bluuebunny/crossref_metadata_2025_split huggingface dataset:
Poly(butylene terephthalate)/ poly(ethylene‐co‐alkyl acrylate)/ carbon black conductive composites: Influence of composition and morphology on electrical properties
Authors: Lagrève C. , Feller J. F. , Linossier I. , Levesque G. 
Published: April 2004

AbstractPoly(butylene terephthalate)/Poly(ethylene‐co‐alkyl‐acrylate)/carbon black (PBT‐EXA‐CB) blends, prepared through extrusion, were characterized as electrical conductive materials. In the composition range studied (55 ≤ PET % ≤ 75 w/w 5.5 ≤ CB % ≤ 11.1 w/w), various conductive behaviors were observed depending mainly on composition and poly(olefin) crystallinity. The observed positive temperature coefficient (PTC) is quite small compared to poly(olefin)‐CB systems, and our blends do not present a negative temperature coefficient (NTC) on complete melting of the CB‐containing phase, thus offering new possibilities for a regular electric power control. Volume expansion of both PBT and EXA was postulated to be the main parameter responsible for the thermal resistivity evolution through the range +20 to +170°C. A double‐percolation system between both the co‐continuous polymer phases and CB‐particles included in the poly(olefin) phase is postulated to explain these results.
Numerical inversion techniques in the recovery of molecular weight distribution expressed in different transformed domains. Experimental validation
Authors: Brandolin A. , Asteasuain M. , Sarmoria C. , López‐Rodríguez A. , Whiteley K. S. , Fernández B. Del Amo 
Published: April 2004

AbstractIn this work we analyze the feasibility of using numerical inversion techniques for recovering MWD of actual polymers from a transformed domain, specifically the one defined by probability generating functions. We start from known experimental MWDs, transform them, and then apply two different numerical techniques to recover the MWD. We analyze the influence of noise in the calculated probability generating functions on the quality of the recovered molecular weight distributions. We also study how the range of molecular weight selected for the inversion procedure affects the results. We compare the recovered distributions obtained by both methods and suggest a criterion for establishing the reliability of a given solution. We find that this general strategy is appropriate for the recovery of MWDs whether they are monomodal, multimodal, wide or narrow. This provides a tool for the treatment of actual polymerization systems for which there is no analytical solution for the mass balance equations.
Reaction injection molding of polyurethane foam for improved thermal insulation
Authors: Koo Myung Sool , Chung Kwansoo , Youn Jae Ryoun 
Published: April 2004

AbstractA study on the apparent thermal conductivity of polyurethane foam was carried out. A HCFC (hydrochlorofluorocarbon) gas and carbon dioxide were used as the physical blowing agent and ultrasonic excitation was applied to increase the rate of bubble nucleation. The thermal conductivity of the binary gas mixture was predicted theoretically to estimate the apparent thermal conductivity of the polymer foam. Effects of conduction and radiation on the apparent thermal conductivity of the cellular polyurethane were considered with respect to the cell size and the effect of convection was neglected because of the small cell size. A laboratory RIM machine was designed and built for foaming experiments. The foaming experiments were performed at various processing conditions, and density, apparent thermal conductivity, number of cells, and cell sizes were measured. Best results such as low thermal conductivity and small bubbles were obtained when the polyol was mixed with the HCFC gas and saturated with carbon dioxide at 0.3 MPa, and foamed with ultrasonic nucleation.
Solid‐phase preparation of ultra‐fine PA6 powder through pan‐milling
Authors: Chen Zhe , Liu Changsheng , Wang Qi 
Published: April 2004

AbstractThe engineering plastic polyamide 6 (PA6) was effectively pulverized to ultra‐fine powder through a sell‐made pan‐type milling equipment. A laser Diffraction Particle Size Analyzer and TEM were used to examine the particle size and the distribution of PA6 powder. The results show that the average particle size of PA6 was reduced to micrometer scale only after 15 milling‐cycles and reached 50–80 nm after 30 milling‐cycles. Pan milling decreased crystallinity of PA6 but did not affect its crystal type. Molecular weight and mechanical properties of PA6 dropped slightly during pan milling. The average particle size of PA6 powder could be controlled by adjusting processing conditions including milling time, temperature and the rotating speed of the milling pan.
Photoinitiating characteristics of benzophenone derivatives as new initiators in the photocrosslinking of polyethylene
Authors: Wu Qianghua , Qu Baojun 
Published: April 2004

AbstractTwo kinds of benzophenone (BP) derivatives, dodecyl‐benzophenone (BP‐D) and hexadecoxyl‐benzophenone (BP‐H), used as new photoinitiators have been synthesized by Friedel‐Crafts reactions and identified by ultraviolet (UV) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The kinetic characteristics of photoinitiating crosslinking of BP‐D and BP‐H comparing with BP in the photocrosslinking of polyethylene (PE) in the melt and their compatibility with PE resin have been examined by gel content measurement and thermal migration experiments. The results show that these two BP derivatives are excellent photoinitiators, which have better compatibility, less volatility, higher photoinitiating efficiencies, and longer storage time than BP itself. These two new photoinitiators are promising for industrial applications of the photocrosslinking of polyolefins and curing of coats.
Maleic anhydride modification of polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model
Authors: Cha Jaehyug , White James L. 
Published: April 2004

AbstractThere has been little effort. to quantitatively understand graft copolymerization in batch and continuous mixers. Little information exists on the evolution of grafting reactions with respect to residence time in an internal mixer or along the screw axis in a twin‐screw extruder. In this study, maleic anhydride was grafted onto polypropylene in both an internal mixer and a twin screw extruder. The influence of residence time on degree of grafting in an internal mixer and a twin screw extruder was studied through measuring reaction yields with respect to reaction time in the internal mixer as well as along the screw axis in the extruder. The dependence of the degree of grafting with monomer and peroxide concentration was determined. A free radical kinetic model of the process was developed and compared to experiment. Kinetic parameters were determined.
Residence time and conversion in the extrusion of chemically reactive materials
Authors: Zhu Weimin , Jaluria Yogesh 
Published: April 2004

AbstractTwin‐screw extruders offer improved control of the residence time distribution (RTD) and mixing in materials such as plastics, rubber and food. Based on the flow and the heat transfer characteristics obtained for a self‐wiping, co‐rotating twinscrew extruder, the residence time and chemical reaction are studied by tracking the particles. For normally starve‐fed twin‐screw extruders, the length of the completely filled section is calculated as function of the process variables using the coupling of the flow with the die. With a model of the solid conveying section, the RTD for the whole extruder is calculated for corn meal at different screw speeds and flow rates. The calculated variation of RTD with the screw speed and the flow rate yields good agreement with observations from many experiments. The variation of the fully filled section length, chemical conversion and mixing effectiveness are also obtained under different operation conditions. Most of the results are in qualitative agreement with experimental results and may be used as guidelines for extruder design and determination of optimal operating conditions.
A uniform phenomenological constitutive model for glassy and semicrystalline polymers
Authors: Duan Y. , Saigal A. , Greif R. , Zimmerman M. A. 
Published: April 2004

AbstractA phenomenological constitutive model is proposed on the basis of four models: the Johnson‐Cook model, the G'Sell‐Jonas model, the Matsuoka model, and the Brooks model. The proposed constitutive model has a concise expression of stress dependence on strain, strain rate and temperature. It is capable of uniformly describing the entire range of deformation behavior of glassy and semicrystalline polymers, especially the intrinsic strain softening and subsequent orientation hardening of glassy polymers. At least three experimental stress‐strain curves including variation with strain rate and temperature are needed to calibrate the eight material coefficients. Sequential calibration procedures of the eight material coefficients are given in detail. Predictions from the proposed constitutive model are compared with experimental data of two glassy polymers, polymethyl‐methacrylate and polycarbonate under various deformation conditions, and with that of the G'Sell‐Jonas model for polyamide 12, a semicrystalline polymer.
Load‐carrying ability of polystyrene products with molded‐in holes
Authors: Heidweiller A. J. , Van Der Zwet M. J. M. 
Published: April 2004

AbstractThe combined influence of stress concentration, weld line, and local distribution of molecular orientation on injection molded polystyrene (PS) plates with a moldedin hole is described. Birefringence measurements were used to investigate the molecular orientation, and three‐point flexure was used to investigate the mechanical properties. Both blunt notch tests and transverse bending tests were carried out. Blunt notch tests showed a strong variation of the material resistance to fracture around the hole. The molecular orientation increased the material resistance not only at the hole equator, but also at the flow split area. In a large domain, wela line fracture was the dominant fracture mechanism. Transverse bending tests also showed a strong influence of the molecular orientation on the load‐carrying ability. The weld line was definitely the weakest region, but the reduction caused by the weld line itself appeared to be small.
Polyethylene compounds containing mineral fillers modified by acid coatings. 2: Factors influencing mechanical properties
Authors: Haworth B. , Raymond C. L. , Sutherland I. 
Published: April 2004

AbstractHigh molar mass medium density polyethylene (MDPE) compounds containing magnesium hydroxide filler, surface‐treated by a range of fatty acid coatings of variable aliphatic chain length were injection molded and subjected to mechanical property evaluation. Surface treatment modifies yield stress and modulus, with property maxima observed close to the monolayer coverage. Acid‐group terminated polyethylene (ATPE) coalings produced the highest yield stress, as a result of physical interaction with the matrix polymer. Retention of high‐energy, ductile mode impact failure of unfilled MDPE was obtained when using short‐chain decanoic acid coating, as a result of enhanced dispersion and reduced particle‐matrix interactions promoting microscopic matrix yielding. A mechanism for enhanced Mg(OH)2 particle dispersion based upon surface energy and molecular adsorption has been proposed, which is consistent with the properties data derived. Fractographic analysis (SEM) has confirmed the predominance of matrix yielding in compounds exhibiting enhanced impact resistance, while X‐ray pholoelectron spectroscopy (XPS) has also highlighted a different crack growth mechanism in MDPE compounds containing coated fillers, which are less prone to agglomeration. In addition, thermomechani‐cal history during processing also modifies physical properties of MDPE/Mg(OH)2 composites to some extent. Anisotropic effects include molecular orientation and filler particle alignment induced by shear stress during injection mold filling, which predominate in compounds containing coated fillers. Overall, the application of organo‐acid coatings reduces polymer‐particle surface interaction and thermody‐namic work of adhesion, leading to improved dispersion and enhanced properties. Appropriate property balances can be tailored by judicious selection of aliphatic chain length and addition level of fatty acid filler coatings.
Effect of starch content on viscosity of starch‐filled poly(hydroxy ester ether) composites
Authors: Zhou Genwen , Willett J. L. , Carriere C. J. 
Published: April 2004

AbstractThe effect of starch volume fraction on starch‐filled poly(hydroxy ester ether) (PHEE) biodegradable composites was analyzed using Mooney, Thomas, Maron & Pierce, and Frankel & Acrivos equations. Corn starch/PHEE materials were extruded using a twin‐screw extruder with starch volume fractions from 0.27 to 0.66. The starch was dried to a moisture content of 0.7% to minimize moisture effect on composite rheology. Dynamic frequency sweep measurements were carried out at 120°C and 1% strain. The equations of Maron & Pierce, Thomas, and Frankel & Acrivos can be used to describe the experimental data. It is found that the relative viscosity at the same shear stress increases with increasing shear stress. The possible existence of yield stress at high starch concentrations was examined using a Casson plot.
Cure shrinkage analysis of epoxy molding compound
Authors: Oota Ken , Saka Masumi 
Published: April 2004

AbstractEGA (ball grid array), one of the structures Used for semiconductor packages, involves a laminated structure. BGA inevitably involves significant warpage, owing to differences in shrinkage among constituent materials. The extent of warpage is governed by total shrinkage (= cure shrinkage + thermal shrinkage) of the epoxy molding compound that encapsulates the IC chip. In particular, the cure shrinkage exerts great influence on warpage. Cure shrinkage has been understood as the decrease in free volume at the time of curing. However, the cure shrinkage rate cannot be sufficiently explained by the free volume of the cured epoxy resin. We have developed an evaluation method based on the epoxy group reaction ratio, and have eventually confirmed that cure shrinkage depends on the reaction ratio of the epoxy group after curing, and on epoxy group density.
Fluorescence based temperature measurements and applications to real‐time polymer processing
Authors: Bur Anthony J. , Vangel Mark G. , Roth Steven C. 
Published: April 2004

AbstractWe have used temperature sensitive fluorescent dyes, doped into polymer resins, to monitor the true resin temperature during extrusion processing. Two types of temperature sensitive fluorescent dyes were used: mobility dyes and fluorescence band definition dyes. When mixed with the resin at dopant concentrations, the fluorescent dye resides in a molecular neighborhood composed of resin molecules. Under these circumstances, its fluorescence spectrum reflects the resin temperature in its neighborhood. We apply this measurement concept to extrusion processing by using an optical sensor that accesses the machine at standard instrumentation ports. We show that, under processing conditions, the true resin temperature is significantly different from The machine temperature. Two examples of real‐time process monitoring arc presented: first, the effects of shear heating during extrusion were measured, and second, the effects of poor temperature control during extrusion were observed. The effects due to pressure on the fluorescence temperature measurements are examined. The fluorescence temperature measurements are compared to melt temperature thermocouple measurements.
Diffusion‐induced bubble growth in viscous liquids of finite and infinite extent
Authors: Venerus David C. 
Published: April 2004

AbstractTransport models of diffusion‐induced bubble growth in viscous liquids of finite and infinite extent are developed and evaluated. Results from the present study are compared with results from the often‐cited papers by Amon and Denson (1984) and Arefmanesh et al (1992) and found to be in good agreement. Predictions for the bubble radius and pressure from the finite‐ and infinite‐liquid models are compared over a range of conditions. As anticipated, predictions from the two models coincide at early stages of the growth process, and differ at late stages of the growth process when the equilibrium bubble radius Is approached for the finite‐liquid model. Agreement between the two models at intermediate stages is observed only for relatively low growth rates.
Prediction of molecular weight distributions by probability generating functions. Application to industrial autoclave reactors for high pressure polymerization of ethylene and ethylene‐vinyl acetate
Authors: Brandolin A. , Sarmoria C. , Lótpez‐Rodríguez A. , Whiteley K. S. , Del Amo Fernandez B. 
Published: April 2004

AbstractWe develop a mathematical model able to describe the complete molecular weight distributions of polyethylene and elhylene‐vinyl acetate copolymers obtained in high pressure autoclave reactors. We apply probability generating function definitions to the mass balances of radical and polymer species in the reacting medium. We use three different definitions of probability generating functions, each one directly applicable either to the number, weight or chromatographic distributions. These probability generating functions are numerically inverted to obtain the corresponding calculated molecular weight distribution. The capabilities of two different inversion methods are compared. Predictions are compared with experimental data obtained in an industrial reactor; good agreement is obtained. The approach presented here is applicable to other types of polymerization reactors and post‐polymerization processes.
Coupled diffusion of water and ethanol in a polyimide membrane
Authors: Ni Xiuyuan , Sun Xiaohui , Ceng Dong , Hua Fengjun 
Published: April 2004

AbstractIn this work, the sorplion and steady state permeation of water‐ethanol mixture in an aromatic polyimidc membrane was investigated with the objective of revealing the coupling cherts of water and ethanol in their course of diffusion. The solubility of the watcr‐ethanol mixture in the membrane was determined by means of swelling‐distillation techniques. The sorption behavior was interpreted in terms of the thermodynamic equilibrium equations. The Maxwell‐Stefan mass transfer model was employed as a framework for modeling diffusion. Model equations derived therefrom enable us to cplculate coupled fluxes of water and ethanol from the experimental data. The coupling effects in the diffusion of water and ethanol were revealed by comparing the calculated coupled flux with non‐coupling flux, which was calculated by integration of the Fickian first law using independent diffusion coefficients. Furthermore, the implication of the sole adjustable parameter included in the derived model equations was discussed.
Modeling heat transfer in screw extrusion with special application to modular self‐wiping co‐rotating twin‐screw extrusion
Authors: White James L. , Kim Eung Kyu , Keum Jong Min , Jung Ho Chul , Bang Dae Suk 
Published: April 2004

AbstractThis paper proposes two important models useful for describing heat transfer and temperature profiles in single and modular self‐wiping co‐rotating twin‐screw extruders. One model predicts heat transfer coefficients. Calculations of the barrel and screw heat transfer coefficients are made for various modules in different diameter extruders. We compare the values of the heat transfer coefficients from the model with those from literature. The second model predicts the axial screw temperature profile when the barrel, but not the screw, is heated, Example calculations of the cup mixing and screw temperature profiles are also made for different diameter extruders.
Reactive blending of functionalized acrylic rubbers and epoxy resins
Authors: Dispenza C. , Spadaro G. , Carter J. T. , McGrail P. T. 
Published: April 2004

AbstractA high molecular weight acrylonitrile/butadiene/methacrylic acid (Nipol 1472) rubber is chosen to control processability and mechanical properties of a TGDDM (tetra glycidyl diphenyl methane) based epoxy resin formulation for aerospace composite applications. The physical blend of rubber and epoxy resin, achieved by dissolution of all the components in a common solvent, forms a heterogeneous system after solvent removal and presents coarse phase separation during cure that impairs any practical relevance of this material. A marked improvement of rubberepoxy miscibility is achieved by reactive blending (‘pre‐reaction’) the epoxy oligomer with the functional groups present in the rubber. The epoxy‐rubber ‘adduct’ so obtained appears as a homogeneous system at room temperature and also after compounding with the curing agent. Depending on the nature and extent of interactions developed between the rubber and the epoxy resin during ‘pre‐reaction,’ materials with different resin flow characteristics, distinctive morphologies and mechanical properties after curing were obtained. The effect of ‘pre‐reaction’ on the resin cure reaction kinetics has been also investigated.
Studies of the aging of nafion®/silicate nanocomposites using 29Si solid state NMR spectroscopy
Authors: Young S. K. , Jarrett W. L. , Mauritz K. A. 
Published: April 2004

AbstractSol‐gel reactions of tetraethylorthosilicate were conducted within the nanophase‐separated morphology of Nafion® films to yield Nafion®/silicate nanocomposites. The chemical aging of silicate phase molecular structure when the nanocomposites were exposed to (1) ambient air, (2) applied heat, (3) liquid water, (4) methanol reflux, and (5) heated sulfuric acid was explored by means of 29Si solid state NMR spectroscopy. In particular, the characteristic chemical shifts and relative Intensities of peaks that identify Qn = (HO)4‐n Si(OSi)n molecular subunits in silicate structures were determined for samples exposed to these aging conditions. Shifts in the Q peak distribution reflected the evolution of degree of Si atom coordination about SiO4 units. The coordination states are always Q4 and Q3 although a small Q2 population is occasionally present. Thus, a significant degree of silicate phase coordination can develop despite constraints posed by the Nafion® medium. Percent Q4 increases in all cases but then reaches a maximum after which it decreases, the greatest de‐polymerization being for samples aged in water. The greatest increase in Q4 relative to the un‐aged control occurred for samples heated at 100°C. Exposure to ambient air produced changes in Q4 that were small, but not insignificant. While the initial increase in Si atom substitution around SiO4 units can be rationalized in terms of gradual condensation reactions between residual SiOH groups, accompanied by the liberation of water molecules and their removal from the site of the reaction, the eventual decrease in coordination is not currently understood.
High internal phase emulsion foams: Copolymers and interpenetrating polymer networks
Authors: Tai Huiwen , Sergienko Anatoly , Silverstein Michael S. 
Published: April 2004

AbstractHigh internal phase emulsion (HIPE) copolymer and interpenetrating network foams were prepared from 2‐ethylhexyl acrylate (EHA), styrene (S) and divinylbenzene (DVB) using a unique process. The morphologies, thermal properties and dynamic and static mechanical properties of these foams were investigated. The glass transition temperatures and damping properties of the EHA/S copolymer foams vary with its composition. IPN foams with very broad tan 5 peaks were obtained. The damping properties of IPN foams were tailored through changing copolymer composition and monomer composition. The IPN foams based on a copolymer foam and styrene had a broader tan δ peak, a higher glass transition temperature and a higher modulus than tne copolymer foams of similar overall styrene contents. It is therefore possible to prepare novel damping foams based on polyHIPE foams through the synthesis of interpenetrating polymer networks.