bluuebunny/crossref_metadata_2025_split huggingface dataset:
Work of fracture of PBT/PC blend: Effect of specimen size, geometry, and rate of testing
Authors: Hashemi S. 
Published: April 2004

AbstractFracture behavior of PBT/PC blend was studied at room temperature using two specimen geometries (SENT and DENT) and a wide range of specimen sizes and crosshead speeds. It was found that the fracture of all SENT and DENT specimens is completely ductile and stable. A linear relationship was obtained between the specific total work of fracture, wf, and the ligament length, L. Extrapolation of this linear relationship to zero ligament length gave the specific essential work of fracture, we, which for PBT/PC blend was 35 ± 5 kJ/m2 and was almost insensitive to geometry and the dimensions of test specimens as well as testing rate.
Novel atropisomeric binaphthol containing comb‐shaped copolymers forming chiral nematic phases
Authors: Shibaev V. P. , Deussen H. J. , Bobrovsky A. Yu. , Shibaev P. V. , Boiko N. I. , Bjørnholm T. , Schaumburg K. , Bechgaard K. 
Published: April 2004

AbstractNovel comb‐shaped liquid crystalline acrylic copolymers consisting of nematogenic methoxy‐phenylbenzoate acrylic monomers (A) together with novel chiral binaphthol (BN) methacrylic monomers (MB‐m) were synthesized in this study. The prepared copolymers differ in spacer lengths of MB‐m (m = 3, 5, 11) and in their compositions. The homopolymers of the three new chiral BN monomers MB‐m were also prepared. Copolymers with a low concentration of BN monomeric units (less than 16 mol %) display a cholesteric mesophase. The induced chirality in the polymers is due to atropisomerism (chirality due to hindered rotation around single bonds) of the BN molecules. The helical twisting power β (HTP) caused by the atropisomeric units in the synthesized copolymers was shown to decrease significantly on heating. The unusually high negative temperature coefficient of HTP observed above the glass transition temperature (Tg) could be explained in terms of conformational changes of the BN molecules in the copolymers.
Synthesis and characterization of new water‐soluble precursors of polyimides
Authors: Clemenson P. I. , Pandiman D. , Pearson J. T. , Lavery A. J. 
Published: April 2004

AbstractWe have successfully synthesized and characterized new water‐soluble precursors of polyimides based on dianhydrides with diaminobenzene sodium sulfonate (DABSS) and diaminostilbene disodium sulfonate (DASBDSS). The precursors are soluble in water and methanol as well as in several aprotic solvents. The optimum inherent viscosities of the poly(amic acids), obtained by varying reaction temperatures, were measured using a conventional Ubbelohde viscometer. The average molar mass of the polymers expressed as the “poly(ethylene oxide)‐PEO/poly(ethylene glycol)‐PEG equivalent” molecular masses obtained by gel permeation chromatography (GPC) showed significant broad molecular mass distributions with their polydispersities ranging from 2.9 to 4.6. FT‐IR spectra revealed complete imidization of the polyimides. Their thermal properties were studied by techniques such as differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Polyimides derived from the dianhydrides and DASBDSS showed better thermal stability up to 40°C in nitrogen than in oxygen atmosphere. However, polyimides based on the dianhydrides and DABSS were slightly more stable in oxygen than in nitrogen atmosphere. In oxygen, all the synthesized polyimides exhibited weight losses of about 50% in the range of 450–510°C. The overall weight losses of these polyimides under nitrogen were less than 50% at 700°C. New network polymellitimides based on mellitic trianhydride (MTA) and DABSS, and co‐polymellitimides based on MTA, DABSS, and ODA (oxydianiline) were also synthesized and characterized successfully. Their thermal stabilities were compared with the linear polyimides using TGA and DSC.
Composition‐dependent properties of segmented polyurethanes
Authors: Privalko Valery P. , Shapoval Raissa L. , Usenko Andrey A. , Oranskaya Elena I. 
Published: April 2004

AbstractWe studied segmented polyurethanes (SPU) from poly(diethylene glycol adipate) with molar masses MSFT = 780, 1365, 1780 and 3200 g/mol (soft fragments, SFT), 2,4‐toluene diisocyanate and 2,4‐toluene diamine (stiff fragments, STF) with essentially monodisperse molar mass distribution of STF. They were characterized by WAXS, SAXS, heat capacity measurements, mainly from 150–450 K, and enthalpies of solution in dimethyl formamide at room temperature, ΔHsol. The experimental results may be summarized as follows.

The glass transition temperatures of SFT decrease with an increase of MSFT, but remain essentially composition‐invariant at fixed MSFT, whatever the STF volume fraction φ.
The surface‐to‐volume ratio of STF domains exhibits sudden, jump‐like transitions at volume fractions φ* = 0.23 and φ** = 0.40, respectively.
Exothermic (i.e., negative) values of ΔHSOl exhibit a jump‐like decrease at φ* = 0.23.
It has been shown that the main cause of the latter effect is the transition of SFT from a somewhat extended to an essentially unperturbed conformation.
Numerical analysis of injection molding of glass fiber reinforced thermoplastics. Part 2: Fiber orientation
Authors: Greene Joseph P. , Wilkes James O. 
Published: April 2004

AbstractNumerical predictions of fiber orientation during injection molding of fiber‐filled thermoplastics are compared to measurements. The numerical work successfully describes the flow of fiber‐filled plastic during injection molding, using finite‐difference solutions for the transport equations and marker particles to track the flow front. The flow is modeled as a 2‐D, non‐isothermal, free‐surface flow with a new viscosity model dependent upon temperature, pressure, and fiber concentration. The fiber orientation is based upon solution to the Fokker‐Planke equation. The comparison demonstrates fair agreement between predicted fiber orientation and experimental results for slow and fast injection speeds. For the slow speed case at 10 and 20 wt% fibers, the numerical and experimental works show that the fibers are more random at the flow front than at the centerline, and that the fibers become more aligned as they flow from the gate to the midstream region. At fast injection speeds, the agreement between the numerical and experimental works is not as good as at slow injection speed. Possible explanations for the discrepancies are that the flow is assumed to be simple shear when injection molding is known to be a pressure‐driven flow, the fibers have an initial orientation for the runner rather than the assumed random orientation, the fibers that were displayed from the camera were more oriented just behind the flow front (owing to the fast injection speed), and the orientation requires more than a 2‐D video image to represent a 3‐D fiber orientation.
Effect of reactor type on polymer product: A backmix reactor for polymerizations and other viscous reaction media
Authors: Lu Y. , Biesenberger J. A. 
Published: April 2004

AbstractA continuous‐flow, backmix reactor, based upon the principle of drag flow and capable of handling viscous reactions, was designed and constructed. Its backmixing effectiveness was demonstrated via residence time distribution measurements, flow visualization experiments, and a stepwise polymerization reaction. The molecular weight distribution of the resulting polymer, which was measured and contrasted with that produced in a plug‐flow type (extruder) reactor, was significantly altered by backmixing, as predicted computationally.
Modeling of industrial styrene polymerization reactors
Authors: Makwana Y. , Moudgalya Kannan M. , Khakhar D. V. 
Published: April 2004

AbstractSteady‐state modeling and simulation of thermally initiated bulk polymerization of styrene in a train of existing industrial reactors is presented. Two reactors of different geometry and flow arrangement, which operate in series, are modeled as plug flow reactors. The model of Arai et al. (8) for the kinetics of thermal polymerization of polystyrene is used. The model predictions agree well with plant data for different operating conditions. A parametric study shows the feed rate, diluent (ethyl benzene) concentration and reactor temperatures to have a significant effect on final conversion and molecular weight.
Study of mixing efficiency in kneading discs of co‐rotating twin‐screw extruders
Authors: Cheng Hongfei , Manas‐Zloczower I. 
Published: April 2004

AbstractCo‐rotating twin‐screw extruders are widely used for compounding and blending in polymer processing. In a modular machine, the dominant elements determining dispersive mixing efficiency are the kneading discs. A fluid dynamics analysis package ‐ FIDAP, using the finite element method was implemented to simulate the 3‐D isothermal flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK‐53 co‐rotating twin‐screw extruder. The kneading discs simulated are three‐lobe discs. The flow field characteristics relevant for dispersive mixing are shear stresses generated and elongational flow components. We compare these flow characteristics for the three‐lobe kneading discs of the ZSK‐53 with the two‐lobe discs of a ZSK‐30 machine. We also discuss the influence of processing parameters on the flow field mixing efficiency.
Review of die lip buildup in plastics extrusion
Authors: Gander Jesse D. , Giacomin A. Jeffrey 
Published: April 2004

AbstractDie lip buildup, also called plate‐out, die drrool, die drip, or die peel, refers to the unwanted material accumulation on the open faces of extrusion dies. Since this buildup of material can interfere with extrusion, the processing line must be shut down periodically to clean the die. These shutdowns are costly. The mechanism for die lip buildup is not understood, though there are a variety of proposed explanations. Ways to suppress the problem have been developed by trial. Our review of the literature suggests that there are many mechanisms at play in die lip buildup. For a given industrial problem only a few may matter, but which? Here we use a dimensional analysis to develop a unified approach to die drool problems.
Processing and cell morphology relationships for microcellular foamed PVC/wood‐fiber composites
Authors: Matuana Laurent M. , Park Chul B. , Balatinecz John J. 
Published: April 2004

AbstractIn this research, the effects of the materials and the processing conditions on the cell morphology of foamed PVC/wood‐fiber composites were studied with a view to establishing their process‐structure relationships. Each step of microcellular PVC/wood‐fiber composites processing is addressed, including the surface treatment of the wood‐fiber, mixing of polymer and wood‐fiber, manufacture of the composites, the saturation of the composites with gas, microcellular foaming of the composites, and characterization of the cell morphology. The cellular morphologies of the foamed PVC/wood‐fiber composites are a strong function of the content of plasticizer and the surface treatment of wood‐fiber as well as the gas saturation and foaming conditions.
Study of kinematics and dynamics of film blowing of different polyethylenes
Authors: Ghaneh‐Fard A. , Carreau P. J. , Lafleur P. G. 
Published: April 2004

AbstractAn extensive experimental study of the effects of material characteristics and processing parameters on the kinematics and dynamics of film blowing is presented. Three polyethylene resins, a high‐density polyethylene (HDPE), a low‐density polyethylene (LDPE), and a linear low‐density polyethylene (LLDPE) were investigated. The convergent flow analysis of Cogswell was used to characterize the elongational flow behavior of the polymers. Strain rates and pressure inside the bubble (Pi) have been determined over a wide range of film blowing conditions. Moreover, on‐line bubble temperature and birefringence measurements have been carried out along the length of the bubble. The experimental results reveal that the three polymers display different behaviors. The LLDPE requires the highestPivalue and the LDPE, the lowest. Consistent with this, the LLDPE shows the lowest in‐plane birefringence and the LDPE, the highest. Interactions between various process parameters affecting thePivalue are characterized. Bubble instability is correlated to the apparent uniaxial elongational viscosity andPi. The most stable polymer (LDPE) has the highest elongational viscosity and requires the lowestPi. Stresses have been calculated with the help of the birefringence andPidata. The stress and strain rate data were used to calculate an apparent nonuniform biaxial elongational viscosity of the melts, but could not be correlated through any simple constitutive equation.
Compatibilization of blends of polyethylene with a semirigid liquid crystalline polymer by PE‐g‐LCP copolymers
Authors: La Mantia F. P. , Scaffaro R. , Magagnini P. L. , Paci M. , Chiezzi C. , Sek D. , Minkova L. I. , Miteva Ts. 
Published: April 2004

AbstractThe blends of thermoplastics with liquid crystalline polymers show, in general, poor properties because of the lack of adherence between the two phases. The use of ad hoc synthesized copolymers containing the monomer units of the two polymers has been recently considered by some of us for blend compatibilization, and the results appear promising. In this work, new PE‐g‐LCP copolymers, prepared either by the synthesis of the LCP in the presence of a functionalized PE, or by reactive blending of the latter polymer with preformed LCP, have been employed as compatibilizing additives for blends of PE with a semirigid LCP. The morphology and the rheological and mechanical properties of the ternary blends, compared with those of samples without compatibilizers, or containing conventional maleic anhydride grafted PE, indicate that the PE‐g‐LCP copolymers do in fact lead to an improvement of interfacial adhesion, both in the melt and in the solid state, as well as to a modest enhancement of the mechanical properties. The results may be rationalized considering that the PE‐g‐LCP copolymers used by us consist of fairly short PE backbones with LCP grafts of various length. The molecules with longer LCP branches are thought to become mixed at the surface of the LCP particles and to give rise to fairly weak interaction with the PE matrix. It is argued that new PE‐g‐LCP copolymers synthesized from higher molar mass functionalized PE samples might show much better compatibilizing performance.
Numerical simulations of annular extrudate swell of polymer melts
Authors: Otsuki Yasuhiko , Kajiwara Toshihisa , Funatsu Kazumori 
Published: April 2004

AbstractNumerical viscoelastic simulations were carried out using a K‐BKZ type of separable integral constitutive equation. Both reversible and irreversible models were tried for several types of damping functions to calculate the annular extrudate behavior of high‐density polyethylene (HDPE). There are two aims in this study; first, to clarify the properties of these dumping functions, and second, to investigate the influence of rheological characteristics on annular extrudate swell. In these numerical simulations, relaxation spectrum and shear viscosity were fixed, and the other characteristics were varied. The reversional response of the damping function mainly has an effect on the magnitude of the area swell even if the die is straight. The irreversible model expresses the experimental results of annular extrudate swell better than the reversible model. The accurate fitting of N1 by the damping model is important for predicting it. The magnitude of N1 predicted from the Wagner exponential model is lower than that of the PSM model, and the area swell shows the same tendency as N1. A modified PSM model that allows the N1 curve to shift can fit the magnitude of area swell. The relationship between the diameter and thickness of the extrudate depends on N2/N1, and it was estimated by simple linear elasticity of solids. The time dependent viscosity varies with the type of damping function, and it influences the time‐dependent swell.
Polymerization of acrylic bone cement investigated by differential scanning calorimetry: Effects of heating rate and TCP content
Authors: Yang Jen‐Ming , Shyu Jiing‐Shen , Chen Hsin‐Lung 
Published: April 2004

AbstractThe polymerization reaction of a bone cement (standard Surgical Simplex‐P Radiopaque) upon heating has been investigated by differential scanning calorimetry (DSC). The effects of the addition of tricalcium phosphate (TCP) on the rate and the heat of polymerization during DSC heating were evaluated. The rate and polymerization heat (ΔH) were characterized by the initial curing temperature (Ti), peak temperature (Tp), completing curing temperature (Tf), the curing range (ΔT = Tf − Ti) and the area of the DSC exotherm. It was found that Ti, Tp, Tf, ΔT, and ΔH all increase with increasing heating rate. Increasing TCP content also induced increases in Ti, Tp, Tf, ΔT, and ΔH. From the kinetic analysis, the polymerization of acrylic bone cement was found to be a first order reaction. The effects of heating rate and TCP contents on the rate and the heat of polymerization could be explained based on the frequency factor and the activation energy extracted from the kinetic analysis. Increases in both heating rate and TCP content depressed the frequency factor and the activation energy.
Film formation and crack development in plasma polymerized hexamethyldisiloxane
Authors: Zuri L. , Narkis M. , Silverstein M. S. 
Published: April 2004

AbstractPlasma polymer thin coatings can be used in a variety of applications that require thin ultrasmooth, defect‐free homogeneous films. In this study both film formation and crack development are described and related to the structure of the plasma polymer. The growth of a plasma polymer film reproduces the topography of the porous (polysulfone) PSf support and the time needed for complete coverage depends on the rate of deposition which is a function of the plasma power and monomer flow rate. The plasma polymerized hexamethyldisiloxane, PPHMDSO, film on a PSf porous support is under compressive internal stress causing the membrane to bend convexly with respect to the film. Despite these stresses, the composite membrane (film/support) did not crack when freely immersed in water and alcohols. Cracks developed in the mechanically constrained PPHMDSO composite membrane on exposure to alcohols. Films with more organic character showed high adhesion among the plasma polymer nodules and between the plasma polymer and the PSf substrate, resulting in substrate tearing and cracking straight through the plasma polymer layer.
Effect of processing and thickness on the structure in a polyimide film of poly(pyromellitic dianhydride‐oxydianiline)
Authors: Saraf Ravi F. 
Published: April 2004

AbstractIt is well known that poly(pyromellitic dianhydride‐oxydianiline) (PMDA‐ODA), orders at curing temperature well below its Tg with chains oriented parallel to the film plane. Structure analysis using X‐ray scattering reveals two structural features: (a) The ordered structure range from biaxial‐nematic‐like to crystalline; (b) the symmetry of orientation of the ordered regions change from a fiber, to planar to isotropic as a function of depth. Both of these structural features are attributed to surface effects and solvent retention during curing. The solvent profile is estimated during the imidization process using a theoretical model. The model considers the change in temperature, imidization rate, diffusivity, and film thickness with time during the curing. The model indicates that solvent content after most of the imidization is complete is crucial in determining the order and texture in the film. At the air/film interface, a thin skin formation due to solvent depletion and surface ordering is suggested from the model. Depending on the process condition the overall structure of the film can vary from crystalline to mesomorphic. The biaxial nematic and smectic like structure are probably not equilibrium structures but are frustrated order due to limited solvent‐induced mobility. The process condition affect the quality and quantity of order, and the texture due to chain's anisotropic cross‐section is affected primarily by film thickness. By replacing a single component precursor with a blend of precursors of the same polyimide, both higher isotropy and order can be obtained in thin PMDA‐ODA films. The order and extended chain conformation is better than that observed in the top 10 nm nearsurface‐structure.
Kinetic and rheological relationships of dicyanate ester polycondensation for the resin transfer molding process
Authors: Texier C. , Taha M. , Maazouz A. , Pascault J. P. 
Published: April 2004

AbstractKinetic and rheological behavior of a liquid dicyanate ester catalyzed by a copper salt was studied with a view to controlling the RTM process. The kinetics are satisfactorily modeled with a simple second order model until vitrification occurs. Independent of the catalyst concentration, the relationship between glass transition temperature Tg and conversion x was well validated, indicating that vitrification occurs well before Tg(x) reaches the curing temperature. The rheological study allowed gelation (tanδ crossover) and vitrification times at different curing temperatures to be determined. The values of tanδ at gel point were found to be slightly higher than those usually found. In order to carry out a simulation of the RTM process, viscosity and conversion were also linked with an empirical model.
Rheological and rheo‐optical properties of high molecular weight syndiotactic and atactic polyvinylalcohol solutions
Authors: Lyoo Won Seok , Kim Byoung Chul , Ha Wan Shik 
Published: April 2004

AbstractThe rheological and rheo‐optical properties of solutions of high molecular weight polyvinylalcohol (PVA) with different syndiotactic diad contents in dimethylsulfoxide (DMSO) were investigated in terms of tacticity, molecular weight, and degree of saponification. Tacticity played a significant role in rheological behavior. Over the frequency range of 10−1 to 102 rad/s PVA with syndiotactic diad content of ∼53% (atactic PVA) exhibited almost Newtonian flow behavior whereas PVA with syndiotactic diad content of ∼63% (syndiotactic PVA) exhibited Bingham flow behavior. On the plot of storage modulus (G′) against loss modulus (G″) atactic PVA gave slopes of ∼2 while syndiotactic PVA gave slopes of ∼1. With syndiotactic PVA, an increase of shear rate notably increased flow birefringence (Δnf) at shear rates higher than 5 sec−1. On the other hand, only a slight increase in Δnf was observed in the case of atactic PVA. The effects of molecular weight and degree of saponification were discussed as well.
Simulation of thermomechanical processes in crystallizing polymer
Authors: Shardakov I. N. , Matveyenko V. P. , Pistsov N. V. , Beghishev V. P. 
Published: April 2004

AbstractConstitutive equations are developed to describe the interrelation between thermomechanical behavior and phase transitions in crystallizing polymers. A crystalizing polymer is considered as a two‐component mixture of amorphous and crystalline structures, the fraction of which is defined by the degree of crystallinity. Numerical realization is performed using a variational method and a finite element procedure. The key feature of the calculation algorithm is reduction of a nonstationary problem to a sequence of stationary problems on a nonuniform time mesh. The validity of the proposed mathematical model is supported by the results of experiments performed to study the evolution of the stress‐strain state for a disk‐shaped polyamide 6 plate on crystallization.