bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractIn 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

AbstractHIPS/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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThis 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

AbstractMethods 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

AbstractPolyurethane 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

AbstractThe 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

AbstractThe 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

AbstractTerpolymers 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

AbstractA 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

AbstractBis{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

AbstractThe 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

AbstractAn 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

AbstractBrittle 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

AbstractStereolithography 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

AbstractSolubilities 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.