bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites
Authors: Xie X. L. , Li R. K. Y. , Mai Y. W. , Tjong S. C. 
Published: April 2004

AbstractLiquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (Fmax), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.
Relating the generation of dynamic strain energy to crack propagation in polymers
Authors: Dear John P. 
Published: April 2004

AbstractWith many fracture research studies, there is a need to compare frequently experimental findings and modeling simulations. One example is when studying the relationships between crack velocity and dynamic strain energy generated in polymers. It helps in these cases if the same computer can perform the modeling simulations as used to capture and process experimental data. Personal computer (PC)–size machines are often used to capture experimental data, and a fracture simulation model has been devised that can be hosted on a personal computer. In this study, the model is used with the frozen tongue experimental technique to research steady state crack propagation in medium‐density polyethylene (MDPE). This is to study the generation of dynamic strain energy in the material and the factors affecting its availability to the crack tip. This includes the effects of changes in the material's properties immediately about the crack tip, the conditions that determine the threshold to just maintain crack propagation, and the conditions that determine the relationship between crack velocity and strain energy up to the limiting crack velocity.
Gross melt fracture of polyethylene. I: A criterion based on tensile stress
Authors: Kim Seungoh , Dealy John M. 
Published: April 2004

AbstractWe propose the use of a critical tensile stress as a criterion for the onset of gross melt fracture (OGMF). This stress is estimated from the entrance pressure drop using the method of Cogswell. Carbon black tracer was used to verify that what we deemed to be GMF, based on the inspection of extrudate, was indeed the result of a brittle rupture. An orifice die was used to eliminate the complications arising from the presence of a capillary. Polyethylenes having a variety of molecular structures were used to evaluate the usefulness of the critical tensile stress for characterizing polymers. The critical stress was found to be independent of temperature and contraction ratio. It is also independent of entrance angle, as long as this is equal to or greater than 90 degrees. The critical stress is thus a material property and can be used to rate the tendency of polymers to exhibit gross melt fracture.
Development of a curvilinear viscoelastic constitutive relationship for time dependent materials. Part A: Theoretical discussion
Authors: Stephenson M. J. , Dargush G. F. 
Published: April 2004

AbstractA viscoelastic constitutive relationship derived from a solid mechanics viewpoint using the curvilinear form of Hooke's law as opposed to an Eulerian context was developed. This approach has the advantage of obtaining the deformation relative to the original configuration as opposed to the current one. A constitutive model was derived for viscoelastic fluids where the stress depends on the history of the first spatial gradient of the displacement. A material (convected) coordinate system and body tensor mathematics were invoked to formulate the viscoelastic relationship. Complicated integration of a Jaumann or convected rate derivative was not required. Development of the model and its theory are given here in part A.
Hot embossing in microfabrication. Part I: Experimental
Authors: Juang Yi‐Je , Lee L. James , Koelling Kurt W. 
Published: April 2004

AbstractThe relationship among processing conditions, material properties, and part quality in hot embossing was investigated for three optical polymers: polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl butyral (PVB). A series of systematic embossing experiments was conducted using mold inserts having either single or multiple feature depths. The feature dimensions varied from 90 to 3000 μm. The processing conditions studied include embossing pressure, thermal cycles, and heating methods. The displacement profile, replication accuracy and molded‐in stresses were measured experimentally. It was found that for isothermal embossing, both replication accuracy and birefringence pattern depend strongly on the processing conditions. For non‐isothermal embossing, the molded parts showed excellent replication as long as the feature transfer was completed. The flow pattern under isothermal embossing resembles a biaxial extensional flow. Under non‐isothermal embossing, the polymer deformation involves an upward flow along the wall of mold features, followed by downward compression and outward squeezing. Rheological characterization and hot embossing analysis are presented in Part II.
Experimental investigation of the cure‐dependent response of vinyl ester resin
Authors: Flores F. , Gillespie J. W. , Bogetti T. A. 
Published: April 2004

AbstractThe objective of this research is to understand the influence of the thermochemical and thermomechanical material response of low temperature cured vinyl ester resin (Dow Derakane 411‐C‐50) on the development of residual stress and warpage during processing. The primary experimental technique is the bimaterial specimen experiment, in which the warpage of a bimaterial beam is used as a measure of residual stress. The bimaterial specimen experiment was developed to isolate the chemical and thermal contributions to curvature. Existing material models for shrinkage, modulus, and glass transition temperature as a function of cure were evaluated. These material models were used as input into the bimaterial equation for curvature prediction. The predicted curvatures were used along with the experimental curvatures to evaluate the material models and their ability to accurately describe the material response of the vinyl ester resin. Results showed that the model captured the overall experimental trend in curvature buildup during processing but overestimated the curvature from chemical effects during isothermal cure. Improved correlation was achieved by incorporating a time shift in the model to account for viscoelastic stress relaxation of the resin.
The payne effect for particle‐reinforced elastomers
Authors: Drozdov Aleksey D. , Dorfmann Al 
Published: April 2004

AbstractThe study deals with the Payne effect (a substantial decrease in the storage modulus of a particle‐reinforced elastomer with an increase in the amplitude of mechanical oscillations). The influence of temperature, concentration of filler and amplitude and frequency of strains is analyzed on the mechanical response of filled rubbery polymers. Constitutive equations are derived using the concept of two interpenetrating networks: one comprises semiflexible polymeric chains connected to temporary junctions, whereas the other is formed by filler clusters. Adjustable parameters are found by fitting experimental data for natural rubber, bromobutyl rubber and styrene‐butadiene rubber reinforced by carbon black and polymeric particles. The critical concentration of particles is determined that characterizes transition from an ensemble of disjoint clusters to the network of filler. The volume fraction of filler corresponding to this transition is found to be close to the theoretical predictions based on the percolation theory, as well as to experimental data for isolator—conductor transition.
Effect of graft ratio on the dynamic moduli of acrylonitrile‐butadiene‐styrene copolymer
Authors: Ahn Kyung Hyun , Ha Doo Han , Lee Byung Do , Doh Jae Goo , Choi Jin Hwan 
Published: April 2004

AbstractThe effect of graft ratio on the dynamic moduli of ABS (Acrylonitrile‐Butadiene‐Styrene Copolymer) has been investigated. Unlike previous papers, the storage modulus at low frequency shows both minimum and maximum as graft ratio increases, and the rubber particles do not agglomerate significantly at high graft ratios. The dependence of the rheological properties on the graft ratio is quite complicated. This arises from its morphological change that leads to different interactions between the rubbery phase and the matrix phase. The minimum has been reported previously, and is explained in terms of rubber dispersion. However, the maximum at high graft ratio has never been reported. The origin of maximum seems to come from the repulsive forces between the long graft chains of neighboring rubber particles. Analogy between our experimental results and simulation results has been discussed to deduce the mechanism of maximum storage modulus at high graft ratio.
Flow through a convergence. Part 2: Mixing of high viscosity ratio polymer blends
Authors: Meller Mika , Luciani André , Mårnson Jan‐Ander. E. 
Published: April 2004

AbstractDispersive mixing of high viscosity ratio blends was studied in a converging flow using a capillary rheometer equipped with dies having different entry profiles. Three inhomogeneous bimodal polyolefin blends, with stress‐dependent viscosity ratios ranging from 8 to 450, were used in this work. Such magnitudes of viscosity ratio indicate that the dispersed droplets can be mixed only in an elongational flow field. The mixing efficiency was found to be dependent on both the profile of the convergence and flow rate. At the lowest flow rates, the dispersive mixing efficiency was very low, but it increased with an increasing flow rate until a profile‐dependent maximum. This maximum mixing efficiency was observed prior to fracture of the matrix material, after which the efficiency decreased. Stress and deformation fields within different profiles were estimated by numerical simulation using the K‐BKZ equation, and the results were used to interpret experimental results. The dispersive mixing efficiency was found to be proportional to the maximum elongational stress within the converging section, and to the length of the region where the critical conditions for elastic fracture of droplet material were met. It is shown that the dispersive mixing mechanism in high viscosity ratio blends is mainly dictated by elastic fracture of the droplet, and hence is applicable over a wide range of polymer blending processes.
The flow of polymer melts through the clearance over a barrier flight in extruders
Authors: Hong Bo Ki , Kim Hyun Seog , Chung Chan I. 
Published: April 2004

AbstractThe flow of polymer melts through the clearance over a barrier flight in extruders involves high, rapidly changing shear rates. Polymer melts, being viscoelastic, are expected to exhibit a high elasticity when they flow through the clearance, so the flow through the clearance may not be predictable or stable. The flow through the clearance over a barrier flight was investigated using a shear refining (SR) module connected to an extruder. Three polymers with different melt properties were tested: branched low density polyethylene (BLDPE), high‐density polyethylene (HDPE), and polystyrene (PS). The measured drag flow rate through the clearance was found to be equal to the prediction for a purely viscous fluid, which gives a linear velocity profile in the clearance. At the threshold rotor speed of the SR module whereupon the predicted drag flow rate through the clearance is the same as the extruder output rate, the melt pressures at the inlet and the outlet of the SR module were nearly equal and stable. Below the threshold rotor speed, the inlet pressure was higher than the outlet pressure. Above the threshold rotor speed, the inlet pressure was nearly zero and the outlet pressure fluctuated. The magnitude of the pressure fluctuation increased with increasing rotor speed and decreased with increasing melt temperature. HDPE, which had a higher melt elasticity, showed more pressure fluctuation than BLDPE and PS. The pressure fluctuation probably results from the flow instability through the clearance caused by the melt elasticity.
Reactive extrusion of recycled bottle waste material
Authors: Hettema R. , Pasman J. , Janssen L. P. B. M. 
Published: April 2004

AbstractThe objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co‐rotating twin‐screw extruder and a Buss co‐Kneader single‐screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%, with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n‐butylmethacrylate (BMA), t‐butylamino ethylmethacrylate (TBAEMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half‐lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration.
Ejection force modeling for stereolithography injection molding tools
Authors: Pham Giang T. , Colton Jonathan S. 
Published: April 2004

AbstractStereolithography (SL) molds have proven effective for short injection molding runs. However, they are susceptible to failure because of their poor mechanical properties, especially at elevated temperatures. A majority of these failures occur during the ejection stage, as a result of excessive ejection forces. An ejection force model was developed by combining the effects of thermal shrinkage and mechanical interlocking due to stair‐steps on the surface of SL tools. Finite element analyses were performed to validate and complement the ejection force equation. Measured forces and temperatures from injection molding experiments indicated that the ejection force model is valid for SL molds of both circular and non‐circular shape. The average differences between measured and predicted ejection forces were approximately 10%.
A comparison of induction time and crystallization rate for syndiotactic polystyrene
Authors: Sudduth Richard D. , Kyarala Pavan , Sheng Qin 
Published: April 2004

AbstractOne objective of this study was to measure the crystallization parameters for syndiotactic polystyrene (MW = 244,000) to support a computer simulation of this material in an injection molding application. A second objective was to introduce a new crystallization rate equation that adequately predicts crystallization rates over a broader temperature range than the Hoffman‐Lauritzen equation. A third objective was to establish a new clearly defined method for determining the true induction time of a semicrystalline polymer as a function of temperature. The new crystallization rate equation introduced in this study has been formulated to give appropriate crystallization rate constants for all the temperatures currently usable with the Hoffman‐Lauritzen equation. In addition, this new equation also predicts appropriate crystallization rate constants outside the range of the Hoffman‐Lauritzen equation from temperatures significantly below the glass transition temperature, Tg, to temperatures significantly above the melting point, Tm. Interestingly, the isolation of the true isothermal induction times from apparent induction times in this study nicely mirrored the isothermal crystallization rates at each specific temperature. Both the true induction time and the crystallization rate curves were found to be similarly unsymmetrical as a function of temperature. Also, the temperature at the minimum induction time and the temperature at the peak crystallization rate determined from nonisothermal crystallization rate measurements were found to be nearly identical. Consequently, the results from this study strongly suggest that there is a significant and potentially very useful relationship between induction time analysis and crystallization rate kinetics.
The mass transport of ethyl acetate in syndiotactic polystyrene
Authors: Chiang I. J. , Chau C. C. , Lee Sanboh 
Published: April 2004

AbstractThe mass transport of ethyl acetate in syndiotactic polystyrene (sPS) has been studied. Two groups of specimens were prepared using press‐cooling and water‐quenching. The press‐cooled and water‐quenched specimens were identified as crystalline and amorphous structures, respectively, by X‐ray diffraction. The weight gain of ethyl acetate in sPS was monitored at temperatures from 50°C to 70°C. The crystallinity of a press‐cooled specimen prior to solvent sorption was greater than that after solvent sorption. However, solvent‐induced crystallization was observed in the water‐quenched specimen. The transport of ethyl acetate in both press‐cooled and water‐quenched specimens was anomalous and consisted of two stages. Each stage of the sorption curves was well fitted with Harmon's model. Both the diffusion coefficient and velocity component satisfy Arrhenius behavior. For the press‐cooled specimen, fluxes of Case I and Case II transport flow from the outer surface to the center, but for the water‐quenched specimen, the solvent is squeezed out. Pure Case II transport did not appear in the water‐quenched specimen.
Gross melt fracture elimination: The role of surface energy of boron nitride powders
Authors: Seth Manish , Hatzikiriakos Savvas G. , Clere Thomas M. 
Published: April 2004

AbstractBoron nitride (BN) is an effective processing aid for the extrusion of polyethylenes. It postpones the onset of gross melt fracture to significantly high shear rates not previously attained with conventional fluoropolymers. However, BN particles containing relatively high amounts of boron oxide (B2O3) do not perform well as processing aids. A reliable procedure has been developed for measurement of surface energy of powders using the capillary rise technique through the use of Washburn's equation. It is based on finding the contact angle from liquid penetration experiments with polar and non‐polar liquids. Both the dispersive and non‐dispersive components of surface energy are determined. With this technique, the surface energy of a number of different powders has been assessed. These results of the surface energy of BN powders have been found to correlate well with the critical shear rate for the onset of melt fracture, indicating the important role that surface energy plays in gross melt fracture elimination.
Effects of flow on polymeric reaction
Authors: Yang I‐Kuan , Lin Jyh Dar 
Published: April 2004

AbstractThe esterification of the maleic anhydride residue (MA) in a hydrogenated styrene‐butadiene‐styrene block copolymer (SEBS‐g‐MA) with a polycaprolactone diol (PCL) was carried out in a melt. Experiments in static melts found that the reaction had an induction period followed by a rapid consumption of the reactants. The gel content accumulation was found synchronous to the consumption of the acidic groups during the reaction process, indicating that the crosslinking between the copolymer molecules prevailed over the esterification of the pendant acid group generated by the ring opening of the MA residue. The reaction rate was strongly affected by both the intensity and the pattern of flow. The reaction rate increased as the flow intensity increased. A back‐and‐forth shear was more effective in promoting the reaction rate than a one‐way shear. This reaction rate enhancement is due to the increase in the interfacial area and concentration gradient caused by the breakup of the dispersed droplets in the melt.
Modeling of a cokneader for the manufacturing of composite materials having absorbent properties at ultra‐high‐frequency waves. Part 1: Modeling of flow from residence time distribution investigations
Authors: Hoppe S. , Detrez C. , Pla F. 
Published: April 2004

AbstractThe purpose of this study is to gain better understanding of flow patterns and mixing conditions in a particular single‐screw extruder: the Buss Cokneader. To this end, the residence time distribution (RTD) of the polymer was investigated experimentally for different combinations of the operating variables (i.e. feed rate, screw rotation speed). The measurement of RTD used a standard stimulus‐response technique. Two kinds of tracer were used: free anthracene and anthracene grafted on the polymer. It was shown that only the second could characterize the actual flow of the polymer in the extruder. It does not perturb the flow and has the same rheological behavior as the studied fluid. Thanks to the RTD data, a model of the extruder based on the combination of ideal reactors, such as continuous stirred tank reactors or plug flow reactors, was finally set up. The establishment of relationships between model parameters and extrusion conditions allowed the prediction of RTD with good agreement.
Improved cathodic disbondment performance of polyethylene blends
Authors: Roy Debashis , Simon George P. , Forsyth Maria 
Published: April 2004

AbstractCathodic disbondment (CD) performance of a range of modified polyethylenes (PE) compression molded on to steel plates at 320°C is reported. Adhesion strength was measured by the 90° peel test and good dry adhesion strength was obtained for all modified polyethylene materials and blends, as well as for the neat polymer. It is shown that dry bond strength does not correlate with CD performance. Initial results of wet peel tests of samples in various concentrations of NaOH are presented where it is observed that for samples with improved wet adhesion strength, CD performance was also improved. Surface polarity was determined from contact angle measurements, and it is shown that increased surface polarity of the coating was not the only determinant for improved CD performance. Inorganic fillers such as talc were also found to improve CD performance by changing the bulk properties, with little measurable change in polarity. Some mechanistic aspects of CD performance are also discussed.