bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processing and properties of polyimide melt blends containing a thermotropic liquid crystalline polymer
Authors: Blizard K. G. , Haghighat R. R. 
Published: December 2004

AbstractSeveral polymer blend compositions of LaRC‐TPI 1500 and New TPI 450 (Mitsui Toatsu) with Xydar SRT 900 LCP (Amoco Performance Products) were extrusion processed. In addition to binary blends containing one TPI with an LCP, ternary blends consisting of an alloy containing both TPIs as the matrix were also processed. By varying the ratio of the polyimides in the matrix, the blends' thermal behavior could be tailored. This paper addresses both processing issues and film properties of these blends. Rheological and thermal studies were conducted on both blends made in a torque rheometer and on biaxially oriented film produced with a counter‐rotating annular die. These biaxial blend films were further characterized by measuring tensile and electrical properties. For 70/30 New TPI/Xydar equal biaxial films of 50 μm thickness, a modulus of 3.8 GPa and a stress at break of 100 MPa were measured. For near uniaxial blend films (±3°) a modulus of 14.5 GPa and a strength of 220 MPa in the machine direction (MD) were measured. The transverse direction (TD) properties were still higher than the neat New TPI. The electrical properties of these blends were outstanding. The dissipation factor was typically less than 0.01 for most blend compositions. Similarly, the dielectric constant was typically less than 3 up to temperatures as high as 300°C.
Rheological behavior and processability of neoprene and acrylic rubbers
Authors: Kumar Nalini R. , Gupta B. R. , Bhowmick Anil K. 
Published: December 2004

AbstractRheological behavior of neoprene and acrylic rubbers and their carbon blackfilled compounds has been studied using a Monsanto Processability Tester. These systems show pseudoplastic flow behavior. Die swell increases with increase in shear rate up to a limit beyond which it decreases. It also decreases with increase in filler loading and temperature. The maximum recoverable deformation has been calculated by assuming that the viscous response of the rubbers obeys the power law model and elastic behavior is described by Hooke's law and has been correlated with die swell. A linear generalized relationship has been obtained between the die swell and the recoverable deformation. The principal normal stress difference has been found to increase nonlinearly with shear stress. Activation energy of melt flow process increases with increase in shear rate up to a limit, after which it decreases for acrylic rubber and 10 phr filled neoprene rubber.
Basic ideas of microwave processing of polymers
Authors: Chen M. , Siochi E. J. , Ward T. C. , McGrath J. E. 
Published: December 2004

AbstractThe objective of this effort has been to investigate the relationship between polymer structure and microwave absorptivity. Dielectric loss factor, ε″, loss tangent, tan δ, and oscillator strength, (εS −‐ ε∞), were used to evaluate potential material processability under applied microwave radiation. Numerous polymeric materials varying in chemical and physical structures were irradiated in a low power (≤ 100W) electric field at 2.45 GHz. Electromagnetic radiation was applied as either traveling or resonant wave modes in cylindrical and rectangular waveguides. In general, heatability was found to be a direct function of the dielectric loss dispersion dependence on temperature and frequency. The dielectric loss factor obtained at low frequency measurements was found to be directly proportional to the heatability of polymers. A WLF plot was used to predict the shift of dielectric loss maxima into or out of the microwave frequency range.
A slightly compressible transient finite element model of the packing phase in injection molding
Authors: Tanguy P. A. , Grygiel J. M. 
Published: December 2004

AbstractA 2‐D finite element model of the packing phase using an Augmented Lagrangian approach is described. The model is tested for various geometrical configurations. The influence of the cavity thickness, length, and shape on the packing time and flow patterns is investigated, showing a good agreement with published data.
Construction of fast‐response heating elements for injection molding applications
Authors: Jansen K. M. B. , Flaman A. A. M. 
Published: December 2004

AbstractA new type of heating element was developed capable of changing the mold surface temperature by about 70 K in 0.2 s, thus enabling reduction of frozen‐in orientation and stresses in injection molded products without undue increase in cycle time. The heater, which consists of two insulation layers with a resistance layer in between, is discussed in this paper. The thickness of this insulation layer proves to be the most important design parameter. Too thick an insulation layer increases the cooling time too much, whereas with a thin layer the surface temperatures will stay too low. Temperature measurements at the heater surface and in the mold wall are reported and demonstrate the extreme fast response characteristics.
Instrumented impact evaluation of a toughened carbon fiber epoxy composite
Authors: Woo E. M. , Chen J. S. 
Published: December 2004

AbstractInstrumented impact testing and analysis were performed on an interlaminartoughened carbon fiber epoxy composite (Toray 3900‐2/T800H) and a conventional (untoughened) epoxy composite (Fiberite 934/T300). Severity of impact was varied by using a wide range of impact energy. The effect of difference in the tup of the impact instrument was discussed. The residual compressive strengths after compact (CAI's) were measured by using a universal mechanical tester. The impact damage and delamination resistance of the toughened and conventional composites were quantitatively compared. At the same impact energy, the extent of damage was much less severe and the CAI was higher for the toughened composite. Relationships between the CAI's, the state of impact damage, and impact energy were investigated. Impact damage mechanisms for these two composites were not exactly the same. The impact damage of the conventional composite exhibited much greater extents of delamination. By contrast, interlaminar delamination in the toughened composite was found to be significantly suppressed, and the impact damage was more dominated by controlled matrix cracking/fiber damage, instead of catastrophic delamination. As a result, the CAI's of the toughened composite exhibited a monotonous decrease with increase in the impact energy and in the linear dimension of extents of damage.
Microwave processing of two‐phase systems: Composites and plymer blends
Authors: Chen M. , Hellgeth J. W. , Ward T. C. , McGrath J. E. 
Published: December 2004

AbstractThe objective of the current paper was to extend the relationships between complex polymer structures and microwave absorptivity that were formulated in the first three papers of this series (1–3). The microwave processing of composite and polymeric blends via a cylindrical resonance wave cavity and a rectangular standing wave applicator is described. These polymeric materials were irradiated in a low power (< 100W) electric field at 2.45 GHz. Graphite‐epoxy laminates were processed in both standing and traveling wave applicators. Rapid heating and curing were achieved in both cases. An observation of significance was that, with proper tuning of the traveling wave device (the precursor of a protable repair tool), it proved to be highly effective in processing. Additionally, a compatible blend of poly(methyl methacrylate) and poly(vinylidene fluoride) was heated in and applicator and the rates of temperature rise were demonstrated to depend upon morphology.
A state variable model for high strength polymers
Authors: Krempl Erhard , Bordonaro Christine M. 
Published: December 2004

AbstractDisplacement controlled experiments on nylon 66, poly(etherether ketone), and poly(ether imide) at room temperature suggest that nonlinear elastcity is not a good model for these polymers. Rather, qualitative evidence is presented that a state variable model shows promise. In this model, the rate of deformation is the sum of the elastic and the inelastic rates of deformation. The elastic rate of deformation is given by an objective formulation of Hooke's law, and the inelastic deformation is an increasing function of the overstress, the difference between the Cauchy stress and the equilibrium stress. The equilibrium stress is a state variable, and represents the stress that can be sustained at rest following deformation. Load controlled tests, intended to verify or falsify the model, show that the creep rate at the same stress level can be different on loading and unloading, and that the creep rate need not increase with an increase in creep stress level. These anomalous results can easily be explained by the introduction of the overstress concept, and by proper evolution of the equilibrium stress. They confirm the usefulness of the overstress concept for the modeling of these polymers.
Plastic behavior and deformation textures of poly(etherether ketone) under uniaxial tension and simple shear
Authors: Dahoun A. , Aboulfaraj M. , G'Sell C. , Molinari A. , Canova G. R. 
Published: December 2004

AbstractSamples of poly(etherether ketone) (PEEK) were subjected to large plastic deformations under uniaxial tension and simple shear by means of a new video‐controlled testing method at constant true strain rate. The “equivalent” stress‐strain curves obtained under the two loading modes are close at the yield point, but diverge drastically at large strains, with a rapidly increasing hardening in tension and a moderate hardening under simple shear. X‐ray diffraction goniometry shows that these contrasting behaviors are associated with the different textures developed in the crystallite orientations. Under tension, the PEEK lamellae are progressively tilted in such a way that the chain axis becomes oriented parallel to the tensile axis; in the other mode, the final chain orientation is near to the shear axis. DSC analyses of deformed samples in both modes are carried out. The results show that the tension loading induces a fragmentation of the thin lamellae, while the shear mode generates less fragmentation. A quantitative model is presented that involves a composite approach: (i) the viscoplastic deformation of the crystalline lamellae, which is controlled by chain slip and transverse slip systems on planes parallel to the c axis, and (ii) the hyperelastic deformation of the amorphous phase, which depends on the affine unfolding of statistically distributed subchains. A discussion of the influence of the CRSS values on the stress‐strain curves and textures is developed by means of this model.
A constitutive model for the nonlinear viscoelastic viscoplastic behavior of glassy polymers
Authors: Hasan O. A. , Boyce M. C. 
Published: December 2004

AbstractTwo features of the glassy state of an amorphous polymer, which play a key role in determining its mechanical properties, are the distributed nature of the microstructural state and the thermally activated (temporal) evolution of this state. In this work, we have sought to capture these features in a mechanistically motivated constitutive model by considering a distribution in the activation energy barrier to deformation in a thermally activated model of the deformation process. We thus model what is traditionally termed the nonlinear viscoelastic behavior as an elastic‐inelastic transition, where the energetically distributed nature of inelastic events and their evolution with straining is taken into account. The thermoreversible nature of inelastic deformation is modeled by invoking the notion of strain energy stored by localized inelastic shear transformations. The model results are compared to experimental data for constant true strain rate uniaxial compression tests (nonmonotonic) at different rates and temperatures; its predictive capabilities are further tested by comparison with compressive creep tests at different stress levels and temperatures.
Solidification of thermoviscoelastic melts. Part II: Effects of processing conditions on shrinkage and residual stresses
Authors: Bushko Wit C. , Stokes Vijay K. 
Published: December 2004

AbstractThe solidification of a molten layer of thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and the buildup of residual stresses in the injection‐molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification, so that this model can be used to assess packing‐pressure effects in injection molding. Parametric results are presented on the effects of the mold and melt temperatures, the part thickness, and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in‐plane and through‐thickness shrinkages, and on residual stresses in plaque‐like geometries. The packing pressure is shown to have a significant effect on part shrinkage, but a smaller effect on residual stresses. Packing pressure applied later in the solidification cycle has a larger effect. Mold and melt temperatures are shown to have a much smaller effect. The processing parameters appear to affect the through‐thickness shrinkage more than the in‐plane shrinkage. While the results are presented in terms of normalized variables based on the properties of bisphenol‐A polycarbonate, they can be interpreted for other amorphous thermoplastics such as modified polyphenylene oxide, polyetherimide, and acrylonitrile‐butadiene‐styrene.
Low temperature melting behavior of CO2 crystallized modified PETs
Authors: Mensitieri G. , Del Nobile M. A. , Apicella A. , Guerra G. , Al Ghatta H. 
Published: December 2004

AbstractDifferential scanning calorimetry (DSC) analysis has been performed on modified and commericial amorphous samples of poly(ethylene terephthalate) (PET) crystallized by high pressure carbon dioxide (CO2). Two endothermic peaks are present in the DSC scans of all the carbon dioxide‐treated samples. A qualitatively analogous behavior has been detected in the case of amorphous samples heat treated at temperatures slightly exceeding the glass transition temperature of virgin material. Wide angle X‐ray scattering analysis has confirmed the structural analogies between samples CO2 crystallized at 50°C and thermally crystallized slightly above Tg. A differential scanning calorimeter capable of working at high pressure of CO2 has been adopted in order to examine the effect of carbon dioxide on the crystallization temperature range.
Numerical simulation of blow molding—Viscoelastic flow analysis of parison formation
Authors: Tanoue Shuichi , Kuwano Yoshifumi , Kajiwara Toshihisa , Funatsu Kazumori , Terada Kousuke , Yamabe Masashi 
Published: December 2004

AbstractThe simulation of the parison formation process in blow molding has been studied. The flow field was divided into two regions, namely, the extrudate swell region near the die lip and the parison formation region after the exit swell. In the swell region, we predicted the swelling ratio and residual stress distribution for high Weissenberg numbers for steady planar well using the 1‐mode Giesekus model. In the parison formation region, the flow is assumed to be an unsteady unaxial elongational flow including drawdown and recoverable swell and is modeled using the 10‐mode Giesekus model. We calculated the time course of parison length and thickness distribution, and compare the calculation results of parison length with experimental data. It was found that the predicted values agreed rather well with the experimental values. The calculation results could especially predict the shrink‐back, which is the phenomenon where the parison length becomes shorter after the cessation of extrusion, and it was found tat this was caused by the recoverable swell of the parison, which depends on the tensile stress generation in the die. Various flow rates and die geometries were studied and confirmed the reliability and usefulness of the method.
Dynamics of uni and biaxial deformation and its effects on the thickness uniformity and surface roughness of poly (ether ether ketone) films
Authors: Cakmak M. , Simhambhatla M. 
Published: December 2004

AbstractThe uniformity of films and their surface roughness are of great importance in applications involving information recording (videotapes etc.). These properties of polymers processed with such film production techniques as tenter frame operations are not well understood. To understand the relationships between the process variables, such as stretching mode, rate of stretching, temperature of stretching, and material characteristics, melt cast amorphous PEEK films were subjected to systematic experiments involving variations of the process parameters. The results reveal that stress hardening in the stress strain curves plays an important role in defining the level of thickness uniformity and surface roughness. It the films are stretched in a way that they do not experience stress hardening, the resulting films were found to have significant variations in thickness, sometimes worse than those of precursor materials. In all cases, where films are subjected to substantial stress hardening, the above two parameters improved dramatically. This indicates that no matter what the stress response of the film, those films stretched to intermediate stretch ratios have poor thickness uniformity and surface quality. Once the stress hardening takes effect, the deterioration of the dimensional parameters was found to stop and reverse and ultimately reacha point in deformation space where the film quality was better than that of the original films. This is solely attributed to the stress hardening that allows the thinned sections of the films to sustain higher loads, thereby propagating the deformation to other underformed areas in the films, which in turn causes a “self‐leveling” effect. An important implication of this finding is that to obtain films of optimum thickness and surface quality, they need to be stretched beyond the (global) stress hardening point. Otherwise, less than desirable film quality may result.
Stress‐Strain curves for solid polymers
Authors: Kitagawa Masayoshi , Zhou Dexin , Qui Jianhui 
Published: December 2004

AbstractIn order to provide nw experimetnal facts required for constructing a nonlinear constitutive equationfor solid polymers, some tests wee conducted on amorphous pojymers of polycarbonate and poly(methyl methacrylate) and for a crystalline polymer of polyxymethylene under varous strain paths such as comprssion, torsion and combined tension‐torsion. It is shown that (1) the stress‐strain behavior for the strain paths without strain reversal is described well not only for amorphous polymers, but also for crystalline polymers by an overstess theory proposed by Krempl, and (2) at the strain paths wth stran reversal, the stress responses are considerably differetn from what is expected for the fstress responses of metals and their alloys.
Biopolyester melt behavior by torque rheometry
Authors: Melik D. H. , Schechtman L. A. 
Published: December 2004

AbstractA torque rheometer method has been developed to evaluate the melt behavior of biopolyesters. The main features of this technique include: (i) a modified equipment configuration, so as to maintain the melt temperature within ± 1°C pf the set temperature after the first few minutes of polymer melting and thermal equilibration, and (ii) a kinetic equation that can be used to determine the melt behavior from the torque‐time data. Applying this methology to a poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerte) copolymer shows that the degradation kinetics follow Arrhenius behavior with temperature, that the degradation rate increases with increasing hear, and that the activation energy for random chain scission is independent of shear rate. This effect of shear on the degradation process may be a result of viscous heating. The degradation rate is increased because of the increased internal energy of the polymer chains as a result of the mechanical deformation. There is no evidence of direct mechanical degradation. Last, the viscosity values obtained with the torque rheometer are consistent with those obtained by capillary rheometry.
Comparisons of experimental data to indices of adhesion derived from dielectric models
Authors: Iwamoto N. E. 
Published: December 2004

AbstractA perspective of adhesion is offered using average property indices such as dielectric constant, dipole moment, and thermal conductivity. These indices have been derived by comparisons of dielectric theories of adhesion and cohesion with comparisons to experimental data found in the literature. For example, it was found that adhesion generally increases with increased dielectric constant, or with the inverse of the thermal conductivity, for metal substrates. It was also found that ranges in the experimental data found were primarily caused by changes in surface roughness, which meant that interaction densities were not predictable.
Effects of mixing porcedures on properties of compatibilized polypropylene/nylon 6 blends
Authors: Lee Jae‐Dong , Yang Seung‐Man 
Published: December 2004

AbstractThe paper consides the effects of compatibilization with maleic anhydride grafted polypropylene (PP‐g‐MAH) on the propertie of immiscible blends of polypropylene (PP) and nylon 6 (N6). We prepared the blends by three different mixing processes; single‐step blending, two‐step blending with reactive premixing, and two‐step blending with nonreactive premixing, to determine the effective mixiing process for fine morphological structure thermal stability, and mechanical properties. Dynamic melt reheological properties were measured to examine the modification of elastic properties by the compatibilizer. In addtion, thermal analysis was also carried out to detect the change in crystallization and thereby to probe the degree of compatibilizaton. The results show that compatibilized blends prepared by teh single‐step process exhibit improved phase morphology, thermal stability, and mechanical properties for dried conditions, compared with other blend types. Finally, the water absorption test indicates that the added compatibilizer yields enhanced water resistance in spite of the strong intrinsic hydrophilicity of N6. In particular, two‐step blending with reactive premixing is most effective in improving water resistance and reducing degradation of mechanical properties after moisture absorption.
Extrude distortion in the capillary/slit extrusion of a molten polypropylene
Authors: Kazatchkov Igor B. , Hatzikiriakos Savvas G. , Stewart Charles W. 
Published: December 2004

AbstractExperiments were carried out in both sliding plate and capillary rheometers with a polypropylene resin to determine the conditions for the onset of slip, surface, and gross melt fracture. It was found that there was no distinction between surface and gross melt fracture, which is commonly observed in the case of polyethylenes. Furthermore, the flow curves determined by using capillaries having various diameters are diameter independent implying the absence of slip. However, experiments with slit dies having rough surfaces suggest wall slip. Further analysis has shown that the effect of viscous heating masks the detection of slip from the diameter‐dependency of the flow curves. The effect of a thin layer of fluoropolymer (Teflon PA, DuPont) on the critical shear stress for the onset of wall slip and melt fracture, as well as on the relationship between the wall shlip and the shear stress, were also examined. It was found that the presence of such layers increases the slip velocity, while it decreases the critical shear stress for the onset of slip.