bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of polyethylene cable insulation by chemiluminescence measurements. I. Method development
Authors: Cooper Anthony R.
Published: December 2004

Chemiluminescence (CL) measurements have been performed on polyethylene electrical cable insulation. Matched pairs of unaged and aged materials were used where possible. The polyethylene materials investigated included crosslinked polyethylene, low density polyethylene, and ethylene‐propylene rubber. Various experimental techniques were examined to see if any distinctions could be made between unaged and aged samples. Chemiluminescence spectra were obtained for the first time for these materials. The spectra show differences between materials and also between unaged and aged samples.
Polymerization of ε‐caprolactam in an extruder: Process analysis and aspects of industrial application
Authors: Menges G. , Bartilla T.
Published: December 2004

The polymerization of caprolactam into polyamide 6 on corotating twin‐screw extruders provides the processor with technically and economically interesting aspects of application. Using the extruder as a small reactor, it is possible, on the one hand, for small batches of polyamide to be optimized for specific applications, and, on the other hand, for large quantities of polymerized polyamide melts to be fed into different processes. Apart from the extrusion of filaments, films, and profiles, the continuous polymerization process also can be coupled up to discontinuous processes. This so‐called rapid polymerization in the extruder not only brings price advantages as compared with standard polyamides, but also gives higher molecular weights and, hence, improved properties.
Transesterification reactions in molten polymers
Authors: Lambla M. , Druz J. , Bouilloux A.
Published: December 2004

The transesterification reaction of molten ethylene and vinyl alcohol copolymers (EVA), in presence of paraffinic alcohols and basic catalysts, leads to high conversion of the ester groups to secondary alcohol in both discontinuous and continuous processing equipment. Various kinds of alcohols and two different catalysts were used. Sodium methoxide is a powerful catalyst for the equilibrated transesterification reaction, but we also observed side reactions, such as cross‐linking with low‐molecular‐weight alcohols and hydrolysis of the catalyst followed by partial saponification of the EVA. Kinetic studies were performed in the presence of dibutyltin dilaurate, an efficient catalyst without any side reactions. The solubility of the main alcohol reagents was verified by diffusion measurements. The general reaction scheme and the related kinetics, corresponding to a homogeneous system, lead to a fair evaluation of the rate constants.
Solvent‐induced crystallization of a compatible polymer blend
Authors: Waywood W. J. , Durning C. J.
Published: December 2004

We studied solvent‐induced crystallization (SINC) in a compatible blend of poly (butylene terephthalate) (PBT) and a polyarylate (PAr) over a range of blend compositions and temperatures; liquid acetone was the crystallizing agent. Acetone transport kinetics were followed by mass uptake measurements in thin films and by optical microscopy. Crystallization kinetics were followed by density measurements. For the 0.2 mm thick films used, those with higher weight fractions of PST (50 to 60 percent by weight) exhibit diffusion controlled transport and crystallization over the entire range of temperatures studied (0 to 55°C). Those with lower weight fractions of PBT (∼30 percent by weight) display Case II sorption and crystal growth controlled crystallization at 0°C. The latter is rare for SINC in homopolymers and results from a sharp reduction in the PBT crystallization rate in the presence of the noncrystallizable PAr.
Application of rigid polyurethane integral‐skin foams to thermal insulating unit cases for car air conditioners
Authors: Gotoh Masao , Iida Makoto , Waragai Kenichi , Iijima Kazumi
Published: December 2004

Integral‐skin foams of rigid polyurethane are sandwich structures consisting of a core layer of closed cells enclosed in rigid surface layers on both sides. We examined the layer composition of integral‐skin foam with the objective of maximum flexural strength, and then studied possibilities of reconciling the strength and thermal insulating properties in housings for evaporators in car air conditioners; i.e., unit cases. This examination showed that the most practical density range (250 ≦ ρpall ≦ 500 kg/m3) provides vibratile resistance and thermal insulating properties. In actual car‐running tests, a maximum 0.1 MPa stress was generated on unit cases with overall densities of 350 kg/m3, We found this to be 0.4% of the flexural strength of an integral‐skin foam and 2% of the fatigue strength. In the forcible vibratile test, a stress of 0.5 to 1.0 MPa was generated at the resonance point of a unit case with 250 to 500 kg/m3 overall density. We found that these values are 2 to 5% of integral‐skin foam's flexural strength and 10 to 25% of its fatigue strength. These values are of the same level as the conventional unit case made of polypropylene blended with talc. An integral‐skin foam with an overall density of 250 kg/m3, nearly equal to half the weight of polypropylene, has the same level of resistance to vibration.
The effect of orientation on the CO2 sorption of polystyrene
Authors: Carfagna C. , Nicodemo L. , Nicolais L.
Published: December 2004

The chain orientation, induced by hot drawing, decreases the sorption capacity of polystyrene due to the tighter packing of macromolecules in the oriented material. Density measurements and decay of birefringence indicate that the loss of orientation Is a much more rapid phenomenon than the thermal shrinkage of the polymer.
Internal mixing: A practical investigation of the influence of intermeshing rotor configuration and operating variables on mixing characteristics and flow dynamics
Authors: Freakley P. K. , Patel S. R.
Published: December 2004

This paper deals with the measurement and interpretation of pressures and temperatures produced by the mixing of a rubber compound in the chamber of an internal mixer equipped with interlocking rotors. Pressure transducers and infrared/fiber optic temperature sensors were sited flush with the inner surface of the mixing chamber of a Francis Shaw KO Intermix of 2 L chamber volume. The variation of pressure with transducer position In the chamber wall and with rotor position was measured for selected fill factors and rotor speeds at “equilibrium” conditions (quasi‐static power requirement for the mixer) and at intervals during a complete mixing cycle. Two rotor designs were studied. Interpretation of the results was carried out with reference to biconical rotor rheometer measurements on the mixed rubber compounds and by reference to four regimes of viscoelastic behavior identified for two‐roll mill mixing. A basic flow analysis was carried out by use of the lubrication approximation in conjunction with an isothermal power‐law model.
Simulation of planar welding flows: Part 2. Strain history, stress calculation, and experimental comparison
Authors: Wei K. H. , Nordberg M. E. , Winter H. H.
Published: December 2004

A numerical method is described for calculating the stress a viscoelastic melt exhibits in a flow, based on approximate kinematics. The method assumes that the kinematics are reasonably close to those of a shear‐thinning fluid such as the Carreau model. The strain history of a given flow and the resulting stress are calculated via a tracking method from finite element kinematics. Fullfield flow birefringence experiments were done for lowdensity polyethylene and polystyrene flowing past a thin plate divider in a 1.254‐mm planar slit die. By digitally analyzing birefringence photographs of the flow field, the birefringence was measured over two dimensions. These birefringence results are in good agreement with birefringence fields calculated from the numerical simulations and the stress‐optical law. The flow fields were most highly oriented in a region surrounding the weld interface just downstream of the plate divider. This orientation relaxed farther downstream, with polystyrene relaxing faster than low‐density polyethylene.
Thermal effects in the necking of polymers
Authors: Liu Tuo‐Min , Harrison I. R.
Published: December 2004

A certain fraction of the mechanical work performed on a specimen is converted into heat during necking of plastic material. A method for measuring this fraction is proposed when specimens are drawn in two different surroundings, air and water. Differences in the heat transfer coefficients of these two media influence the temperature rise during necking. The fraction (α) of mechanical work converted into heat can be calculated using data determined at only one draw rate. The value of α calculated for polypropylene is 0.55 and for polyethylene it is 0.48.
The effects of residual stress on the mechanical properties of glassy polymers
Authors: Hornberger L. E. , Devries K. L.
Published: December 2004

Residual stresses can have either beneficial or detrimental effects on the mechanical properties of plastics. Manufacturing processes frequently impose residual stresses on plastics. In this study, controlled thermal processes were used to impose surface compressive stresses on polycarbonate beam samples (6.4 by 12.5 by 80 mm). Resistance strain gage and photoelastic techniques were developed to measure the magnitude of these stored stresses. The compressive surface stresses were found to be between 14 MPa (2000 psi) and 31 MPa (4500 psi) and to vary with process method and cooling rate. The mean fatigue life (in bending) of the treated beam samples was found to improve by a factor of 10 over that of untreated samples. The increase in the fatigue life of the treated samples appears to be directly related to the magnitude of the surface compressive residual stress in the samples. The imposed residual stress, as determined by photoelastic measurements, has not appreciably relaxed after 1 year of storage at room temperature.
Phase behavior of ternary polymer blends
Authors: Su A. C. , Fried J. R.
Published: December 2004

The effect of varying interaction parameters on the phase diagrams of ternary polymer blends was explored by simulating spinodals through use of the Flory‐Huggins lattice theory. Results indicate that miscibility is favored for the case of ternary mixtures of marginally miscible or marginally immiscible pairs where all pair interactions are nearly athermal. Miscibility is restricted for asymmetric ternary blends when one of the polymer pairs is either strongly miscible or strongly immiscible. For symmetric blends of partially immiscible pairs, both two‐phase and three‐phase miscibility gaps are predicted.
Failure modes for polycarbonate under clearance‐fit pin‐loading
Authors: Naik R. A. , Prabhakaran R.
Published: December 2004

The failure modes and failure sequences for polycarbonate specimens loaded by a clearance‐fit pin were investigated. Specimens were tested in various configurations to produce failures by different engineering failure modes. Photographs of the isochromatic fringe patterns were taken at different levels of damage development to examine the failure modes. A finite element stress analysis was used to explain the observed failure onset modes. Damage onset predictions were made based on a modified von Mises criterion. Failures involving net‐tension damage initiated in the net‐tension mode and failed ultimately in the same mode. Cleavage failures were observed for specimens with very small end‐distances. Bearing failures were preceded by damage onset in a net‐tension mode. Certain large‐hole specimens failed in a buckling failure mode.
Microstructural diagnosis of block copolymer nonlinear mechanical properties I. Uniaxial stress/strain
Authors: Diamant Joram , Williams Michael C. , Soane David S.
Published: December 2004

An earlier study on the linear dynamic properties of triblock copolymers was continued into the nonlinear property regime. Uniaxial tensile tests were performed on styrene‐butadiene‐styrene block copolymers. The three polymers, having polystyrene (PS) fractions 0.27, 0.29, and 0.48, also represented three molecular weights (0.49, 0.58, and 1.0 × 105). Specimens were prepared by casting from three solvents (methyl ethyl ketone, MEK; cyclohexane; and a 9:1 mixture of tetrahydrofuran and MEK). This wide range of variables led to a correspondingly wide spectrum of properties, including the “plastic‐to‐rubber” transition in some cases. Stress‐strain curves were characterized by modulus, yield stress, general elevation, and fracture stress and elongation. Results were interpreted in terms of microstructural parameters obtained from the earlier linear tests, including interphase properties, and molecular features as well. Special insight emerged from comparison of first‐cycle (to 300 percent elongation) and second‐cycle tests, including changes in modulus, yielding, level, and the appearance of set. Additional data on sample preparation influences and PS continuity effects on sample properties were also obtained.
The modeling of batch and continuous emulsion polymerization reactors. Part I: Model formulation and sensitivity to parameters
Authors: Rawlings J. B. , Ray W. H.
Published: December 2004

A detailed model for the prediction of the behavior of batch or continuous emulsion polymerization reactors has been formulated, and an efficient numerical scheme for simulation developed. The model makes use of population balance equations and detailed mechanisms for chemical and physical rate processes. The numerical procedure chosen for its solution is orthogonal collocation on finite elements. In this paper, a few comparisons with experimental data are presented to demonstrate the model validity. Finally, a parametric sensitivity study is carried out to identify the most important kinetic and physical parameters. In the sequel, a comprehensive comparison of model predictions with a wide variety of experimental data will be presented.
Numerical simulation of wire‐coating low‐density polyethylene: Theory and experiments
Authors: Mitsoulis E. , Wagner R. , Heng F. L.
Published: December 2004

The wire‐coating process was analyzed numerically making use of a particular die design employed in highspeed industrial operations. Both the lubrication approximation theory and a fully two‐dimensional finite element analysis were applied under isothermal and nonisothermal conditions, respectively. Particular emphasis has been given to the heat transfer effects between the melt arid the solid and free boundaries. A variety of thermal boundary conditions was studied, ranging from adiabatic to constant temperature walls. The influence of dimension less groups such as Peclet, Nahme, and Biot numbers is examined. Oscillation‐free solutions are obtained for the temperature field by using a standard finite element Streamline‐Upwind/Petrov‐Galerkin technique. Rheological data for a wire‐coating low‐density polyethylene (LDPE) resin (Alathon‐3535) were used in the analysis. The predictions include pressure and temperature distributions, shear stresses and shear rates both at the die wall and the wire, and wire tension for different wire speeds. The numerical results are compared with a set of experimental data for LDPE in a typical die used by Du Pont Co. It is found that the isothermal lubrication approximation for power‐law fluids overestimates pressure distributions when applied at die operating temperature. The nonisothermal finite element analysis gives better predictions, especially when realistic thermal boundary conditions are imposed, with the experimental results lying between those found from simulations assuming isothermal walls (upper limit) and adiabatic walls (lower limit).
Performance study of barrier screws in the transition zone
Authors: Amellal K. , Elbirli B.
Published: December 2004

This paper defines through a mathematical model the advantages and disadvantages of barrier screws as far as their melting and mixing performances in the transition zone are concerned. The melting analysis is based on the Tadmor's original model, and the flow in the melt channel is considered to be non‐Newtonian and nonisothermal. The performance of these barrier screws is investigated for the solids channel in terms of melting rate/interface a I contact area; melting efficiency; melting length; solid bed velocity profile; and power consumption in the melt film at barrel surface. For the melt channel, their performance is investigated in terms of pressure buildup; average bulk temperature; power consumption in the melt channel and in the main flight clearance at barrel surface; and average bulk mixing. The present study confirms that the increased‐pitch multichannel screw (Ingen Housz screw) outperforms clearly the other barrier screws investigated, since it gives the highest melting rate with reasonable pressure buildup in the melt channel. When compared with conventional screws, all the barrier screws examined give better melting performance.
Deep drawing of polypropylene sheets under differential heating conditions
Authors: Machida T. , Lee D.
Published: December 2004

Means of improving the deep drawability of thermoplastic sheets were explored by introducing temperature gradients in the deforming material during deep drawing of initially flat sheets. The specific experimental procedure consisted of either limiting the heating to the flange section of the deforming sheet or exposing the entire material to higher temperatures. At the same time, the initial blank size and the clamping force at the flange section were varied systematically. Both polypropylene and polypropylene with 40 percent calcium carbonate in the form of sheet were tested up to 130°C. It is demonstrated that the draw‐ability increases markedly with increasing temperature gradient between the flange and punch sections. The results of measured strain distribution in the deformed part indicate that the magnitude of temperature difference between the flange and punch sections determines the relative amount of deep drawing and stretching in the wall of the formed part, which in turn dictates the drawability of the material.
A method for estimation of polymer melt temperature fluctuation in a single screw extrusion process
Authors: Wilczyński Krzysztof
Published: December 2004

A method for estimating the polymer melt extrudate temperature fluctuation in the single screw extrusion process is proposed. Predictions of the melt temperature fluctuation is feasible if the extrusion process parameters are known. The method is superior to these in the literature because it incorporates effects of the melting process on the temperature fluctuation. The method has been verified experimentally.
Low pressure rheology of granular powders using a drawing plate technique
Authors: Lee Biing‐Lin
Published: December 2004

An analysis of a drawing plate test for easily monitoring the low‐pressure frictional characteristics of powders is presented. The test is performed by measuring the force required to withdraw a plate from a cylindrical bed of dry powder. The characteristics of the drawing force profile are analyzed using Janssen's classical differential element approach to relate the product μK of powders as a function of packing of powder medium, where μ is the coefficient of friction of the powders against the solid drawing plate, and K is Janssen's constant, an anisotropic pressure distribution factor of a powder bed. The packing arrangement, expressed as the external void fraction, due to tapping, significantly alters the μK value and the effective sustaining strength of a powder bed. Experimental results on spherical glass beads having mono‐ and bimodal size distributions, and on three different poly (vinyl chloride) (PVC) powders are discussed. A spherical, high bulk density PVC powder has the combination of low μK and high, bulk density desirable for rigid powder compounding applications.
Characterization of linear copolymers by methods sensitive to the refractive index increment
Authors: Rodríguez Rogelio
Published: December 2004

For linear copolymer molecules, the refractive index increment depends on the chemical composition of the molecules. However, the polydispersity in chemical composition of the sample introduces a great complexity in the data analysis in order to obtain a true molecular weight distribution. Even when the mean chemical composition does not depend on the molecular weight, a correction has to be applied when the output of an instrument depends quadratically on the refractive index Increment of the sample, such as in a light‐scattering measurement. For that purpose, the light‐scattering expressions are written in terms of polydispersity in chemical composition, which in turn is modeled using linear copolymerization equations. The microstructure effects, which are related to the order in which two different kinds of monomers appear along the chain, are not as yet taken into account in this approach.
Characterization of polymer molecular weight distribution by transient viscoelasticity: Polytetrafluoroethylenes
Authors: Wu Souheng
Published: December 2004

The relationship between the relaxation time spectrum H(τ) in the terminal zone and the volume‐fraction differential molecular‐weight‐distribution function P(M) is derived by considering binary chain contacts for stress transmission,

equation image

where β and λ are constants for a given chemical type. This is used to determine the molecular‐weight‐distribution curves from the stress relaxation modulus spectrum (above the crystal melting point) at 370°C for a number of commercial and experimental poly(tetrafluoroethylenes) (PTFEs). It is found that PTFEs typically have bimodal molecular‐weight distributions. The lower‐molecular‐weight peak conforms essentially to the “most‐probable” distribution, and the higher‐molecular‐weight peak to the binary coupling distribution. The entanglement molecular weight Me is 5490, and the number of main‐chain atoms between entanglement points is 110, consistent with a flexible chain. The zero‐shear melt viscosity at 370°C is η0 = 1.79 × 10−13 Mw2.94±0.13, where η0 is in Pa.s and Mw/Me = 2,000 to 12,000. The monomeric friction coefficient is also determined.
The effect of thermal history on the deformation mechanism of 2,6‐dimethylpoly(phenylene oxide)
Authors: Dalal V. F. , Moet A.
Published: December 2004

Stress‐strain relationship of 2,6 dimethyl poly(phenylene oxide)(2,6 MPPO) was established simultaneously with optical micrographic examination as a function of thermal history. Films (5–7 μm) were solvent cast and annealed below their glass transition and melting point. As‐cast film showed ductile behavior associated with shearband formation, whereas thermally treated material exhibited marked embrittlement; the slower it cooled the more brittle it became. Thermally treated material showed mixed mode deformation: crazing and shearbanding. The correlation between the deformation mechanism and its solid state structure was studied using differential scanning calorimetry, wide angle x‐ray diffraction, and density measurement.
Properties of segmented block copolyurethane II. Adhesion between PET cord and rubber by poly(styrene‐b‐butadiene) polyethylene terephthalate block copolyurethane
Authors: Yamashiro Seiichi , Kuratsuji Takatoshi
Published: December 2004

Hydroxy‐terminated copoly(fstyrene‐b‐1,2‐butadiene) (HPSB) containing rubber‐affinitive vinyl side chains and having a molecular weight of 2000 to 4000 were prepared, and block copolyurethanes were synthesized by using a low molecular weight hydroxy‐terminated poly (ethyl en e terephthalate) as a PET‐affinitive component and 4,4′‐diphenylmethane diisocyanate as a chain extender. The relationships between the molecular weight of HPSB, copolymerization ratio of styrene to butadiene and the adhesive strength of PKT/rubber in high temperature atmospheres were examined. A peak of adhesive strength was observed at styrene copolymerization ratio of 20 wt percent and a HPSB molecular weight of 3000. The adhesion mechanism was estimated from the behavior of the characteristic infrared absorption of block Copolyurethane in heating.
Process control of profile extrusion using thermal method. Part II: Closed loop control
Authors: Yang B. , Lee L. J.
Published: December 2004

The analytical flow model developed in Part I was applied to the online control of profile extrusion. A rubberized polystyrene was extruded through a simple L‐shaped profile die with one thin section and one thick section. Take‐up speed was used to control the size of the extrudate, and die temperature was used to control the shape of the extrudate. Two different control algorithms, a dual single‐loop feedback PI controller and a multivariable feedforward plus feedback control method (FFC), were carried out for set point changes of the extrudate shape and size, and load disturbances of screw speed. Results showed that the PI feedback controller was satisfactory for long‐term set point changes but not for load changes. The FFC worked well for load disturbances lower than 10 cycles/min. Owing to the slow dynamic response of die temperature, the shape loop can only be controlled for long‐term disturbances.
Vibration welding of thermoplastics. Part II: Analysis of the welding process
Authors: Stokes V. K.
Published: December 2004

The vibration welding process for thermoplastics is known to consist of four phases: (1) initial heating of the interface to the melting temperature by Coulomb friction; (2) unsteady melting and flow in the lateral direction; (3) steady‐state flow; and (4) unsteady flow and solidification of the film after the vibratory motion is stopped. Simple analytical models are developed for the first three phases. These models are used for estimating the molten film thickness, the size of the heat affected zone, and the weld time as functions of the weld parameters: the amplitude and frequency of the weld motion, and the weld pressure. The steady‐state film thickness and the heat‐affected zone are shown to be very small.
Practical characterization of the structure of crystalline polymer moldings
Authors: Samuels Robert J.
Published: December 2004

The thermal and flow gradients present during thick polymer molding processes can produce layered structures through the thickness which vary in crystallinity, orientation, and axiality. Such structural complexity is difficult, expensive, and time consuming to characterize and presently impossible to predict. In order to overcome these problems emphasis in our laboratory has been directed toward the development of rapid, nondestructive techniques for the quantitative characterization of the structure of thick polymer samples. This includes the characterization of the average structure, the surface structure, and the internal layer structure. The present paper discusses some of these techniques and illustrates their application.
Orientation technology and commercial products from a unique roll orientation process
Authors: Gould Russell J.
Published: December 2004

It is well known that orientation can produce, at a minimum, an order of magnitude improvement in physical properties of low cost plastic resins. A unique, large‐scale, commercial rolling mill process for continuous orientation of plastic sheet has been developed, A number of oriented materials have been commercially produced by this rolling mill process with a wide variety of physical properties attained. This has resulted in large volume sales of many interesting commercial products. Over the last thirty years, numerous researchers have conducted studies to evaluate the theoretical aspects of the rolling process, and the resultant properties. Most commercial oriented products are of relatively small cross sectional size such as fibers and film. The process reported herein produces heavy cross section oriented sheet. A new class of high strength thermoplastic materials is now available for design engineers to use. Long‐term strength properties are often 10 to 100 times better than with unoriented thermoplastics.
Dynamic mechanical behavior of polymers containing carbon black
Authors: Gandhi Khushroo , Salovey R.
Published: December 2004

The dynamic mechanical behavior of carbon black filled polymers of styrene and butyl methacrylate was examined at low strain amplitude and frequency in order to minimize destruction of the composite structure and elucidate the basis of yield and plasticization observed in steady shear. For specific filled systems, both G′ and G″ became independent of frequency and temperature at low frequencies, consistent with a yield phenomenon and the formation of a carbon black network. On the other hand, although the high molecular weight polystyrene showed plasticization effects at higher shear rates in steady shear rheology, such, plasticization effects were never observed in dynamic mechanical analysts. Yield behavior was observed most readily for the low molecular weight polystyrene. Limiting moduli for filled polystyrenes were independent of temperature, whereas, for polybutyl methacrylate, were sensitive to temperature. It is suggested that an independent network of carbon black is strongest in the low molecular weight polystyrene and weakest in poly (butyl methacrylate).
A polymer complex as a new type of electron beam resist for dry development
Authors: Yoneyama Sachiko , Oguchi Kiyoshi , Watanabe Masayoshi , Sanui Kohei , Ogata Naoya , Takahashi Yoichi , Nakada Tomihiro
Published: December 2004

Polymer complex of poly (4‐vinylpyrldine) and malonic acid was investigated as a new type of electron beam (EB) resist for dry development, as malonic acid was decomposed by EB irradiation. It was found that the polymer complex could be developed with O2 plasma etching and that the positive resist patterns with high resolution could be obtained. The mechanism for this lithography process was studied by means of IR and ESCA spectra.
Vibration welding of thermoplastics. Part III: Strength of polycarbonate butt welds
Authors: Stokes V. K.
Published: December 2004

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration; The effects of these parameters on weld quality were systematically studied by first butt‐welding polycarbonate specimens under controlled conditions over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests, A significant result is the apparent existence of a weld‐penetration threshold above which high weld strengths are attained, but below which the strength drops off. Under the right conditions, the strengths of polycarbonate butt welds are shown to equal the strength of the virgin polymer.
Foaming characteristics of filled solutions of nitrile butadiene rubber
Authors: Hoontrakul P. , Szamosi Janos , Toeing S. D.
Published: December 2004

During the development of nitrile‐butadiene‐rubber‐based coatings, persistent foaming—a grave obstacle in such applications—was encountered, An investigation was undertaken to study the behavior of foams in order to prevent their formation. Both the apparent viscosity and the foam stability were found to attain their minimum values at the same filler level. It is plausible that the observed phenomenon is due to the binding of polymer chains to filler particles, which takes place most effectively at a certain proportion of filler and polymer.
Moldability diagrams for the reaction injection molding of a polyurethane crosslinking system
Authors: Manas‐Zloczower I. , Macosko C. W.
Published: December 2004

A trial and error approach reflects the state of the art in reaction injection molding. Material and process parameters determine the “moldability” of a specific system in a particular application. The concept of “molding areas” on the critical parameters plane can be extended form thermoplastic injection molding (TIM) to reaction injection molding (RIM).

In this work moldability diagrams for the filling and curing stages of a RIM process are obtained based on a simplified engineering approach. The key process parameters chosen for the filling stage are initial material temperature and filling time. In the curing stage, the critical parameters are considered to be mold wall temperature and demold time. Experimental results obtained on a laboratory‐scale RIM machine on a Crosslinking polyurethane system are used to check the validity of the predicted molding areas. The agreement obtained is satisfactory considering the broad range of processing parameters used.
An efficient algorithm of computation of molecular weight distributions and its moments for reversible step growth polymerization in homogeneous continuous flow stirred tank reactors
Authors: Kumar Anil
Published: December 2004

The reversible step growth polymerization in homogeneous continuous flow stirred tank reactors (HCSTRs), in which the condensation product (W) leaves the reactor through flashing, has been analyzed. The molecular weight distribution (MWD) of the polymer formed is governed by nonlinear coupled algebraic relations to be solved simultaneously. To find the MWD numerically a large number of these are normally solved simultaneously using a suitable iterative procedure. In this paper, these have been decoupled using the technique proposed in our earlier works (1, 2) and the MWD can now be obtained sequentially without any trial and error. This leads to considerable saving in computation time compared to methods currently used. To demonstrate the efficacy of the algorithm, the polycondensation step of the poly(ethylene terephthal‐ate) (PET) formed in HCSTRs has been analyzed. The MWD, the average chain length and the polydispersity index of the polymer have been computed and it takes 0.1 CPU seconds on a DEC 1090 as opposed to the earlier method which would take seventy minutes for similar computations. The simple model of the HCSTR for the PET formation gives the effect of reactor temperature and pressure and the quantitative results have been presented in this paper.
Shrinkage forces and birefringences of an amorphous stretched copolyterephthalate
Authors: Pereña J. M. , Benavente R.
Published: December 2004

Measurements of shrinkage stress and birefringence have been undertaken on drawn samples of a copolyterephthalate based on ethylene glycol and 1,4 cyclohexane‐dimethanol. The temperature location and the peak value of the maximum shrinkage stress have been related to the drawing conditions (temperature, strain rate and draw ratio), comparing the results with those reported for poly (ethylene terephthalate). Moreover, a value of the stress optical coefficient of the copolymer equal to 14.5 × 10−9 m2 N−l has been obtained.
Molecular structure, crystallization behavior, and morphology of fractions obtained from an extrusion grade high‐density polyethylene
Authors: Gedde U. W. , Jansson J‐F. , Liljenström G. , Eklund S. , Holding S. R. , Wang P‐L. , Werner P‐E.
Published: December 2004

An extrusion‐grade of high density polyethylene (HOPE) (3 ethyl groups per 1000 carbons) has been divided into 16 fractions by preparative GPC and selective p‐xylene extraction. The fractions, with molecular weights ranging from 900 to 1,000,000, have been studied by IR spectros‐copy, DSC, WAXS, polarized microscopy, and small‐angle light scattering (SALS), The average degree of chain branching (percent C2H5) is 0.5 percent for the part of the sample having a molecular weight lower than 10,000 and it decreases monotonically with increasing molecular weight, finally approaching 0.1 percent C2H5. A crystallinity depression with respect to linear PE equivalent to 20 percent/(percent C2H5) is recorded for all samples except for the very low molecular weight samples for which the crystallinity depression is much larger (30 to 35 percent/ (percent C2H5)). The unit cell volume increases with increasing percent C2H5, presumably due to the inclusion of ethyl groups in the crystals as interstitlals at 2gl kinks. The concentration of ethyl groups in the crystals (ϵc) unanimously follows the relationship: ϵc(percent) = 0.32 + 0.25 log(percent C2H5) except for the low molecular weight fractions which have significantly lower values for ϵc. Our admittedly speculative explanation for this major discrepancy between high and low molecular weight samples is based on the idea that segments with ethyl groups close to chain ends have a greater difficulty in crystallizing than segments containing ethyl groups located at positions far from the chain ends. The fractions obtained from the extrusion‐grade HDPE show a solidification temperature depression with respect to linear PE which can only be explained by the presence of chain branches in these samples. The depression is particularly pronounced for the low molecular weight samples as is expected from the data on molecular structure. Well‐developed non‐banded spherulites are observed in rapidly cooled (crystallized at about 35 K supercooling), low molecular weight samples (6,000 < Mw < 8,000)from the extrusion‐grade HDPE in contrast to the axialites observed in linear PE of the same molecular weight and thermal treatment. This discrepancy in morphology has been related to the presence of ethyl groups in the extrusion grade HDPE fractions. Higher molecular weight samples (20,000 < Mw < 1,000,000)from the extrusion‐grade HDPE and linear PE both display well‐developed banded spherulites of similar nature as is expected due to the similarity in molecular structure of the two sets of sample.
Blends of thermoplastic polyesters with amorphous polyamide. I. Thermal and crystallization behavior
Authors: Nadkarni V. M. , Shingankuli V. L. , Jog J. P.
Published: December 2004

The thermal and crystallization behavior of blends of three thermoplastic polyesters with different degrees of crystallizability, with an amorphous aromatic polyamide is reported. The thermoplastic polyesters used in the investigation were poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET) and a co‐polyester of 1,4 cyclohexane‐dimethanol, ethylene glydol and terephthalic acid (PETG). The blends exhibited a single glass transition temperature indicating mlseibility in the amorphous phase. The results of thermal analysis indicated that the crystallization of all the three polyesters is facilitated in the molten phase as a result of blending. The blending significantly Increased the degree of crystallinity of PET, but there was no change in the crystallinity of PBT. It is thus observed that the extent of change in both the crystallization rate and the degree of crystallinity of polyesters depend on the inherent crystallizability of the individual polyester.
Liquid‐liquid phase behavior of mixtures according to the Simha‐Somcynsky theory
Authors: Stroeks Alexander , Nies Erik
Published: December 2004

It is well known that equilibrium, thermodynamic properties are governed by different functional derivatives of the thermodynamic functions of state. For example, the phase behavior of mixtures of low and/or high molar mass components is determined by the compositional derivatives of the free energy. In this contribution, the merits of the Simha‐Somcynsky theory in describing and predicting the phase behavior of mixtures are considered. The influence of temperature and composition on the miscibility behavior for practically binary polymer solutions are studied. Furthermore, the important aspect of polydispersity, inherent to synthetic polymer systems will be addressed.
Characterization of blends of naphthalene‐containing polymers with poly(alkyl methacrylates) by combined steady‐state fluorescence spectroscopy and fluorescence decay measurements
Authors: Holden David A. , Strauss John
Published: December 2004

The extent of mixing in two‐component solution‐cast films of poly(2‐vinyl naphthalene) (P2VN) and poly(2‐iso‐propenyl naphthalene) (P2IPN) with poly(methyl methacrylate) and poly(n‐butyl methacrylate) was studied by steady‐state and time‐resolved fluorescence spectroscopy. The steady‐state fluorescence spectrum of 1% P2IPN in the two poly(alkyl methacrylates) evolves from 100% monomer emission (λmax = 340 nm) to >70% excimer emission (λmax = 390 nm) as its molecular weight increases from 1900 to 278000. Despite such clear‐cut changes in the steady‐state spectra on phase separation, the fluorescence decays were nonexponential for all mixed films. Triple‐exponential decay functions were necessary to describe excimer decays at 430 nm and monomer decays at 340 nm. Moreover, the fluorescence decays varied slightly across the excimer emission band, and changed significantly when the polymer films were annealed. Studies on blends containing from 1 to 100% of P2VN and P2IPN established that this multicomppnent fluorescence decay behavior is intrinsicto the naphthalene‐containing polymer phase, it is proposed that excimers formed between chromophores in meso and racemic dyads have different mean decay times and that imperfectly aligned chromophore pairs lead to an additional short‐lived excimer decay component.
Compositional variations in cast films of blends of copolymers of siloxanes and poly(methyl methacrylate) determined by energy dispersive spectroscopy and X‐ray image analysis
Authors: Blahovici T. F. , Brown G. R.
Published: December 2004

Films cast on gold surfaces from 3% methylene chloride solutions of syndiotactic poly(methyl methacrylate) (PMMA) (Mn = 23,000) and random copolymers of PMMA and 4‐(methacryloyloxybutyl) pentamethyldisiloxane (MBPD) (Mn = 40,000) are all heterogeneous with visible phase separation occurring over most of the compositional range. Energy dispersive spectroscopy (EDS) shows that for PMMA blended with the copolymers there is an excess of silicon, ranging from 1.9 wt% to 9.7 wt%, in the surface exposed to air during casting, while the lower surface exposed to the gold is depleted in silicon. X‐Ray mapping and image analysis show that for blends containing 50% or less of siloxane copolymer the upper surface is composed of large siloxane rich domains in a PMMA matrix while the lower surface is composed of much smaller and less abundant siloxane domains in a PMMA matrix. In addition, the siloxane domains of the upper surface contain small PMMA domains. For blends with a greater siloxane content, the upper surface is composed of a siloxane matrix while the lower surface remains PMMA rich.
Rheological evaluation of polystyrene/polyethylene blends
Authors: Utracki L. A. , Sammut P.
Published: December 2004

The dynamic shear behavior at 200°C of low density polyethylene, LDPE, polystyrene, PS, and their blends was studied. Two series of blends were prepared containing LDPE:PS = 1:2, 2:1 and 17:3; the first series contained 0, the second 5 wt% of the compatibilizing, partially hydro‐genated poly(styrene‐b‐isoprene) di‐block copolymer, SEB. From the Casson plot the relative values of apparent yield stress were found to be G′y > G″y the addition of SEB decreased both these functions, but the inequality remained valid. After subtracting the yield stress values the frequency relaxation spectrum was computed from the relation G″ = G″(ω). The linear viscoelastic functions determined from the spectrum were found to agree with experimental values within a range of error below 5%. The blends were found to be thermorheologically complex with the time‐temperature shift factors depending on both temperature and frequency. A compositional dissymmetry of blend morphology was observed: PS dispersed in LDPE formed spheres, while at corresponding concentration LDPE in PS formed fibers. A difference in surface tension of the two polymers, leading to different spreading coefficients (SPE/PS≠SPS/PE), or dissymmetry of the interfacial tension coefficient, could provide a possible explanation.
J Integral measurements of ultra high molecular weight polyethylene
Authors: Rimnac Clare M. , Wright Timothy M. , Klein Robert W.
Published: December 2004

Fracture of ultra high molecular weight polyethylene (UHMWPE) contributes to damage modes occurring on the articulating surfaces of total joint replacement components. To minimize damage through the optimization of component design requires an understanding of the fracture behavior of UHMWPE. A fracture/mechanics approach was taken in which J integral tests were performed on three‐point bend specimens of two thicknesses. JIC was determined to be 99.5 kJ/m2 and was independent of specimen thickness. The fracture surfaces for both specimen thicknesses showed extensive orientation and failure through multiple layers of material, suggesting that UHMWPE experiences plane stress conditions at the crack tip, regardless of thickness.
Phase equilibrium in the binary and ternary blend system: Polycaprolactone‐polyvinyl chloride‐styrene acrylonitrile copolymer
Authors: Huarng Jyh Chiarng , Min Kyonsuku , White James L.
Published: December 2004

An experimental study of binary and ternary phase equilibrium in the system polycaprolactone (PCL) poly(vi‐nylchloride) (PVC)‐77/23 styrene‐acrylonitrile copolymer (SAN) is described. Miscibility is determined using differential scanning calorimetry (DSC) and turbidity. PCL/PVC and PCL/SAN are largely miscible systems but PVC/SAN is immiscible. The ternary system shows considerable miscibility. The blends are characterized by polarized light microscopy and wide‐angle X‐ray diffraction. The former measurement characterizes the structure of the spherulites. Additions of PVC, SAN, or PVC/SAN causes the spherulites observed in PCL to grow in size and become coarse. X‐ray diffraction shows no movement of crystallographic peaks indicating the crystallographic unit cell is composed of PCL. Melting point depression measurements are used to calculate Flory χ interaction parameters for PCL/PVC and PCL/SAN. The melting point depression is also considered and used to investigate PVC/SAN interaction. An effort is made to compute the ternary phase diagram and tie lines.
Memory effects in polymers. IV. Processing history vs. crystallization rate—effect of polymer structure
Authors: Khanna Y. P. , Kumar R. , Reimschuessel A. C.
Published: December 2004

Our earlier work on this series has shown that the processing history, e.g., melt‐extrusion, freeze‐grinding, or solution precipitation of virgin nylon 6 leads to a marked increase in the crystallization rate. Similar studies have now been extended to several other polymers. Results indicate that the processing history effects on the crystallization rate are most pronounced for polymers with high intermolecular forces, e.g. nylon 6, nylon 66, nylon 6/66, nylon 11, and nylon 12. Interestingly, polymers of intermediate polarity, e.g., polyethylene terephthalate (PET) and chlorotrifluoroethylene (CTFE)/vinylidene fluoride (VDF) copolymer (96/4, Aclar®) also reveal similar effects although to a much lesser extent. On the other hand, non‐polar polymers, e.g. polyethylene, are not influenced in terms of crystallization behavior by the processing history.
Polyesters II: A review of phase behavior in binary blends: Amorphous, crystalline, liquid crystalline, and on transreaction
Authors: Porter Roger S. , Jonza James M. , Kimura Masao , Desper C. Richard , George Eric R.
Published: December 2004

Thermal and mechanical studies on many linear polyesters have revealed their behavior in crystalline, liquid crystalline, and amorphous phases. Their phase behavior in binary compositions has also been studied by a range of additional techniques and in combinations including the polycarbonate of bisphenol‐A. Regions of amorphous compatibility and incompatibility have been identified and measures made of transition temperature changes with composition. The conditions for transreaction have also been determined and the properties measured for the resultant new copolymers.