bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheology of low nematic transition temperature thermotropic liquid crystalline copolyester HBA/HQ/SA
Authors: Gao P. , Lu X. H. , Chai C. K. 
Published: April 2004

AbstractThe rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroquinone, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystalmesophasic and a broad mesophasic‐isotropic transition at 170°C and 220°C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220°C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250°C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is > 100% in the nematic phase, ∼20% in the biphases, and only about 5% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole‐Cole plot of G′ vs. G″ indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 ∼ 10,000 s−1, in which the power law index is about 0.6 ∼ 0.8, and the viscosity is < 10 Pa.s at shear rates >1 s−1.
Filling of poly(lactic acid) with native starch
Authors: Jacobsen S. , Fritz H. G. 
Published: April 2004

AbstractPoly(lactic‐acid) (PLA), a biodegradable polyester with excellent properties for different polymer applications, will play a major role in future markets for biodegradable polymers. But only if the currently very high price level can be reduced significantly to at least 4 $US/kg. Therefore, studies to fill poly(lactic acid) (PLA) with relative inexpensive native corn starch were conducted. Because PLA is a very brittle material with a glass transition point at 54°C, filling of PLA with native starch might seem unrealistic, as the brittleness is increased by the dispersed starch granules. To avoid this, low molecular weight poly(ethylene glycol) (PEG) is introduced into the PLA to enhance crystallization and to lower the glass transition temperature significantly under possible usage temperatures. The polymer that is modified in this way is then filled with native starch. The thermal behavior of the achieved di‐ or triblends is determined by means of differential scanning calorimetry (DSC) and the degradation behavior at high temperature has been looked at with the help of thermogravimetric analysis (TGA).
Rheological properties of phenophthalein poly(ether ether ketone)
Authors: Nobile M. R. , Di Yingwei , Acierno D. , Li Binyao 
Published: April 2004

AbstractThe rheological properties of the novel engineering thermoplastic phenophthalein poly(ether ether ketone) (PEK‐C) have been investigated using both a rotational and a capillary rheometer. The dependence of the viscosity on the shear rate and temperature was obtained. The activation energy was evaluated both from the Arrhenius and the Williams‐Landel‐Ferry (WLF) equation. An estimate for the proper Eη (dependent only on the chemical structure of the polymer) has been found from the WLF equation at temperatures about Tg + 200°C. Measurements of the die swell have been performed. The first normal stress differences were evaluated from the die swell results and compared with the values obtained from the rotational rheometer at low shear rates.
Thermal stresses in dual layer loose tubes of optical fiber cables
Authors: Gao Z. , Pfandl W. 
Published: April 2004

AbstractOptical fibers are usually protected by a loose tube formed by extrusion. The loose tube can consist of one or more plastic layers. In this paper, the thermal stresses in the dual layer loose tubes, which are caused by the inhomogeneous cooling at the end of the extrusion phase, have been calculated based on a numerical method. It was found that the thermal stresses in these loose tubes depend on the adhesion of the two layers and the ratio of the wall thickness between the two layers as well. In general, if there is a good adhesion between the two layers of the loose tube, higher thermal stresses are found in the inner layer.
Scale‐up rules for mixing in a non‐intermeshing twin‐screw extruder
Authors: Bigio D. , Wang K. 
Published: April 2004

AbstractVarious scale‐up rules and theories have been presented for extrusion, including both single‐ and twin‐screw extruders. Until now, however, most of these theories have concerned fully‐filled channels, not only for twin screw extruders of the co‐rotating fully intermeshing type (COTSE) or non‐intermeshing counter‐rotating type (NITSE), but single screw extruders as well. As the demand for distributive mixing and devolatilization devices increases, more and more nonintermeshing twin screw extruders with regions of partially‐filled channels are being used. Therefore, developing scale‐up rules for such screw extruders is imperative. In this paper, scale‐up rules are developed, theoretically and experimentally, by examining the relationship between distributive mixing and important flow parameters. Two partially‐filled NITSE's, with screw diameters of 0.8 and 2 inches, have been studied by using a flow visualization technique entailing a dye tracer to study the effects of distributive mixing by varying such parameters as: percentage of drag flow, screw stagger, and screw velocity. Qualitative evaluation of the spread of the dye with the number of screw revolutions was obtained from videotape of the experiments. Factorial experimental design method has been applied for evaluating these results. Finally, new scale‐up rules were developed and compared with rules in the literature.
Closed loop viscosity control of reactive extrusion with an in‐line rheometer
Authors: Broadhead T. O. , Patterson W. I. , Dealy J. M. 
Published: April 2004

AbstractA novel in‐line melt rheometer (ILR) measured viscosity to control ionomer neutralization during reactive extrusion. The ILR has the advantages of an in‐line location to minimize measurement delay and a “partial Couette” flow geometry, which affords independent control of the shear rate. The reactive extrusion process for ethylene methacrylic acid (EMAA) ionomer neutralization was modeled as a first order plus dead time process. A comparison of the process responses to experimentally determined residence time distributions for the extruder showed that there was an appreciable inherent delay despite the advantage of the rheometer's in‐line location. Proportional‐integral and minimum variance control algorithms were implemented. The quality of control was generally good, but demonstrated the non‐linearity of the neutralization process, suggesting that adaptive control techniques could improve control performance.
Stress relaxation behavior of 3501‐6 epoxy resin during cure
Authors: Kim Yeong K. , White Scott R. 
Published: April 2004

AbstractEpoxy resins and other thermosetting polymers change from liquids to solids during cure. A precise process model of these materials requires a constitutive model that is able to describe this transformation in its entirety. In this study the viscoelastic properties of a commercial epoxy resin were characterized using a dynamic mechanical analyzer (DMA). Specimens were tested at several different cure states to develop master curves of stress relaxation behavior during cure. Using this experimental data, the relaxation modulus was then modeled in a thermorheologically complex manner. A Prony (exponential) series was used to describe the relaxation modulus. An original model was developed for the stress relaxation times based on similar work by Scherer (16) on the relaxation of glass. Shift functions used to obtain reduced times are empirically derived based on curve fits to the data. The data show that the cure state has a profound effect on the stress relaxation of epoxy. More important, the relaxation behavior above gelation is shown to be quite sensitive to degree of cure.
Tensile stresses in the edges of injection moldings: Roles of packing pressure, machine compliance, and resin compression
Authors: Kambour R. P. , Caraher J. C. , Schnoor R. C. , Todt M. L. , Wang H. P. , Willey S. J. 
Published: April 2004

AbstractThe slow spontaneous development of cracks in the edges of injection moldings under “field” conditions has been observed for 30 years or more. While environmental stress cracking agents have long been implicated, the magnitude and distribution of the stresses associated with cracking have been obscure. The current study of these stresses involved polycarbonate as a model test material that was molded under systematically varied molding conditions. Surface tensile stresses, though rarely great enough alone to cause “dry” crazing or cracking were revealed through exposure to environmental stress crazing and cracking (ESC) agents. Using an old technique involving a set of calibrated ESC liquids, edge tensile stresses as great as 18 MPa were found in the edges of the moldings. Other, independent methods of stress assessment gave results in semiquantitative agreement with those of the ESC tests. Packing force, machine compliance, injection hold time, and mold flashing emerged as major variables either raising or mitigating stress levels. The root cause of the edge tensions is the mismatch in the times and pressures at which the skins and cores of moldings solidify. In short, skins quench at low pressure first, while cores solidify later during the packing stage. Upon release from the mold, elastic recovery of the core stretches the skin. More importantly, machine and mold compliances allow expansion of the part in the packing stage, during which certain areas of the skin are stretched. Solidifying the core during the packing preserves part of the skin extension as elastic strain. These effects are capable of outweighing the classical tendency of quenching to generate skin compression and core tension. A number of other effects, including release from the mold before the core has solidified, and flashing of the mold, have been found to limit the rise of skin tension.
Dependence of crack trajectories on stress distributions in the surfaces of injection moldings produced under high packing pressure
Authors: Tirosh J. , Kambour R. P. 
Published: April 2004

AbstractThe curved trajectories of solvent‐induced cracks in the surfaces of polycarbonate injection moldings produced under high packing pressures have been rationalized in terms of the residual body stresses that exist largely in a thin surface layer. The analysis indicates that the residual tensile stress in the skin of the molded plaque can reach values as large as 5 MPa and the tangential tensile stress values as large as 12 MPa, depending on location in the plaque and on molding conditions. The inward penetration of the crack is stopped eventually by the interior compressive stresses that counterbalance the tensile stresses in the “skin.” The crack tends to turn sideways and grow further in Mode II as a result of the intense interlayer shear stress set up at the crack tip by the difference between the skin tension and core compression. The most important practical conclusion from this analysis is that in the absence of externally applied stress, these so‐called edge cracks are unlikely to penetrate the molding's interior since the tensile stress in the surface layer is necessarily counterbalanced by the subsurface compression.
Correlation between die opening gauge and die swell for steel‐rubber composite extrusion
Authors: Lin Yueh‐Jaw , Gregg Eric D. 
Published: April 2004

AbstractSteel‐belted tires are usually made by extruding rubber onto a bank of wires. The resulting steel‐polymer composite must meet a gauge specification. However, the composite swells extensively after leaving the die throat, taking on a more or less corrugated appearance. This paper presents an experimental study to understand the influences different parameters have on die swell for this sort of extrusion. Basically, the experiment is conducted to correlate die opening gauge to die swell. Parameters that affect die swell extrudate expansion are identified and investigated. Die opening is varied throughout the experimental process, and the die opening and belt gauge are measured to calculate die swell. To achieve a more uniform gauge across the width of the belt, the die throat opening is divided into five zones. Each zone of each die throat is considered. Experimental parameters held constant include wire parameters, polymer parameters, and setup parameters. The experimental data result in an overall plot of die swell percent vs. die throat opening gauge. This plot can be used as a guideline for predicting required gauge opening in a steel belt gauge development. The study shows that die swell percents for extruded belts is more predictable than previously thought, and debunks the notion that die swell percent is constant. With regard to the time and effort for optimizing future die throat development, some concluding remarks and recommendations are made based on the analysis of the experimental results obtained in this study.
Antioxidant efficiency loss by precipitation and diffusion to surrounding media in polyethylene hot‐water pipes
Authors: Viebke J. , Hedenqvist M. , Gedde U. W. 
Published: April 2004

AbstractThe extensive initial loss of efficiency of antioxidant [4,4′‐thiobis(3‐methyl‐6‐tertbutylphenol)], during hydrostatic pressure testing of medium density polyethylene pipes at 95 and 105°C has been studied. Samples from the pressure‐tested pipes were subsequently investigated by scanning electron microscopy and energy dispersive spectroscopy. Antioxidant‐containing particles were found in the pipe wall. The particles had evolved during the early stages of exposure and consisted of antioxidant that had phase separated and precipitated from the polymer matrix because the initial antioxidant concentration was greater than the solubility limit at the pressure testing temperatures. Relative antioxidant concentration profiles over the pipe wall, as measured by calorimetric oxidation induction time analysis, showed losses of >80% of the initial effective antioxidant content during the first 1000 h of pressure testing. A model assuming diffusion of antioxidant into precipitates was developed. Values for the diffusivity of the antioxidant in different parts of the pipe wall were obtained by fitting a previously developed model to long‐term antioxidant concentration profiles. Using these values, and by using the distance between two adjacent precipitates as an adjustable parameter, it was possible to fit the newly developed model to the experimental short‐term antioxidant concentration profiles.
Characterization of spherical microlatex particles made of linear uncrosslinked polystyrene chains
Authors: Gao Jun , Zhou Shuiqin , Wu Chi 
Published: April 2004

AbstractLaser light scattering (LLS), including both angular dependence of the absolute scattering intensity (static LLS) and of the line‐width distribution G(Γ) (dynamic LLS), were used to characterize two kinds of pauci‐chain polystyrene (PCPS) microlatices (latex‐1 and latex‐2). Each PCPS particle contains only a few linear uncrosslinked polystyrene chains. In static LLS, the weight‐average particle molar mass (Mw) was measured; and simulataneously in dynamic LLS, the diffusion coefficient distribution was obtained from Laplace inversion of precisely measured intensity‐intensity time correlation function. Our results reveal that, on average, latex‐1 and latex‐2 contain ∼13 and ∼7 linear polystyrene chains, resp. A combination of both static and dynamic LLS results enables us to calculate the average density of PCPS. Our results have also shown that the particle density of latex‐1 and latex‐2 are 0.90 and 0.80 g/cm3, respectively, which are lower than the density of conventional polystyrene latex particles or bulk polystyrene. Our results imply that the particle density decreases as the average number of polystyrene chains inside the particles decreases.
Unsaturated polyester resins from poly(ethylene terephthalate) waste for polymer concrete
Authors: Abdel‐Azim Abdel‐Azim A. 
Published: April 2004

AbstractDepolymerization of poly(ethylene terephthalate), PET, textile waste was performed with a manganese acetate catalyst. Different ratios of diethylene glycol (DG) to propylene glycol (PG) were used for glycolysis. The weight ratio of PET to the glycol mixture was 1:0.65. The glycolyzed products were analyzed for hydroxyl value and the amount of free glycol. These glycolyzed products were reacted with mixtures of sebacic acid (SE) and maleic anhydride (MA) to prepare a series of unsaturated polyesters having different molecular weights. The molecular weights of the unsaturated polyesters produced were determined by the end group analysis. The obtained polyesters were dissolved in styrene (Sty) monomer and their curing behavior was investigated. Polymer concretes (PC) made with these resins were investigated for their compressive strength. The data revealed that the properties of the PC based on recycled PET are comparable to PC made from virgin materials. We concluded that recycling of PET waste may provide a potentially lower cost source of resin, and its recycling in PC will also help reduce an environmental problem.
Scratch hardness and deformation maps for polycarbonate and polyethylene
Authors: Briscoe Brian J. , Pelillo Enrico , Sinha Sujeet K. 
Published: April 2004

AbstractThis paper presents results obtained from the scratching of an ultrahigh molecular weight polyethylene (UHMWPE) and a polycarbonate (PC). The data are used to obtain various surface mechanical properties such as the hardness and also the prevailing deformation mechanisms. Scratch results are reported for the case of rigid conical indenters for various tip included angles, bulk temperatures, scratch velocities, and applied normal loads. Scanning electron microscopy (SEM) and laser profilometry data are used to study the surface deformation and damage mechanisms, and to assess the topography of the surfaces after scratching. Deformation maps are provided for these polymers under different experimental conditions, which describe the various deformation characteristics. In general, these polymers show both increasing and decreasing trends for the scratch hardness values with variation of cone angle, (4qW/ηd2; where W is the normal load, d the width of the residual scratch, and q is a characteristic contact parameter, which ranges between 1 and 2). The scratch velocity, which governs the imposed strain rate, imparts an increasing effect on the hardness values, whereas a higher bulk temperature of the material decreases the scratch hardness. The measured responses of the surface properties of these polymers are shown to greatly depend upon the kind of deformation mechanism prevalent during the scratching and associated material removal processes.
On the impact essential work of fracture of ductile polymers
Authors: Fasce Laura , Bernal Celina , Frontini Patricia , Mai Yiu‐Wing 
Published: April 2004

AbstractThe essential work of fracture methd (EWF) to evaluate the fracture toughness of ductile materials in plane stress with prevalent gross yielding conditions was originally developed by the Cotterell‐Mai research group in Sydney University more than ten years ago. Since then, the EWF method has been proven independently by many researches to be a valid tool for a range ofductile metals, polymers, paper sheets and fiorous composites. The current interest in the technical community of the plastics industry is to extend the EWF methodology to high‐rate impact testing of polymers and their blends and to determine the impact specific essential work of fracture. Since the literatures related to the applicability of this mehodology under dynamic loading conditions appear controversial, our purpose in this work is to clarify under what conditions the impact EWF method is applicabe. The EWF methodology was applied to the energy impact data obtained on two PP copolymers and one ABS polymer at different specimen thickness and geometry. The results showed that the EWF method can be applied to high‐rate testing provided the ligament is fully yielded and the plastic zone is scaled with the square of the ligament length. When these conditions are fully satisfied, the impact specific EWF is a material constant independent of specimen geometry for a given sheet thickness in plane stress; and it is also invariant with specimen thickness when plane strain conditions are met.
A thermally stimulated depolarization current study of polymers in the glass transition region
Authors: Sedita Joseph S. , O'Reilly James M. 
Published: April 2004

AbstractThe low‐frequency dielectric properties of a number of polymers, composites and blends have been studied using a thermally stimulated depolarization current (TSDC) apparatus that was designed and constructed in‐house. The TSDC technique can be used to determine the glass transition of a polymer sample. This TSDC glass transition temperature has been shown to be very similar to that obtained from differential scanning calorimetry (DSC). The actual difference between these two values depends on the heating rates used with each technique, however. TSDC data can also be combined with AC dielectric data to produce a data set, which possesses a very wide frequency range. Finally, individual TSDC relaxation peaks can be fit with the Williams‐Walts distribution function to obtain an estimate of their distributions. This is especially useful when studying polymer blends, but could also be utilized in the study of other systems.
Roles of additives in scratch resistance of high crystallinity polypropylene copolymers
Authors: Xiang C. , Sue H.‐J , Chu J. , Masuda K. 
Published: April 2004

AbstractScratch behavior in neat and talc‐filled high crystallinity polypropylene (PP) copolymers containing various additives is investigated using a cosntant load scratch test and two types of indentation tests (Rockwell and Shore D). The talcfilled PP copolymer exhibits high scratch visibilityand scratch depth. The addition of a nucleating agent or lubricant improves the scratch resistance of the talc‐filled PP copolymer. Differential scanning calorimetry, scanning electron microscopy and attenuated total reflectance Fourier transform infrared spectroscopy are used to characterize crystallinity morphology and scratch mechanisms in PP systems. It is found that the scratch resistance of the PP copolymer systems investigated, in terms of scratch depth and scratch visibility, depends mainly on the fracture features generated during the scratch process. The influences of talc, nucleating agent and lubricant on the scratch behavior of PP are discussed.
Homogeneity of multilayers produced with a static mixer
Authors: Van Der Hoeven J. C. , Wimberger‐Friedl R. , Meijer H. E. H. 
Published: April 2004

AbstractA multiflux static mixer can be used to produce multilayered structures. The flow is repeatedly cut, stretched and stacked by mixing elements in the channel of such a device. In the standard design, however, the obtained layer thicknesses are inhomogeneous. The causes for the multiflux static mixer's deviation from ideal behavior are identified by 3D numeical simulations as unequal pressure drops in the separating flows. Changes in the arrangements of the elements are proposed and their effects are verified by simulations and experiments. A significant improvement of the layer homogeneity is achieved by introducing additional elements with separatings walls at the inlets and at the outlets of the mixing elements.