bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of high modulus films by solid state rolling
Authors: Bigg D. M. , Smith E. G. , Epstein M. M. , Fiorentino R. J.
Published: December 2004

Solid state rolling of semicrystalline polymers represents a high speed process for producing oriented, high modulus films, tapes, and sheets. The important process variables include roll temperature, thickness of initial sheet, roll speed, take‐up tension, roll diameter, and initial morphological state of the polymer. Roll temperature controls both the extent of maximum deformation and the rate of rolling. A minimum temperature exists for each polymer below which the orientation process is sharply limited. This condition is similar to the limitation present in the hydrostatic extrusion process, in which the alpha crystallization temperature limits the orientation process. Roll speeds as high as 20 m/min have been realized. It is apparent that film thickness and thickness reduction ratio have a strong effect on the ultimate rolling rate. The process, as currently practiced, is adiabatic, and therefore, heat transfer limited. The take‐up tension influences the extant of orientation in the amorphous phse of of the polymer. This in turn affects its thermal and chemical stability. The effect of roll diameter is to limit the extent of thickness reduction by causing roll‐film slippage when the roll dianmeter to thickness reduction ratio is below some as yet undetermined value. The initial morphological state of the polymer affects the amount of crystalline deformation possible, the surface texture of the rolled film, and the tear resistant of the oriented film.
Molecular orientation of polydimethylsiloxane induced by elongational and shearing strains
Authors: Santerre J. P. , Picot J. J. C.
Published: December 2004

A study examining the molecular orientation of poly(dimethylsiloxane) for different combinations of elongational and shear strains is presented. Three different cases were studied: (1) pure elongational strain; (2) increasing shear and decreasing elongational strains; (3) increasing shear and increasing elongational strains. The experiments were performed in a converging flow cell (at room temperature), where elongational and shearing strain rates achieved values of 370 s−1 and 640 s−1 respectively. Values of the Hermans orientation function were obtained from measurements of birefringence and polarization angles while strain rates were estimated from laser Doppler anemometry velocity measurements. Prospects for predicting molecular orientation from the stress‐optical laws and rheological flow models are outlined and commented on.
The dynamic properties of glass‐fiber‐reinforced polypropylene subjected to pure bending
Authors: Worth R. A.
Published: December 2004

The dynamic tensile properties of glass‐fiber‐reinforced polypropylene have been measured for pure bending. The specimens were cut from the injection molded outer drum of a washing machine. Fiber orientation within the specimens was investigated using a scanning electron microscope, and was observed to be predominantly in the direction of flow, throughout the thickness of the material. It was found that the stiffness was greater in the direction of fiber orientation, while the damping was greater in the transverse direction. The results were in general agreement with values obtained from torsion pendulum experiments.
Characterization of stress relaxation curves of plastic foams
Authors: Miltz Joseph , Ramon Ori
Published: December 2004

Stress relaxation curves of plastic foams can be normalized and presented as a linear function of time. The two parameters derived from this model provide information about the residual modulus and relaxation rate. This simple method was found to describe relaxation curve as well as the more complex successive residuals method. It was found that the residual relaxation modulus as determined by the normalization and linearization technique depends on the strain history of the samples.
Glass transition relations in ionomeric “comb” polymers
Authors: Wollmann D. , Gauthier S. , Eisenberg A.
Published: December 2004

The glass transition temperatures (Tg) and dynamic mechanical properties of random copolymers of styrene‐4‐vinylpyridine quaternized with iodoalkanes are presented for vinylpyridine contents up to ten percent and pendant alkyl chains up to ten carbons in length. Two linear relationships, between ion content and glass transition temperature and between pendant alkyl chain length and theTg, are observed. An equation is presented that can be used to predict theTgfor such copolymers based on their ion contents and alkyl chain lengths.
Dielectric behavior of carbon black filled polymer composites
Authors: Yacubowicz J. , Narkis M.
Published: December 2004

This paper reports results on the dielectric properties of carbon black filled crosslinked polyethylene composites. These systems are shown to follow percolative type models. The dielectric constant increases slowly, with carbon black concentration, up to roughly the percolation concentration and then increases rapidly over the whole concentration ranges studied. The dissipation factor‐concentration curves are bell‐shaped with maximum values at approximately the percolation concentration. The dielectric properties of these systems are discussed in terms of interfacial Maxwell‐Wagner polarization effects.
Predicting large strain deformation of polymers
Authors: Nimmer Ronald P.
Published: December 2004

Although yield stress and its dependence upon temperature and strain rate are well characterized for many thermoplastics, there are a number of scientific and engineering situations that require additional information regarding post‐yield deformation behavior. For example, the prediction of formability in plastics will require a quantitative description of constitutive behavior for strains between 40 and 300 percent, depending on the plastic. Data characterizing this behavior now exists for a number of plastics, and an analytical understanding of its effect on mechanical behavior has also been established. The purpose of this investigation is to apply the experimentally measured large‐strain constitutive behavior of polycarbonate to the analysis of several simple forming experiments and illustrate the accuracy of current predictions in comparison to experiment. Analyses of a tensile test, a “bend‐stretch” forming experiment, and the indentation of a circular disc by a hemispherical punch are compared with experiments. Agreement between analysis and experiment is very good for all geometries considered.
Fracture and toughness of crystalline polymer solids
Authors: Narisawa Ikuo
Published: December 2004

The development of plastic deformation and crazing in the neighborhood of a notch has been studied in connection with nonlinear fracture processes of crystalline ductile polymers, polyethylene, polypropylene, and propylene‐ethylene block copolymers. After revealing the morphology of plastic deformation around the notch and studying the effects of crystalline structure on ductile fracture processes, the J‐energy analysis was applied to give a criterion for crack initiation in the fracture of these elastic‐plastic materials. The material resistance to stable and unstable cracking was characterized using the curves of J against crack extension Δα.
Shear and craze competition in subcritical fatigue crack growth: Fatigue lifetime inversions
Authors: Takemori Michael T.
Published: December 2004

In some ductile amorphous polymers, the fatigue lifetime behavior can exhibit two distinct crack propagation modes: a craze dominated sub‐critical discontinuous crack growth mode, which leads to a low stress, short fatigue lifetime branch and a shear fracture mode, which produces a higher stress, long lifetime branch. When both branches coexist, the fatigue lifetimes at higher stress amplitudes are often longer than those at lower stress amplitudes! This unusual lifetime inversion has been explored for a polyestercarbonate at various temperatures, frequencies, degrees of physical aging, and fatigue overload histories.
Fracture of adhesive joints and laminated composites
Authors: Lee Shaw Ming
Published: December 2004

The mechanisms of resin controlled failure in adhesive joints and composites (delamination and transverse cracking) are examined. An in‐situ failure model based on the fracture mechanics principles is applied here to describe the failure processes involved. The model centers on the crack tip plastic zone developed in the thin resin layer between the fibers or the adherends. The plastic zone in the resin layer is heavily influenced by a dominant slow varying stress distribution, approximated to be r−m/2 dependent with m ≪ 1 (r is the distance from the crack tip). The adhesive or composite fracture toughness G*IC can then be expressed as a function of several resin properties of comparable importance: modulus E, yield stress σy, resin GIC and residual stress. The relative significance of the resin properties on the adhesive or composite fracture is discussed. The effects of temperature, loading rate, and resin toughening on such failure as a result of the corresponding variations in resin properties are also addressed.
High‐Temperature large‐strain behavior of polycarbonate, polyetherimide and poly(butylene terephthalate)
Authors: Nied H. F. , Stokes V. K. , Ysseldyke D. A.
Published: December 2004

A noncontacting experimental procedure has been used for characterizing the high‐temperature large‐strain uniaxial behavior of polycarbonate (PC), polyetherimide (PEI), and poly(butylene terephthalate) (PBT), through controlled tests on flat specimens cut from extruded sheet. While each of these polymers exhibits stable necking over a broad temperature range, the transition to the necked state is shown to be more gradual at higher temperatures, resulting in a less sharply defined neck transition region during the drawing process. These trends in necking behavior, and other phenomena such as double necking, which only occur at high temperatures, are illustrated through contour plots of the Cauchy‐Green deformation tensor. Elevated temperature true‐stress versus stretch data are given for each of these polymers.
Nonlinear response and thermomechanochemical degradation of a urethane elastomer
Authors: Mead Joey , Singh Sachchida , Roylance David , Patt Jacob
Published: December 2004

We have studied the failure of a urethane elastomer due to cyclic compressive loading, using loading frequencies and specimen sizes for which internal heat generation is an important factor. The eventual failures were generally manifest by internal cracks growing transverse to the loading direction. A variety of experimental analyses indicate that this failure is primarily thermal, in that the temperature rise due to viscous dissipation eventually leads to a melting of the hard segment domains which act to reinforce the material. No strong indication of thermal or thermomechanical bond scission was obtained, although a progressive reduction in the rubbery modulus was noted.
The torque in the metering zone of single screw extruders
Authors: Mennig G.
Published: December 2004

To study the energy dissipation in the different zones of an extruder, a special barrel has been designed where local torques Tq can be measured at the beginning of the conveying, the transition, and the metering zone. Experiments carried out for a commercial polyethylene and poly(vinyl chloride) at different processing conditions show that in some cases negative Tq in the metering zone may occur. A very basic analytical treatment of the flow situation in the metering zone shows that for a given drag flow Tq is dependent on the pressure gradient and particularly on its sign. Tq decreases with decreasing positive pressure gradient until there is pure drag flow. It further decreases with increasing negative pressure gradient until it becomes zero and even negative. A comparison of theoretical and experimental results for the metering zone shows good quantitative agreement though the main aim of the paper is to provide a better general understanding of the complex situations inside an extruder.
Thermal and cure analysis in sheet molding compound compression molds
Authors: Castro J. M. , Lee C. C.
Published: December 2004

Sheet molding compound (SMC) compression molding growth will benefit from faster cycles and more uniform cure so as to reduce in‐plane thermal residual stress and resulting warpage in the molded part. These improvements require an in‐depth study of the mold thermal design. Here we use a finite element model to analyze the quasi‐steady temperature distribution in a plane perpendicular to the heating channels of a representative mold, and a finite difference model to investigate the cure dynamics at critical regions. Several changes in the mold heating system and operating conditions were considered and their effects on the temperature distribution and cure time were studied. It was assumed that the steam condensate is well drained and enough steam is supplied so that the steam tube walls are kept at a constant temperature. An important conclusion of the present study is that better insulation of the mold from the press does not help much in improving the uniformity of cavity surface temperature or cure. It was also found that reducing the distance between two consecutive steam tubes beyond the distance from the steam tube to cavity surface will not yield a significant change. The most practical way to give both more uniform cavity surface temperature and faster cure is to have higher steam temperature for the region where the charge is initially placed.
An analytic study of tensile and puncture test behavior as a function of large‐strain properties
Authors: Nimmer Ronald P.
Published: December 2004

The mechanics of “cold‐drawing” in ductile thermoplastics are examined analytically. The fundamental postyield, strain hardening behavior of these thermoplastics as defined by a true stress versus true (natural) strain relationship is related to macroscopic, large deformation behavior in unidirectional tension tests arid axisymmetric puncture tests. The phenomena of load‐drop after yield and propagating necks are examined with respect to tension tests and are related to draw strain and large deformation strain hardening modulus. In addition, these same fundamental material properties are also shown to have a significant effect upon the energy absorption capability of thermoplastics as measured by puncture tests.
Unnotched impact bend test assessment of the degree of gelation in unplasticized poly(vinyl chloride) pipe
Authors: Kim H.‐S. , Cotterell B. , Mai Y.‐W.
Published: December 2004

It is suggested that the unnotched impact test is suitable for quantitative quality control of unplasticized poly(vinyl chloride) pipe. The relative level of processing is assessed by the probability that failure is nucleated at a surface flaw. Tests show that this assessment is very sensitive to the level of processing.
A diffusion coefficient model for polymer devolatilization
Authors: Misovich Michael J. , Grulke Eric A. , Blanks Robert F.
Published: December 2004

Polymer devolatilizers are in widespread use in the polymer industry for removing solvents and monomers from polymer melts prior to product fabrication. Design equations for describing the solvent flux usually include both the diffusion coefficient of the solvent in the polymer melt and the equilibrium concentration of the solvent at the polymer‐vapor interface. Several models make the as sumption that the solvent diffusivity is constant over the ranges of solvent concentrations and temperatures in the devolatilizer. This is a critical assumption that may be difficult to check without obtaining diffusivity data at the operating temperatures and concentrations of the process equipment. There are three models that can be used for diffusion coefficients in devolatilizer design: the free volume model developed by Duda, Vrentas, and coworkers; a new linear model proposed in this study; and a constant diffusivity model, The linear model is obtained by combining a new correlation for solvent activity coefficients in molten polymers with free volume theory and linearizing the resulting equation. The error between using the complete free volume theory and using the linear model, or alternatively, using a constant diffusion coefficient, is calculated for several solvent‐polymer systems. The linear model is convenient to use for determining the effects of the solvent activity coefficient on the diffusion coefficient. A method is presented for determining whether the complete model, the linear model, or the constant diffusivity model is appropriate for a given devolatilizer design.
A study on poly(vinyl chloride) blends with chlorinated polyethylene and polyethylene
Authors: Xi Xu , Xiande Meng , Keqiang Chen
Published: December 2004

By means of a twin‐roll masticator and Brabender rheometer, the effect of chlorinated polyethylene (CPE) and polyethylene (PE) on the impact strength and processability of poly(vinyl chloride) (PVC) was studied. The experimental results show that CPE can promote the plasticity of PVC and the effect increases with the amount of CPE. Addition of a small amount of PE in PVC/CPE (100/12) makes an impressive improvement in the impact strength of the mixture. The impact strength of PVC/CPE/PE (100/ 12/2.5) at 20°C is 30.0 kJ/m2 higher than that of PVC/CPE (100/12). The dynamic viscoelastic spectra, tensile strength, and elongation test reveal that CPE is incompatible with PVC but may act as a compatibilizer for PVC/PE. The disperse state of the polyblend was studied by differential scanning calorimetry (DSC); it was found that the mixing sequence has an influence on the impact strength of the blend.
Numerical analysis of the temperature profile in the melt conveying section of a single screw extruder: Comparison with experimental data
Authors: Bruker I. , Miaw C. , Hasson A. , Balch G.
Published: December 2004

The prediction and measurement off the developing radial temperature profile in a single‐screw extruder is essential since excessive extrudate temperature and poor temperature uniformity at the die affect the quality of coextrusion and film/sheet extrusion processes. A finite‐difference scheme is used to predict the development of the radial temperature profile in the metering section of a single‐screw extruder for power‐law fluids. A finite‐element analysis of the flow around the screw‐tip transposes this temperature profile onto an on‐line temperature measuring device consisting of 10 thermocouples for a comparison of numerical results with experimental data on polycarbonates.
Uniaxial roll‐drawing of isotactic polypropylene sheet
Authors: Burke P. E. , Weatherly G. C. , Woodhams R. T.
Published: December 2004

The process described as “roll‐drawing” has been applied to commercial extruded sheets of isotactic polypropylene (M̄n = 70,900). Preheated billets were drawn into thin, clear, transparent sheets in a single pass, producing uniaxial orientation of the polymer molecules in the draw direction. At the maximum draw ratio of 20, the ultimate tensile strength and Young's modulus in the draw direction were 0.5 GPa and 20 GPa respectively. The mechanical properties transverse to the draw direction were virtually unchanged. The theory of fiber reinforcement for unidirectional anisotropic plates was applied to interpret the orientation dependence of the stress‐strain behavior of the drawn sheets. From these results, it was estimated that the mechanical properties of biaxially laminated polypropylene sheets equaled the performance of aramid and carbon fiber composites, The roll‐drawing process appears to be economically attractive for the production of ultra‐high modulus crystalline thermoplastics in sheet form having excellent uniaxial or biaxial properties.
Determination of the mode of termination in free‐radical copolymerization
Authors: Chen Chuh‐Yung , Wu Zen‐Zli , Kuo Jen‐Feng
Published: December 2004

In this study the apparent rate constant model was used to determine the mechanism of termination and other rate constants for free radical copolymerizations that are chemically controlled with no penultimate effect. The data required were the number average molecular weight and the conversion obtained at various initial initiator concentrations and monomer compositions, and two rate constants of propagation of the homopolymerizations of its two monomers. The bulk free radical copolymerization of methyl methacrylate (MMA) and styrene(St) at 60°C was studied. Three published literature values of the propagation rate constants k11 and k22. 750, 150; 515, 145; 705, 145, were used for the determination. The unit of the rate constants used was liter/mole/s. The modes of the termination reaction obtained, depending on k11, k22 used, are given as follows:

mole percent Combination in the Termination

(k11, k22)
MMA‐MMA radicals
St‐St radicals
St‐MMA radicals

(750, 150)
17
99
96

(515, 145)
54
99
91

(705, 145)
40
98
87

The modes of termination obtained by the case of k11 = 750 and k22 = 150 are in good agreement with those shown by Bevington, Melville, and Taylor (1).
26‐Year creep and recovery of poly(vinyl chloride) and polyethylene
Authors: Findley William Nichols
Published: December 2004

Creep experiments on two thermoplastics at constant values of tensile stress, temperature, and relative humidity previously reported for 132,000 h were continued to about 230,000 h. An equation of the form ϵ = ϵo + ϵ+tn was used to predict the creep, where t is time and ϵo, ϵ+, and n are constants for a given stress. ϵo, ϵ+, and n were determined from the first 1900 h of data and were used to predict the creep to 230,000 h. The subsequent recovery on unloading was predicted using the same equation together with the superposition principle. Also reported are creep and recovery of companion specimens aged for about 98,000 h.
Practical aspects of physicochemical kinetics using thermal techniques
Authors: Khanna Y. P. , Taylor T. J.
Published: December 2004

A number of studies on the kinetics of physicochemical processes are described. The methods used are shown to be potentially useful for making time‐temperature predictions and for optimizing process variables. Examples described include (1) the long‐term prediction of the performance of a plasticized polyvinyl chloride and doped polyacetylenes; (2) the polymerization of a monomer and the optimization of time, temperature, and initiator concentration variables; (3) analysis of an order/disorder transition in a thermochromic polymer; (4) the crystallization of polymers and the effect of a nucleating agent; and (5) the crystallization of an amorphous metallic glass. The theoretical background, significance, scope, and limitations of these measurements are also discussed.
The effect of thermal history on the rheology and texture of thermotropic liquid crystalline polymers
Authors: Done D. , Baird D. G.
Published: December 2004

This paper is concerned with the effect of thermal history on the rheology of three liquid crystal copolymers. The polymers were heated to temperatures above their melting points and then cooled down. During the cooling cycle, the dynamic mechanical properties were monitored. It was found that these properties remained unchanged at temperatures as low as 30°C below the normal melting points for two copolyesters of 60 mole percent p‐hydroxybenzoic acid (PHB) and 40 mole percent poly(ethylene terephthalate) (PET) (60‐40 PHB/PET) and 80 mole percent PHB and 20 mole percent PET (80‐20 PHB/PET). For a copolymer of PHB and 2,6‐dihydroxynaphthaic acid, there was a gradual increase in the properties with decreasing temperature. However, at a critical temperature all three systems exhibit a sudden increase In dynamic mechanical properties. The kinetics of solidification were also monitored, and it was found that at temperatures well below the melting point, it took 4 to 6 min before the solidification process impeded flow. Extrusion studies on these materials were also carried out, and it was observed that in this supercooled state, the polymers exhibited significant die swell. The samples also exhibited a fibrous texture and were more oriented than when extruded isothermally above the melting point.
Analysis of epoxy resin curing kinetics using the Avrami theory of phase change
Authors: Pollard M. , Kardos J. L.
Published: December 2004

To przoduce efficiently high quality structural parts from fiber‐reinforced epoxy materials systems, it is necessary to develop detailed process models. One key component in any such model involves the prediction of the cure kinetics, which in turn governs the viscosity, resin flow, void formation, and other important processing parameters. In this study, a series of isothermal and dynamic differential scanning calorimetry experiments was performed using Hercules 3501‐6 and 3502 resins (TGDDM epoxy with DDS curing agent). The hypothesis of a dispersion of growing microgel particles, which become a continuous‐phase solid at the gel point, was used as a basis to apply the Avrami theory of phase change to describe the polymerization kinetics up to the gel point. The extended equations for nonisothermal conditions properly accounted for the temperature effects on the kinetics. Comparison of the theoretical predictions with experimental data suggests that the Avrami theory of phase change may model adequately the cure kinetics of these systems, at least up to the gel point.
A review of recent experimental results concerning the strength and time dependent behavior of fibrous poly(paraphenylene terephthalamide)
Authors: Schwartz Peter
Published: December 2004

A review of recent investigations of the strength and stress rupture of single filaments of poly(paraphenylene terephthalamide) (PPTA) is given. The experimental results are presented within an activation energy/power law breakdown framework. The statistics for tensile failure of individual filaments and epoxy impregnated strands and the lifetime of filaments in stress rupture are shown to fit the standard two‐parameter Weibull distribution, as predicted from the model.
Biaxial orientation of polypropylene by hydrostatic solid state extrusion. Part III: Mechanical properties and deformation mechanisms
Authors: Tang H. I. , Hiltner A. , Baer E.
Published: December 2004

The deformation of biaxially oriented polypropylene sheet produced by the BeXor process has been examined in terms of the hierarchical solid state structure described previously. The mechanical properties have been examined over a range of temperatures and strain rates. The anisotropic nature of uniaxial tensile deformation was analyzed from simultaneous measurements of longitudinal extension and lateral contraction in the width and thickness directions, by determining the shape of uniaxially deformed spherulites, and by examining fracture surfaces in the scanning electron microscope (SEM). It was determined that deformation proceeds by elastic extension of the amorphous network and plastic shear deformation of the crystalline regions in the plane of the sheet, and in the thickness dimension, by voiding with induced fibrillation. It is suggested that the property improvements, particularly at low temperatures and high strain rates, which are achieved by the BeXor process, result from changes in the hierarchical structure at the size scale of the crystalline lamellae. Specifically it appears that the small crystalline blocks formed by breakup and recrystallization of lamellae are more easily deformed than the original large coherent lamellae.
A simulation of the effects of high strain energy storage in large plastic structures
Authors: Groshans V. L. , Takemori M. T.
Published: December 2004

Brittle failures of large plastic structures observed in the field may have occurred at much higher loads than implied from the fracture surfaces, indeed, as if very ductile failures had occurred. It has been demonstrated that these brittle failures may be a direct result of high energy storage upon impact in large compliant systems. A rubber‐toughened blend of polybutylene terephthalate (PBT) and polycarbonate (PC) was highlighted in this study. Soft steel springs were used in series with compact tension samples to simulate the high energy‐storing capability of large compliant structures, Ductile and stable fractures of compact tension samples of the blend were observed at all of the temperatures tested down through −30°C. With the insertion of springs to simulate large compliant structures, however, unstable failures resulted. At 25°C, initial ductile crack growth was followed by ductile but unstable failure. At −30°C, initial ductile crack growth was followed by brittle unstable failure. These instabilities resulted from the excessive amount of stored energy released by the system during initial crack growth. A higher rubber variant of the PBT/PC blend as well as acrylonitrile‐butadiene‐styrene (ABS) and polycarbonate exhibited similar behavior.
Phenomenological and mathematical analysis of the orientation in biaxially drawn polymeric films
Authors: Jungnickel B.‐J.
Published: December 2004

Equations are derived that relate the orientation of “pseudo‐affine” reoriented structural units after a biaxial deformation to the degrees and the directions of the effective drawings. The connection between these drawing parameters and those externally applied is analyzed in detail. It is shown how a comparison of these two sets of drawing parameters allows conclusions regarding the distribution throughout the material of the stresses that cause the deformation, the inhomogeneity of the deformation, and the role of non‐orienting flow during deformation. In particular, the orientation of biaxially drawn poly(ethylene terephthalate) films is investigated, and it is shown what general information can be obtained on the deformation behavior of this material on the basis of these considerations.
Thermodynamic interaction in polybutadiene/solute systems by inverse gas chromatography
Authors: Tseng Hsiao‐Show , Wong Pak‐Choy , Lloyd Douglas R. , Barlow Joel W.
Published: December 2004

The dependence of polymer‐solute interactions on temperature In the range was 66 to 96°C was studied by inverse gas chromatography (IGC). A correlation equation was developed for estimation of the specific retention volume of nonpolar and slightly polar solutes in polybutadiene (PBD). Using equation of state solution theory, thermodynamic interaction was discussed in terms of contact energy and equation of state contributions in polybutadiene/solute systems. It was found that equation of state theory serves better than the Flory‐Huggins theory as a comprehensive model to describe the temperature dependence of thermodynamic interaction.
The rheological characterization of a series of thermotropic liquid crystalline polymers
Authors: Tuttle J. R. , Bartony H. E. , Lenz R. W.
Published: December 2004

Dynamic rheological experiments were performed on a series of two copolymers and a homopolymer based on units of terephthaloyl chloride and isophthaloyl chloride at 90/10 and 75/25 mole ratios combined with 1,10‐bis(4‐hydroxyphenyl)‐decane. Optical microscopy and wide angle X‐ray diffraction (WAXD) confirmed that all of the polyesters in the present series formed nematic liquid crystals with nematic‐to‐isotropic temperatures in the range of 270 to 320°C with increasing terephthaloyl unit content. Broad nematic‐to‐isotropic transitions observed by differential scanning calorimetry (DSC) were indicative of biphasic regions where the nematic and isotropic phases coexist. The rheological behavior of each polymer was more complex in the nematic phase than in the isotropic phase with shear thinning occurring in the former but Newtonian behavior in the latter. There were also some indications that nematic flow behavior could be induced in these polymers by dynamic oscillatory shear flow above the nematic‐to‐isotropic transition, Ti. A form of hysteresis was observed with the homopolymer in that measurements of the dynamic viscosity, η*, taken with ascending frequency sweeps were higher than those taken with descending frequency sweeps.
Microstructure and mechanical behavior of reinforced reaction injection molded (RRIM) polyurethane
Authors: Kamal M. R. , Singh P. , Samak Q. , Kakarala S. M.
Published: December 2004

A study was carried out to characterize the microstructure and distribution of some mechanical properties in reinforced reaction injection molding panels (RRIM). The panels were prepared under a variety of processing conditions. Scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared analysis were employed for microstructure characterization. The following mechanical tests were carried out: dynamic mechanical, tensile, and impact. The results indicate significant relationships between processing conditions, microstructure, and mechanical properties. In particular, the skin/core structure of the panels and the size distribution of bubbles in the matrix have an important effect on the impact properties. Furthermore, the balance between the distributions of cure and crystallinity, which is difficult to define clearly, plays an important role in determining panel behavior.
Estimation of the speed of propagation of intergranular stress waves using a simple elastic contact model
Authors: Stephenson Stuart E.
Published: December 2004

A model of a granular bed is used to obtain an estimate of the speed of propagation of intergranular stress waves. In the analysis, a simple elastic contact between neighboring grains is assumed. The model may be extended to include more complex Intergranular interaction mechanisms, but at the expense of such a simple analytical solution as that obtained here. The predicted dependence of compression of a granular bed on compressive load is compared with experimental measurements and is found to describe the relationship very well. The simplified analysis gives a general insight into the dependency of wave speed on bed geometry, indicating for example that while wave speed is independent of grain size, it does depend on the Initial porosity of the bed.
Countercurrent cooling of blown film
Authors: Strater K. F. , Dealy J. M.
Published: December 2004

Presently used methods for the external cooling of blown film involve the use of an air ring located at the base of the bubble that blows air upward along the surface of the bubble. The air is heated as it rises, while the film is cooling and moving in the same direction. This is an example of cocurrent heat exchange, and the result is the accumulation of heated air around the upper portion of the bubble, which interferes with the cooling in this region. While rapid initial cooling is required to maintain bubble stability, we have explored the possibility of using countercurrent cooling for the upper region of the bubble. A standard air ring is mounted at the base of the bubble, and a circular shroud surrounds the bubble above this air ring. All the heated air is collected in an upper chamber surrounding the shroud and is exhausted by means of a secondary blower. The proposed scheme was found to increase heat transfer in the upper regions of the bubble and to permit the ducting of all heated air away from the film line.
Tensile creep tests, internal pressure tests, and scanning electron microscopy of electrical conduits of poly(vinyl chloride)
Authors: Johansson Lennart , Törnell Bertil
Published: December 2004

Electrical conduits prepared from a mixture of suspension and emulsion poly(vinyl chloride) (PVC) resins were subjected to internal pressure tests at 60°C, covering a wide range of pressures. Some axial tensile creep tests were also carried out at the same temperature. As expected, the ability to withstand internal pressure decreased when the amount of lubricant was increased above the level used in normai commercial production. Fracture surfaces obtained in the two test methods were investigated by scanning electron microscopy. Incompletely melted primary particles or other fragments of resin grains were not observed in any of the fracture surfaces studied in this work. However, a peculiar skinlike structure was found in the fracture surfaces formed at intermediate stress levels in the internal pressure test. This structure was not observed in the fracture surfaces obtained in the notched tensile tests at constant load.
Linear low density polyethylenes and their blends: Part 5 extensional flow of LLDPE blends
Authors: Schlund B. , Utracki L. A.
Published: December 2004

The uniaxial extensional flow at 150°C of two series of blends: I. LLDPE/LLDPE and II. LLDPE/LDPE was examined in full range of concentrations as well as that of accessible in the rheometer strains and strain rates. It was concluded that Series‐I blends containing different LLD‐type polymers are miscible. Their properties can be predicted on the basis of molecular weight and molecular weight distribution. By contrast, excepting low concentration limits, blends of Series‐II are immiscible. Both series show strain hardening, due to higher values of the maximum strain at break. Series‐II seems to be superior (under the test conditions). The stress growth function in shear, computed from the frequency relaxation spectrum, provided a good prediction of the linear viscoelastic component of the stress growth function in uniaxial extension.
Thermal analysis studies on thermoplastic rigid rod molecular composites
Authors: Wiff D. R. , Hwang W‐F. , Chuah H‐H. , Soloski E. J.
Published: December 2004

Rigid rod molecular composites involve molecular level mixing of two polymers having greatly disparate chain conformations (one rodlike and one flexible coil like). Morphology studies have shown that in such materials the bundle diameter of these rigid rod molecules is less than 5 nm. The rigid rod molecule used is poly(para‐phenylene benzobisthiazole) (PPBT). The thermoplastic flexible polymer matrix is Nylon‐66, DuPont's Zytel 42. Thermal analysis studies on these materials indicate that the expected Tg shifts, as observed for blends of two flexible polymers, and depression of Tm with increased rod molecule composition does not occur.
Polystyrene‐polyethylene melt blends obtained through reactive mixing process
Authors: Baker W. E. , Saleem M.
Published: December 2004

Reactive polystyrene (OPS) and reactive polyethylene (CPE) with oxazoline and carboxylic acid functionality, respectively, were melt blended in a Rheomix mixer under a variety of conditions. The properties of these blends were examined and correlated with the compositions and mixing conditions such as shear rate, time, and temperature. An increase in torque was observed, which is believed related to chemical reaction between OPS and CPE. The difference between the maximum and minimum torque (Tmax‐Tmin), increases from 48 to a maximum of 510 m‐g for 10 and 40% CPE reacted blends, respectively, But on further increase in the CPE amount in the blend the torque increase drops reaching a final minimum value of 133 m‐g for a blend with 90% CPE. Differential Scanning Calorimetry (DSC) studies reveal a single first order transition, due to CPE, for each of these polymer blends. Furthermore, evidence of the glass transition temperature for OPS diminishes with increasing CPE content and mixing time. Scanning Electron Micrographs (SEM) show a fine dispersion in these reactive blends, with particle size much smaller than a micron. Blends with 50% or more CPE have no distinguishable features as such. Mechanical properties such as elongation at break of reacted blends are improved over the nonreactive polyethylene (PE) and polystyrene (PS) blends. An intermolecular reaction between the OPS and CPE results in a graft polymer, which imparts improvement in the overall properties of these reacted blends. The maximum grafting reaction corresponds to 40% CPE blend, which is being evaluated as a potential compatibilizer.
On the pressure of water of crystallization at filler inclusions
Authors: Ashbee K. H. G.
Published: December 2004

On water uptake, plaster of Paris sets to gypsum, and the volume expansion associated with this particular hydration reaction has been long exploited to make casts for statuary. Immobilization of molecules of liquid water into the crystal lattice of water of crystallization gives rise to a decrease of entropy, and this is manifested by the so‐called heat of hydration. When it occurs at a calcium sulfate inclusion inside a polymer, the plaster of Paris → gypsum reaction generates a pressure, and the dependence of the equilibrium value of this pressure on temperature is expressed by Clapeyron's equation. From published data for the volume expansion ΔV and entropy decrease ΔS, it is shown that

Using as a benchmark the fact that p is zero at 100°C, the temperature at which plaster of Paris, gypsum, and liquid solution can exist in thermodynamic equilibrium (1), we find that hydration at ambient temperatures of a typical calcium sulfate filler composition will, under conditions of thermodynamic equilibrium, generate sufficient pressure to cause internal cracking. Attention is drawn to the fact that creation of water of crystallization pressures of similar magnitude can be expected for any other filler that can exist in more than one state of hydration. As a corollary, the Clapeyron equation is used to make a similar analysis of the phenomenon of frost shattering in polymeric materials that contain free water.
Viscosity of homogeneous polymer blends: An altered free‐volume state model
Authors: Sood R. , Kulkarni M. G. , Dutta A. , Mashelkar R. A.
Published: December 2004

An altered free‐volume state (AFVS) model was developed for the zero‐shear viscosity of homogeneous polymer blends. The model involves a single adjustable parameter and is capable of predicting several complex features of the blend viscosity‐composition behavior. These include negative and positive deviations from additivity, maxima, minima, and sigma‐shaped curves. The validity of the model was tested by comparison of the model predictions with experimental data for several homogeneous blend systems. It is shown that the model is valid within a broad molecular weight range and is more accurate than some of the currently accepted models such as the kinetic network model. Besides, it appears that the AFVS model also may be applicable to blends of incompatible polymers under certain conditions.
Anomalous penetrant transport in glassy polymers VI. Effect of temperature on transport
Authors: Urdahl Kent G. , Peppas Nikolaos A.
Published: December 2004

Transport of liquid cyclohexane through well characterised, initially glassy, crosslinked polystyrene slabs was Investigated at 20, 30, 40, and 50°C. The samples used were produced by bulk polymerization of styrene and divinyl benzene (DVB) at 90°C for 43 hr using benzoyl peroxide as an initiator. The samples tested had initial cross‐linking ratios, X, between 5 and 25 × 10−3 mol DVB/mol styrene. The initial thickness of the samples tested varied from 0.25 mm to 1.80 mm, and the aspect ratio (length to thickness ratio) was maintained above 10;1 in order to analyze the results by one‐dimensional transport equations. Cyclohexane uptake was followed as a function of time along with dimensional changes in the thickness and area of the samples. The results of penetrant uptake as a function of time were analyzed using a simplified exponential expression and employing all the data points from the beginning of the experiment until the time of observation of the maximum in uptake. Good correlations were established between the penetrant uptake and the transport temperature. These results were interpreted in terms of competitive relaxational and diffusional mechanisms.
Optimal anticipatory control of ram velocity in injection molding
Authors: Pandelidis I. O. , Agrawal A. R.
Published: December 2004

This paper discusses a computer control system for ram velocity of an injection molding machine using optimal state feedback based on the linear quadratic control theory. A new approach for the selection of appropriate weighting matrices is presented in this context. The simulation results reveal that the optimal controller has improved performance over the conventional PID controller presently used, having faster speed of response, significantly better tracking performance, and better noise filtering properties. The execution speed and the core storage requirements would allow implementation even on a small online computer.
Hydrolysis of polycarbonate/polybutylene terephthalate blend
Authors: Golovoy A. , Cheung M. F. , Van Oene H.
Published: December 2004

The hydrolysis of a polycarbonate/polybutylene terephthalate (PBT) blend (50/50) was investigated by immersing molded samples in water baths between 21 and 98°C. Samples were also placed in a 100°C air circulating oven (dry environment). Changes in impact properties, dynamic mechanical properties, molecular weight, and thermal properties were followed. In 80°C water bath the material was found to embrittle in five to six days, and in circulating air oven at 100°C in less than 90 days. A sharp decline in molecular weight and changes in thermal and mechanical properties were observed. The activation energy for the embrittlement process in water was found to be 22 kcal/ mole. This value is between the activation energy for the hydrolysis of PC and that of PBT.
Effect of crosslink density on molecular relaxations in diepoxide‐diamine network polymers. Part 2. The rubbery plateau region
Authors: Charlesworth John M.
Published: December 2004

A comparison of the prediction of the theory of rubber elasticity with the experimentally observed variation of the shear storage modulus, G, as a function of crosslink concentration shows that deviations occur when the network strand concentration in diepoxide‐diamine polymers exceeds approximately 1.5 mole kg−1. The rapid rise in G above this level is accounted for in terms of the increasing importance of non‐Gaussian chain statistics and steric interactions. It is also established that the contribution from entanglements is significant and the behavior over the entire crosslink density range can be described by the following equation

where v and ϵTe are the concentrations of elastically active strands which orginate from fixed points and entanglements respectively, ψ is an empirical constant related to the importance of the non‐ideal behavior, and ϕ is the so‐called “front factor”. This latter constant is found to depend on the functionality of the network junctions, varying from 0.9, for a system with tetrafunctional junctions, to an average of 0.53 for those networks with trifunctional junctions.
Mold‐filling simulations for the injection molding of continuous fiber‐reinforced polymer
Authors: Chan A. W. , Hwang S.‐T.
Published: December 2004

Injection molding can be used to fabricate fiber‐reinforced polymer composites by impregnating a continuous fabric mat preplaced in a mold cavity with a polymer resin. The mold‐filling time is dependent on the flow and heat transfer behavior in the mold. A model is proposed that considers the non‐Newtonian How through the porous fabric mat and the heat transfer between mold, fabric mat, and flowing fluid. The model was simulated for the mold filling of a carbon fiber mat with a pseudoplastic polymer solution. The results from the simulation provide Information for optimizing mold‐filling parameters through proper selection of inlet fluid pressure, heat source temperature, and type of polymer‐solvent system.
Cure analysis of printed wiring boards containing reactive adhesive layers
Authors: Fullerton Rhonda , Roylance David , Allred Ronald , Acton Adra
Published: December 2004

This paper presents a method for analyzing the cure of multilayer circuit boards containing chemically reactive adhesive interlayers. The cure kinetics of the adhesive are first quantified by differential scanning calorimetry, using the method of Freeman and Carroll to obtain the numerical kinetic parameters. These parameters are then used in a finite‐element model of the circuit board which solves the heat and species transfer equations simultaneously. It is then possible to predict the temperature and extent of reaction at any time and position within the laminate, enabling the curing program to be optimized.