bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and mechanical properties of pre‐localized polypyrrole/poly(vinyl chloride) conductive composites
Authors: Ouyang Meng , Chan Chi Ming
Published: April 2004

A novel process for preparation of conductive polypyrrole/poly(vinyl chloride) (PPy/PVC) composites by pre‐localization of an intrinsically conducting PPy phase in a PVC matrix has been developed. This process involves encapsulating PVC particles with a thin layer of PPy, and subsequently compacting this PPy‐encapsulated PVC powder by compression molding. The current‐voltage characteristics and electrical conductivity of the pre‐localized PPy/PVC composites were determined. The change of the current‐voltage characteristics from linear to nonlinear behavior with increasing PPy content in the composites is discussed in the view of the intermolecular hopping and tunneling of electrons. The tensile properties, dynamic mechanical behavior, and microhardness of the pre‐localized PPy/PVC composites were studied as a function of PPy content. A percolation threshold of 0.3 wt% is achieved in the pre‐localized PPy/PVC composites. This value is much lower than those of the conventional conductive composite materials containing a random distribution of PPy fillers. The samples with a PPy content of 1.6 wt% or above have high conductivity and still preserve reasonable mechanical properties.
Stability of Newtonian‐PTT coextrusion fiber spinning
Authors: Ji Ching‐China , Yang Jyh‐Chau , Lee Woei‐Shyong
Published: April 2004

Linear stability analysis has been applied to a coextrusion fiber spinning flow that consists of a Newtonian fluid as a core layer and a Phan‐Thien/Tanner (PTT) fluid as a skin layer. These two chosen fluids show entirely different rheological behaviors. The stability of this coextrusion system was affected by the choice of three characteristic parameters: the skin layer fraction (f), the extensional parameter (ϵ), and the shear thinning parameter (ξ) in the Phan‐Thien/Tanner model. The linear stability results indicate that the viscoelastic skin layer (PTT fluid) has a stabilizing effect that delays the onset of draw resonance. Under fixed compositions (f is fixed), the stability envelopes changed from upturned curves to flattened ones as extensional force dominated the system. The neutral stable curves closed to the horizontal line at a critical draw ratio of around 20, showing similar behavior to a Newtonian fluid where the system has a very high Deborah number or it is dominated by shear thinning effects.
Thermal properties and morphology of blends of poly(ether imide) and polycarbonate
Authors: Chun Yong Sung , Lee Heon Sang , Kim Woo Nyon , Oh Taeg Su
Published: April 2004

Blends of poly(ether imide) (PEI) and bisphenol‐A polycarbonate (PC) have been investigated by differential scanning calorimetry, dynamic mechanical thermal analyzer, scanning electron microscopy, and transmission electron microscopy. Three different molecular weights of polycarbonate have been used in the PEI‐PC blends. Blends were prepared by screw extrusion and solution casting with weight fractions of PEI in the blends varying from 0.90 to 0.10. From the measured glass transition temperature (Tg), the maximum decrease of Tg(PEI) is observed for 0.9 weight fraction PEI in the PEI‐PC blends. In the study of the morphology, the size of minor component domains (about 0.1 to 0.3 µm) in the 90/10 PEI‐PC blend is small compared to the size of minor component domains (about 0.2 to 2.0 µm) in the 10/90 PEI‐PC blend. This morphological behavior is attributed mainly to the difference of viscosity ratio between the dispersed phase and continuous phase. No considerable differences in the thermal behavior and morphologies have been observed among the blends of PEI and PC having different molecular weights.
Injection and transport in glassy polymeric coatings
Authors: Abkowitz Martin A.
Published: April 2004

Organic electrophotographic receptors have been enabled by the development of unique classes of high dielectric strength glassy polymer coatings, which, though insulating, are nevertheless capable of transporting injected charge with relatively high mobility and negligible loss to deep traps. Key features of electronic transport in these materials and the underlying physics are described. Additionally, it is demonstrated that these trap‐free transport polymers provide a unique venue for the exploration of contact behavior and the factors controlling injection efficiency in disordered organic solids.
Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film: Effects of counter‐rotating die on fiber orientation and film properties
Authors: Chinsirikul W. , Hsu T. C. , Harrison I. R.
Published: April 2004

Polyethylene blends (LLDPE:HDPE ≈ 2:1 by wt) used in NASA's balloon film applications can be effectively reinforced by addition of a small amount of liquid crystalline polymer (LCP). Cast and blown PE films containing ≈ 10% LCP show an appreciable enhancement in tensile modulus ≈400% over that of the neat PE matrix. Anisotropy in these in‐situ composites was reduced by controlling LCP molecular orientation via a counter‐rotating (C/R) annular die. LCP/PE blend blown films with nearly isotropic properties are obtained. Based on microscopy studies, LCP domains were generally present as fibrils with diameters of ≈ 1 to 3 µM and lengths of ≈ 100 to 300 µM. Films, produced using a C/R die, had fibrillated LCP phases and variable orientation through the film thickness. This paper describes the influence of some key process variables including temperature profile, number of extrusion cycles, degree of mixing, adapter geometry, and die counter‐rotation on LCP/PE blend film morphology and mechanical properties. The structure of LCP/PE blend blown films was also evaluated using scanning electron microscope (SEM) and wide angle X‐ray scattering (WAXS) techniques.
Mechanisms of fatigue in short glass fiber reinforced polyamide 6
Authors: Horst J. J. , Spoormaker J. L.
Published: April 2004

An adaptation to existing failure models for fatigue fracture of short fiber reinforced thermoplastics is presented, based on results using some new experimental methods. These results lead to the following conclusion: Cracks in polyamide remain bridged (by plastically drawn matrix material and/or fibers) until just before final fracture. Important is the conditioning of the polyamide: conditioned to equilibrium water content, this mechanism occurs, but not when it is dry as molded. Fatigue damage measurements were done on thin foils cut from the fatigued specimen. When tensile tested, these foils show a change in both strength and fracture strain after fatigue. Further observations during the experiments and SEM fractography strengthen the conviction that fatigue damage initiates and grows in the form of bridged cracks. A correlation between tensile strength and fatigue strength was found; the degree of fiber alignment has a similar effect on both tensile and fatigue properties.
Residual stresses in epoxy systems by 3‐D photoelastic method
Authors: Pawlak Andrzej , Galeski Andrzej
Published: April 2004

The new 3‐D photoelastic method was applied to the studies of residual stresses around spherical inclusion in polymeric matrices. Full stress tensor for several model samples was measured. The extent of significant stresses is not greater than three radii of an inclusion. It was found that the stress follows the 1/R3 rule at distances far from the inclusion, while in the narrow zone at the interface a plateau is observed. The level of stress ranges from few MPa up to the plastic yield of the polymeric matrix. The radial stress component is usually twice as large as the tangential stress component. Radial negative stress and tangential positive stresses are found in configuration with a hard inclusion, while radial positive stress and tangential negative stresses are in the systems with soft inclusion. The pressure in the matrix at points around inclusions calculated from the stress tensor is always near zero MPa, which indicates the action of purely deviatoric stresses in the matrix.
Photoelastic method of three‐dimensional stress determination around axisymmetric inclusions
Authors: Pawlak Andrzej , Galeski Andrzej
Published: April 2004

Using Aben's approach to three‐dimensional photoelasticity, a method for the determination of the stress tensor in a transparent matrix around an isolated axisymmetric inclusion is detailed. The method is useful for studies on a microscopic scale, the inclusion preferably above 10 to 20 µm in diameter, especially when the total retardation is below the first fringe order of isochrom. The polarization and phase data for normal and oblique light beams are necessary for full determination of the stress tensor, including the information on pressure. The analysis is nondestructive of the composite material studied.
Viscoelasticity of rubber‐toughened poly(methyl methacrylate). Part II: Fracture behavior
Authors: Mariani P. , Frassine R. , Rink M. , Pavan A.
Published: April 2004

The fracture behavior of a rubber toughened poly(methyl methacrylate) has been studied at several times and temperatures, using SE(B) and SE(T) testing geometries. Schapery's local approach to fracture in polymers has been used to interpret the results. The theory, originally formulated for fracture of linearly viscoelastic materials, has been modified to account for the non‐linear behavior exhibited by the material at higher temperatures. It has been shown that the stress intensity factor at initiation substantially decreases with time and temperature, while fracture energy at initiation, 2Γ, is constant, in the range explored. As for propagation, the stress intensity factor increases with crack speed. The time‐temperature equivalence has been successfully applied, and stress intensity factor master curves for both fracture initiation and propagation have been derived. Predictions made using Schapery's theory agree well with experimental data.
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

The 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

Poly(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

The 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

Optical 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

Various 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

A 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

Epoxy 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

The 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

The 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

Steel‐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

The 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

Laser 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

Depolymerization 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

This 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

The 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

The 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

Scratch 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

A 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.
Phase separation in epoxy resin‐reactive dendritic hyperbranched polymer blends
Authors: Plummer Christopher J. G. , Mezzenga Raffaele , Boogh Louis , Månson Jan‐Anders E.
Published: April 2004

Equilibrium phase diagrams in composition‐conversion space have been calculated for stoichiometric blends of an epoxy resin with a diamine hardener and dendritic hyperbranched polymers, to which various numbers of epoxy groups have been grafted. An attempt has been made to incorporate both the effects of the polydispersity of the resin and the reactivity of the functionalized hyperbranched polymers for any given value of the interaction parameter. However, if the reactivities of all the epoxy groups are comparable, the presence of a highly functionalized modifier is expected to lead to a reduction of the gel point conversion and a narrowing of the composition‐conversion window available for cure induced phase separation. The experimental cloud point data are consistent with the model, although they sugget that the functionalized hyperbranched polymers may be significantly less reactive than the resin. Moreover, in the present system, the influence of functionalization on the phase behavior is also strongly linked to the accompanying changes in the interaction parameter.
Effects of inhibitors and retarders on low temperature free radical crosslinking polymerization between styrene and vinyl ester resin
Authors: Li Ling , Lee L. James
Published: April 2004

Many composite manufacturing methods are room temperature processes, which require the resins to be cured at low temperatures. Examples are Seemann Composite Resin Infusion Molding Process (SCRIMP)—a vacuum assisted resin transfer molding (VARTM) process, hand lay‐up and spray‐up. Vinyl ester resins have been widely used in this type of processes because of their versatility as a composite matrix. Low temperature polymerization between styrene and vinyl ester tends to be complex because of the presence of different curing agents. This paper reports on (1) the effects of a promoter (cobalt naphthenate) on the initiatin at low temperatures, and (2) the effects fo a retarder (2,4‐pentanedione) and an inhibitor (1,4‐benzoquinone) on the pot life, gel time, and cure kinetics. A differntial scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer were used to investigate the reaction kinetics of vinyl ester resins. The influence of the retarders and inhibitors on the rheological changes of the resin during curing was also studied using a Rheometris Dynamic Analyzer (RDA).
Mechanical behavior of a semicrystalline polymer before necking. Part 1: Characterization of uniaxial behavior
Authors: Brusselle‐Dupend N. , Lai D. , Feaugas X. , Guigon M. , Clavel M.
Published: April 2004

The behavior of the semicrystalline polymer polypropylene (PP) was studied in the pre‐necking domain. Mechanical tests were performed to characterize its viselastic and its viscoplastic behavior. The usual approach for studying metals was adopted to investigate the effect of heterogeneities caused by spherulitic morphology. The macroscopic stress was split into an effectie stress and a back stress so that the interactions between crystalline lamellae and amorphous phases could be taken into account. An understanding of the relationship between microstructure and the macroscopic strain mechanisms was developed.
Reactive compatibilization and in‐line morphological analysis of blends of PET and a thermotropic liquid crystalline polymer
Authors: Qiao Fang , Migler Kalman B. , Hunston Donald L. , Han Charles C.
Published: April 2004

The reactive extrusion of a compatibilized polyethylene terephthlate and thermotropic liquid crystalline copolyester blend system is investigated via in‐line optical microscopy and light scattering. The reactivity, morphology, rheological behavior and mechanical properties were studied. It was found that a droplet‐fiber transition in the liquid crystalline polymer can occur, and this transition is dependent upon the reactivity, the viscosity ratio of the blend components and the shear fields. The fibers are strongly oriented along the flow direction when specific processing conditions are met. An enhancement in the mechanical properties correlates with the morphology. The formation, deformation and stability of the fiber microstructure under different flow conditions are discussed.
Molecular structural evolution in crosslinking low density polyethylene–trimethylolpropane trimethacrylate systems
Authors: Tai Horng‐Jer
Published: April 2004

A Monte Carlo simulation algorithm for investigation the structural growth in a polymer‐polyfunctional monomer system and the method to obtain the required simulation parameters are proposed. Combining the Monte Carlo sampling technique and swell ratio experiments, the molecular structural evolution in crosslinking LDPE‐TMPTMA systems is explored. The crosslinking level can be effectively promoted at high TMPTMA concentrations and at high cure temperatures. With increasing overall crosslinking density, gelation occurs at lower degree of conversions; the gel corsslinking density, increases: the TMPTMA densities in both sol and gel fractions also increase; while the sol polymer molecular weights and the sol crosslinking density decrease. The implications of the simulated results to the processing of LDPE‐TMPTMA compounds are also discussed.
Improving polymer blend dispersion in mini‐mixers
Authors: Marić Milan , Macosko Christopher W.
Published: April 2004

The simple cup and rotor mini‐mixer, designed to blend very small polymer batches (0.3 g, MiniMAX), was compared to larger lab scale extruder (5 g, DACA): and a 16 mm co‐rotating twin screw (300 g/hr. PRISM). All were compared at the maximum shear rate in the cup and rotor mixer, 110 s−1. Particle sizes of poly(propylene) [PP] dispersed in poly(styrene) (80 wt% PS) were meausred by dissolving the PS, filtering and using scanning electron microscopy. The 16 mm twin screw gave somewhat smaller particle sizes than the lab scale mixers (102 μ vs 1.7 and 1.9 μ), but dispersion in the cup and rotor mini‐mixer was much poorer. Simply adding three steel balls to the cup as suggested by Maréchal et al. (Polym Networks Blends, 1997) greatly improved the dispersion (1.8 μm). Modifying the rotor design to allow recirculation yielded similar improvement. The benefit of adding three balls was confinmed in blends of low viscosity poly(dimethyl siloxane) PDMS in PS. When anhydride terminal PDMS was blended with amino terminal PS, the particle sizes were much smaller (10 vs. 0.3 μm) and the differences between the three versions of the cup and rotor were much less pronounced.
Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter
Authors: Hobbs Terry , Lesser Alan J.
Published: April 2004

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO2 using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO2 drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO2 drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.
Melting and densification of thermoplastic powders
Authors: Kontopoulou M. , Vlachopoulos J.
Published: April 2004

The present work focuses on the transformation of a loosely packed, low density powder compact, to a fully densified polymer part, when processed at temperatures above the melting (or glass transiton) point of the polymer. The purpose of this study is to dlucidate the mechanisms involved in the process and to examine the applicability of models available in the materials science literature for the description of the overall densification of molten polymer particles. The evolution of density as a function of time during sinter‐melting was measured experimentally using a heating oven. The results revealed that the overall process consists of two stages. The first stage involves particle coalescence, which depends on viscosity, surface tension and powder properties. During this stage air pockets, which eventually become bubbles, are entrapped inside the melt. The second stage involves the diffusion controlled shrinkage and eventual disapperance of the bubbles. The experimental results were compared to models commonly used for the densification of particulate compacts in the ceramics, glass and metals processing literature. Application of models based solely on viscosity and surface tension phenomena, can describe satisfactorily the process until the point where closed pores (bubbles) form. Abubble dissolution model has been successfully applied to provide predictions of density as a fuction of time for late stages of densification.
Toughened carbon fiber prepregs using combined liquid and preformed rubber materials
Authors: Hayes Brian S. , Seferis James C.
Published: April 2004

Model epoxy resin formulations were modified with defferent concentrations of liquid rubber and preformed crosslinked rubber particles and impregnated into unidirectional carbon fibers. The liquid rubber was used to increase the mode I fracture toughness of the interlayer toughened prepreg systems, which already have high mode II fracture properties. In this paper it is shown that the mode II fracture toughness is not sacrificed by the incorporatiom of carboxyl terminated butadiene acrylonitrile rubber (CTBN) in the matrices, while mode I fracture toughness can be increased by as much as 100%.
In situ fibrillar reinforced PET/PA‐6/PA‐66 blend
Authors: Evstatiev M. , Fakirov S. , Schultz J. M. , Friedrich K.
Published: April 2004

Ternary fibrillar reinforced blends are obtained by melt‐blending of poly(ethylene terephthalate) (PET), polyamide 6 (PA‐6) and polyamide 66 (PA‐66) (20/60/20 by weight) in the presence of a catalyst, followed by cold drawing of the extruded bristles to a draw ratio of about 3.4 and additional annealing of the drawn blend at 220 or 240°C for 4 or 8 h. The blend samples are studied by DSC, X‐ray diffraction, SEM, and static and dynamic mechanical testing (DMA). SEM and DMA show that PA‐6 and PA‐66 form a homogeneous, continuous matrix in which PET regions are dispersed. X‐ray and DSC measurements of the drawn and annealed at 220°C samples suggest mixed crystallization (solid solubility) of PA‐6 and PA‐66, and cooperative crystallization of PET with the two polyamides. After annealing at 240°C (above the melting point of PA‐6 and below that of PET), the polyamide matrix becomes partially disoriented, while the oriented, fibrillar PET is preserved and plays the role of a reinforcing element. The DSC results for the same samples suggest in situ generation of an additional amount of copolymer. This additional copolymerization, together with that generated during blend mixing in the extruder, improves the compatibility of the blend components (mostly at the PET‐polyamide interface) and alters the chemical composition of the blend.
Thermo‐electric behavior (PTC) of carbon black–containing PVDF/UHMWPE and PVDF/XL‐UHMWPE blends
Authors: Mironi‐Harpaz I. , Narkis M.
Published: April 2004

This paper describes the structure and electrical performance of PTC/NTC (positive temperature coefficient/negative temperature coefficient) effects and their reproducibility upon healing/cooling cycles. The following three‐component blends were studied: PVDF/UHMWPE/CB, PVDF/XL‐UHMWPE/CB and γ‐irradiated compression molded plaques of these blends. Carbon black (CB) particles are attracted to the UHMWPE (ultra high molecular weight polyethylene) and XL (cross‐linked)UHMWPE particles, which constitute the dispersed phase in the PVDF (polyvinylidene fluoride) matrix, but practically cannot or only very slightly penetrate them because of their extremely high viscosity. A double‐PTC effect was exhibited by all unirradiated samples. Irradiation of compression molded PVDF/UHMWPE/CB plaques does not add to their already outstanding reproducibility, and it results In a wide single‐PTC effect. Irradiation of compression molded PVDF/XL‐UHMV/PE/CB plaque, slabilizes their structure upon heating/cooling cycles and thus makes them reproducible PTC/NTC materials, still exhibiting a double‐PTC effect. The carbon black concentrations studied in this report are extremely low (< 2 phr CB) in comparison to other literature reports.