bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the effect of crystallinity on the elastic properties of semicrystalline polyethylene
Authors: Doyle Michael J. 
Published: April 2004

AbstractThe small strain elastic response of a semicrystalline polyethylene has been simulated with a simple finite element model comprising a composite microstructure of alternating amorphous and crystalline layers arranged in a multi‐layered spherical shell structure. The crystalline lamella is modeled as an isotropic solid having the experimentally determined modulus properties of bulk linear polyethylene and extrapolated to 100% crystallinity. The amorphous layer is modeled as an elastomeric solid with the modulus that of molten linear polyethylene extrapolated to room temperature. Assuming constancy of these phase properties, the finite element calculations of elastic modulus versus crystallinity fit quite well the experimental data of Crist for linear polyethylene above 55% crystallinity. At lower crystallinity the experimental modulus data, which are for copolymers, fall below the model calculations. Two possible causes are discussed: the loss of deformation constraint in lamellae of finite and decreasing width as crystallinity declines, and an expansion of the crystal lattice as a result of the crowding of the comonomer units excluded from the crystal lamella. Either effect would reduce both the modulus and the yield stress as is observed.
Modeling of peroxide initiated controlled degradation of polypropylene in a twin screw extruder
Authors: Berzin F. , Vergnes B. , Dufossé P. , Delamare L. 
Published: April 2004

AbstractIn this work, experimental and theoretical studies of the free‐radical initiated molecular weight degradation of polypropylene in a modular self‐wiping corotating twin screw extruder have been investigated. Our objective was to build a model that would be able to predict the evolution of the average molecular weight along the screws, in relation to the processing conditions and the geometry of the twin screw extruder. Modeling the process involves resolving interactions occurring between the various flow conditions encountered in the extruder, the kinetics of the reaction and the changes in viscosity with changes in molecular weight. We have studied the influence of operating parameters such as the initial peroxide concentration, the feed rate and the screw speed on the degradation reaction. Good agreement was found between theoretical results and experimental values obtained by size exclusion chromatography measurements.
Correlation of thermally stimulated current and blow molding condition in poly(ethylene terephthalate) bottles
Authors: Satoto Rahmat , Hama Takashi , Morikawa Junko , Hashimoto Toshimasa 
Published: April 2004

AbstractThermally stimulated current (TSC) was used to study molecular relaxations in polyethylene terephthalate (PET) bottles. Unstretched PET film, which was used as a model for the bottle preform, exhibited two peaks at 77 and 90°C that correspond to the α and ρ relaxation processes, respectively. The bottles exhibited only the ρ relaxation, which is located within the temperature range for blow molding PET bottles. The α peak is associated with the main glass transition temperature (Tg) and the ρ peak may be associated with a second Tg. The second Tg is attributed to a “constrained state,” which shows dipolar behavior. Heat‐shrinkage behavior was examined at 90°C. The maximum TSC (Im) of the ρ peak decreased with increasing heat set temperature, and with decreasing shrinkage. Bottles blown at 113°C showed a lower Im and shrinkage than those blown at 103°C for equivalent heat set temperatures. The higher blowing temperature allowed a higher stretch speed that produced higher crystallinity bottles with self‐heat generation during rapid deformation. A relationship between the shrinkage mechanism and the dipole relaxation was proposed.
Continuous production of solid polystyrene in back‐mixed and linear‐flow reactors
Authors: Chen Chi‐Chin 
Published: April 2004

AbstractA mathematical model has been developed to predict the steady state performance of a continuous bulk styrene polymerization process with catalytic initiation for solid polystyrene. The polymerization section contains one boiling CSTR, followed by multiple linear‐flow reactors. The devolatilization section consists of two polymer pre‐heaters and two high‐solids flashes. The polymer moment equations were solved simultaneously with the reactor modeling equations. The non‐linear algebraic equations were solved by a Newton‐Raphson iteration technique to give the steady‐state styrene monomer weight fraction in a CSTR. The coupled, non‐linear ordinary differential equations were numerically integrated using a single‐step, 4th‐order Runge‐Kutta technique, followed by a multi‐step Adams‐Moulton technique. The resulting computer simulation model is capable of evaluating how the production rate and product quality are affected by feed composition, temperature, initiator type, initiator concentration, and residence time. Several case studies were given for commercially important crystal‐clear and impact‐resistant resins. A binary initiation system gives a good balance of monomer conversion, polymer molecular weights, and rubber grafting compared to a single initiation system. The styrene dimer/trimer occur in low concentrations but can be substantially reduced with a low temperature initiator. The ideal mean residence time is approximately one minute or less in a shell‐and‐tube devolatilization pre‐heater. Low flash chamber vacuum is more effective than high polystyrene melt temperature to reduce the volatile content of the final product. The water injected to the low volatile melt shows promising improvement in the second‐stage polystyrene devolatilization.
Polyurethane/poly[bis(carboxylatophenoxy)phosphazene] blends and their potential as flame‐retardant materials
Authors: Reed Carey S. , Taylor Jonathan P. , Guigley Kevin S. , Coleman Michael M. , Allcock Harry R. 
Published: April 2004

AbstractA functionalized polyphosphazene, poly[bis(carboxylatophenoxy)‐phosphazene], was blended with a structural polyurethane via reactive mixing of the polymer with diisocyante and diol prepolymers. The thermal stabilites of the resultant foams were analyzed by thermogravimetric analysis (TGA). The char yields at both 400°C and 600°C increased relative to the pure polyurethane upon increasing the amount of polyphosphazene from 5 wt% to 20 wt%. At higher incorporations, the char at 400°C remained the same, but the char at 600°C continued to increase. The combustion behavior of these foams was analyzed both qualitatively, by a horizontal flame test, and quantitatively, by oxygen index (OI) measurements. Both of these tests indicated an increase in flame resistance at loadings of 20 wt% and above.
Optimizing the impact strength of rotationally molded parts
Authors: Liu Shih‐Jung , Lai Cheng‐Chih , Lin Shun‐Tien 
Published: April 2004

AbstractRotational molding of thermoplastics has become an important process in industry. However, the optimization of this technique has been essentially based on a trial‐and‐error process. In this report, an L'16 experimental matrix design based on the Taguchi method was conducted to optimize the impact strength of rotationally molded parts. Oven temperature and oven time were found to be the principal factors affecting the impact property of rotationally molded thermoplastics. Density and melt flow index measurements were also employed to identify the material and structural parameters. The part density increased with increasing total energy transmitted into the molding system. The melt flow index provides an easy indication of the mechanical properties of rotationally molded parts.
Dynamic slip and nonlinear viscoelasticity
Authors: Lan Seon Keat , Giacomin A. Jeffrey , Ding Fan 
Published: April 2004

AbstractSeveral significant problems arise when film is fabricated on a large scale. One of these is the appearance of irregularities on the extrudate surfaces when the polymer melt is extruded at high rates. These irregularities vary in intensity and form and are generally known as sharkskin melt fracture. This phenomenon, which occurs when the wall shear stress exceeds a critical value, is a limiting factor for production rates in many industrial extrusion operations such as film blowing of polyethylene. We used a sliding plate rheometer incorporating a shear stress transducer to study slip in both steady and unsteady flows. By combining a dynamic slip model with a nonlinear viscoelastic constitutive model, we determined the slip model parameters for LLDPE film resin with and without a fluoropolymer sharkskin suppressant. The models give good prediction of our slip data in steady shear but show insufficient gap dependence in exponential shear. Our own film blowing studies demonstrated the efficiency of the sharkskin suppressant; it has more than doubled the throughput in our laboratory setup. The fluoropolymer additive was found to profoundly affect both the steady and dynamic slip parameters. Hence, the sharkskin suppressant alters how the LLDPE remembers its past slipping motions.
Dynamic modeling of a gas pressure control system for a gas‐assisted injection molding process
Authors: Chao Sher‐Meng , Wang Shih‐Ming , Chen Shia‐Chung 
Published: April 2004

AbstractThis study presents the development of dynamic models for gas injection pressure that may be implemented in the design of control systems for gas‐injection units. A nonlinear dynamic model was first derived and then verified by experimental measurements. This was done by using a laboratory‐built, gas‐assisted injection unit. The agreement between the prediction and measurement indicates that the present nonlinear dynamic model adequately predicts the dynamic behavior of gas injection pressure during the process. Although the resulting model is useful for understanding the behavior of the process and the effects of different process variables, its complexity may cause difficulties in a real control application. Therefore, a second‐order model based on the basic characteristics of the nonlinear model was proposed to approximate the gas injection pressure. In order to determine the model parameters, the algorithm of recursive least‐square system identification was employed. A comparison of simulated results of an identified model with experimental data showed that the model accurately predicted the transient behavior of gas injection pressure. Consequently, this low‐order model can be easily implemented into the control system design of a gas‐injection unit.
Effect of compatibilizer on morphology and mechanical properties of TPU/SAN blends
Authors: Jaisankar S. N. , Radhakrishnan Ganga 
Published: April 2004

AbstractMelt blends of thermoplastic polyurethane (TPU) and Poly(styrene‐co‐acrylonitrile), (SAN) of various compositions were prepared using a two‐roll mill. Two blends of composition 70:30 and 50:50 TPU/SAN were selected for compatibility studies. The compatibility effect of SMA on these incompatible blends was studied. The morphology and physical properties of blends were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectra (FTIR) and mechanical properties. TPU/SAN/SMA 70:30:5 showed better compatibility than other blend ratios.
Fatigue crack growth in polyethylene: Material dependence. I: Tensile/compressive loading
Authors: Harcup J. P. , Duckett R. A. , Ward I. M. , Capaccio G. 
Published: April 2004

AbstractDynamic fatigue crack growth has been investigated in polyethylenes of various molecular weights and branch concentrations. Square load waveforms were applied to sharply notched samples and the load was adjusted so that for all tests the maximum stress intensity factor was constant and tensile, Kmax, but different experiments featured different values of minimum stress intensity factor Kmin, which was either zero or compressive. The crack growth rate increased as Kmin became more compressive. Subsidiary experiments were made using static loads and these confirmed that, as previously reported, the slow crack growth rate decreased with increasing branch concentration and molecular weight. In all the materials studied, fatigue crack growth rates were significantly greater than those under steady loads. However, materials possessing higher branch concentrations showed a relatively greater increase in crack growth rates. For negative values of Kmin, increasing branch concentration has a deleterious effect on the fatigue crack resistance. In the fatigue loading experiments studied here it was found that for Kmin/Kmax ≈ −1, the ranking of materials in terms of crack growth resistance was reversed with respect to that seen under steady loads.
Nondestructive and in‐situ monitoring of mechanical property buildup in epoxy adhesives for civil applications by propagation of ultrasonic waves
Authors: Frigione M. , Maffezzoli A. , Acierno D. , Luprano V. A. M. , Montagna G. 
Published: April 2004

AbstractUltrasonic inspection for nondestructive analysis is already widely applied to the control of structural integrity of concrete, presenting among other advantages the reliability, the simplicity and low costs. Although ultrasonic testing are mainly used for nondestructive evaluation of defects, it may be also applied to follow the changes of mechanical properties occurring in a material which evolves in time, such as during the crosslinking of thermosetting resins. These time dependent properties may be measured by longitudinal and shear ultrasonic velocity operating by pulse‐echo and/or through‐transmission methods. In this work, ultrasonic wave propagation has been applied to the monitoring of the progress of the curing reaction of an epoxy adhesive for civil applications. The data have been collected in isothermal conditions on the neat resin, as well as in a coupled system concrete‐resin‐concrete. The measurements of longitudinal and shear velocity have been used for the calculation of Young and shear moduli. The change of velocity during cure must be considered a powerful tool for the measurement of the progress of ambient temperature cure reactions like in the case of adhesives for civil applications.
Some aspects of a plastics pulverization technology by extrusion
Authors: Ivanov George K. 
Published: April 2004

AbstractThis study presents results, observations and new developments on the pulverization of low density polyethylene (LDPE) by a nontraditional technology. A twin screw conical counter‐rotating extruder, a mixer head with roller blades and a single screw extruder attached to a C.W. Brabender PL2000 Plasti‐Corder were utilized as pulverization apparatuses. The pulverization phenomenon was studied over a wide range of shear rates and at resin processing temperatures below and above the Vicat softening point, i.e., at solid and soft (visco‐elastic/rubbery‐like) state of the material. A hypothesis about the pulverization mechanism of LDPE at a temperature between melting/crystallization temperature and Vicat softening point is presented.
Dynamical modeling of chaos single‐screw extruder and its three‐dimensional numerical analysis
Authors: Hwang W. R. , Kwon T. H. 
Published: April 2004

AbstractThe Chaos Screw (CS) nonlinear dynamical model is proposed to describe the development of chaos in a single‐screw extrusion process and the model is verified by three‐dimensional numerical simulations. The only‐barrier channel is the unperturbed Hamiltonian system, which consists of two homoclinic orbits and nested elliptic tori of nonlinear oscillation in periodic (extended) state space. A periodically inserted no‐barrier zone represents a perturbation. For small perturbations, homoclinic tangle leads to the Cantor set near the homoclinic fixed point and elliptic rotations are changed into the resonance bands or KAM tori, depending on the commensurability of frequency ratio of the corresponding orbits. A finite element method of multivariant Q̧1+PO elements is applied to solve the velocity fields and a 4th order Runge‐Kutta method is used for the particle tracing. The resulting Poincaré section verifies the proposed dynamical model, showing the resonance band corresponding to rotation number 1/3 under small perturbations. As the strength of perturbation increases, the Poincaré sections indicate wider stochastic regions in which random particle motions take place.
Steady bi‐directional drag flow of non‐newtonian liquids in shallow channels
Authors: Lindt J. Thomas 
Published: April 2004

AbstractThis paper reexamines the analytical framework for the steady, fully developed two‐dimensional flow in shallow channels, typical of screw extruders, and provides comprehensive solution sets for the Carreau‐Yasuda and the Ostwald‐deWaele model fluids. An application example for polymethylmethacrylate (PMMA) is included to compare the relative merits of the two models under specific extrusion conditions. The Ostwald‐deWaele model, standard in engineering practice, can produce gross misrepresentations of the flow in extruder channels. Particularly, when dealing with highly shear‐sensitive polymers, n < 0.3, or polymers with extended Newtonian plateau, ∧ ∼ 1, the Carreau‐Yasuda model becomes preferable. The inclusion of the Carreau model does not necessarily add to the complexity of the analysis.
Three‐dimensional simulation of microchip encapsulation process
Authors: Han Ruihua , Shi Linhuo , Gupta Mahesh 
Published: April 2004

AbstractA finite element simulation of moving boundaries in a three‐dimensional inertiafree, incompressible flow is presented. A control volume scheme with a fixed finite element mesh is employed to predict fluid front advancement. Fluid front advancement and pressure variation in a flow domain similar to the mold cavity used for microchip encapsulation are predicted. The predicted fluid front advancement and pressure variation are in good agreement with the corresponding experimental results. As the difference in the thicknesses of mold cavities above and below the microchip is changed, the weld line location and pressure variation during mold filling are found to change significantly.
Determination of the fracture toughness of polybutylene terephthalate (PBT) film by the essential work method: Effect of specimen size and geometry
Authors: Hashemi S. 
Published: April 2004

AbstractThe fracture behavior of PBT films of thicknesses 0.125, 0.175, 0.275, 0.375 and 0.5 mm was investigated according to Essential Work of Fracture (EWF) method. Single edge and double edge notched specimens of varying ligament lengths were tested in tension producing load‐displacement traces that were typical of ductile failure. A linear relationship was obtained between the total specific work of fracture (Wf) and ligament length (L). This linearity was maintained as ligament length exceeded the plastic zone size or one third of sample width. It was found that while the specific essential work of fracture (We) was independent of thickness, the specific non‐essential work of fracture (βWp) decreased with increasing thickness. It was found also, that work of fracture parameters were independent of the specimen width for the range of thicknesses used in the present study. Nevertheless, for a sample width of 20 mm, a lower weand a higher βwpvalue was obtained. Good agreement was found between values of Weobtained from SENT and those obtained from DENT specimens; the value of βwpwas consistently higher for SENT specimens.
Morphology change in polytetrafluoroethylene (PTFE), porous membrane caused by heat treatment
Authors: Kitamura Taketo , Okabe Shohei , Tanigaki Masataka , Kurumada Ken‐Ichi , Ohshima Masahiro , Kanazawa Shin‐Ichi 
Published: April 2004

AbstractThe morphological changes and improvement of membrane properties caused by heat treatment were investigated for polytetrafluoroethylene (PTFE) porous membranes prepared from a fine powder by extrusion, rolling and stretching. The properties of the membrane were significantly changed by heat treatment at temperatures higher than 320°C. Shrinkage diminished and the mechanical strength increased due to the partial melting of PTFE. The increase in mechanical strength was caused by suppression of new fibril formation as a result of the loss of folded ribbon‐like crystalline structures that facilitated fibril structures to be pulled out of the original PTFE particle. The decrease in shrinkage was caused by the transformation of fibrils, formed as a collection of ribbon‐like structures, into a massive fibrous structure, which inhibited the reformation of particles. The most important change of the porous structure caused by the heat treatment was the union of nodes in the direction of stretching resulting in a PTFE porous membrane with larger spatial periodicity. A heat treatment above melting temperature of PTFE was the most effective. However, it was necessary to control the temperature and time in order to restrict the coarseness of the porous structure of the membrane.
Studies on the phase transition and thermal stability of Xydar and Zenite series liquid crystalline polymers
Authors: Chung Tai‐Shung , Jin Xing 
Published: April 2004

AbstractFour commercially available main‐chain LCPs, Xydar and Zenite series, are characterized by FTIR spectroscopy, DSC, polarized light microscopy (PLM), TGA, TGAFTIR, and elemental analysis. The FTIR spectrum of Zenite 8000B is found to be more similar to that of Vectra A950 than those of the other three LCPs. Xydar SRT900 and 1000 have almost the same FTIR spectra. Zenite LCPs have broader crystal‐mesophase transition (TCM) and less clear liquid crystalline textures at TCM than those of Xydar LCPs. Xydar SRT1000 and Zenite 8000B have lower TCM than Xydar SRT900 and Zenite 6000, respectively. For all the four LCPs, the glass transitions can not be easily observed by DSC without the aid of annealing and the isotropic phase does not appear before thermal degradation. Xydar SRT1000 and Zenite 8000B have lower thermal stabilities as well as lower TCMS than Xydar SRT900 and Zenite 6000, respectively. It is interesting to find that Ea (Apparent activation energy of thermal degradation) curv of Xydar SRT900 and SRT1000 have the similar shapes as those of Zenite 6000 and 8000B, respectively. For the first time, we have found that there is a minor degradation maximum for Zenite 8000 at about 2.5% weight loss in N2. For all the four LCPs, the Ea values in an air atmosphere begin to decrease at a temperature close to the deflection points on the first derivative curves. The first stage of the thermal degradation in an air atmosphere has similar mechanisms as that in N2.
Double bubble tubular film extrusion of polybutylene terephthalate–polyethylene terephthalate blends
Authors: Song Kwangjin , White James L. 
Published: April 2004

AbstractA technology has been developed to produce biaxially oriented films of blends of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) using double bubble tubular film extrusion. The mechanical instabilities and the mechanisms associated with their sources of occurrence are described. Bubble stability varies substantially with deformation and composition. The films have been structurally characterized with wide angle X‐ray diffraction and optical techniques. The individual phases in the blends oriented differently. We have proposed a model of crystalline morphology in biaxially oriented PBT/PET blend films. The structure of the film is related to processing conditions.