bluuebunny/crossref_metadata_2025_split huggingface dataset:
Residual thermal stresses in injection moldings of thermoplastics: A theoretical and experimental study
Authors: Kamal M. R. , Lai‐Fook R. A. , Hernandez‐Aguilar J. R. 
Published: April 2004

AbstractInternal stresses in injection molded components, a principal cause of shrinkage and warpage, are predicted using a three‐dimensional numerical simulation of the residual stress development in moldings of polystyrene and high‐density polyethylene. These residual stresses are mainly frozen‐in thermal stresses due to inhomogeneous cooling, when surface layers stiffen sooner than the core region as in free quenching. Additional factors in injection molding are the effects of melt pressure history and mechanical restraints of the mold. Transient temperature and pressure fields from simulation of the injection molding cycle are used for calculating the developing normal stress distributions. Theoretical predictions are compared with measurements performed on injection molded flat plates using the layer removal method on rectangular specimens. The thermal stress development in the thinwalled moldings is analyzed using models that assume linear thermo‐elastic and linear thermo‐viscoelastic compressible behavior of the polymeric materials. Polymer crystallization effects on stresses are examined. Stresses are obtained implicitly using displacement formulations, and the governing equations are solved numerically using a finite element method. Results show that residual stress behavior can be represented reasonably well for both the amorphous and the semicrystalline polymer. Similarities in behavior between theory and experiment indicate that both material models provide satisfactory results, but the best predictions of large stresses developed at the wall surface are obtained with the thermo‐viscoelastic analysis.
Improved modeling for the reheat phase in thermoforming through an uncertainty treatment of the key parameters
Authors: Yousefi A. , Bendada A. , Diraddo R. 
Published: April 2004

AbstractThis work focuses on the treatment of parameter uncertainty in the simulation of the sheet reheat phase of the thermoforming process. The approach aims to improve the quality of predictions through more accurate evaluation of the input parameters. First, the modeling approach is employed to perform a sensitivity analysis on the reheat phase. Then, a series of specialized experiments with heat flux and temperature sensors are performed on a thermoforming machine. The key parameters identified through the sensitivity analysis are the subject of these experiments. The natural convective heat transfer coefficients are evaluated by two different approaches. Through treatment of the uncertainty associated with the input parameters, the prediction of sheet reheat phase is significantly improved.
Oxidative graft polymerization of aniline on Si(100) surface modified by plasma polymerization of glycidyl methacrylate
Authors: Chen Yongjun , Kang E. T. , Neoh K. G. , Zhang Yan , Tan K. L. 
Published: April 2004

AbstractModification of argon plasma‐pretreated Si(100) surfaces via plasma polymerization of glycidyl methacrylate(GMA), followed by reactive coupling of the epoxide groups of the plasma deposited GMA chains with aniline, and finally by oxidative graft polymerization of aniline was carried out. An alternative approach involved the modification of the argon plasma‐pretreated Si(100) surfaces via plasma polymerization of glycidyl methacrylate(GMA), followed by direct oxidative graft polymerization of aniline and thermal curing. The compositions and chemical states of the modified Si surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). The two methods of surface modification of the Si(100) surfaces produced similar results. The protonation‐deprotonation behavior, the interconvertible intrinsic redox states, and the metal reduction behavior (the electroless plating of Pd from the Pd(II) ion solution) of the grafted polyaniline (PANI) chains on the Si(100) surface were grossly similar to those of the PANI homopolymer. The coupling of PANI to the covalently tethered GMA chains on the Si(100) surface was suggested by the cohesive failure inside the epoxy adhesive that was applied to the modified Si surface in an attempt to peel off the PANI layer from the GMA plasma‐polymerized Si (GMA‐pp‐Si) substrate.
Effect of addition protocol on mixing in miscible and immiscible polymer blends
Authors: Burch Heidi E. , Scott Chris E. 
Published: April 2004

AbstractThe effects of the addition protocol are investigated for very‐low‐viscosity‐ratio model miscible and immiscible blends consisting of two polyethylenes (PE) and polystyrene (PS)/polyethylene (PE), respectively, are investigated. Miscible and immiscible blends with a matched viscosity ratio of 0.003 are compounded using three different addition protocols: simultaneous solids addition; sequential solids addition; and sequential liquids addition. These protocols correspond to addition of a solid additive to the feed hopper of an extruder; addition of a solid additive into the melting zone in an extruder; and addition of a liquid additive into the melting zone of an extruder. Both of these blends are shown to exhibit phase‐inversion‐like behaviors using a simultaneous solids addition protocol, regardless of concentration. Using either of the sequential addition protocols results in macroscopic segregation of the minor‐phase material to high‐shear‐rate regions of the mixer, delaying mixing. At long mixing times, however, all three protocols achieve a similar dispersed droplet morphology. Furthermore, the simultaneous solids addition protocol is shown to be the least energetically intensive, and the simultaneous solids requires the least amount of time of the three protocols to achieve maximum mixing torque for blends consisting of 20 wt% minor phase.
Quantification of the slip phenomenon and the effect of shear thinning in the capillary flow of linear polyethylenes
Authors: Pérez‐González José , De Vargas Lourdes 
Published: April 2004

AbstractThe slip phenomenon in the capillary flow of linear polyethylenes and its relation to their shear‐thinning behavior was studied in this work. A simple macroscopic analysis that allows a description of the trend of the slip length and the contribution of slip to the average fluid velocity as functions of the shear stress is presented. From this analysis it is shown that an increase or decrease of the slip length for increasing shear stress is determined by the polymer architecture and the competition between slip and shear thinning. A similar behavior is observed for the ratio between the slip and whole average fluid velocities. The analysis is validated using experimental data obtained during the continuous extrusion of linear low‐density polyethylene melts under strong slip conditions in a brass die.
Properties of polytetrafluoroethylene (PTFE) paste extrudates
Authors: Ariawan Alfonsius B. , Ebnesajjad Sina , Hatzikiriakos Savvas G. 
Published: April 2004

AbstractIn this work, we have studied the effects of extrusion die design, resin molecular structure, and lubricant concentration on the properties of PTFE paste extrudates by performing macroscopic extrusion pressure measurements, Raman spectroscopy, differential scanning calorimetry and mechanical testing on the extrudates. Five resins of different molecular structures were tested. We have found that a balance between fibril quantity and quality (in terms of fibril orientation and continuousness) is necessary to ensure acceptable products, as illustrated through the effects of the operating variables on the extrudate tensile strength. The number of fibrils formed during extrusion can be increased by extruding the paste through a die of larger reduction ratio or by decreasing the lubricant content in the paste, thereby increasing the extrusion pressure. However, excessive pressure will cause fibril breakage. By using a die of larger entrance angle, the extent of fibrillation is also increased, although the quality of the fibrils is somewhat compromised. Increasing the die aspect (L/D) ratio does not increase the extent of fibrillation. However, it increases the degree of fibril orientation and ensures smoother extrudate. Finally, we have found that extrudates obtained using a paste of higher molecular weight are mechanically superior.
Estimation of Weibull parameters for the flexural strength of PMMA‐based bone cements
Authors: Riccardi Carmen C. , Vallo Claudia I. 
Published: April 2004

AbstractThe wide scatter of data observed in the strength of bone cements based on poly(methyl methacrylate) (PMMA) can be described properly by the two‐parameter Weibull function. However, the statistical character of the distribution leads to an uncertainty in the parameters evaluated from a limited number of experiments. This study is concerned with the analysis of the methods of estimation as well as sample size on the estimates of the Weibull parameters. The maximum likelihood method, moments method, and linear regression method were studied. Monte Carlo simulations were carried out in order to assess the influence of the number of specimens tested on the Weibull parameters calculated by the different methods. The number of specimens tested displayed a large influence upon the calculated Weibull modulus. By applying weighing factors to the linear regression method, the standard deviation of Weibull parameters decreased significantly. As a compromise between minimizing both the dispersion of the evaluation method and the experimental effort, the use is suggested of the linear regression method with a minimum number of 20 specimens in a nonweighted analysis and 10 in a weighted analysis.
The formulation of powder coatings using solid state shear extrusion
Authors: Wojcik B. , Teymour F. , Arastoopour H. , Mostovoy S. 
Published: April 2004

AbstractThe feasibility of producing homogeneous powder coating formulations without melting is investigated using Solid State Shear Extrusion (SSSE). A detailed comparison between conventional melt extrusion and SSSE processing conditions of identical formulations is accomplished by following the behavior and degree of polymerization during curing. Commercially available polyester and epoxide powder coating premix formulations were processed by SSSE using a Brabender® laboratory‐scale twin‐screw extruder and further pulverized in a ball mill. Calculations based on particle size before and after comminution in single batch ball mill studies indicate a reduction in energy requirements for SSSE during pulverization. Metal coupons were coated with dry pulverized formulations using an electrostatic fluidized bed coating system. The dynamics of curing were followed for a series of bake time exposures. The sol was separated from the gel using Soxhlet methods and characterized by gel permeation chromatography (GPC). A comparison of experimentally determined gel points and gelation dynamics showed general agreement between both processing methods. The critical yield stress, determined from preliminary mechanical testing of modified thick adherend specimens crack‐line‐loaded in compression, was also determined. Results showed the SSSE process to be equivalent to melt extrusion.
Nonlinear temperature control of a batch suspension polymerization reactor
Authors: Shahrokhi Mohammad , Fanaei Mohammad Ali 
Published: April 2004

AbstractThis paper concerns nonlinear temperature control of a batch polymerization reactor where suspension polymerization of methyl methacrylate (MMA) takes place. For this purpose, four control algorithms, namely, a fix proportional‐integral (PI) controller, an adaptive proportional‐integral‐derivative (PID) controller and two globally linearizing control (GLC) schemes, one for known kinetic model (GLC‐I) and the other for unknown kinetic model (GLC‐II), are selected. The performances of these controllers are compared through simulation and real‐time studies in the presence of different levels of parameter uncertainty. The results indicate that GLCI and GLC‐II have better performances than fix PI and adaptive PID, especially in case of strong gel effect. The worst performance belongs to adaptive PID because of rapid model changes in gel effect region. GLC‐II has a simpler structure than GLC‐I and can be used without requiring the kinetic model. In implementation of GLC‐I the closed loop observer should be used because of model uncertainties.
Morphology development during blending of immiscible polymers in screw extruders
Authors: Tyagi Sandeep , Ghosh Anup K. 
Published: April 2004

AbstractThe present work reports evolution of morphology from initial (presence of striation) to final (droplet formation) stages in a single‐screw extruder. Morphology development during the blending process controls the final size of the dispersed phase, which in turn significantly affects the properties of the blends. The experiments were carried out using a 70/30 wt% polypropylene/ethylene vinyl acetate (PP/EVA) blend; samples were collected along the length of the screw, by screw pullout experiment, to analyze the size and size distribution of the dispersed phase present both as striated layers and subsequently as droplets. Average size of the dispersed phase and standard deviation were taken into account to monitor the morphology evolution along the length of the screw. Pre‐breakup morphology development was studied by analyzing the sample collected from the feed zone of the extruder in terms of upper and lower layers along the cross section of screw channel. Examination of micrographs revealed the existence of pattern of ordered striations along the length of the melting zone containing striations from average size of 1000 μm down to 50 μm decreasing rapidly along the length of the screw. The breakup process was captured at the start of compression zone where step‐up in the shear as well as elongational flow was applied due to decrease in the channel depth along the compression zone. The observed droplet size formed by the breakup of filaments is found to be in accordance with theory. The final droplet size is found to be governed by the emulsification process occurring as a result of stretching, breakup and coalescence in the metering section of the screw and is in the order of 2 μm.
Free radical bulk polymerization in cylindrical molds
Authors: Fontes C. E. , Lage P. L. C. , Pinto J. C. 
Published: April 2004

AbstractBulk styrene homopolymerization in cylindrical molds was studied in order to simulate the reactive injection process when the reaction kinetics was much slower than the filling process. Mathematical models were built and implemented, allowing the analysis of certain kinetic phenomena, such as the gel‐effect, and the relevance of natural convection. Based on a detailed kinetic mechanism, the polymer properties (average molecular weight and polydispersity) and monomer conversion were calculated as functions of spatial coordinates and time. The results obtained show that polymer properties and monomer conversion may be very heterogeneous inside the cylindrical mold, although insensitive to variations of the diffusion coefficient, so that defects are expected to appear as a consequence of the heterogeneity of polymer properties inside the mold. Experiments confirmed the simulation results. Simulations indicate that heterogeneities may be expected to increase when the reaction rates are one order of magnitude higher, as in acrylic acid polymerizations.
Modeling/simulating the injection molding of isotactic polypropylene
Authors: Hieber C. A. 
Published: April 2004

AbstractA unified formulation is presented for modeling the injection molding of isotactic polypropylene (i‐PP). The crystallization kinetics are based upon the differential Nakamura equation in which the characteristic time is dependent upon temperature, pressure and flow‐induced shear stress, without any explicit need for an induction time. A Cross/WLF model is used to represent the shear viscosity in which ηO is dependent upon temperature, pressure and crystallinity. Use is made of a recent correlation for the PVT behavior of i‐PP with an explicit dependence upon crystallinity. A finite‐difference implementation of the modeling is applied to two independent molding experiments available from the literature, with notable results concerning the late‐time cavity pressure traces and time‐dependent gapwise shrinkage prior to ejection.
Techniques for reducing residual monomer content in polymers: A review
Authors: Araújo P. H. H. , Sayer C. , Giudici R. , Poço J. G. R. 
Published: April 2004

AbstractReducing the residual monomer content is a desire of every polymer producer, as a product with no or very low levels of residual monomer would have a different commercial appeal. The presence of residual monomer may create hazards to workers as a result of long‐term exposure during polymer processing and sometimes even to customers. There are several techniques for reducing residual monomer content and the industrial importance that has been given to the presence of residual monomers in polymeric products is reflected in the number of patents involving residual monomer reduction techniques. Nevertheless, choosing the best, or the most adequate, technique is not always an easy task, and one still observes a relative lack of scientific literature on this subject. The technique to be employed will depend upon polymer application, which determines the grade of purity, and also on polymer quality, as some monomer reducing techniques might change polymer properties. The main objective of this review is to summarize and discuss the principal methods employed for reducing residual monomer content.
Ultradrawing behavior of gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends at varying drawing conditions
Authors: Yeh Jen‐taut , Chang Sheng‐shan 
Published: April 2004

AbstractA systematic study of the influence of the drawing temperature and rate on the ultradrawing properties of film samples prepared from gel solutions of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends is reported. At a fixed drawing rate, the achievable draw ratios reached a maximum value when each film specimen was drawn at a temperature near its optimum temperature (Top). It is interesting to note that the Top values of each film sample increased consistently with the drawing rate. The achievable draw ratio of each film sample drawn at a constant rate and a temperature near Top is referred to as the Draop, which reached another maximum value as the drawing rates approached an optimum value. Dynamic mechanical analysis of the film sample exhibited an extraordinary high transition peaked at temperature near 95°C, which is again very close to the Top value found for the film sample drawn at a relatively low rate. On the other hand, the birefringence values and tensile strengths of the film specimen were found to improve significantly with the draw ratios, although the improvement of these properties reduced significantly at high draw ratios. Moreover, both the drawing temperature and rate showed beneficial influence on the birefringence, and tensile strengths of the drawn film specimens. Possible mechanisms accounting for these interesting deformation properties are suggested.
Energy absorption capability of recycled plastic bottles
Authors: Muller Mark K. , Majerus John N. 
Published: April 2004

AbstractThe main objective of this study was to explore the potential effectiveness of using recycled plastic bottles as a material for roadside crash‐barriers. A test program was conducted to compile data on the energy‐absorbing potential of commonly available plastic bottles. The main and secondary factors in plastic bottle energy‐absorption were identified and orthogonal arrays were used to define the test matrix, thereby avoiding the full factorial number of experiments. The results of the study were energy‐absorption data for a range of commercially available plastic bottles. The data are for various filler materials and two loading directions on the bottles. Analysis‐of‐variance was used to identify the most significant factors in energy absorption. The main conclusion of the study was that commercially available plastic bottles, when filled with the appropriate filler materials, are capable of absorbing significant amounts of crush energy. The main recommendation was that the economic feasibility of recycled plastic bottles in various types of crash barriers be explored, including more efficient or more practical filler materials.
Replication of sub‐micron features using amorphous thermoplastics
Authors: mönkkönen Kari , Pakkanen Tuula T. , Hietala Joni , Pääkkönen Esko J. , Pääkkönen Pertti , Jääskeläinen Timo , Kaikuranta Terho 
Published: April 2004

AbstractA comprehensive experimental study was carried out to replicate sub‐micron features using the injection molding technique. For the experiments, five different plastic materials were selected according to their flow properties. The materials were polycarbonate (PC), styrene‐butadiene block copolymer (SBS), impact modified poly(methyl methacrylate), methyl methacrylate‐acrylonitrile‐butadiene‐styrene polymer (MABS), and cyclic olefin copolymer (COC). Nanofeatures down to 200‐nm line width and with aspect ratios (aspect ratio = depth/width) of 1:1 could be replicated. In all selected materials, the greatest differences between the materials emerged when the aspect ratio increased to 2:1. The most favorable results were obtained with the use of high flow polycarbonate as the molding material. The best replication results were achieved when melt and mold temperatures were higher than normal values.
Electrical properties of composites as affected by the degree of mixedness of the conductive filler in the polymer matrix
Authors: Kalyon Dilhan M. , Birinci Elvan , Yazici Rahmi , Karuv Bahadir , Walsh Shawn 
Published: April 2004

AbstractThe development of the electrical properties of composites as a function of the degree of mixedness of a conductive filler distributed into an insulating polymer is investigated. A wide‐angle X‐ray diffraction (WAXD)‐based quantitative phase analysis method was used to characterize the variations of the concentrations of the insulating binder and the conductive particles around their mean values as a function of mixing time in an intensive batch mixer. Increasing the time and hence, the specific energy input, during the mixing process results in a more homogeneous spatial distribution of the conductive filler in the polymeric matrix, which in turn results in a decrease of the volume conductivity of the composite. The decreasing conductivity of the composite is attributed to the better coating and hence the isolation of the conductive particles from each other, thus hindering the formation of a conductive network “percolation”. Overall, these results suggest that the control of the electrical properties of conductive composites could benefit from a good understanding and adequate control of the dynamics of the mixing process and the resulting degree of mixedness of the conductive particles in the polymer matrix.