bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation, stability, and properties of in‐situ composites based on blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer
Authors: Machiels A. G. C. , Denys K. F. J. , Van Dam J. , De Boer A. Posthuma 
Published: April 2004

AbstractThis paper describes the preparation and properties of in‐situ composites based on polymers with no overlap in processing temperatures. The polymers used were Vectra A900, a thermotropic liquid crystalline copolyester (TLCP), and Arnitel em630, a thermoplastic elastomer. Blends were generated by feeding the two components from separate extruders into a Ross static mixer. Different morphologies were obtained by varying the number of mixing elements of the static mixer. Using 8 mixing elements led to a stratified morphology of Vectra layers in Arnitel, using 11 mixing elements resulted in the desired continuous fiber/matrix morphology whereas a pronounced skin‐core morphology was obtained with 14 mixing elements. It is argued that in‐situ composites can be generated by a distributive mixing process without the formation of an intermediate droplet/matrix morphology as occurs in common dispersive blending equipment. Tensile modulus and strength of all blends increased with extrudate draw ratio as a result of increased molecular orientation of the TLCP phase. The level of reinforcement, however, was lower than expected, probably due to the low temperature of drawing. Annealing and capillary instability experiments showed that above the melting point of the TLCP the fiber/matrix morphology rapidly breaks up into a droplet/matrix morphology. This process takes just a few seconds for fibers of thickness ∼ 1 μm. It is shown to be the probable cause of the skin‐core morphology obtained in case of 14 mixing elements.
Cavity pressure control during the cooling stage in thermoplastic injection molding
Authors: Gao F. , Patterson W. I. , Kamal M. R. 
Published: April 2004

AbstractThe evolution of cavity pressure during the injection molding cycle has a strong influence on the quality of the molded part. The injection molding cycle can be divided into three stages: filling, packing, and cooling. In a previous paper, the authors reported on the design and implementation of a strategy to control cavity pressure during filling and packing. This paper deals with cavity pressure control during the cooling phase. A coolant temperature control system has been designed for the control of cavity pressure during the cooling phase. Alternative variables have been defined to describe changes in cavity pressure during the cooling phase. The concept of controlled pressure cooling time (CPCT) has been defined and selected as the most appropriate controlled variable. The dynamics of CPCT have been studied in relation to coolant temperature. A control system for CPCT has been designed and implemented. Finally, the paper shows that the control of CPCT is an effective approach for the control of cavity pressure during cooling.
Study of thermoplastic foam sheet formation
Authors: Lee Shau‐Tarng , Ramesh N. S. , Campbell Gregory A. 
Published: April 2004

AbstractThis paper discusses theory and experiments on nonisothermal foam growth during foam sheet formation in an extrusion process. The extruded foam sheet expands and cools simultaneously when exposed to ambient temperature. A viscoelastic cell model in the literature was modified to include heat transfer and gas loss effects during foam sheet formation. Experiments were conducted using a twin‐screw extruder to study the effect of ambient temperature and initial sheet thickness on foam characteristics. The foam was made using low‐density polyethylene with CFC‐12 as the blowing agent. The experimental results are compared with theoretical predictions to check the validity of the model. The results reveal that heat transfer effects become important when sheet thickness decreases to the millimeter range. Agreement between theory and experiment is good when an appropriate boundary condition, to account for the gas loss, is included in the model.
Air bubble migration through a cast solution of poly(methyl methacrylate)
Authors: Schruben Dale L. , Kumble Dinesh 
Published: April 2004

AbstractTransport of air (with solvent vapor) bubbles that sometimes appear in a polymer/solvent liquid are followed in the process of solvent casting the polymer. The concentration profile of the solvent in the developing casting is found to be the primary controller of bubble rise velocity. This velocity dependence on concentration is developed through experiment over the range of conditions in the casting [∼90 to 0% methylene chloride in poly(methyl methacrylate), molecular weight 300,000, and Tg 110°C]. Assumptions of quasi steady‐state and penetration type theories are used to generate this simplest model, qualitatively (and semi‐quantitatively) correct in predicting the skin layer/bubble layer/bulk layer structure in solid polymer pieces produced by the solvent casting process.
Thermal characterization and morphological study of polyphenylene sulfide–polycarbonate blends
Authors: Lim Soonho , Kim Junkyung , Park Min , Choe Chul‐Rim , Lee Jeongmin , Kim Daeheum 
Published: April 2004

AbstractThe thermal behavior and phase morphology of binary blends of poly(phenylene sulfide) (PPS) with polycarbonate (PC) have been investigated. Differential scanning calorimetry and dynamic mechanical thermal analysis indicate the blends are immiscible, but the glass transition temperature of PC in the blends was found to be decreased due to the degradation of the PC. The PC degradation was investigated by measuring the molecular weight of PC extracted from the blends. Rheological properties of the blends were also studied using a rheodynamic spectrometer. An inversion of the phase morphology was observed from the scanning electron microscopy and dynamic mechanical thermal analysis. The increase of crystallinity of the PPS in the blends was found from a DSC study.
Simultaneous prediction of the modulus and yield strength of binary polymer blends
Authors: Kolarik Jan 
Published: April 2004

AbstractA new scheme is proposed for the simultaneous prediction of the modulus and yield (or tensile) strength of binary blends, which employs a two‐parameter equivalent box model and the data on the continuity of constituents acquired from the percolation theory. Prediction of the elastic modulus in the linear stress‐strain region assumes “perfect” interfacial adhesion; at yielding (or breaking), the upper and lower bounds have to be distinguished, those bounds being related, respectively, to the interfacial adhesion sufficient and insufficient for the transmission of the acting stress. The modulus and the upper bound of yield (or tensile) strength are monotonic functions of the blend composition within the interval delimited by the values characterizing the components. The lower bound of strengths passes through a minimum (close to the 50/50 composition) linked to the minimum sum of the continuity parameters of the constituents. Predicted dependences of the modulus and of the yield (or tensile) strength on the blend composition are in a good accord with experimental data selected from literature.
Effects of thickness on the specific essential work of fracture of rigid PVC
Authors: Levita G. , Parisi L. , Marchetti A. , Bartolommei L. 
Published: April 2004

AbstractThe fracture behavior of sheets of rigid poly(vinyl chloride), PVC, 2 to 10 mm thick, was investigated according to the Essential Work of Fracture (EWF) approach in order to find evidence of thickness effects. Test pieces were doubly notched and loaded in tension. Critical values of the J‐integral were measured, in three‐point bending, either complying with or violating the size requirements dictated by the ASTM 813.89 protocol. It was found that Jc did not depend on sample thickness; on the contrary, the value of the Specific Essential Work of Fracture, obtained by means of test pieces with ligaments larger than three times the thickness, was strongly affected by the sample thickness. The size of the plastic zone that developed around the ligaments was measured by optical means. At small ligaments the height of this zone linearly increased with ligament size and tended to level off at large ligaments. In the linear range, the rate of increase of the size of the plastic zone did not depend on sample thickness. It was found that the value of the Specific Essential Work of Fracture obtained by test pieces whose plastic zones were in the linear range was independent of thickness.
A calibration technique to evaluate the power‐law parameters of polymer melts using a torque‐rheometer
Authors: Marquez Alfredo , Quijano Jafet , Gaulin Marc 
Published: April 2004

AbstractIn this work we develop an empirical method to calibrate the measuring head of a torque‐rheometer to obtain the power‐law parameters of polymer melts. This method is based on a similar analysis developed by Lee and Purdon. However, in this work, only one geometrical parameter, with well‐defined physical limits, is needed for calibration, instead of the two arbitrary parameters proposed by the previous authors. Moreover, this parameter is closely related to the ordinate of the logarithmic relationship between the torque (MT) and the angular velocity (S1), obtained from the torque‐rheometer data. This allows us to define a calibration function for this parameter, which is used to evaluate the consistency index (m) of the melt. On the other hand, experimental results confirm the equivalence between the slope of the logarithmic values of torque and angular velocity obtained from the torque‐rheometer data and those of shear stress vs. shear rate obtained from capillary rheometry. This further highlights the feasibility of evaluating the melt flow index (n) and the consistency index (m) from the torque‐rheometer data.
Viscoelastic features of molten blends of poly(vinyl chloride)/poly(ethylene‐vinyl acetate)
Authors: Hernández R. , Del Agua J. A. , Peña J. J. , Santamaría A. 
Published: April 2004

AbstractDynamic viscoelastic measurements and extrusion rheometry results of immiscible and partially miscible PVC/EVA blends from 50 to 90 wt% in PVC are presented and compared with those of plasticized PVCs. From loss modulus data the plateau modulus, GNo, associated with entanglements, is calculated. The variation of GNo with composition is analyzed using the theory of Tsenoglou. A simple model, which accounts for the effect of a structural parameter and the effect of free volume, is used to adjust viscosity data, taken at several frequencies and shear rates. For both types of blends, best fits are obtained using a model that establishes that the free volume of each polymer is not measurably altered by the other.
Reaction injection molding: Analyzing the filling stage of a complex product with a highly viscous thermoset
Authors: Haagh G. A. A. V. , Peters G. W. M. , Meijer H. E. H. 
Published: April 2004

AbstractAlthough numerical simulation has proved to be a useful tool to predict the filling behavior of injection molding products, few applications in reaction injection molding (RIM) have been reported. This is mainly due to the lack of appropriate descriptions of the material behavior, and to the lack of accurate material data. The analysis of the filling stage of the RIM process requires the determination of the cure kinetics and the rheological, pvT, and thermal behavior of the material, which in this study is a highly filled copolymer of ethylene and vinyl‐acetate (EVA). Since this copolymer yields some viscosity anomalies, due to the amount of filler, the rheology of a similar EVA compound with low filler content was also investigated. The viscosity of this compound can be described by a Carreau model at low conversions levels (<1%), whereas a conversion‐dependent Power‐Law model proves appropriate for higher conversion. Moreover, the viscosity behavior of both compositions is similar in the processing range. The combined Carreau/Power Law viscosity model is used for the numerical simulations of a complex product. The simulation results agree well with experimental molding results. The analysis shows that a combination of material characterization and modeling, numerical simulation, and experimental verification is necessary to make simulation programs a useful design tool for RIM products and molds.
Antiplasticization behavior of polycaprolactone/polycarbonate‐modified epoxies
Authors: Don Trong‐Ming , Bell J. P. , Narkis M. 
Published: April 2004

AbstractAntiplasticization behavior was found in the polycaprolactone (PCL)/polycarbonate (PC)‐modified epoxy system, cured with an aromatic amine. The initial modulus increased and the fracture toughness and the elongation at break decreased with the addition of the PCL/PC modifier. The glass transition temperature (Tg) decreased slightly. In this system, the antiplasticization phenomenon can be explained well by the formation of hydrogen bonding between the carbonyl groups in the PCL/PC and the hydroxyl groups in the epoxy. The hydrogen bonding proportion, as analyzed from Fourier transform infrared spectra, increased with the addition of PCL/PC up to 15 parts. This is consistent with the trend observed in the mechanical properties. It was thought that for antiplasticization to occur, a strong molecular interaction is necessary for a restriction of molecular motion, in turn decreasing the free volume of the matrix and thereby causing an increase in the modulus of the material. The dynamic mechanical thermal behavior of these systems was also studied. It was found that there was no change in the molecular weights between crosslinks, which excluded the effect of crosslink density on the changes of the properties. Instead, the activation energy was increased and the peak area was decreased for the β relaxation because of the restriction of the molecular motion by hydrogen bonding. The results indirectly support the hypothesis that the motion of the 2‐hydroxypropyl ether is responsible for the β relaxation process.
Electrical and mechanical properties of pre‐localized polypyrrole/poly(vinyl chloride) conductive composites
Authors: Ouyang Meng , Chan Chi Ming 
Published: April 2004

AbstractA 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

AbstractLinear 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

AbstractBlends 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

AbstractOrganic 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

AbstractPolyethylene 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

AbstractAn 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

AbstractThe 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

AbstractUsing 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

AbstractThe 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.