bluuebunny/crossref_metadata_2025 huggingface dataset:
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

This 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

Melt 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

Dynamic 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

Ultrasonic 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

This 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

The 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

This 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

A 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

The 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

The 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

Four 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

A 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.
Resin transfer molding (RTM) process of a high performance epoxy resin. I: Kinetic studies of cure reaction
Authors: Lee Chang‐Lun , Ho Jia‐Chong , Wei Kung‐Hwa
Published: April 2004

The cure kinetics of a high performance PR500 epoxy resin in the temperature range of 160–197°C for the resin transfer molding (RTM) process have been investigated. The thermal analysis of the curing kinetics of PR500 resin was carried out by differential scanning calorimetry (DSC), with the ultimate heat of reaction measured in the dynamic mode and the rate of cure reaction and the degree of cure being determined under isothermal conditions. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion‐controlled curing behavior of the resin. A reasonable agreement between the experimental data and the kinetic model has been obtained over the whole processing temperature range, including the mold filling and the final curing stages of the RTM process.
Resin transfer molding (RTM) process of a high performance epoxy resin. II: Effects of process variables on the physical, static and dynamic mechanical behavior
Authors: Lee Chang‐Lun , Wei Kung‐Hwa
Published: April 2004

The effects of processing variables on the mechanical behavior and the void content of one‐part epoxy based glass fabric composites produced by resin transfer molding (RTM) were investigated. The variables studied included injection pressure, injection temperature, and fabric structure. Image analysis was used to measure the void content in the composites. Variations in injection pressure and temperature were found to have a significant effect on the quality and the mechanical performance of composites. The optimized physical and mechanical performance of the composites was obtained by processing the resin at 160°C under 392 kPa pressure. Molding of highly permeable EF420 fabric required a shorter mold filling time, but resulted in reduced flexural strength and storage modulus in the resulting composites as compared with that of the composites containing 1581 fabric.
A fuzzy multiobjective approach for minimization of injection molding defects
Authors: Tan K. H. , Yuen M. M. F.
Published: April 2004

This paper describes a fuzzy multiobjective optimization approach for determining the set‐points of the injection molding processing parameters to minimize the defects formed on the molded parts. The severities of the defects are represented by membership functions using the fuzzy set theory. The minimization of these membership functions, which is a multiobjective optimization problem, is transformed into a substitute problem. The preference function in the substitute problem is original and is proposed specifically for characterizing the quality requirements of the injection molding defects. The formulated optimization problem is solved with design of experiments, in which the process behavior is approximated empirically by a set of quadratic polynomials that can be easily optimized. Experimental results are presented to emphasis the workability of the proposed methodology.
Mixing analysis of reactive polymer flow in a single‐screw extruder channel
Authors: Strutt David , Tzoganakis Costas , Duever Thomas A.
Published: April 2004

In this study, the finite element method was used to investigate the influence of screw speed, entering peroxide distribution, pressure‐to‐drag flow ratio, and channel geometry on the mixing characteristics of steady non‐isothermal reactive flows. The reaction considered was the peroxide‐initiated degradation of a polypropylene resin in the metering zone of a single‐screw extruder. The predicted average degree‐of‐freedom profiles from the simulations largely conformed to expectations. The average flow efficiencies for all runs were found to vary little along the channel length, remaining at values close to that for two‐dimensional flow. No significant effect of either screw speed or peroxide distribution was found on the flow efficiencies. However, both the pressure‐to‐drag flow ratio and the channel aspect ratio were found to have significant influences.
Electrical properties of structured HIPS/gamma‐irradiated UHMWPE/carbon black blends
Authors: Breuer O. , Tchoudakov R. , Narkis M. , Siegmann A.
Published: April 2004

HIPS/UHMWPE and HIPS/XL‐UHMWPE containing carbon black (CB) are unique systems in which CB is attracted to the PE, and thus structuring takes place affecting the morphology and the resultant electrical properties. UHMWPE, having a very high viscosity, was chosen as the dispersed phase within HIPS in place of a conventional polymer in order to explore possibilities of obtaining unique structures that would induce the CB to segregate and form a conductive network. XL‐UHMWPE particles also constitute an interesting dispersed phase, maintaming their highly porous and intricate structure even subsequent to melt processing. In both cases the CB is located at the interface; however, differences in resistivity values are observed. When low UHMWPE or XL‐UHMWPE contents are incorporated, the HIPS/XL‐UHMWPE/CB compositions have lower resistivities due to the heterogeneity of the interface, even at high shear rates. When high UHMWPE or XL‐UHMWPE contents are utilized, the trends reverse: HIPS/UHMWPE/CB depict enhanced conductivity, due to the dominance of UHMWPE particle coalescence and the resultant decrease in surface area. This is contrary to what happens with the XL‐UHMWPE particles, where the surface area increases with their higher contents, since they do not coalesce.
Mechanical properties of vinyl alcohol—ethylene copolymers
Authors: Cerrada M. L. , Pereña J. M. , Benavente R. , Pérez E.
Published: April 2004

The stress‐strain behavior of vinyl alcohol‐ethylene copolymers, with vinyl alcohol as main component, was studied. Films of the copolymer samples, either quenched or slowly cooled from the melt, were stretched at 23, 40 and 80°C. The two former temperatures are below the glass transition (Tg) and the latter is well above the Tg of the studied samples. The drawing process was carried out at different strain rates, and the influence of the stretching parameters (temperature, strain rate) as well as the thermal history and composition of the copolymer samples are discussed in relation to the corresponding homopolymers, poly(vinyl alcohol) and polyethylene. The copolymer with the highest vinyl alcohol content exhibited a critical strain rate, showing maximum values of Young's modulus at a deformation rate around 0.66/min.
Rheological behavior of highly filled ethylene propylene diene rubber compounds
Authors: Markovic M. G. , Choudhury N. R. , Dimopoulos M. , Matisons J. G. , Dutta N. K. , Bhattacharya A. K.
Published: April 2004

The rheological behavior of highly filled ethylene propylene diene rubber (EPDM) compounds was studied with respect to the effect of curative system, grafted rubber, shear rate, temperature and die swell using a Monsanto Processability Tester (MPT) to gain an understanding of the molecular parameters that control the surface finish. All systems show pseudoplastic behavior. At a particular shear rate, shear viscosity increases with blend ratio. The dependence of flow behavior on extrusion velocity indicates a surface effect. The extrudate die swell and maximum recoverable deformation are related by a linear relationship, which is independent of sulfur/accelerator ratio, extrusion temperature and shear rates and blend ratio. The principal normal stress difference increases nonlinearly with shear stress. Activation energy decreases with shear rate in most cases. The faster relaxing system produces extrudate of better surface quality.
Modeling of the plasticating process in a single‐screw extruder: A fast‐track approach
Authors: Lai Eugene , Yu Ding Wen
Published: April 2004

A new mathematical model has been developed to analyze the entire flow field of a single screw extruder under steady‐state conditions. Intended as a rational design tool for practising engineers in the polymer processing industry, the model contains no partial differential equations and hence does not require the use of numerical solution techniques. To achieve generality, a generic approach is proposed and has been adopted in the derivation of governing algebraic equations from general conservation laws covering channel geometry, polymer flow speed, equivalent radius in a pipe, material properties, power consumption and heat transfer. The model makes no use of empirical factors or correlation. The validity of the new model has been assessed by comparison with published experimental results. Good agreement was achieved with respect to its ability to predict (a) the solid‐bed width profile; (b) the axial pressure profile and (c) the temperature and pressure of the melt pool at the extruder exit. Furthermore, the model can predict other information including the solid‐bed velocity in the axial direction and the power consumption. The work has demonstrated the potential of a fast track approach to designing helical extruder screws, while maintaining a level of accuracy comparable with more complex 3D models but without the penalty of computational efforts.
Spatial and temporal control of the degree of cure in polymer composite structures
Authors: Shull P. J. , Hurley D. H. , Spicer J. W. M. , Spicer J. B.
Published: April 2004

This paper describes current efforts to apply spatially and temporally localized microwave processing techniques to ensure uniformity of material properties in polymer composite materials. In large polymer composite structures, high temperatures caused by exothermic resin cure can degrade the mechanical properties of the composite. In this work, resin cure temperature data was obtained during microwave processing from a series of thermocouples embedded at various lateral locations relative to the microwave source and uniformly through the thickness of the composite structure. Using this temperature information, the potential for localized microwave‐accelerated cure to reduce the occurrence of material degradation from resin over‐temperature was evaluated. In addition, a theoretical model is presented that helps elucidate the influence of the microwave parameters on the temperature profile.
Phosphorylation of phosphazenes and its effects on thermal properties and fire retardant behavior
Authors: Allcock Harry R. , Taylor Jonathan P.
Published: April 2004

Methods for the incorporation of phosphate and phosphonate units into the side groups of phosphazenes, at both the high polymeric and cyclic trimer levels, are described and evaluated. Halogenated organophosphates were used as the phosphorylating agents and were allowed to react with hydroxyl‐ or lithio‐functionalized phosphazenes. Well‐defined phosphorylated cyclic trimers were synthesized from the hydroxyl‐functionalized precursors, and these were examined as flame‐retardant additives to polystyrene. The thermal stabilities of the high polymers made by this route were analyzed by TGA.
Structure‐property relationship in polyurethane elastomers containing starch as a crosslinker
Authors: Desai Sonal , Thakore I. M. , Sarawade B. D. , Devi Surekha
Published: April 2004

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties were compared with those of polyurethanes containing 1,1,1 ‐trimethylol propane (TMP) as the crosslinker. Starch‐based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch‐based PUs exhibited two glass transitions, whereas TMP‐based PUs exhibited one Tg. No significant difference in the Tgs of the two PUs was observed. The activation energy of St‐PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP.
Improvement of the mechanical properties of chitosan films by the addition of poly(ethylene oxide)
Authors: Alexeev V. L. , Kelberg E. A. , Evmenenko G. A. , Bronnikov S. V.
Published: April 2004

The mechanical properties of films prepared from mixed acetic acid aqueous solutions of chitosan (Mw = 400,000; Mw/Mn = 3.8) and poly(ethylene oxide) (PEO) (viscosity average molecular weight of 200,000 or 600,000) were determined. A chitosan:PEO weight ratio of 10:2 improved the mechanical properties compared with pure chitosan films. The improvement of the mechanical properties correlated with a small reduction of the correlation length measured by small‐angle neutron scattering (SANS).
On the properties and processing of polyethylene terephthalate/styrene‐butadiene rubber blend
Authors: Sánchez‐Solís A. , Estrada M. R. , Cruz J. , Manero O.
Published: April 2004

The mixing of incompatible polymers such as polyethylene terephthalate (PET) and styrene‐butadiene rubber (SBR) produces a blend with poor mechanical and impact properties, because polymeric phases interact weakly with each other and segregate. The use of SBR grafted with maleic anhydride (MAH) increases the compatibility of the SBR‐PET system by generating higher interactions and chemical links between the ingredients of the blend. The induced compatibility is reflected in the 2.5‐fold increase in the impact resistance of the blend as compared to that of pure PET. The grafting reaction to produce SBR‐g‐MAH is carried out by reactive extrusion using a reaction initiator, benzoyl peroxide (BPO), and the extent of the reaction depends on the concentration of MAH and BPO. Results indicate the close relationship between processing conditions and microstructural parameters, such as particle diameter and interparticle distances of the dispersed rubber phase, necessary to achieve the optimum impact resistance.
Thermoanalysis and rheological behavior of emulsion copolymers of methyl methacrylate, N‐phenylmaleimide and styrene
Authors: Jungang Gao , Guodong Liu , Liting Yang , Liucheng Zhang
Published: April 2004

Terpolymers of methyl methacrylate (MMA), N‐phenylmaleimide (PMI) and styrene (St) were synthesized by emulsion copolymerization. The thermal stabilities of terpolymers were studied by a programmed thermogravimetric analysis (TGA) technique. Terpolymers show a considerable increase in decomposition temperature with increasing feed content of PMI and St. The glass transition temperatures (Tg) of copolyniers were measured by differential scanning calorimetry (DSC) and torsional braid analysis (TBA). The terpolymer's Tg increases markedly with the increasing PMI feed content, while it decreases with increasing St feed content. The rheological behaviors of copolymers were also studied. The terpolymer's apparent viscosity in melt decreases with increasing feed contents of PMI and St. The terpolymer's flow index n increases with the increasing feed content of PMI. The results also show that the difference value between TgDSC and TgTBA' ΔTg increases with an increase in the terpolymer's flow index. M̄w and M̄n of copolymers were also determined by gel permeation chromatography (GPC).
Production of injection molding tooling with conformal cooling channels using the three dimensional printing process
Authors: Sachs Emanuel , Wylonis Edward , Allen Samuel , Cima Michael , Guo Honglin
Published: April 2004

A Solid Freeform Fabrication Process called Three Dimensional Printing is applied to the fabrication of injection molding tooling with cooling channels which are conformal to the molding cavity. The tool is created by spreading layers of stainless steel powder and selectviely joining the powder in the layers by ink‐jet printing of a binder material. Unbound powder is removed from without and within the green part thus defined. The green part is sintered and infiltrated with a copper alloy to produce a fully dense tool. The infiltrant is kept out of the cooling channels by elevating the tool above the free surface of the pool of infiltrant in the crucible, thus creating a controlled negative pressure within the infiltrant. An upper limit to the separation of tooling cavity and cooling channel was derived based on transient heat transfer considerations. A tooling set was created to mold a split ring shape and conformal cooling channels were placed in both the cavity and core sides of the tool. The performance of this tool was compared against the performance of a tooling set with straight cooling channels. Thermocouples buried in the core and cavity showed that the conformal tool had no period of transient behavior at the start of molding, while the tool with straight channels took 10–15 cycles to come to an equilibrium temperature some 40°C above the temperature of the coolant. The conformal tool was also found to maintain a more uniform temperature within the tool during an individual molding cycle. The gap in the molded split rings did not change from cycle to cycle with the conformal tool, while it did with the conventional tool. A 2‐D finite difference model accurately captured the observed temperature histories of the mold with conformal cooling channels.
Two‐component photoresists containing thermally crosslinkable photoacid generators
Authors: Moon Seong‐Yun , Chung Chan‐Moon
Published: April 2004

Bis{4‐[2′‐(vinyloxy)ethoxy]phenyl}‐4‐methoxyphenylsulfonium triflate (TPS‐2VE‐Tf) and tris{4‐[2′‐(vinyloxy)ethoxy]phenyl}sulfonium triflate (TPS‐3VE‐Tf) were synthesized as thermally crosslinkable photoacid generators (PAGs) and used in a two‐component chemically amplified photoresist system. The photoresist films formulated with poly(p‐hydroxystyrene) (PHS) as a binder polymer and a thermally crosslinkable PAG are insolubilized in aqueous base by prebaking due to the thermal crosslinking reaction between PHS and the PAG. The insolubilization temperature of the resists and conversion of vinyl ether groups are greatly influenced by the PAG concentration and prebaking temperature, respectively. Upon exposure to deep UV and subsequent postexposure bake, the crosslinks are cleaved by photogenerated acid, leading to effective solubilization of the exposed areas. Photoresists containing TPS‐2VE‐Tf and TPS‐3VE‐Tf exhibited sensitivities of 12 and 45 mJ/cm2, respectively. Positive‐tone images were obtained using a 2.38 wt% aqueous tetramethylammonium hydroxide developer.
Time‐cure‐temperature superposition for the prediction of instantaneous viscoelastic properties during cure
Authors: Eom Yongsung , Boogh Louis , Michaud Véronique , Sunderland Paul , Månson Jan‐Anders
Published: April 2004

The relative sequence of shrinkage and evolution of modulus of a thermoset resin during cure leads to the build‐up of internal stresses, especially if the resin is constrained by the presence of other materials in the form of a substrate or reinforcing fibers. To enable prediction of the levels of internal stress generated during processing and to determine appropriate processing windows, the evolution of the modulus of an epoxy‐amine system during cure has been characterized and described with a phenomenological model. A combined reaction kinetics model is used to determine the degree of conversion of the epoxy over any complete range of cure. The chemorheological properties of the resin are measured as a function of curing temperature with a torsional parallel plate rheometer. A new phenomenological approach for time‐cure‐temperature superposition is proposed for predicting the relaxation modulus at any moment during cure and at any cure temperature. The combination of these two models provides a full description of the instantaneous viscoelastic properties during cure. This approach, which can be adapted to any curing resin, provides suitable tools for the analysis of viscoelastic stress build‐up following any industrially relevant cure cycle.
Nonisothermal crystallization kinetics of polytetrafluoroethylene
Authors: Seo Yongsok
Published: April 2004

An analysis of the crystallization kinetics of polytetrafluoroethylene (PTFE) under nonisothermal conditions is presented. A simple method is proposed to remove the limits of the Ozawa theory. The Avramic exponent, n, can be reasonably well determined from the nonisothermal crystallization exotherm. An n value of ∼1.49 was obtained for PTFE, which indicates the formation of one‐dimensional crystallites (fibrillar type) after thermal nucleation or two‐dimensional crystallites (discs) after athermal nucleation. Both these morphologies were experimentally observed. For PTFE crystallization from the melt, activation energy was obtained as 34 kcal/mol. This is much smaller than those of PEEK and PET, indicating a very fast crystallization of PTFE.
High temperature slow crack growth in polyoxymethylene
Authors: Plummer Christopher J. G. , Scaramuzzino Pascal , Kausch Hans‐Henning , Philippoz Jean‐Michel
Published: April 2004

Brittle failure has been observed in polyoxymethylene during long‐term low‐level tensile loading at elevated temperatures. It is argued to be associated with slow crack growth via the breakdown of the localized planar fibrillar damage zones that form under these conditions. This phenomenon has been characterized using notched compact tension specimens tested under various static loads and at different temperatures. The specimen lifetime at a given load is found to decrease strongly with increasing temperature and to increase with molar mass at a given load and temperature. The associated crack‐tip fibrillar damage zones are shown to arise from the breakdown of more localized microfibrillar deformation zones, which in turn result from interlamellar cavitation in the early stages of tensile deformation.
Thermal effects on stereolithography injection mold inserts
Authors: Colton Jonathan S. , LeBaut Yann
Published: April 2004

Stereolithography is a process in which a photopolymerizable resin is used to make parts. This method is used here to produce mold inserts for small injection molding runs. This paper focuses on the effects of the heat due to the injection of the polymer on these mold inserts. As the number of shots increases, the degree of cure of the insert changes. Differential Scanning Calorimetry (DSC) was used to determine the thermal property changes of the material. The evolution of the ejection forces for different post‐cure treatments was investigated. The ejection force decreased with increasing cure of the mold inserts.
Solubility of hydrofluorocarbon (HFC‐134a, HFC‐152a) and hydrochlorofluorocarbon (HCFC‐142b) blowing agents in polystyrene
Authors: Sato Yoshiyuki , Iketani Toru , Takishima Shigeki , Masuoka Hirokatsu
Published: April 2004

Solubilities of blowing agents (HFC‐134a, HCFC‐142b, and HFC‐152a) in polystyrene (PS) were measured at temperatures from 348 to 473 K and pressures up to 3.2 MPa with a volumetric method. For all conditions, the solubility of the blowing agents in PS decreased with increasing temperature. At a given temperature and pressure, the solubility of HFC‐134a, HFC‐152a, and HCFC‐142b in PS increased in that order. Solubilities could be correlated with the Sanchez‐Lacombe equation of state with temperature‐dependent binary interaction parameters to within 3.4% average relative percent deviation. The temperature dependence of the Henry's constants, Kp, for the blowing agents were found to have a linear relationship between ln(1/Kp) and (Tc/T)2, where Tc is the critical temperature of the blowing agent.
Effect of processing conditions and reactive compatibilizer on the morphology of injection molded modified poly(phenylene oxide)/polyamide‐6 blends
Authors: Son Younggon , Ahn Kyung Hyun , Char Kookheon
Published: April 2004

The effect of injection molding conditions and reactive compatibilization on the morphology of maleic anhydryde‐modified poly(phenylene oxide)/polyamide‐6 blends was investigated. The injection flow rate primarily influenced the position of the subskin layer, and the injection temperature affected the aspect ratio of the dispersed phase. A reduction of the sue of the dispersed phase occured during the converging flow in the barrel‐to‐sprue zone. The reactive compatibilization reduced the flow induced deformation, the coalescence and the breakup of particles and improved the dispersion of the minor phase.
Blends of a bottle grade polyethylene terephthalate copolymer and a liquid crystalline polymer. Part I: Injection molding morphology and rheological properties
Authors: Da Silva L. , Bretas R. E. S.
Published: April 2004

Blends of a bottle grade polyethylene terephthalate copolymer (PET) with a liquid crystalline polymer (LCP) were prepared by injection molding. The thermal transitions, the morphology and the rheological properties of the pure components and of the blends were measured by dynamic mechanical analysis (DMTA), scanning electron microscopy (SEM) and capillary and parallel plates rheometry, respectively. The blends displayed only one Tg; the B60 and B80 compositions showed the highest LCP β‐transition, which has been correlated to good barrier properties. In all the blends a “skin‐core” type morphology was observed; the core region had two phases while the skin region showed only one fibrillar phase. The viscosity measurements gave an indication that the interface was strong, probably due to transterifications reactions that occurred during the tests. On creep recovery, the increasing addition of the LCP to the PET increased the blends elastic recovery. On stress growth, the highest stress overshoot was displayed by the pure LCP; this polymer actually presented two overshoots that were also observed in some of the blends at high shear rates.
Effect of catalyst residues on the chain structure and properties of a Phillips type polyethylen
Authors: Epacher Edina , Kröhnke Christoph , Pukánszky Béla
Published: April 2004

A large number of high‐density polyethylene (HDPE) powder samples produced by Phillips technology were taken from an industrial polymerization reactor and their catalyst residue content was determined by X‐ray fluorescence spectroscopy. The chemical structure of the powder was characterized by diffuse reflectance infrared spectroscopy (DRIFT), while the functional group content of samples processed in the presence and absence of a phenolic antioxidant was determined by Fourier transform infrared spectroscopy (FTIR). The melt flow index (MFI) of all processed samples was measured. Oxygen induction time (OIT) measurements were carried out to characterize the oxidative stability of 15 selected stabilized samples. The results indicate that the distribution of both the amount of chromium‐based catalyst residues and their composition are very heterogeneous in the produced polymer. With increasing catalyst residue content, the concentration of double bonds increases in the samples extruded with or without stabilizer. Viscosity was not influenced by catalyst residues, while discoloration increased slightly with increasing catalyst residue content. The stability of the processed polymer also depends on the concentration of double bonds and on other factors. Since other components of the catalyst, including the SiO2 support, also take part in the reactions occurring during processing, chromium content is not the sole, and perhaps not even the decisive, factor determining the properties and especially the stability of HDPE produced by a Phillips catalyst.
Interface in mechanically fastened polymer joint, studied by contact electrical resistance measurement
Authors: Luo Xiangcheng , Chung D. D. L.
Published: April 2004

A polymer‐polymer joint obtained by mechanical fastening at a compressive stress of 5% (or less) of the 1% offset yield strength of the polymer (nylon‐6) was found to exhibit irreversible decrease in the contact electrical resistance upon repeated fastening (loading) and unfastening (unloading). The decrease occurred after up to 10 cycles of fastening and unfastening, although the decrease diminished with cycling. It is primarily due to local plastic deformation of the matrix. Moreover, the stress required for the resistance to reach its minimum in a cycle decreased with cycling, owing to softening of the matrix.
A preliminary investigation of conductive immiscible polymer blends as sensor materials
Authors: Srivastava S. , Tchoudakov R. , Narkis M.
Published: April 2004

This paper discusses the feasibility of the application of conductive immiscible polymer blends as sensor materials for detection of organic liquid solvents. Immiscible polymer blends of polypropylene (PP), nylon 6 (Ny6) and carbon black (CB) have been used to produce a series of electrically conductive filaments by a capillary rheometer process. In these immiscible blends, PP serves as a semi‐crystalline matrix and Ny6 as the semi‐crystalline dispersed phase. The enhancement of conductivity in these blends is due to the attraction of CB to Ny6 and localization of CB particles at the PP/Ny6 interface, giving rise to conductive networks. The dc electrical resistivity of extruded filaments, produced at different shear levels, is found to be sensitive to various organic liquid solvents. The shear rate at which the filaments are produced has an important effect on the PP/Ny6/CB filament's sensitivity. The compositions studied were close to the double‐percolation structure believed to perform best as sensor materials. In addition, it seems that the PP/Ny6 interface plays a major role in the sensing process. Liquid contact/drying cycling of the filaments indicates stabilization of the sensitivity change making the sensing process reversible.
Mechanical properties and interfacial interaction of CaCO3 filled HDPE compatibilized with HDPE functionalized by ultraviolet irradiation
Authors: Lei Jingxin , Zhou Rong
Published: April 2004

The mechanical properties of CaCO3 filled high density polyethylene (HDPE) compatibilized with ultraviolet (UV) irradiated HDPE (uHDPE) were studied and the interfacial interactions between CaCO3 and the polymers were evaluated by SEM, the Molau test, and ESCA. UV irradiation in air introduces the following functional groups on HDPE: >COOH, >CO, OOH and OH. The concentration of these groups increases with irradiation time. The addition of a small amount (<10% by wt) of uHDPE to the HDPE/CaCO3 improves the tensile and impact strength. For example, the addition of 3% HDPE irradiated for 500 hours (u500HDPE) increases the tensile and impact strength of HDPE/CaCO3 from 16.7 MPa and 210 J/m to 25.2 MPa and 430 J/m, respectively. Chemical reactions between uHDPE and CaCO3 promote interactions between HDPE and CaCO3. The morphology of the compatibilized compound is nearly homogenous, and no CaCO3 sediment was observed in a hot xylene solution of HDPE/u500HDPE/CaCO3 when the content of u500HDPE exceeded 30% (wt).
Silane grafting and moisture crosslinking of polypropylene
Authors: Beltraán M. , Mijangos C.
Published: April 2004

Peroxide initiated vinylsilane grafting of polypropylene in an intensive mixer, and the subsequent water crosslinking process were studied. Different concentrations of vinyl trimethoxysilane and dicumyl peroxide were used. The materials obtained after mixing in the rheocord were hot pressed at 190°C. The melt viscosity of the obtained sheets, the melting enthalpy and melting temperature (DSC, differential scanning calorimetry), the mechanical properties and the thermal decomposition behavior (TG, thermogravimetric analysis) were studied. No evidence of grafting during the rheocord processing was observed. Nevertheless, for the hot pressed sheets with concentrations higher than 4 phr of vinyl silane an important increase in the melt viscosity was observed. This increase agrees with the change observed in the mechanical properties, which show a maximum for the water crosslinked samples containing 4 phr of vinyl silane. The modulus increases by 39% at 90°C and 33% at 130°C, while the tensile strength rises by ∼22% at both temperatures. The silane grafted water crosslinked samples show a more stable thermal behavior than both the silane grafted samples and the unmodified polypropylene.
Influence of rheological properties on the sagging of polypropylene and abs sheet for thermoforming applications
Authors: Lau H. C. , Bhattacharya S. N. , Field G. J.
Published: April 2004

The isothermal sagging resistance of different grades of conventional and a high melt strength (HMS) PP has been correlated with the rheological characteristics of the polymers, such as dynamic shear properties, melt strength, and zero shear viscosity. A thermoforming grade of acrylonitrile‐butadiene‐styrene (ABS) was used as a reference material. At 190°C, ABS had the highest viscosity and elastic modulus in the frequency range measured, showing that this polymer is highly elastic. HMS PP had a greater shear thinning behavior than conventional PP because of its broader molecular weight distribution. The tan δ of the polymers showed that conventional PP had a higher tendency to flow than HMS PP and ABS when heated above 172°C. This was confirmed with sagging experiments performed in an air circulating oven, where the rate of sagging decreased as the melt strength and the zero shear viscosity of the polymer increased.