load is not linear but curved and the strain recovery at zero stress is significant. It occurs at an ever decreasing rate and does not exceed three percent in a 12 h period. Like the relaxation behavior the recovery rate increases with prior strain rate. Repeated relaxation periods during zero‐to‐tension cycling can show a stress magnitude decrease during loading but a stress magnitude increase during unloading. The results suggest that a unified model with an overstress dependence of the inelastic rate of deformation could be useful in modeling.
Conformational changes in a polyethylene model under tension and compression
Authors: Pfeffer G. A. , Sumpter B. G. , Noid D. W.
Published: December 2004

Using a realistic model for polyethylene (PE), the molecular dynamics technique is used to simulate atomic motion in a crystal. The calculations reveal conformational disorder above a critical temperature. The rate of isomerization computed from molecular dynamics is compared to transition‐state theory and leads to an activation energy under stress of ∼ 30 kJ/mol, 15 kJ/mol above the single‐bond rotation value. In the unstressed case, the activation energy for the process is less.
The development of surface texture in injection stretch‐blow molded polypropylene
Authors: White S. A. , Doun S. K.
Published: December 2004

The development of surface texture in biaxially deformed polypropylene is examined. Two polypropylenes formed into bottles under similar conditions by the injection stretch‐blow molding process exhibit different levels of clarity. Vertical cracks of light scattering dimensions are found by optical microscopy to be the source of haze. Rheological measurements indicate the resin that develops surface cracking has a much higher extensional viscosity and exhibits a significant increase above the linear case of its extensional stress growth function. Possible mechanisms for the formation of surface texture are discussed.
Thermal and viscoelastic behavior of polyurethane/polyvinylchloride blends
Authors: Lavallée C. , Carmel M. , Utracki L. A. , Szabo J. P. , Keough I. A. , Favis B. D.
Published: December 2004

The potential of melt processing polymer blends to prepare damping materials was investigated. Binary and ternary blends of polyvinylchloride (PVC) with thermoplastic polyurethane elastomers (TPU) were studied. The soft segments of the polyurethanes for the first series were of the ether type and of the ester type for the second series of blends. A series of polymer blends were prepared by mechanical melt mixing and the apparent miscibility was evaluated from the thermal, dielectric, and dynamic mechanical behavior as well as from transmission electron microscopy. Some samples exhibited a single damping peak at low PVC content, indicating miscibility of the blends at the detection scale of the test method. The relationship between the properties and the morphology of the blends was studied.
Extrudate swell of high density polyethylene. Part III: Extrusion blow molding die geometry effects
Authors: Koopmans R. J.
Published: December 2004

Two high density polyethylene resins—801 and 802— are examined with regard to their isothermal, time‐dependent, and nonisothermal swelling properties when emerging from two annular and three diverging dies. The short time swelling characteristics of samples 801 and 802 are very important for these dies, resulting in a lower diameter swell for the latter, independent of the die geometry or flow rate. Output variations have much less impact on the swelling behavior than small changes in the geometry of the die mandrel. Accordingly, shear stress and shear rate parameters alone cannot be used to explain the swelling properties of a HDPE resin in the different die geometries. Straight annular dies induce higher diameter swelling than diverging dies.
Temperature dependence of polyolefin melt rheology
Authors: Mavridis H. , Shroff R. N.
Published: December 2004

The rheology of polymer melts depends strongly on temperature. Quantifying this temperature dependence is very important for fundamental, as well as practical, reasons. The purpose of this paper is to present a unified framework for handling the temperature dependence of rheological data. We considered the case (by far the most common in polymer melts) where all relaxation times (in the context of linear viscoelasticity) have the same temperature dependence (characterized by a “horizontal shift activation energy”) and all relaxation moduli have the same temperature dependence (characterized by a “vertical shift activation energy”). The horizontal and vertical activation energies were extracted from loss tangent vs. frequency and loss tangent vs. complex modulus data, respectively. This is the recommended method of calculation, as it allows independent estimation of the two activation energies (statistically uncorrelated). It was shown theoretically, and demonstrated experimentally, that neglect of the vertical shift leads to a stress (or modulus) dependent activation energy and necessitates different activation energies for the superposition of loss and storage modulus data. The long standing problem of a stress‐dependent activation energy in long chain branched LDPE was identified as originating from the neglect of the vertical shift. The theory was applied successfully to many polyolefin melts, including HDPE, LLDPE, PP, EVOH, LDPE, and EVA. Linear polymers (HDPE, LLDPE, PP) and EVOH do not require a vertical shift, but long chain branched polymers do (LDPE, EVA). Steady‐shear viscosity data can be superimposed using activation energies extracted from dynamic data.
Analysis of stresses arising during the processing of polymeric films on tentering frames
Authors: Jennings Robert M. , Farris Richard J.
Published: December 2004

A model based on linear elasticity is presented describing the stresses arising during the processing of polymeric films on tenter frames. The model demonstrates that large in‐plane shear stresses, resulting from gradients in the line, produce anisotropic stresses in the film. The magnitude of the anisotropy is found to vary transversely across the line, becoming isotropic in the center and achieving maximum values at the edges of the line. The principal directions of the stress tend to lie at ±45° to the machine direction but may be altered by machine and transverse drawing by the frame. These results agree with orientation measurements reported in the literature on polyimide films produced on tentering frames.
Development of polymer blend morphology during compounding in a twin‐screw extruder. Part I: Droplet dispersion and coalescence—a review
Authors: Utracki L. A. , Shi Z. H.
Published: December 2004

The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ⩾ 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, ϕd ⩾ 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin‐screw extruder. Their value is limited to serving as general guides to the process modeling.
Development of polymer blend morphology during compounding in a twin‐screw extruder. Part II: Theoretical derivations
Authors: Shi Z. H. , Utracki L. A.
Published: December 2004

In Part II of the work, the intermeshing twin‐screw extruder is briefly described and the theoretical procedures used to model its operation are summarized. Based on the microrheological considerations discussed in Part I, a predictive procedure of the morphology evolution during compounding of two immiscible polymers is proposed. In this first generation model, only the shear flow effects are considered. Furthermore, to avoid complications due to coalescence a low concentration of the dispersed phase was assumed. In the procedure, two drop breakup mechanisms are discussed. The first assumes that the drops do not break under flow while the second postulates that breakup occurs under flow. Two dispersion mechanisms are considered, the first postulating continuously increasing polydispersity of drop size and the second postulating that drop polydispersity is inversely proportional to deformation strain. The influence of the screw configuration and operating conditions on blend morphology evolution is studied. It is expected that the computed drop size distribution provides limiting values for the experimental data. Dependency of predicted morphology on operating conditions is also investigated. Increasing screw rotating speed (resulting in increasing energy consumption) and decreasing throughput (resulting in decreasing productivity) lead to prediction of finer drop size. In practice, therefore, a compromise would be required. The proposed procedure is limited to melt flow (excluding the die region) within the region of large capillary parameter values, k > 4kcrit.
Damage and the nonlinear viscoelastic response of glassy polycarbonate and LaRC‐TPI
Authors: Crook R. A.
Published: December 2004

In the bulk, the nonlinear viscoelastic response of glassy polymers is due to the irreversible work done on the body by the surroundings. The source of the irreversibility is plastic flow of material near distributed shear bands or microcracks in the polymer. Shear bands and microcracks also form new traction free boundaries in the body. The presence of these new boundaries diminish the load bearing capacity of the polymer. These changes in polymer lattice structure are a mechanism that promotes the release of stored strain energy. If the release of stored strain energy is stress controlled, then at sufficiently high levels of stress to cause a permanent structural arrangement of the polymer chains, polycarbonate and LaRC‐TPI behave as nonlinear viscoelastic materials. If the current stress is less than the maximum stress the polymer has experienced, then the current energy release rate for the propagation of shear bands, crazes, etc., is less than the critical energy release rate. In this instance, damage production is a constant and the material can be modeled using linear viscoelasticity. It will be shown that the stress‐induced nonlinear shift factors are a measure of the rate of damage production in glassy polycarbonate.
On‐line prediction of final part dimensions in blow molding: A neural network computing approach
Authors: Diraddo R. W. , Garcia‐Rejon A.
Published: December 2004

Control over final part thickness distributions in extrusion blow molding would be very useful in resin optimization. An on‐line measurement is essential for process monitoring and control of the part dimensions. Excessive resin usage results in material waste and increased cycle times because of increased cooling requirements. An inadequate thickness results in decreased mechanical strength, especially in regions along the part where large blow ratios or complex geometries exist. Neural networks are investigated as a method for the on‐line prediction of the final part distribution from the parison dimensions. The purpose of this work is to demonstrate the feasibility, for preliminary use, of neural networks for this application. The network inputs include the initial parison thickness and tempera‐ture profiles, the bottle mold geometry and a rheological parameter representative of the material. Varying blow‐up ratios are obtained from the bottle mold geome‐try. The network accesses data from a pool of eighty data sets for the training sequence. The data sets are broadly distributed with regard to the operating conditions, so as to give the network a wide range of applicability. The simulations are performed on data sets not present in the access pool used for training.
The effect of surface roughness and crystallinity on the light scattering of polyethylene tubular blown films
Authors: Larena Alicia , Pinto Gabriel
Published: December 2004

An experimental study of the effect of surface roughness and crystallinity on the light scattering of polyethylene tubular blown films is reported. Several films were prepared by varying the raw polyethylenes and the extrusion temperature. Other processing variables were maintained constant. We have made a statistical analysis of data and we have obtained multiple regressions between light scattering for a given wavelength of incident light and a given film thickness (30 μm, 50 μm, and 70 μm) and the independent variables average surface roughness and degree of crystallinity. It was demonstrated that, for the polymeric films studied, the surface texture evaluates better than crystallinity the variation of light scattering, but crystallinity has also some importance.