bluuebunny/crossref_metadata_2025_split huggingface dataset:
The reactive extrusion of polyethylene/polypropylene blends
Authors: Cheung P. , Suwanda D. , Balke S. T. 
Published: May 2005

AbstractThe objective of this work was to investigate the compatibilization of a blend of linear low density polyethylene with polypropylene by Injection of a free radical initiator during extrusion. The reactive extrusion process utilized a single screw extruder equipped with two static mixers. The initiator was injected into the extruder feedport and temperature programming used to cause most reaction to occur within the static mixers. Although elongation at yield was increased by 37 percent, impact strength and yield strength decreased by 17 and 54 percent, respectively. Scanning electron microscopy showed that the maximum size of the dispersed phase decreased from a maximum size of four microns to less than two microns upon addition of initiator. Size exclusion chromatography (SEC), temperature rising elution chromatography (TREF), and differential scanning calorimetry showed that the polypropylene in the blend was degrading while the polyethylene was increasing in molecular size. The combination of SEC and TREF was particularly useful in elucidating this result. No copolymer was discerned by any of the methods used.
Deep drawing self‐reinforced thermoplastic sheet
Authors: Pede Sandro Di , Woodhams Raymond T. 
Published: May 2005

AbstractThe conventional sheet metal forming technique known as Deep Drawing was used to investigate the formability of self‐reinforced thermoplastic sheets. The materials studied included uniaxially roll‐drawn oriented polypropylene (OPP), cross‐rolled biaxially oriented polypropylene (BOPP), and cross‐ply laminated OPP (LOPP). OPP exhibits poor room temperature formability as determined by its Limiting Drawing Ratio (LDR). Its formability is improved at elevated temperatures, but samples suffer from non‐uniform material flow, temperature sensitivity during forming, and a loss of mechanical properties due to the relaxation of orientation caused by the need for forming temperatures above the normal melting point. Although BOPP attains only moderate Improvements in mechanical properties compared to the machine direction of OPP, it exhibits much better room temperature formability. This difference in drawability between uniaxial and biaxial orientation states is a consequence of the difference in planar anisotropy between these two materials. LOPP has the potential of producing a material with superior performance compared to BOPP while still possessing the desirable formability of BOPP. The formed parts, however, undergo cracking in the outer ply parallel to the orientation direction as a consequence of the OPP small elongation to break in the transverse direction. In addition to forming problems, ordered polypropylene exhibits large shrinkage stresses at elevated temperatures. This may preclude its use in applications requiring a high level of dimensional stability. Classical plasticity theory for metals was appropriately modified to model the radial drawing stress for planar isotropic thermoplastic sheet materials.
Constrained optimal batch polymerization reactor control
Authors: Secchi Argimiro R. , Lima Enrique Luis , Pinto José Carlos 
Published: May 2005

AbstractThe theory of optimal control is used to analyze the performance of a batch PMMA (poly(methylmethacrylate)) polymerization reactor. Optimal dynamic profiles of temperature, initiator feed rate, and initiator concentration in the reactor are generated in order for specified conversion of monomer, number molecular weight, and polydispersity of the final product to be obtained. Based on tae physical limitations of the system, some restrictions are imposed to the control variable variations. The application of Pontryagin's Minimum Principle leads to a mixed initial/final value problem, which is solved by discretizing the control law in the state‐space, with the usage of a first order holder. A gradient method is used to minimize the Hamiltonian. The simulation results show that the gel‐effect equation and restrictions imposed on the system are of primary importance to the analysis of the reactor performance.
Biaxially oriented polypropylene blown films. I: Morphological analysis of orientation in the machine direction
Authors: Savolainen Antti 
Published: May 2005

AbstractIn biaxial blown film technology of isotactic polypropylene, PP, the film tube drawn over the mandrel contains considerable morphological disorder. This disorder changes on further treatment to greater order i.e. the para‐crystallinity and the metastable crystal forms diminish as the monoclinic crystal form increases. The morphology change in PP was stimulated by further treatment of the drawn film tube over a mandrel corresponding to conditions of biaxial bubble forming. Analyses were by SEM, Wide‐angle X‐ray diffraction (reflection), DSC, and IR Dichroic measurements. A condenser quality PP, Mw/Mn = 7 and MFI = 3.7, shows a tensile yield at 110°C of 11.4 MPa. A tensile stress of 17.7 MPa was obtained at a blow up ratio of 7; the morphology of PP corresponds to deforming spherulites. The fraction of “perfectly” oriented molecules is 0.53.
Yielding, anisotropy, and deformation processing of polymers
Authors: Batterman S. D. , Bassani J. L. 
Published: May 2005

AbstractConstitutive equations that characterize the deformation induced anisotropy in polymers at large strains are developed for both flow and deformation (nonlinear elastic) theories of plasticity. These equations are used first to predict the evolution of yield surfaces for anisotropies that develop under simple plane strain deformations. Then, non‐uniform deformations are considered including neck propagation and extrusion. Finite element solutions are based on the flow theory version of the constitutive models. Neck propagation loads and draw ratios are found to be sensitive to the degree of anisotropy and pressure sensitivity, while extrusion forces are less so. The results are compared to solutions for an isotropic material with the same effective stress‐strain behavior.
An experimental and anaiytical investigation of the large strain compressive and tensile response of glassy polymers
Authors: Boyce M. C. , Arruda E. M. 
Published: May 2005

AbstractIn this investigation, the plastic flow of polycarbonate (PC) was examined by obtaining true stress‐strain data over a range of strain rates at room temperature through homogeneous, uniaxial, constant strain rate compression testing to strains as high as 125 percent. Uniaxial compressive loading conditions give rise to a planar molecular orientation process which results in the observed strain hardening in compression. Uniaxial tensile tests on PC were also conducted. The necked region of the tensile specimen is being cold drawn resulting in a uniaxial state of orientation. Therefore, the observed macroscopic strain hardening in uniaxial tension distinctly differs from that obtained In uniaxial compression, giving different stress‐strain curves. The major differences experimentally obtained between the large strain response in compression and tension indicate a need for an orientation‐based model of the strain hardening process. The experimental program also acts to uncouple the effects of strain softening and strain rate providing more accurate data for future modeling of the true strain softening process. A constitutive law which directly relates the strain hardening response to the state of molecular network stretch in the polymer is used to model and analyze the experiments. The model is found to simulate the observed rate dependent yield and post yield strain softening and hardening of the compressive data over the entire range of strain rates very well. The model is then utilized in a finite element analysis of the tensile tests on PC. Numerical results compared favorably with the experimental data including: load vs, contraction curves, natural draw ratio, and the axial stress‐strain response of the cold drawing region.
Effect of damage on fatigue crack propagation in polystyrene
Authors: Chudnovsky A. , Huang W.‐L. , Kunin B. 
Published: May 2005

AbstractIn this paper we examine a conventional approach to correlate the fatigue crack growth rate with fracture mechanics parameters such as stress intensity factor or elastic energy release rate. To simulate a complex loading history we grow a fatigue crack in a vicinity of a hole in a single edge notched specimen under tension‐tension. It is found that the correlation between the crack speed and stress intensity factor, etc. may exist only for limited experimental conditions. In general, fatigue crack growth is inseparable from the evolution of the damage zone preceding the crack, and damage evolution parameters should enter constitutive equations of fatigue crack growth. The essential role of the damage zone in determining the crack trajectory and speed is demonstrated.
Three‐dimensional finite element simulation of thermoforming
Authors: Nied H. F. , Taylor C. A. , Delorenzi H. G. 
Published: May 2005

AbstractThe development of a finite element program specifically designed to simulate thermoforming in complex three‐dimensional geometries is described. The large strain finite element model developed for simulating thermoforming processes is based on a total Lagrangian formulation which results in a nonlinear system of equations that must be solved iteratively. The nonlinear material behavior and contact between the polymer and mold surf aces ieads to additional complications in the numerical solution of the thermoforming simulation problem. In an effort to verify the accuracy of the finite element model developed in this study, analyses are compared with measurements obtained from three‐dimensional three‐formed parts.
A numerical study of bubble growth during low pressure structural foam molding process
Authors: Arefmanesh A. , Advani S. G. , Michaelides E. E. 
Published: May 2005

AbstractThe bubble size distribution created by the expanding foam plays a key role in controlling the load‐bearing and other mechanical properties of the manufactured structural foam part. A numerical method to study the bubble growth and predict the bubble size distribution in polymeric foams is presented. On the microscopic scale, a cell model has been used. A cell is a system composed of a hypothetical spherical gas bubble and an envelope of polymer with constant mass surrounding the bubble. On the macroscopic scale, the foam has been modeled as a compressible medium consisting of a number of cells growing in close proximity to each other. The coupled system of the bubble growth equations for a cell and the field equations for the polymeric fluid are solved numerically to predict the spatial bubble size distribution and the flow front movement during the expansion process. The influence of different dimensionless parameters on the growth of spatially distributed bubbles and on the relative reduction in the transient bulk foam density, under isothermal condition; has been predicted. The existence of an axial pressure gradient in the mold due to the spatial variation of bubble growth is demonstrated through numerical experiments.
Flow induced polymer‐filler interactions: Bound polymer properties and bound polymer‐free polymer phase separation and subsequent phase inversion during mixing
Authors: Akay G. 
Published: May 2005

AbstractThe irreversible absorption of macromolecules on to solid filler particles during mixing in the melt is investigated. The molecular weight and concentration dependence of the absorbed layer thickness are evaluated and the chemical and morphological nature of the irreversibly absorbed polymer (bound polymer) are determined. It is found that the thickness of the bound polymer is not only dependent on the filler concentration but also dependent on polymer molecular weight. Bound polymer in high density polyethylene/colloidal silica systems is more amorphous and contains higher concentration of oxidation products (which are induced by a mechanochemical reaction during mixing) when compared with free polymer. As a result of bound polymer formation, flow induced crystallization and polymer entrapment during mixing, a phase separation between bound polymer and free polymer takes place which eventually leads to a liquid to solid phase inversion when the phase volume of the solids exceed a critical value under isothermal conditions. If the mixing is continued after phase inversion, the particle size of the newly formed powder is reduced and particle size distribution, is narrowed. This process of phase inversion and subsequent size reductions are termed as crumbling which can take place at filler concentrations well below the expected maximum packing fraction of solids, if the filler particle size is small and/or the molecular weight of the polymer is high. Crumbling phenomena are utilized in the agglomeration of fine powders and microencapsulation of solids and/or liquids.
Numerical and experimental studies of the flow in the nip region of a partially intermeshing co‐rotating twin‐screw extruder
Authors: Sastrohartono T. , Esseghir M. , Kwon T. H. , Sernas V. 
Published: May 2005

AbstractThe flow pattern within a partially intermeshing co‐rotating twin‐screw extruder is three dimensional and extremely complex. In order to simplify the problem, a slice perpendicular to the axis of the twin‐screw extruder has been considered for flow analysis as a two‐dimensional or a quasi‐three‐dimensional problem. The flow in this slice may be considered to consist of a nip region (located between the two screws) and a translation region in which the movement of the material is very similar to the one found in single‐screw extruders. The flow in these two regions have been studied separately. This paper presents the numerical and experimental results of the nip region study. The flow division in the nip region has been quantified and results are presented in terms of a flow division ratio Xf. The flow field patterns have also been obtained. Newtonian as well as non‐Newtonian behavior has been investigated. The influences of such factors as (i) the geometry (the radius of the barrel, radius of the screw, distance between the two screws), (ii) the material properties (the power‐law index for shear rate dependent viscosity), and (iii) processing conditions (the screw speed), have also been studied.
Mechanical property and residual stress development during cure of a graphite/BMI composite
Authors: White S. R. , Hahn H. T. 
Published: May 2005

AbstractResidual stresses in composites are developed during processing due to chemical shrinkage of the resin and the thermal mismatch between the constituent materials. How these residual stresses develop during cure is not fully understood. Furthermore, to model their development during cure the effect of cure on composite mechanical properties must be understood. This study addresses such concerns. Warpage of [04/904];T cross‐ply specimens was measured to monitor residual stress build‐up. Fiber‐dominated properties were found to increase moderately with cure extent. Matrix‐dominated properties increased significantly and were highly dependent on degree of cure. The curvature development was found to be elastic and could be predicted by laminated plate theory while neglecting chemical shrinkage. Thermal strains were found to remain essentially constant with cure time.
Scale‐up of counter‐rotating closely intermeshing twin screw extruders without and with reactions
Authors: Ganzeveld K. J. , Janssen L. P. B. M. 
Published: May 2005

AbstractMany scale‐up rules and theories have been presented in the area of extrusion. Until now all the theories concerned the single screw extruder. As the use of counter‐rotating twin screw extruders is increasing, it becomes important to propose scale‐up rules for this kind of extruder. Therefore a basic analysis of scale‐up in a twin screw extruder has been developed. It can be concluded that important factors scaling up a twin screw extruder are the fully filled length and the leakage flows of the extruder. So hydrodynamic similarity has to be assured in the scale‐up of most processes. However no serious constraints are put on the throughput of the extruder by this consideration. When the extruder is scaled up on the basis of thermal similarity the Brinkmann number is of importance. At low Brinkmann numbers the throughput is unfavorably affected by scale‐up. If the Brinkmann number is high the throughput is proportional to the diameter cubed. If the extruder is used as a chemical reactor for polymerization, an increasing area of research, the scale‐up rules are dependent on the Damköhler IV number. For low Damköhler IV numbers no consistent scale rules are found. However if the Damköhler IV number is high, useful rules for the scale‐up can be derived.
Extrudate swell and drawdown effects on extruded profile dimensions and shape
Authors: Huneault Michel A. , Lafleur Pierre G. , Carreau Pierre J. 
Published: May 2005

AbstractPlastic profile die design is a complex task because of cross section area and shape changes occurring after die exit. Dimensions of the profile are increased by the extrudate swell phenomenon and decreased by drawdown and shrinkage. An experimental study on the effect of processing conditions on extrudate swell and on the shape of a rectangular profile was done for rigid poly(vinyl chloride), PVC, and high density polyethylene, HDPE, resins. Extrudate swell was found to be a strong decreasing function of residence time in the die and also, for short dies, of entrance geometry. For PVC, equilibrium swell increased with melt temperature. The differences in swelling for the two polymers are explained with the help of creep/recovery data obtained on a stress rheometer. Drawdown, die land length, and melt temperature were shown to have an important effect on the shape of a rectangular profile. Decreasing the die land and increasing the melt temperature had the effect of increasing preferably the thickness while drawdown, by inhibiting the swelling, decreased the thickness.
371°C (700°F) properties of celion 6000/N‐phenylnadimide modified pmr polyimide composites
Authors: Pater Ruth H. 
Published: May 2005

AbstractThe 371°C (700°F) properties of Celion 6000/N‐phenylnadimide modified PMR‐15 polyimide composites were investigated to determine the feasibility of using these materials at a 371°C (700°F) service temperature. The processing characteristics and physical and mechanical properties of the composite systems are presented. The results of the 371°C thermooxidative stability study suggest that the composite materials can be considered for short‐term (at least 100 hours) application at 371°C.
Phase morphology of injection‐molded blends of nylon‐6 and polyethylene and comparison with compression molding
Authors: Ghiam Farid , White James L. 
Published: May 2005

AbstractAn experimental study is presented of the development of phase morphology in injection and compression molding of 80/20 and 60/40 nylon‐6/polyethylene blends and its evolution during annealing. The phase morphology of the compression‐molded part is isotropic, while that of both screw and ram injection‐molded parts is both heterogeneous and anisotropic through the cross section. In the injection‐molded parts, the morphology exhibits its greatest level of isotropy in the core and becomes increasingly anisotropic approaching the mold wall (through the thinnest cross section); i.e., the 2 direction. There is an intermediate position of maximum anisotropy. Sections made in various directions indicate that the dispersed phase forms platelets oriented in the plane of the machine and width directions. The position of maximum anisotropy seems to represent a frozen layer thickness that increases with decreasing mold temperature and with decreasing injection rate into the mold. Annealing studies show coalescence in both compression‐ and injection‐molded bars. The greatest coalescence occurs in the injection‐molded parts near the positions of greatest anisotropy of morphology. This suggests that coalescence is associated with collisions between dispersed phase globules as their sphericity increases.
Characteristics of binary and ternary blends of poly (p‐phenylene sulfide) with poly(bis phenol A) sulfone and polyetherimide
Authors: Akhtar Sania , White James L. 
Published: May 2005

AbstractAn experimental study of the phase morphology and mechanical properties of binary blends of poly(p‐phenylene sulfide) (PPS) with both polyetherimide (PEI) and poly(bis phenol A) sulfone (PSF) is described. We also study the ternary system PPS‐PEI‐PSF. Differential scanning calirometry indicated the blends are immiscible; these findings were confirmed by scanning electron microscopy. Both PEI and PSF were found capable of improving the impact strength and elongation‐to‐break characteristics of PPS in binary blends and ternary systems.
A unified simulation of the filling and postfilling stages in injection molding. Part I: Formulation
Authors: Chiang H. H. , Hieber C. A. , Wang K. K. 
Published: May 2005

AbstractThis study employs a unified theoretical model to simulate the filling and postfilling stages of the injection‐molding process. Implementation of such a model is based on a hybrid finite‐element/finite‐difference numerical solution of the generalized Hele‐Shaw flow of a compressible viscous fluid under nonisothermal conditions. The shear viscosity of the polymeric material is represented by a Cross model for the shear‐rate dependence and a WLF‐type functional form for the temperature and pressure dependence, whereas the specific volume is modeled in terms of a double‐domain Tait equation. The analysis also handles variable specific heat and thermal conductivity of the polymer as a function of temperature. Complex thin parts of variable thickness can be modeled and discretized by flat, triangular finite elements which may have arbitrary orientation in three‐dimensional space, whereas runners and possible round pins or bosses in the part are represented as one‐dimensional circular‐tube elements. A control‐volume scheme is employed that leads to automatic melt‐front advancement during the cavity‐filling stage.
The effects of physical aging on the thermal and mechanical properties of an epoxy polymer
Authors: Jo Won Ho , Ko Kyoung Jin 
Published: May 2005

AbstractThe effects of free volume on the thermal and mechanical properties of epoxies from diglycidyl ether of bisphenol A (DGEBA) and ethylene diamine (EDA) were investigated. The degree of free volume was controlled by the different thermal history. For fully cured expoxy systems, the density and modulus of both aged and quenched specimens decreased with increasing EDA concentration. However the yield stress of quenched specimens showed a maximum at about equal stoichiometric formulation, while that of aged ones decreased with increasing EDA concentration.