bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of “gas fingering” behavior in gas‐assisted injection molding
Authors: Lu X. , Chiang H. H. , Fong L. , Zhao J. , Chen Shia Chung S.
Published: April 2004

A common problem encountered in gas‐assisted injection molding (GAIM) is “gas fingering,” i.e., gas bubbles penetrating outside designed gas channels and forming finger‐shaped branches. Severe gas fingering can result in significant reductions in part stiffness. In this paper, nondestructive techniques have been used to quantitatively characterize gas bubble geometry in specially designed GAIM parts. Based on the quantitative measurements, the most crucial process parameters to control gas fingering have been identified through factorial design experiments. More detailed process studies reveal that there is an intrinsic relationship between gas fingering and cross‐sectional gas bubble shape. By examining the effects of gas channel design and material type on the gas bubble shape, some useful gas channel design guidelines have been obtained.
Enhancement of fiber structure formation of a liquid crystalline copolyester via ultra‐high speed bicomponent spinning with poly(ethylene terephthalate)
Authors: Radhakrishnan J. , Ito H. , Kikutani T. , Okui N.
Published: April 2004

A thermotropic liquid crystalline copolyester, poly(hydroxybenzoic acid‐co‐ethylene terephthalate) (LCP), and poly(ethylene terephthalate) (PET) were coextruded using two different extrusion systems to form sheath‐core type biocomponent fibers. The bicomponent fibers could be spun up to a take‐up velocity of 8 Km/min. The structural characterization of the individual components in the as‐spun fibers showed that the orientation development in the PET component was significantly suppressed compared with the corresponding single component fibers. A significant increase in the tensile modulus of the LCP core component, which was estimated by the simple rule of mixtures, was observed above a take‐up velocity of 4 km/min. The increase in tensile modulus was attributed to the increase in the overall orientation of the LCP core resulting from the combination of the high levels of stress generated during spinning at very high speeds and the altered thermal and stress generated during spinning at very high speeds and the altered thermal and stress histories provided by the bicomponent spinning process. On‐line study of the thinning behavior of single component and bicomponent spinning was carried out in order to gain an understanding of the spinline dynamics, which improved the processability and structure development of LCP.
Synthesis of protective coatings on steel by surface spontaneous polymerization. 3: Process development and coating property studies
Authors: Zhang Xu , Bell James P.
Published: April 2004

We have previously reported a new method for applying protective coatings on metal surfaces, the Surface Spontaneous Polymerization Process (1). In this process, polymerization occurs spontaneously on the substrate upon immersion into a monomer solution, forming a layer of uniform coating in‐situ. No initiator is added. In this paper, studies on the development of the process and coating properties are reported. A monomer reaction system containing phenylmaleimide/styrene/bismaleimide/2‐(methacryloyoxy)ethyl acetoacetate has been developed to afford protective coatings on steel. The coatings obtained from this system have good thermal, dielectric, and adhesion properties. Corrosion resistance of 4CPMI coatings, as measured by the ASTM B‐117 salt spray test, is excellent after 700 hours of salt spray. The effects of several process variables on the polymer molecular weight were also studied, including monomer concentration, solution temperature, solution pH, and monomer feed composition. Solution stability studies indicate that polymerization occurs only on the surface and does not propagate into the solution.
Numerical simulation of three‐dimensional viscoelastic flow within dies
Authors: Kihara S. , Gouda T. , Matsunaga K. , Funatsu K.
Published: April 2004

In recent years, the development of CAE (Computer Aided Engineering) in polymer processing has been remarkable, and it is expected to be more realistic in viscoelastic numerical simulation, particularly in three‐dimensional complex geometry. Because of the problems of computational memory capacity, CPU time, and the numerical convergence of viscoelastic flow simulation, three‐dimensional viscoelastic simulation applicable to industrial flow behaviors has not yet been attempted. In this paper, we developed the numerical simulation of three‐dimensional viscoelastic flow within dies using a decoupled method, streamwise integration, and penalty function methods to decrease memory, and the TME (“Transformation of Equation of Motion to the Elliptic Equation,” S. Tanoue, T. Kajiwara, and K. Funatsu, The Eleventh Annual Meeting, the Polymer Processing Society Seoul, Korea, Extended Abstracts p.439) method, which raises the stability of convergence. We confirmed the reliability of this simulation technique to compare simulation results with experimental data of the stress field at a downstream wall shear rate of 5.41s−1 within a 60° angle tapered contraction die. We compared the predictions of a viscoelastic model (Phan‐Thien and Tanner model) with a pure viscosity model (Carreau model) at a downstream wall shear rate of 120s−1 and discovered a remarkable effect of viscoelasticity in the shear stress and first normal stress difference in particular in the tapered region.
Formation of integral skin polyurethane foams
Authors: Gupta V. K. , Khakhar D. V.
Published: April 2004

Polyurethane integral skin foams comprise a low density foamed core surrounded by a high density skin of the same material, and are made in a single molding operation. Polyurethane integral skin foams find wide application as structural materials, and the mechanical properties of such foams are significantly affected by the foam structure, which in turn is determined by the foaming process. An experimental and theoretical study of the foam formation process is presented. Experimental results show that increase in the mold wall temperature results in an increase in the upper skin thickness, a decrease in the lower skin thickness, and a decrease in the density of both skins. The core density increases with increasing wall temperature. Increase in the blowing agent concentration produces a small increase in the skin thickness. Computations based on the model of Marciano et al. [Polym. Eng. Sci., 26, 717 (1986)] are presented using an efficient numerical technique. Predictions of the model for the skin thickness, core density and pressure and temperature variation with time are in reasonable agreement with experimental data. The model, however, predicts higher skin densities than the experimental measurements. A modification of the initial condition of the model to account for the air bubbles dispersed during mixing gives better agreement between theory and experiment.
Controlled orientation of reflective pigment and optical property characterization of injection‐molded polypropylene
Authors: Rawson Keith W. , Allan Peter S. , Bevis Michael J.
Published: April 2004

The aims of the research reported were to explore the possibility of removing surface weld lines from highly reflective aluminum pigmented polypropylene injection moldings. Moldings were optically characterized and their characteristics attributed to pigment orientation present in the samples. Conventional injection molding and two novel molding techniques were employed for this investigation, Shear Controlled Orientation Injection Molding (SCORIM) and Bright Surface Molding (BSM). Further, the two techniques, SCORIM and BSM, were used in series and termed SBM to remove surface weld lines. The use of SBM enabled the re‐orientation of the pigment in order to induce a uniform direction for the “flip‐flop” effect where flow fronts have impinged from different directions. These moldings were then quantitatively characterized using a gonio‐spectrophotometer. Their different reflective surface characters were then related to the angle of orientation induced by the respective processing technologies used.
Shear yield behavior of calcium carbonate–filled polypropylene
Authors: Wang Yeh , Wang Jyun‐Jye
Published: April 2004

The rheological properties of calcium carbonate‐filled polypropylene has been examined using a Rheometrics dynamic analyzer RDAII. The study included a steady shear test, a transient stress growth test, and a dynamic oscillatory shear flow. Yield behavior was observed in all kinds of rheological tests for highly filled compounds when the volume loading exceeded a critical value at about 20%. The empirical Cox‐Merz rule, which is usually applicable to an unfilled polymer, was found to be invalid for highly filled compounds. The modified Cox‐Merz rule, in which the apparent viscosity versus the shear rate is equal to the complex viscosity versus the frequency‐amplitude in the nonlinear region, was found to be valid only for highly filled compounds. The viscosity and the apparent yield values appear to increase with increasing volume loading of filler particles. The surface treatment of fillers, which presumably reduces the interaction between filler particles and the extent of agglomeration, results in major viscosity reductions and decreases in apparent yield values. The yield values determined from various tests are not the same. The results are interpreted in terms of a system forming a filler network due to weak inter‐particle forces. The yield stress resulting from the breakdown and recovery of the network is thus dependent on the characteristic time of the individual test.
A continuous test data method to determine a reference curve and shift rate for isothermal physical aging
Authors: Bradshaw R. D. , Brinson L. C.
Published: April 2004

The mechanical response of a material undergoing isothermal physical aging is governed by a reference curve (typically time‐dependent modulus or compliance) and a shift rate (which describes the rate of aging). In the standard analysis approach, these parameters are determined from a series of load/unload creep or relaxation tests, in which only the load portion data is used for property evaluation. In this paper, a new continuous test data (CTD) method is presented to determine these parameters using both the load and unload data from such a test series. This is accomplished by employing effective time theory to predict the full load/unload data set, with the reference curve and shift rate obtained as those which best fit the experimental data. It is demonstrated that the references curve obtained via the standard approach is not capable of predicting the full load/unload data set, while the CTD method using a Prony series fits this same data very well. Several concerns regarding the CTD method are addressed, including the differences in the CTD and standard method shift rate, the effect of vertical shifting or material nonlinearity on the results, and application of the method to other loading scenarios. Results are presented for long‐term and variable stress tests. The data used in the study was obtained from polyimide resin and polyimide/carbon fiber composite specimens at several temperatures below Tg.
Relationship between surface potential and second harmonic generation in chromophore‐doped poly(ethylene oxide)/atactic‐poly(methyl methacrylate) blends
Authors: Vannikov A. V. , Vernel J. , Mal'Tsev E. I. , Savel'Ev V. V. , Rychwalski R. W.
Published: April 2004

The intensity of second harmonic (SH) light, generated by passing a laser beam through corona poled films of poly(ethylene oxide)/atactic‐poly(methyl methacrylate), PEO/a‐PMMA blends molecularly doped by 4‐anilino‐4'‐nitroazobenzene (DO3), is studied as a function of time, temperature, and composition. SH intensity decay kinetics at room temperature is entirely controlled by the time‐dependent surface potential decrease (SPD). In turn, the SPD is determined by the conductivity of polymeric films and the free volume. The latter is a function of temperature history and blend composition.
Environmental stress cracking of poly(acrylonitrile‐butadiene‐styrene)
Authors: Kawaguchi Takafumi , Nishimura Hiroyuki , Miwa Fumiaki , Abe Kazuhiro , Kuriyama Takashi , Narisawa Ikuo
Published: April 2004

The environmental stress cracking (ESC) of acrylonitrile‐butadiene‐styrene (ABS) copolymer caused by a non‐ionic surfactant (poly‐oxyethylene alkylether) was studied by constant‐load tensile creep tests and edge crack tension (ECT) tests. The fracture surfaces were investigated by a scanning electron microscope (SEM) and the morphology of the crack tip was investigated by a transmission electron microscope (TEM). It was found that the results of the creep tests performed in the non‐ionic surfactant were very different from those performed in air. SEM images of the fracture surfaces showed that there were three different mechanisms of fracture and that specimens had a tendency to rupture by ESC when the stress was small. The results of the ECT tests and the TEM images showed that the change in the mechanism of the fracture was attributable to the change of morphology at the crack tip.
Effect of compatibilizers on mechanical properties and morphology of in‐situ composite film of thermotropic liquid crystalline polymer/polypropylene
Authors: Bualek‐Limcharoen Sauvarop , Samran Jareerat , Amornsakchai Taweechai , Meesiri Wiriya
Published: April 2004

An in‐situ composite film of a thermotropic liquid crystalline polymer (LC3000)/polypropylene (TLCP/PP) was produced using the extrusion cast film technique. The compatibilizing effect of thermoplastic elastomers, styrene‐ethylene butylene‐styrene (SEBS), maleic anhydride grafted SEBS (MA‐SEBS), and maleic anhydride grafted polypropylene (MA‐PP) on the mechanical properties and morphology of the TLCP/PP composite films was investigated. It was found that SEBS provided a higher value of tensile modulus than MA‐SEBS, which in turn was higher than MA‐PP, despite the expected stronger interaction between the MA chain and TLCP. The observation of the morphology under optical and scanning electron microscopes suggested that all three compatibilizers helped improve the dispersion of the TLCP fibers and increased the fiber aspect ratio to a different extent. The fractured surface of the specimens showed more fiber breakage than pull‐out when a compatibilizer was added, which suggested the improvement of interfacial adhesion. The surface roughness of fibers with an added elastomeric compatibilizermay also provide mechanical interlocking at the interface. It is suggested that the increase in the viscosity ratio of TLCP/PP due to the added elastomeric compatibilizer, SEBS and MA‐SEBS, compared with the thermoplastic compatibilizer, MA‐PP, is more effective in improving the composite mechanical properties.
The adhesion between electrolessly deposited copper and a photoimageable polymer
Authors: Suzuki Masao , Kawamoto Mineo , Takahashi Akio
Published: April 2004

We investigated the relationship between the peel adhesion of copper, deposited by electroless plating, to a photoimageable polymer and the time of chemical etching before plating. Mechanical interlocking is generally considered as being the adhesion mechanism between deposited metals and substrates. However, we found that the peel strength decreased with an increase in the etching time though the polymer roughness did not change. The glass transition temperature of the photoimageable polymer became lower as the etching time increased. The pretreatment not only roughened the surface of the photoimageable polymer, but also affected the bulk polymer and the adhesion.
Extrusion characteristics of thermoplastic melts containing fluoropolymers
Authors: Lee Eonseok , White James L.
Published: April 2004

This paper investigates the influence of fluoropolymers on the extrusion characteristics of three different thermoplastic melts. The presence of a small amount of fluoropolymer reduced the pressure drops, extrudate swell, and retarded the onset of surface defects in linear low density polyethylene (LLDPE), while little or no effect was found in polystyrene (PS) and polyamide 12 (PA 12). Among the fluoropolymers investigated in this study, vinylidene fluoride‐hexafluoropropylene (VDF‐HFP) copolymer was the most effective additive in reducing the pressure drop and extrudate distortion of LLDPE, polyvinylidene fluoride (PVDF) intermediate, and tetrafluoroethylene‐hexafluoropropylene (TFE‐HFP) copolymer exhibited the least effectiveness. Contact angle measurements on the die surface indicated that all fluoropolymers preferentially deposit on the die surfaces during the extrusion of LLDPE and PS blends with small amounts of fluoropolymers.
Long fiber reinforcement of polypropylene/polystyrene blends
Authors: Inberg J. P. F. , Hunse P. H. , Gaymans R. J.
Published: April 2004

The recycling of inseparable polymer mixtures usually results in blends with poor mechanical properties. A mixture of PP and PS was taken as a model compound for a recyclate. The effect of adding glass fibers to a mixture of PP/PS (70/30) was studied, with special attention to long glass fiber reinforcement. Test specimens were made in three different ways: by dry blending (direct injection molding), mild compounding with a single screw extruder, and compounding with a twin screw extruder. The fiber concentration was varied from 0 to 30 wt%. The fiber lengths were determined to investigate fiber attrition. The fiber lengths in the samples were 1.09 mm for dry blending, 0.72 mm for single screw compounding, and 0.33 mm for twin screw compounding. The mechanical behavior was studied by unnotched and notched Izod impact and tensile tests. The PP/PS blend had a low fracture strain and low unnotched Izod impact strength compared with a PP homopolymer. With an increasing fiber concentration and fiber length, the modulus, tensile strength, and particularly the impact strength increased. With a 30 wt% glass fiber of the long fiber compound (dry blended), the modulus was raised by a factor of 3.5, the fracture stress by a factor of 2.5 and the unnotched Izod impact strength by a factor of 10. The product quality as judged by the scatter of the data was best for the twin screw compound and poorest for the dry blend. Compounding with a single screw extruder gave fairly constant injection molding product properties, combined with excellent mechanical properties.
In‐line residence time distribution of dicarboxylic acid oligomers/dioxazoline chain extension by reactive extrusion
Authors: Chalamet Yvan , Taha Mohamed
Published: April 2004

Polyesteramides were prepared by reactive extrusion by a condensation reaction of a fatty dicarboxylic acid [Unichema Pripop (1009) (C36)] or a carboxyl terminated polyamide 12 (CTPA 12) and a dioxazoline coupling agent [(1,3‐Phenylene)‐bis(2‐Oxazoline), (OO)]. The Residence Time Distribution (RTD) was measured using different fillers as in‐line ultrasonic detectable tracers and UV detectable reactive or nonreactive tracers. The apparent RTDs measured using ultrasonic detectable tracers were very different. The analysis of the reaction product and comparing RTDs measured using ultrasonic and UV tracers showed that the addition of a tracer had no effect on the reactive system and that most of the ultrasonic tracers did not flow in an identical manner to the reactive system. No direct correlation was obtained between the rheological or rheokinetic behaviors of the monomers or the reactive system and the apparent RTD. The RTD was obtained by using calcium carbonate as in‐line ultrasonic detectable tracers and UV detectable reactive or nonreactive tracers.
Essential fracture work of short fiber reinforced polymer blends
Authors: Wong Shing‐Chung , Mai Yiu‐Wing
Published: April 2004

Short glass fiber reinforced (SGFR) PA6,6/PP blends with 20 wt% styrene‐ethylene/butylene‐styrene triblock copolymers (SEBS) grafted with different levels of maleic anhydride (MA) were studied using both the essential work of fracture (EWF) and J‐integral fracture toughness techniques. Good linearity was found between the plane strain specific fracture work, Wf, and the ligament length, l, in single‐edge notched bend (SENB) specimens. The two fracture mechanics parameters were compared and there was good agreement between the J‐integral fracture initiation toughness, JIC, and the specific essential fracture work, WIe. The skin‐core morphology characteristic of injection molded short fiber reinforced thermoplastics (SFRT) was also revealed using the EWF approach.
Characterization of recycled cellulose by dynamic and isothermal thermogravimetry investigations
Authors: Devallencourt C. , Saiter J. M. , Capitaine D.
Published: April 2004

Isothermal thermogravimetric measurements were performed on recycled cellulosic materials. The kinetic parameters were determined with the Avrami‐Erofe'ev equation from two different ways. The first one consists of the determination of n from the slope of the variations of ln(–ln(1–α)) versus ln(t) and apparent activation energy ΔE from the slope of ln(k(T)) versus 1/T. The second one also gives the values of n and ΔE from a numerical fit of the experimental data. Both methods lead to the same results and show that the reaction order of the degradation process of the cellulose is close to unity. The value of this reaction order allows the interpretation of the dynamic thermogravimetry data with the Broido method. Using this method on a series of recycled cellulose with different content of chemical and mechanical paper pulps, we show that the apparent activation energies depend linearly onto paper pulp ratio.
Measurement of Tg in epoxy resins by DSC—effects of residual stress
Authors: Wang Hongbing , Siow Kok Siong
Published: April 2004

Differences in the glass transition temperatures (Tg) of epoxy resins were observed when their samples for differential scanning calorimetry (DSC) measurements were prepared by two different methods. The differences (in Tg) are believed to be due to the effects of interfacial residual stress, which is present only in the samples of lower Tg prepared with the formation of a “chemical” contact between epoxy resin and aluminum (pan) which have mismatched thermal expansion coefficients. Both types of the samples also showed, respectively, lower Tg when they were prepared by a fast‐cooling process than when they were prepared by a slow‐cooling process. This suggests that matrix residual stress, which is present in both types of the samples, as well as interfacial residual stress, has similar effects on the Tg of epoxy resins. This conclusion is substantiated by the results of the change of contact pattern and the freezing stress experiments.
Bubble growth in reaction injection molded parts foamed by ultrasonic excitation
Authors: Youn Jae R. , Park Hyeog
Published: April 2004

Processing of microcellular foam was studied for polyurethane. Assuming that the bubble growth is controlled by diffusion, theoretical prediction was carried out numerically to understand the bubble growth mechanism in the cavity during mold filling. Final bubble sizes were also predicted by considering the gelation time and the diffusion boundary. Viscosity change of the mixed polyurethane resin during polymerization reaction was predicted by considering reaction kinetics. The gelation time was determined to terminate the numerical calculation. The diffusion boundary was predicted based on the number of nucleated bubbles that had been determined both theoretically and experimentally. For processing of polyurethane foam by reaction injection molding, ultrasonic excitation was applied to the mixture of polyol and isocyanate. The polyol resin was supersaturated with nitrogen gas at an elevated pressure and ultrasonic excitation was applied to the mixture after impingement mixing of two components of the selected polyurethane system. Bubble nucleation was induced by the ultrasonic excitation and the bubbles were grown as the gas was supplied to the bubble from the resin.
Dynamic‐Mechanical properties and composition of longitudinal polymer liquid crystals
Authors: Woelke Ralf , Hess Michael
Published: April 2004

The temperature dependence of the dynamic‐mechanical behavior of different longitudinal polymer liquid crystals with short, branched spacers was analyzed and compared with results from calorimetric measurements. The combination of different techniques is necessary for interpretation. Torsional braid analysis provides advantages in the low‐temperature range.
Synthesis and physical characterization of semi‐IPNS of linear polyurethane and heterocyclic polymer network
Authors: Bartolotta Antonino , Marco Gaetano Di , Carini Giuseppe , D'Angelo Giovanna , Tripodo Gaspare , Fainleib Alexander M. , Slinchenko Elena A. , Shtompel Vladimir I. , Privalko Valery P.
Published: April 2004

Semi‐interpenetrating polymer networks (semi‐IPN) of linear polyurethane (LPU) and heterocyclic polymer network (HPN) were characterized by IR spectroscopy, small‐angle X‐ray scattering, differential calorimetry with diathermal shells (temperature interval 130‐500 K), and dynamic mechanical analysis (temperature interval 150‐500 K and frequency range 0.3‐30 Hz). The main results obtained may be summarized as follows: (1) The affinity of HPN towards the soft LPU microphase is responsible for the absence of large‐scale heterogeneity of semi‐IPNs on their base (at least, at low HPN/LPU ratios). (2) Phenomenological analysis of small‐scale, Arrhenius‐like subglass relaxations (γ1 and γ2 in LPU and in HPN, respectively) revealed little interference of HPN with relaxation centers (RCs) of LPU in semi‐IPNs, while the local environment of RCs in HPN, on the contrary, strongly depended on semi‐IPN composition.
Microstructure and properties of random heterogeneous materials: A review of theoretical results
Authors: Quintanilla J.
Published: April 2004

We present an overview of some theoretical results that have been obtained to rigorously bound the effective conductivity and effective elastic moduli of random heterogeneous materials. These bounds are obtained through the appropriate use of integrals over certain microstructure functions that capture essential morphological information about random materials. Such a characterization has been obtained analytically for several models, including fully penetrable spheres, totally impenetrable spheres, and the “cherry‐pit” model. These analytical techniques—characterizing the microstructure and using this information to bound the effective properties—will undoubtedly be useful in obtaining sharper bounds on the effective properties of polymers. While we present some advanced ideas and methods, an attempt will be been made to elucidate these methods for the nonexpert.
Laser light‐scattering studies of soluble high performance fluorine‐containing polyimides
Authors: Kwan Simon Chi Man , Wu Chi , Li Fuming , Harris Frank W. , Cheng Stephen Z. D.
Published: April 2004

Two sets of soluble high performance polyimides synthesized from 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′‐(trifluoromethyl)‐4,4′‐diaminobiphenyl diamine (PFMB), and from 2,2′‐bis(trifluoromethyl)‐4,4′,5,5′‐biphenyl‐tetracarboxylic dianhydride (HFBPDA) and 2,2′‐(trifluoromethyl)‐4,4′‐diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser light scattering (LLS) in tetrahydrofuran (THF) at 30°C. The calibrations, for 6FDA‐PFMB:  (nm) = 3.87 × 10−20.568,  (nm) = 2.38 × 10−20.560and  (cm2/s) = 2.13 × 10−4−0.560; for HFBPDA‐PFMB:  (nm) = 2.24 × 10−20.626,  (nm) = 1.27 × 10−20.621and  (cm2/s) = 3.99 × 10−4−0.621, have been established, where , ,  and  are the weight‐average molar mass, the root mean squarez‐average radius of gyration, thez‐average hydrodynamic radius and thez‐average translational diffusion coefficient, respectively. A combination of  and the translational diffusion coefficient distributionG(D) leads to the calibrations ofD(cm2/s) = 2.41 × 10−4M−0.564andD(cm2/s) = 6.16 × 10−4M−0.656for 6FDA‐PFMB and HFBPDA‐PFMB, respectively, whereDandMcorrespond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distributionG(D) into a corresponding molar mass distributionfw(M). On the basis of the Kratky‐Porod wormlike chain model, the persistence lengths (q) were found to be ˜ 3.3 nm and ˜ 4.5 nm, respectively, for 6FDA‐PFMB and HFBPDA‐PFMB, which indicates that both polyimide chains have an extended conformation. In addition,  /  ˜ (1.7‐1.9) shows that they are in coil conformation. Therefore, we conclude that both polyimides have an extended coil conformation.
Polyurethane + polyacrylate latex mixtures: Synthesis, characterization and properties
Authors: Travinska Tamara V. , Lipatov Yuri S. , Maslak Yuri V. , Rosovitsky Valeri F.
Published: April 2004

A series of polyurethane + polyacrylate latexes has been synthesized by putting different quantities of polyacrylate dispersion into an acetone solution of an anionic polyurethane prepolymer with terminal isocyanate groups. Colloid‐chemical and rheological properties of these systems have been investigated. The sorption of solvent vapors by mixtures of polyurethane + polyacrylate latexes has been studied. Some thermodynamical parameters including partial Gibbs functions of the solvent, individual polymers and their mixtures, and the Gibbs function of mixing polyurethane ionomer and acrylate copolymer have been calculated. Structureproperties relationships of the polyurethane + polyacrylate latexes were studied by dynamic mechanical analysis. Effects of varying the composition on the mechanical properties have been determined.
Evaluation of paracrystallinity in blown polyethylene films by generalized Clausius‐Mosotti equation
Authors: Bernabeu E. , Boix J. M.
Published: April 2004

The degree of paracrystallinity in several samples of low‐density blown polyethylene was estimated by assuming that there was a paracrystalline zone at the boundary between the amorphous and crystalline zones. The paracrystallinity was quantified by applying a generalization of the Clausius‐Mosotti equation and using the mean values of the ordinary and extraordinary refractive indices, previously calculated, through solving a special Bruggeman's equation. The final results are consistent with the values found in literature, where the degree of paracrystallinity is considered to be practically identical to the mean paracrystalline distortion parameter in this specific zone where these polymers are found.
Low temperature cure of vinyl ester resins
Authors: Li Ling , Sun Xiudong , Lee L. James
Published: April 2004

Vinyl ester resins are well known for their versatility as a composite matrix. With the development of a promising room temperature molding technology, vacuum‐assisted resin transfer molding, e.g. Seemann Composite Resin Infusion Molding Process (SCRIMP), the processability of vinyl ester resins at low temperatures has attracted considerable attention from the composite industry. The objective of this paper is to provide a better understanding of the reaction kinetics of this resin system at low temperatures. In this study, a differential scanning calorimeter (DSC) coupled with a Fourier transform infrared (FTIR) spectrometer was employed to measure the reaction profile of a vinyl ester resin with different promoter and styrene contents. A kinetic model based on the free radical co‐polymerization mechanism was developed for simulating the reaction rates and conversions of styrene vinyl and vinyl ester vinylene groups. The model parameters were determined from several FTIR experiments under isothermal conditions. This model, in conjunction with heat transfer analysis, was able to successfully predict the temperature profiles during curing in two SCRIMP molding cases based on groove type resin distribution system.
Numerical analysis of notch‐tip fields in rubber‐modified epoxies
Authors: Al‐Abduljabbar A. , Pan J.
Published: April 2004

In this work, the near‐tip fields in notched specimens of pressure‐sensitive nonporous and porous materials are investigated by finite element analysis. The specimen geometry and material properties are adopted from the corresponding experiments on rubber‐modified epoxies. The Drucker‐Prager yield criterion is first used to describe the yielding of nonporous materials. The yielding behavior of porous materials is based on a generalized Gurson yield criterion. The yield criterion for porous materials accounts for both the matrix material pressure sensitivity and the macroscopic pressure sensitivity due to porosity. Modifications are made on the yield criterion under negative mean stresses in order to account for the specific loading and geometry of the specimen. The computational results are compared with observed experimental cavitation zones and intense shear zones near the notch tip in specimens. Moreover, the near‐tip fields and crack initiation sites ahead of the notch tip related to the volume fraction of rubber particles are investigated. The computational results suggest that the lowering of the mean stress ahead of the tip in rubber‐modified epoxies with higher volume fractions of rubber changes the fracture mode from being controlled by high mean stresses at the elastic‐plastic boundary to being controlled by large plastic strains closer to the notch tip.
Conformational motions in immiscible blends of polycarbonate and styrene‐acrylonitrile copolymers
Authors: Belloch G. Pérez , Sanchez M. Salmerón , Ribelles J. L. Gómez , Pradas M. Monleón , Dueñas J. M. Meseguer , Pissis P.
Published: April 2004

Blends of commercial bisphenol‐A‐polycarbonate and styrene‐acrylonitrile copolymers were prepared by precipitation in ethanol from the solution in methylene chloride in order to eliminate the low molecular weight substances contained in the commercial polymers, specially the oligomers contained in commercial SAN copolymers. Two glass transitions appear in the DSC thermograms of the blend at the same temperatures as in the pure components which, in principle, indicates that the blend consists of two phases formed by pure PC and pure SAN. In order to detect small changes in the glass transition process that could be indicative of different mobility of the polymer chains in the blend with respect to the pure polymers, blends of different compositions were subjected to different thermal treatments that included annealing at temperatures below both glass transitions, and then the DSC thermograms were recorded. A broadening in the peaks shown by the cp(T) curves measured on annealed samples in the zone of the PC transition is detected while no significant differences are shown by the glass transition of the San phase of the blend with respect to pure SAN copolymer. Dielectric relaxation experiments in the frequency domain (from 100 to 3·106Hz) were carried out on the blends. The dielectric relaxation spectrum in the zone of the SAN main relaxation process was fitted with the stretched exponential equation showing no significant difference between the blends and the pure SAN copolymer. The region of the main relaxation process of PC was not analyzed due to the small polar activity of PC and the overlapping with the relaxation of the SAN phase.
Electrodeposition of BTDA‐ODA‐PDA polyamic acid coatings on carbon fibers from nonaqueous emulsions
Authors: Chen Yan , Iroh Jude O.
Published: April 2004

Electrochemical deposition of polyamic acid copolymer of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA) and 1.3‐phenylenediamine (PDA) was performed from a nonaqueous emulsion on carbon fibers. The electrodeposited PAA was subsequently dried. The yield and quality of deposited polyamic acid are strongly dependent upon a number of parameters that are related to the formulation and characteristics of polyamic acid emulsion. These parameters include solvent/precipitant ratio, concentration of surfactant, and solids content. The deposition yield of PAA was related to the applied current density, deposition time, and the charge passed, and was found to obey Faraday's laws of electrolysis. The coulombic efficiency was calculated.
Impact fatigue of a polycarbonate/acrylonitrile‐butadiene‐styrene blend
Authors: Ho Ming‐Hsiung , Hwang Jiun‐Ren , Doong Ji‐Liang , Fung Chin‐Ping
Published: April 2004

This study analyzes the impact properties of a polycarbonate/acrylanitrile‐butadiene‐styrene (PC/ABS) blend. The specimens were prepared under various injection molding conditions, including filling time, melting temperature, and mold temperature. Impact tests were performed with a Dynatup drop weight impact tester at different impact energies (10, 15, 20, 25 J). The fracture mechanism was examined with a scanning electron microscopy. The results indicated that the load‐time history of the PC/ABS blend has approximately a sinusoidal form in impact. The best injection molding conditions are a filling time of 12 s, a melting temperature of 260°C and a mold temperature of 80°C. In this case, the specimen shows the highest energy absorbed in single impact, together with the highest impact number in impact fatigue. The impact number and the accumulation energy seem to follow an exponential curve as the impact energy decreases. The PC/ABS blend material clearly exhibited ductile fracture with a continuous reduction in strength by viscoplastic deformation. The higher the impact number, the higher the accumulation energy. The accumulation energy of impact fatigue with impact energy 10 J is about 35–45 times greater than the energy absorbed in single impact. Tearing, shear fracture, and plastic deformation are the major fracture mechanisms of the PC/ABS blend matrix in single impact and repeated impact conditions.
High temperature thermal analysis characterization of honeycomb core
Authors: Shafizadeh J. E. , Seferis J. C.
Published: April 2004

One of the most important processing operations in the fabrication of honeycomb composite structures is the forming of the honeycomb core. High performance honeycomb structures must be precisely formed, or contoured, in order to meet the strict dimensional specifications required by the end user of the core. However, in the composites industry today, there is no basic understanding of the high temperature behavior of honeycomb materials, which is fundamental to understanding the commercial processing of honeycomb composite structures. In this study, the thermal and mechanical responses of Nomex®‐based honeycomb core were investigated and characterized through thermal analysis. In the ribbon direction of the core, specific post‐cure temperatures were identified where the honeycomb core displayed a maximum degree of creep. In the expanded direction of the honeycomb, the core displayed no maximum‐creep temperature. This behavior was attributed to the degradation of the node adhesive. A honeycomb creep time constant (τc) was also defined and evaluated as a function of the honeycomb post‐cure temperature. From this analysis, the softening of the dip resin was determined to play a larger role in creeping and deforming the core than the mechanical properties of the Nomex substrate.
Comparison of crystallization kinetics of miscible blends of syndiotactic polystyrene with atactic polystyrene or poly(1,4‐dimethyl‐p‐phenylene oxide)
Authors: Wu Fu Sun , Woo E. M.
Published: April 2004

Crystallization kinetics were characterized by using isothermal differential scanning calorimetry (DSC) analysis on neat semicrystalline syndiotactic polystyrene (s‐PS) and its miscible blends with atactic (amorphous) polystyrene (a‐PS) or with poly (1,4‐dimethyl‐p‐phenylene oxide) (PPO). The crystallization behavior of neat s‐PS polymer was compared to its miscible blends. The results suggest that the crystal growth in melt‐crystallized s‐PS is nearly of homogeneous nucleation and that the growth pattern of the spherulites is 3‐D spherical. The s‐PS component in its miscible blends was found to crystallize with similar behavior to that of neat s‐PS, but with lower Avrami exponents, suggesting that the nucleation mechanism is likely more heterogeneous with blending.
Non‐contacting tension measurement for molten films
Authors: Bian Baigui , Co Albert
Published: April 2004

A novel air‐nozzle system was developed to perform non‐contacting measurement of film tension in molten films. The measurement is based on correlation between the film tension and the pressure drop across the gap from the nozzle tip to the film. Films with higher tension exhibit less deflection by the impinging air jet and, consequently, produce a higher pressure drop across a smaller gap. The correlation between film tension and pressure drop was obtained with solid films at room temperature. A procedure was developed to extend the correlation to higher temperatures. The correlation was also found to agree with film tension versus pressure drop data obtained from specially designed molten film experiments. The capability of the system was demonstrated in the film casting of a linear low‐density polyethylene melt and a low‐density polyethylene melt. Tensions in the molten films were measured at various values of draw ratio and extrusion speed.
In‐situ generation of polyamide‐6 fibrils in polypropylene processed with a single screw extruder
Authors: Li Xuedong , Chen Mingcai , Huang Yuhui , Cong Guangmin
Published: April 2004

Polypropylene(PP) and polyamide6(PA6) were extruded with a single screw extruder. It was found that when PA6 was in the dispersed phase, it could deform and fibrillate in the PP matrix in the shear force field generated by the rotating screw. Dynamic mechanical analysis and mechanical tests showed that the mechanical properties, such as the tensile strength, impact strength, and modulus, were different in the different processing directions. With the addition of PP‐g‐MAH as a compatibilzer, the number of fibrils decreased and the dimension of the dispersed phase decreased significantly. This indicated that the compatibility has a strong effect on the in‐situ fibrillation.
In situ formation and processing of ultra high molecular weight polyethylene blends into precursors for high strength and stiffness fibers
Authors: Whitehouse C. , Liu M. L. , Gao P.
Published: April 2004

We present a novel process for the manufacture of ultra high molecular weight polyethylene precursors which can be subsequently made into high‐stiffness, high‐strength fibers or films. This process combines solid‐state extrusion and an in situ constrained solvent swelling process into a single stage for precursor preparation. The precursors produced by this process are shown to be highly ductile and porous. The inclusion of a small quantity of nontoxic solvent (10 wt% mineral oil) in the process has also been shown, using DSC and SEM characterization techniques, to provide the following process advantages: (i) better interfacial cohesion, because of the enhanced chain mobility at the particle surface due to the solvating effects; (ii) improved processability; and (iii) more uniform thermal properties and morphology across the extrudates due to enhanced heat transfer.
Control of part weight in injection molding of amorphous thermoplastics
Authors: Kamal Musa R. , Varela Alfredo E. , Patterson W. Ian
Published: April 2004

Two methods are proposed for the control of part weight in injection molding. In the PT method, part weight control is achieved by controlling the temperature and pressure of the melt in the cavity at gate freeze time. This time is considered to occur when the cavity melt pressure starts to decrease from its peak value. For the purposes of control, the bulk melt temperature is estimated from measurements by surface thermocouples at strategic locations in the cavity. A cascade scheme is implemented for the control of bulk temperature from cycle to cycle. A self‐tuning algorithm, with an observer, is employed for controlling the cavity pressure‐time profile, to follow a set point trajectory during a cycle. In PWT control, the coolant temperature is controlled, while the peak cavity pressure is adjusted in a given cycle to compensate for bulk melt temperature deviations measured in the previous cycle. Both PT and PWT control reduce variance in part weight. PWT control appears to yield the best results.
Thermoplastic elastomers based on ionomeric polyblends of zinc salts of maleated polypropylene and maleated EPDM rubber
Authors: Antony Prince , Bandyopadhyay S. , De S. K.
Published: April 2004

Ionomeric polyblends of the zinc salt of maleated EPDM rubber (Zn‐mEPDM) and the zinc salt of maleated polypropylene (Zn‐mPP) in the composition range from 90/10 to 60/40 wt% behave as ionic thermoplastic elastomers (ITPE), which show synergism in physical properties. The ionomeric polyblend shows higher physical properties than the corresponding non‐ionomeric polyblend. Infrared spectroscopy reveals the occurrence of intermolecular ionic interactions between the component ionomers in the blend. Zinc stearate acts as a platicizer in the melt of the ionomeric polyblend, which exhibits a higher melt viscosity than the corresponding non‐ionomeric polyblend. The blend can be reprocessed like a thermoplastic, with no drop in strength even after three extrusion cycles.
Reactive compatibilization of polypropylene/polyethylene terephthalate blends
Authors: Champagne Michel F. , Huneault Michel A. , Roux Claudine , Peyrel Wilfried
Published: April 2004

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP‐g‐GMA) was studied. Two PP‐g‐GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20‐fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub‐micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10–20 μm wide. The low‐GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifiying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated.
Effect of sodium oleate addition on the morphology of polypropylene‐co‐polyamide blends
Authors: Tsebrenko M. V. , Rezanova N. M. , Nikolaeva A. P. , Tsebrenko I. A. , Lazar I. A.
Published: April 2004

The influence of sodium oleate additives on processing and morphology of polypropylene ‐ co‐polyamide (PP/CPA) mixture melts has been investigated. It is shown that sodium oleate is located in the interphase of the components and acts at small additives (up to 3 wt%) as an interfacial tension agent, improving miscibility of polymers, and increasing the kinetic stability of mixtures and the degree of PP dispersion in the co‐polyamide matrix. The plasticizing effect on mixture melt was observed at 7 wt% sodium oleate as a reduction of mixture viscosity. The ultrathin PP fibers (microfibers) strictly oriented in the direction of extrusion are the main type of structure produced during extrusion of a PP/CPA mixture. Addition of sodium oleate changed the PP fiber‐formation in the CPA matrix: the total number of fibers increased, their diameter and diameter distribution decreased.