bluuebunny/crossref_metadata_2025 huggingface dataset:
The hot‐tool and vibration welding of acrylonitrile‐butadiene‐styrene
Authors: Stokes Vijay K.
Published: April 2004

Thermoplastic window frames are made by hot‐tool welding mitered, extruded profiles. The effects of weld process conditions on the strengths of hot‐tool butt joints are investigated for a grade of acrylonitrile‐butadiene‐styrene that was specially developed for window‐frame applications. Vibration‐weld strength data, obtained on a research machine in which all the process variables can be independently controlled, are used to benchmark strengths of hot‐tool welds made on a commercial welding machine. Process differences between hot‐tool butt welding and the hot‐tool welding of mitered, extruded profiles are discussed.
Welding of thermoplastics reinforced with random glass mat
Authors: Gehde Michael , Giese Michael , Ehrenstein Gottfried W.
Published: April 2004

Thermoplastics reinforced with random glass mat have high strength and stiffness; the fibers dominate the mechanical behavior of these composites. The results of this investigation have shown that fibers are ineffective for reinforcing hot‐tool and vibration welded butt welds. The maximum weld strengths attained with GMT are comparable to the strengths of good welds of the unfilled material. The optimum hot‐tool welding parameters for the reinforced materials are different from those for the unfilled material. Unfilled polypropylene is easier to weld than unfilled polyamide. This characteristic is also true of the reinforced materials. In vibration welding, high welding pressures and high amplitudes result in lower mechanical properties. The optimum penetration depends on the fiber content of the bulk material. This penetration dependence is different from that for unfilled thermoplastic, for which the mechanical properties are independent of the penetration once a steady state has been attained.
Friction welding of polyamides
Authors: Potente H. , Uebbing M.
Published: April 2004

Results from different experiments on friction welding are used to characterize the behavior of polyamide over a wide range of welding conditions. Several types and grades of polyamide were joined using the vibration and spin welding processes. The quality of the welds was evaluated by short time tensile tests and microscopy. In addition to the geometry of the parts being joined, the process parameters and the material were found to affect the quality of the weld, so that associated with each application is a different set of optimum welding parameters.
Evaluation of thermodynamic theories to predict interfacial tension between polystyrene and polypropylene melts
Authors: Kamal M. R. , Demarquette N. R. , Lai‐Fook R. A. , Price T. A.
Published: April 2004

The commonly used thermodynamic theories (mean field theory and the square gradient theory) to predict interfacial tension between polymers have been modified. The results of these theoretical developments have not yet been fully tested and compared to experimental data. In this paper, experimental data for the effects of temperature, molecular weight, and molecular weight dispersity on interfacial tension for polypropylene/polystyrene polymer pairs are compared with the predictions of the new versions of the above theories. To evaluate these theories, it is necessary to know the Flory‐Huggins interaction parameter for the polymer pairs studied. The relation correlating the Flory‐Huggins interaction parameter to the Hildebrand solubility parameter was not suitable for evaluating the theoretical predictions of interfacial tension. Instead, the Flory Huggins interaction parameter was expressed as the sum of an enthalpic contribution, χH, and entropic contribution, χs. In the absence of reliable experimental values, a method was developed to evaluate the two contributions, based on interfacial tension data. The procedure provided an interaction parameter that is allowed to depend on molecular weight. When this approach was used, the predictions of only the new version of the square gradient theory were in good agreement with the experimental data for the influence of temperature and molecular weight on interfacial tension. However, the theory predicted the effect of polydispersity on interfacial tension only at high temperatures.
Effects of flow induced orientation of ferromagnetic particles on relative magnetic permeability of injection molded composites
Authors: Fiske Thomas , Gokturk Halit S. , Yazici Rahmi , Kalyon Dilhan M.
Published: April 2004

Composite samples consisting of ferromagnetic asymmetric particles incorporated into a polyolefin binder were injection molded using custom designed molds which produced preferential fiber orientations. The relative magnetic permeability values of the composites were measured as a function of the filler volume fraction, injection rate, gate diameter, temperature, aspect ratio of the fibers, and fiber orientation. Fiber orientation was affected by the molding conditions and controlled the relative magnetic permeability of the composites. The degree of fiber orientation was significantly affected by the size of the opening (gate) to the mold, or by the mold geometry going from an edge‐gated cylindrical to a center‐gated disk cavity. Relative permeability values of the composites were observed to increase when the fiber orientation and the applied field were parallel to one another. For instance, highly aligned composite samples exhibited up to 30% greater relative permeability values compared to those samples which exhibit fiber orientation distributions approaching a random distribution. To our knowledge this is the first study that provides data linking the fiber orientation distribution functions of ferromagnetic asymmetric particles to the relative magnetic permeability values of injection molded composites.
Transesterification reaction of polyarylate and copolyester (PETG) blends
Authors: Oh Taeg Su , Ryou Jin Ho , Chun Yong Sung , Kim Woo Nyon
Published: April 2004

Transesterification reactions between polyarylate (PAr) and a copolyester (PETG) have been investigated by proton nuclear magnetic resonance (NMR), Fourier‐transform infrared spectroscopy (FTIR), and differential scanning calorimetry. Blends of PAr and PETG were prepared by melt mixing and solution‐casting with weight fractions of PAr in the blends varying from 0.90 to 0.10. The PETG is a copolyester containing ethylene‐1,4‐cyclohexylene dimethylene terephthalate. From the thermal analysis of the PAr/PETG melt blends, a single glass transition temperature is observed, which indicates a miscibility between the PAr and PETG. The benzene insoluble fraction of the PAr/PETG (50/50) melt blends and solution‐cast blends were characterized using NMR and FTIR. The results of NMR and FTIR support the conclusion that transesterification reactions between the PAr and PETG occurred under the melt blending conditions applied.
Impact grinding of thermoplastics: A size distribution function model
Authors: Green Janet L. , Petty Charles A. , Grulke Eric A.
Published: April 2004

Separation of poly(ethylene terephthalate) (PET) from poly(vinyl chloride) (PVC) is an important problem when recycling bottles and other consumer products. Previous work has identified a processing window for the selective grinding of a mixture of PET and PVC. Impact grinding for conditions within the processing window will ensure that one polymer fails in the ductile mode and the other fails in the brittle mode, giving differences in sizes and shapes between the ground polymers. The ground mixture can be separated by physical means such as screening. This study develops size distribution models for the impact grinding of PET and PVC chips, an important tool for the operation and control of a selective grinding process. The distribution coefficients can be related to grinding conditions, and to the failure mechanism of the polymer.
Antioxidant diffusion in polyethylene hot‐water pipes
Authors: Viebke J. , Gedde U. W.
Published: April 2004

This paper presents oxidation induction time (OIT) data for samples taken from a range of polyethylene hot‐water pipes before and after hydrostatic pressure testing with internal stagnant water and external air. Linear relationships between OIT and antioxidant concentration were established for the antioxidants/polymers used. A model assuming Fickian diffusion of the antioxidant to the surrounding media and chemical consumption of the antioxidant (Regime B model) was applied to the OIT‐profile data. The Regime B model was successfully applied to OIT‐profile data except for in the case of a pipe with a substantial scatter in the OIT data, indicative of compositional heterogeneity. The choice of initial conditions for the modeling was critical. The use of initial conditions based on insufficiently exposed pipes led to an overestimate of the diffusivities caused by the combined action of Regimes A (internal precipitation) and B loss mechanisms. The time period associated with Regime A constituted up to 25% of the lifetime for the pipes studied. Antioxidants with sterically accessible polar groups showed a higher melting point and greater interaction with dissolved water and carbon black. Obtained radial dependences of the antioxidant diffusivities (D) indicate that the water concentration in the polymer influenced D primarily through cluster formation involving water and antioxidant molecules and by competition between water and antioxidant molecules about adsorption sites on carbon black particles and to a much lesser extent by plasticization. Antioxidant concentration profiles calculated for the failure time interval in pressure testing appeared in the same concentration range, and fracture initiation occurs in the regions in the pipe wall first reaching depletion of the antioxidant system.
Work of fracture of PBT/PC blend: Effect of specimen size, geometry, and rate of testing
Authors: Hashemi S.
Published: April 2004

Fracture 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

Novel 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

We 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

We 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

Numerical 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

A 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

Steady‐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

Co‐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

Die 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

In 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

An 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

The 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

Numerical 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

The 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

Plasma 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

It 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

Kinetic 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

The 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

Constitutive 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.
Creep rate variability in gel‐spun polyethylene fibers
Authors: Yakushev P. N. , Peschanskaya N. N. , Marikhin V. A. , Myasnikova L. P. , Jacobs M. J. N.
Published: April 2004

The phenomenon of stepwise creep has been discovered and studied earlier for unoriented polymers by a new laser interferometer method. This same technique has been used for studying long‐term menhanical properties of UHMWPE gel‐spun fibers of various draw ratios. A variability of creep rate has been observed. The creep rate variability has been characterized by two parameters: the typical period of deformation increment, with enhanced deformation rate (step), and the variability (inhomogeneity) of the deformation rate over a deformation interval. Despite a large scatter of data, at least three levels of deformation steps could be derived: (i) microns, (ii) tens of microns, (iii) hundred and more microns. The larger levels of deformation steps decrease with increasing draw ratio. Their dependence on strain is not observed. The creep rate variability significantly depends on the creep strain. First, it increases with strain and then decreases just prior to rupture. The effect of draw ratio on creep rate variability is not significant. It is assumed that the creep rate variability is a cooperative deformation. It is suggested that interfibrillar slip and slip between fibrillar layers occurs via a slip‐stick motion making a significant contribution to total deformation. The mechanism does not change with draw ratio.
Rheological, mechanical, and adhesive properties of thermoplastic‐LCP blends filled by glass fibers
Authors: Kulichikhin V. G. , Parsamyan I. L. , Lipatov Yu. S. , Shumskii V. F. , Getmanchuk I. P. , Babich V. F. , Postema A. R.
Published: April 2004

Rheological, mechanical, and adhesive properties have been studied of two‐phase polymer blends containing a liquid crystal copolyester of poly(ethylelene terephthalate) and p‐hydroxybenzoic acid plus isotactic polypropylene (PP) with varying compositions and concentrations of glass fibers. Perfect fibrillation of the disperse LC‐phase into the PP‐matrix in capillary flow was observed at LCP concentrations >20 wt% and temperatures >488 K. This effect leads to a decrease of blend viscosity and a reinforcing of the extrudate's mechanical characteristics. At the same time, more essential reinforcement is achieved by the simultaneous addition of the reinforcing agents both of the LCP and glass fibers. Processing of PP is not impaired. It was found that the adhesive strength increases substantially when the amount of LCP in the blend exceeds a definite level, corresponding to a phase inversion. The results are explained by the formation near the interface of two adhesion layers: the first is composed of pure LCP having a higher surface tension, whereas the second layer represents the blend of various compositions. At small amounts of LCP, the adhesion failure proceeds in the interphase between the LCP and the blend. After the phase inversion, where adhesion strongly increases, the failure of adhesion joints proceeds near the interface between LCP and the glass.
Rheokinetics of curing of epoxy resins near the glass transition
Authors: Malkin A. Ya. , Kulichikhin S. G. , Kerber M. L. , Gorbunova I. Yu. , Murashova E. A.
Published: April 2004

The cure of four epoxy‐amine systems was studied by viscometry, dynamic mechanical analysis, and DSC. The investigation was carried on at temperatures below and above the glass transition temperature (Tg) of completely cured products. Viscosity growth in the initial stage of cure is described by an exponential‐type equation, and on approach to the gel‐point by a power law, but the exponent did not coincide with the universal theoretical scaling‐law value. A universal viscosity master curve can be constructed if one reduces viscosity and time by their characteristic values. Gel‐times and activation energies of curing were found by different methods. It was established that the product of the initial rate of a reaction and the gel‐time is constant at various conditions of cure. Time dependences of the degree of conversion (calculated from calorimetric and dynamic mechanical data) in the full range of conversions are described by first‐ and second‐order kinetics, corrected by the factor reflecting self‐accelerating character of the reaction. Kinetic constants found from both methods are the same. If a reaction leads to a transition to the glassy state over the course of curing, a self‐acceleration equation is valid in the initial stage of the process only. The complete kinetic curve can be described by the DiBenedetto method relating shift of the Tg with the degree of conversion. The rate constant for vitrificating systems is presented as a sum of reciprocal values of chemical and diffusion constants. Time and temperature dependences of kinetic and diffusion constants were calculated.
Models for formation of supermolecular oligomeric liquid structures: Theory and experiment
Authors: Arinstein A. E. , Mezhikovskii S. M.
Published: April 2004

Two theoretical models are proposed to describe rearrangement mechanisms for supermolecular structures of oligomeric liquids. The first is based on the concept of associate‐size distribution, varying with the addition of molecules to the associates. These molecules are activated by external action. The other model takes into account the fact that after activation, the equilibrium size distribution function is attained by way of an activated molecule redistribution between associates, owing to “cleavage‐addition.” Within the framework of accepted restrictions, the analytical solutions were obtained adequately to describe rheological and relaxation relationships revealed for various types of oligomeric systems.
Discrete models of failure for particulate polymer composites
Authors: Moshev V. V. , Evlampieva S. E.
Published: April 2004

A stochastic discrete model is offered that simulates the behavior of particulate composites able to generate and accumulate scattered structural microdamages to the final breakdown of the model. The model is quite transparent, which allows us to observe continuously its internal state and effective behavior. Through numerical experiments, it is established that the accumulation of the scattered damage, accompanied by the appearance of the elastic nonuniformity, ends in a loss of the elastic stability of the whole of system and macrocrack formation in the most compliant part of the body. No strength criteria are needed to describe this process. Breaking stresses and strains and their scatter in repeated experiments, as functions of the virgin system specification, can be calculated and used for safety factors or for optimization of composite properties.
Advances in maleated polyolefins for plastics applications
Authors: Roberts Darilyn H. , Constable Robert C. , Thiruvengada Seshan
Published: April 2004

The objective of the paper is three‐fold, covering the use of maleated polyolefins as chemical coupling agents, compatibilizers, and impact modifiers. Introduction of a new chemical coupling agent for glass reinforced polypropylene details its improved properties versus current systems. Discussion of impact modifiers includes three developmental impact modifiers that combine higher melt flow properties and good room temperature notched Izod properties. The third area details the property improvements obtained in nylon/polypropylene blends through compatibilization with a maleated polyolefin.
Fluorescence monitoring of polymer injection molding: Model development
Authors: Bur Anthony J. , Thomas Charles L.
Published: April 2004

We have developed models to describe the behavior of an optical fiber sensor which was used to detect fluorescence from a polymer resin during the cooling phase of injection molding. The optical fiber sensor was positioned at the wall of the mold cavity by using the ejector pin channel as access to the cavity. The sources of fluorescence were dyes, which were chosen because of their sensitivity to temperature and which were mixed with the resin at dopant concentrations (parts per million by weight). The behaviors of a molecular rotor dye, dimethylamino diphenyl hexatriene, doped into polyethylene, and an excimer producing dye, bis‐(pyrene) propane, doped into polystyrene were the subjects of the modeling calculations. The models consist of two modules: (a) a solution to the thermal diffusion equation for the resin cooling in the mold and (b) using temperature/time profiles and, in the case of polyethylene, crystallinity/time profiles obtained from the thermal diffusion equation, fluorescence intensity as a function of time was computed. Factors incorporated in the models are: adiabatic heating and cooling, light scattering due to microcrystals of polyethylene, crystallization kinetics, temperature and pressure shift factors for viscoelastic relaxation near the glass transition temperature of polystyrene, and the thermal resistance at the resin/mold interface.
Physical aging kinetics of syndiotactic polystyrene as determined from creep behavior
Authors: Beckmann Jorg , McKenna Gregory B. , Landes Brian G. , Bank David H. , Bubeck Robert A.
Published: April 2004

Creep experiments in uniaxial extension have been performed to explore the kinetics of the physical aging process in semicrystalline syndiotactic polystyrene (sPS) having two processing histories. Classical time‐aging time superposition behavior was found for both materials at temperatures from 70 to 95°C, with the shift rate μ decreasing as temperature was increased. Virtually no aging was seen at 95°C, the DSC determined glass transition, Tg. This behavior was atypical for a semicrystalline polymer and reminiscent of the behavior of glassy amorphous thermoplastics. Some evidence for a separate crystalline aging mechanism > Tg, which manifests itself as only vertical shifts without timescale shifts, is seen in experiments at T > 100°C. Finally, the two different materials age differently, suggesting that some control of aging can be obtained by altering processing conditions or morphology.
Large deformation response of polycarbonate: Time‐temperature, time‐aging time, and time‐strain superposition
Authors: O'Connell P. A. , McKenna G. B.
Published: April 2004

Data are presented from tests of the stress relaxation response of a polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.08, temperatures from 30 to 135°C and aging times from 1800 to 64,800 s. Individual data sets at each strain, temperature and aging time could be described using a stretched exponential form relaxation function, and time‐aging time superposition was found to be applicable to the data under all test conditions. The double logarithmic aging time shift rate, μ was found to vary significantly with both temperature and strain. Over the range of temperatures studied the data could be superimposed using conventional time‐temperature superposition. However, the master curve was found not to be described by a stretched exponential function. For strains up to 0.07, the data at each temperature could also be superimposed to form a master curve following the principle of time‐strain superposition. Interestingly, the master curves found from time‐strain and time‐temperature superposition did not have the same form. In both the time‐aging time and time‐temperature superposition analyses it was found that the application of vertical shifts was required for superposition of data.
Synthesis and characterization of flame resistant poly(arylene ether)s
Authors: Riley D. J. , Gungor A. , Srinivasan S. A. , Sankarapandian M. , Tchatchoua C. , Muggli M. W. , Ward T. C. , McGrath J. E. , Kashiwagi T.
Published: April 2004

Hydrolytically stable phosphorus‐containing monomers, such as 4,4′‐bis(fluorophenyl)methylphosphine oxide (BFPMPO), 4,4′‐bis(hydroxyphenyl)methylphosphine oxide (BOHPMPO), and 4,4‐bis(hydroxyphenyl)phenylphosphine oxide (BOHPPO), were synthesized and used in nucleophilic aromatic substitution poly‐condensation to prepare poly(arylene ether phosphine oxide) engineering thermoplastics. The synthesis and characterization of these novel polymers are described. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(arylene ether) were substantially improved, such as an increase in Tg, thermal stability in air, modulus, and char yield compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion.
Control of plastic melt temperature: A multiple input multiple output model predictive approach
Authors: Dubay Rickey , Bell Adam C. , Gupta Yash P.
Published: April 2004

Good control of plastic melt temperature for injection molding is very important in reducing operator setup time, ensuring product quality, and preventing thermal degradation of the melt. The controllability and setpoints of other process parameters also depend on the precise monitoring and control of plastic melt temperatures. We experimentally investigated the thermal interactions between the barrel zones of an instrumented plastic injection molding machine (IMM). These interactions result from the zone temperature differences that are used in normal machine operations. From these experimental interactions, multiple‐input‐multiple‐output (MIMO) and single‐input‐single‐output (SISO) models were derived for controlling these zone temperatures using a Model Predictive Control (MPC) strategy. An experimental comparison was made between MIMO MPC and SISO MPC of plastic melt temperature, which showed that the MIMO MPC scheme is more energy efficient, having zero overshoot.
The effect of composition on thermal, mechanical, and morphological properties of thermotropic liquid crystalline polyester with alkyl side‐group and polycarbonate blends
Authors: Chang Jin‐Hae , Choi Bong‐Ku , Kim Jae‐Hoon , Lee Soo‐Min , Bang Myung‐Sik
Published: April 2004

A thermotropic liquid crystalline polymer (LCP) with an alkyl side‐group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases.