bluuebunny/crossref_metadata_2025 huggingface dataset:
Comments on “fracture toughness of impact modified polymers based on the J‐integral”
Authors: Huang D. D. , Williams J. G.
Published: May 2005

In (1), Narisawa and Takemori examined the physical interpretations and some experimental techniques of the J‐Integral (ASTM E813‐81) as applied to toughened polymers. Their results and conclusions are reexamined and discussed in terms of recent developments in J testing.
3‐D flow analysis of non‐newtonian viscous fluids using “enriched” finite elements
Authors: Gupta Mahesh , Kwon Tai H.
Published: May 2005

‘Enriched’ element, Q1+Po, and ‘standard’ element, Q1Po, are compared for the simulation of 3‐dimensional flow of non‐Newtonian fluids. Several 3‐dimensional polymer flow problems are analyzed. The pressure field obtained by using Q1Po elements suffers from spurious pressure modes. For complex flows, depending upon the flow geometry and the boundary conditions used, Q1+Po elements may fall to simulate even the velocity field. Q1Po elements, which satisfy the Babuska‐Brezzi condition, give accurate velocity and pressure distributions for all the problems analyzed here.
How molecular weight distribution and drawing temperature affect polypropylene physical properties and morphology
Authors: Flood John E. , Nulf Steven A.
Published: May 2005

Three polypropylene polymer samples possessing three different molecular weight distributions (MWD) ranging from narrow to broad, but having the same melt flow, were studied. The three resins were used to produce uniaxially oriented stretched tapes, which were evaluated for physical properties and morphological characteristics. In addition, five different drawing temperatures were used to investigate the effect of temperature on the physical properties and molecular morphology of the tape. As the MWD became broader, the tape modulus and tenacity increased slightly and the percent elongation and shrinkage decreased slightly. These effects were attributed to decreases in molecular mobility and increases in the number of tie molecules present in broad MWD resins. Morphological studies determined that the crystalline orientation was not affected by MWD. However, the amorphous orientation, at higher draw temperatures, demonstrated a small increase as the MWD became broader. MWD did not have a large effect on the percent crystallinity but the long period spacing (LPS) did exhibit a small decrease as the MWD broadened.
Mold pressurization as a method to reduce warpage in rotational molding of polyethylene
Authors: Chen Chih Hung , White James L. , Ohta Yasuhiko
Published: May 2005

Warpage and global shrinkage of rotationally molded polyethylene parts can be a serious problem with resins of higher densities with rapid quenches and high mold wall thicknesses. It is shown that relatively low pressurization of molds substantially reduces the warpage of molded polyethylene parts. Samples cut out of parts produced in pressurized molds have the same density distributions, Izod Impact, and uniaxial stress‐strain characteristics as parts fabricated in unpressurized molds.
Blow molding die design for non‐axisymmetric parison extrusion
Authors: Nguyen K. T. , Kamal M. R.
Published: May 2005

The flow distribution in a coat‐hanger die is predicted using a three‐dimensional finite element technique. An iterative procedure is proposed for designing blow molding dies for a non‐axisymmetric parison to provide uniform outflow at the exit. A similar procedure is applicable to dies for film, sheet, or profile extrusion. Comparison with one‐dimensional models show significant differences. The effect of nonlinearity on the multiplicity of solutions and the effect of power law index have been considered.
An experimental study on plasticating single‐screw extrusion
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C.
Published: May 2005

An experimental study was conducted with a plasticating single‐screw extruder, which had the following screw dimensions: (a) the diameter (D) of 6.35 cm; (b) the total extruder length of 24 D; (c) the length of the feed section of 3 D; (d) the length of the tapered section of 4 D; and (e) the length of the metering section of 17 D. The extruder had nine pressure transducers which were mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel, so that we could measure axial pressure profiles during extrusion. Also measured in our study were the solid‐bed width profiles in the screw channel by conducting tracer experiments (i.e., screw ‘pushout’ experiments). For the study, a high‐pressure low‐density polyethylene and a high‐density polyethylene were used. Experimental results were analyzed using the reported Lee‐Han melting model. Theoretical predictions of axial pressure profiles were found to be in good agreement with results. Of particular note are the theoretical predictions that for the particular screw configurations used, which has short feed and tapered sections, and extrusion conditions employed, there was considerable solid‐bed acceleration in the tapered section of the screw.
Thermal contact resistance in injection molding
Authors: Yu Chi J. , Sunderland J. E. , Poli C.
Published: May 2005

This paper describes a method for obtaining the thermal contact resistance (TCR) between an injection molded part and its mold. Due to the absence of TCR the simulated cooling times obtained from Polycool II, a computer aided engineering (CAE) package for cooling simulation of injection molding, have compared poorly with both field and experimental data. This paper shows that an improvement in the accuracy of the simulated data results from making TCR an Input to Polycool II. TCR was obtained through a combination of experimental and analytical procedures. Experimental work was performed to obtain the part surface temperature distribution and the inside cavity pressure gradient. The part surface temperature distribution was then used as a boundary condition in the thermal analysis. The inside cavity pressure gradient was utilized as a basis for determining the inside cavity shrinkage. The results show that due to the thermal expansion of thermoplastics, the compressibility of the plastic melt, and the mold deformation, the inside cavity shrinkage is reduced as the thickness of the part is increased. Therefore, the TCR value of a thicker part is lower than that of a thinner part. The effects of both part thickness and process parameters, such as temperature and pressure, on TCR are also discussed.
An improved flow analysis network (fan) method for irregular geometries
Authors: Lee Ching‐Chih
Published: May 2005

The flow analysis network (FAN) method developed in earlier work, for simulating the isothermal flow of a generalized Newtonian fluid in a narrow‐gap region has been refined to better account for irregularly shaped flow boundaries. The resulting equation, which involves only pressure as an unknown, is solved by successive relaxation; the velocity distribution is then back calculated from pressure values. For Newtonian fluids, overrelaxation with a relaxation factor of 1.75 gives the fastest numerical convergence. For power‐law fluids, it is suggested that one start with the associated Newtonian solution and then use under‐relaxation with a relaxation factor equal to the power‐law index. The FAN solutions for two test problems compared very well with analytical and finite element solutions. The rubber flow in a cavity was analyzed using the FAN program. Compared to a Newtonian fluid, a shear‐thinning fluid gave a larger velocity variation across the flow channel exit due to a stronger dependence of velocity on pressure gradient. Through iterations, the output ratio and velocity uniformity were improved without causing too long residence time.
The design and manufacture of a graphite fiber reinforced poly(ether ether ketone) (PEEK) tetrahedron truss array
Authors: Duthie A. C. , Damon J.
Published: May 2005

Orbital space structures are required to be lightweight, have high specific stiffness, have near‐zero coefficient of thermal expansion, exhibit low outgassing, and be cost‐effective. Graphite‐reinforced thermoplastics have the potential to satisfy the criteria noted. However, prior to committing the materials to specific projects, technology demonstration and risk reduction is necessary. In order to demonstrate the application of fiber‐reinforced thermoplastic composites for truss structure applications, a graphite‐reinforced poly(ether ether ketone) (PEEK) composite tetrahedron truss array was designed and manufactured. The resulting structure clearly demonstrated that fiber‐reinforced thermoplastic composites are a viable alternative to epoxy composites for orbital structures.
Photothermal methods for the measurement of thermal properties of thin polymer films
Authors: Coufal H.
Published: May 2005

The absorption of radiation in a sample gives rise to local heating. With a suitable modulated or pulsed source of radiation, a spatially well defined instantaneous heat source can be readily implemented. Radiation induced thermal transients are, therefore, the ideal heat sources for studies of thermal processes in thin films. Application of this method for measurements of thermal diffusivity and temperature dependent properties of thin polymer films are discussed. Imaging of inhomogeneities and depth profiling are another important area of application for these techniques. A number of applications emphasizing the various photoacoustic and photothermal techniques, their advantages and drawbacks are covered in detail.
Tensile yield in poly(chlorotrifluoroethylene) and poly(vinylidene fluoride)
Authors: Hartmann Bruce , Lee Gilbert F.
Published: May 2005

Uniaxial tension tests to the yield point were performed on poly(chlorotrifluoroethylene) (PCTFE) and poly(vinylidene fluoride) (PVF2) from room temperature to near the melting point at a strain rate of 2 min−1. At room temperature and at least two elevated temperatures, measurements were also made at strain rates from 0.02 to 8 min−1. The properties of these polymers were found to be similar to those of other semicrystalline polymers. In the absence of other transitions, yield energy was found to be a linear function of temperature extrapolating to zero near the melting temperature. The ratio of thermal to mechanical energy to produce yielding is smaller than for glassy polymers. Yield stress is a linear function of log strain rate. The ratio of yield stress to (initial) Young's modulus is about 0.03 at room temperature for both polymers. Yield stress is a linear function of unstrained volume. Yield strain, elastic, and plastic strain all initially increase with temperature, but PCTFE shows a decrease with temperature starting at about 100°C, thus behaving like a glassy amorphous polymer in this region.
Effect of rubber/matrix interfacial modifications on the properties of a rubber‐toughened epoxy resin
Authors: Chen Teng Ko , Jan Yi Hung
Published: May 2005

The interface of a rubber‐toughened epoxy resin was modified by using epoxide end‐capped carboxyl‐terminated butadiene and acrylonitrile random copolymer (CTBN). The end‐capping epoxides were formulated with different ratios of flexible diglycidyl ether of propylene glycol (DER732) and rigid diglycidyl ether of bisphenol‐A (Epon 828). The microstructure and the fracture behavior of these rubber‐modified epoxy resins were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The thermal and mechanical properties were also investigated. With an increase in the amount of end‐capping DER732, the interfacial zone of an undeformed rubber particle and the degree of cavitation of the rubber cavity on the fracture surface were greatly increased. At the maximal addition of DER732, fracture energy (GIc) for this toughened epoxy resin containing 10phr CTBN rubber increases up to 2.4 fold compared to that of a conventional CTBN‐toughened epoxy resin, but the thermal and the mechanical properties remained quite unaffected. The modification on the interfacial property provides a new technique in the improvement of fracture toughness of a rubber‐toughened epoxy resin.
Orientation and properties of acrylonitrile copolymers
Authors: Jabarin Saleh A.
Published: May 2005

The orientation characteristics and the physical properties of acrylonitrile copolymers are studied as a function of orientation temperature, stretch ratio, and rubber modification content. The mechanical, barrier, and thermal properties are evaluated and discussed with respect to the influence of rubber content on these properties. The data indicate unique differences in the orientation behavior of rigid and rubber‐modified copolymers. An explanation of these differences is offered on the basis of microscopy and dynamic mechanical analysis.
Transverse orientation dies for solid‐state extrusion of polymers. Part II: Orientation and properties of extrudates
Authors: Mascia L. , Zhao J.
Published: May 2005

Biaxial orientation in polymer products is normally brought about by the application of planar tensile stresses to sheets or films in either the “plastic” or “rubbery” state. More recently, other techniques have been explored as, for instance, the superimposition of rotational components in planes perpendicular to compressive forces. The present work is concerned with the solid‐state extrusion of very high molecular mass crystalline polymers, such as poly(tetra)fluoroethylene (PTFE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE), using dies featuring converging and diverging walls perpendicular, to each other and with a cross‐section area at the entry being the same as at the exit. Measurements of birefringence and tensile strength on solid section extrudates have shown that dies with small converging angles, known as fish tail dies, produce a uniaxial type of orientation along the transverse direction, while dies with large converging angles at the entry region give rise to an unbalanced biaxial orientation.
Electronic structure of poly(p‐phenylene sulfide)
Authors: Tanabe Yoshikazu , Shimizu Hiroshi
Published: May 2005

The electronic structure of poly(p‐phenylene sulfide) (PPS) was studied through steady state photocurrent spectra and temperature dependence of dark conductivity for undoped film, by changes in the in situ optical absorption and ESR spectra under photoirradiation, and optical absorption spectra for doped film. The charge carriers in the undoped state are electronic since the photoconductivity is large and the kink point in the temperature dependence of dark conductivity is higher than the glass transition temperature. A sharp peak near the absorption edge in the photocurrent spectrum of undoped PPS is caused by the diffusion of photocarriers in a sheet with high surface recombination under conditions of low applied field. The in situ optical absorption and ESR spectra of SO3‐doped PPS were similar to those of di‐p‐tolyl sulfide (a monomer unit of PPS) and the formation of sulfur‐centered radical cations was suggested rather than bipolaron states. The stable conduction of SO3‐doped PPS after exposure to atmosphere was analyzed by the classical Lorentz model and the existence of nearly free carriers within subchains was suggested. Their conductivity and mobility were estimated to be 2 S/cm and 3.6 cm2/Vs, respectively. Inter‐chain conduction appears to be very low.
Aging mechanism of phenolic resin–nitrile butadiene composites
Authors: Cooper Anthony R.
Published: May 2005

The aging mechanism of phenolic resin‐nitrile butadiene composites has been investigated. Using solvent extraction and chromatographic analysis of the extract using dual detectors it was shown that the rubber component was well crosslinked. The phenolic component however was not fully crosslinked, although it would have been expected from the cure conditions employed. With increased time, at temperatures near ambient, the phenolic resin continued to react and caused increased brittleness of the composite.
Preparation and properties of a liquid crystalline segmented block copolyester
Authors: Wang Jing , Lenz Robert W.
Published: May 2005

A segmented block copolyester with a liquid crystalline (LC) “hard block” and poly(tetramethylene glycol) (PTMG) “soft block” was prepared and characterized by intrinsic viscosity [η], by gel permeation chromatography (GPC) for number average molecular weight and molecular weight distribution, by differential scanning calorimetry (DSC), and by dynamic mechanical thermal analysis (DMTA). The “soft block” had a melting transition at about −30°C and the hard block had a glass transition at about 70°C and a nematic‐to‐isotropic transition at 260°C. Mechanical testing, which included tensile testing, hysteresis analysis and stress relaxation at small strains, revealed that the block copolyester was a flexible rubbery material with an elongation at break of about 1000% and showed reversible extension below 50% strain.
Processing‐Property interactions in vinylidene fluoride/trifluoroethylene random copolymers
Authors: Khomami B. , Langton C. A.
Published: May 2005

The effect of flow history, processing temperature, and exit draw ratio have been studied for copolymers of vinylidene fluoride/trifluoroethylene of molar compositions 66/34 and 75/25%. The copolymers were extruded through an impinging channels film die which produces a mixed extension and shearing flow as well as a slit die. Stress fields during flow were measured using flow birefringence. Differential Scanning Calorimetry (DSC) analyses were used to characterize the thermal behavior; and flat film and Wide Angle X‐ray Scattering (WAXS) were used to evaluate the crystal structure and morphology of the extrudates. Extensional melt stresses on the order of 6.35 × 105 Pa were necessary to induce sufficient orientation for crystallization of water‐cooled 66/34 mol % copolymers into the all‐trans configuration. Preorientation of the melt by extensional stresses enhanced the transformation of the 3/1 helical to an all‐trans structure in the 66/34 copolymer as well as producing a more compact unit cell in the 75/25 mol % copolymer leading to as much as a 7°C higher Curie transition temperature.
Surface analysis of plasma‐treated poly(ethylene terephthalate) film
Authors: Nakayama Y. , Soeda F. , Ishitani A. , Ikegami T.
Published: May 2005

Surface structures of poly(ethylene terephthalate) films produced by stretching after Ar plasma‐treatment were analyzed by X‐ray photoelectron spectroscopy, combined with a gas chemical modification technique, secondary ion mass spectrometry, and transmission electron microscopy. The formation of ultra‐fine protrusions that produce good slip and a smooth film surface after the stretching procedure was confirmed. The height of the protrusions was almost the same as the thickness of the osmic acid‐dyeable layer. The thickness of the modified layer was found to change according to the Ar pressure of the plasmatreatment. Carboxylic and hydroxyl groups produced by the plasma‐treatment were quantified. The formation of these functional groups can explain good adhesion of the film.
Numerical simulation of mold filling in reaction injection molding
Authors: Hayes R. E. , Dannelongue H. H. , Tanguy P. A.
Published: May 2005

A two dimensional finite element model for the simulation of the advancing front in reaction injection molding (RIM) is presented. The model is based on the solution of the full Navier‐Stokes equation for the computation of the velocity and pressure. The arbitrary Lagrange‐Euler method is used for the moving front. The method of characteristics is used for the solution of the mass‐and energy equations. An automatic remeshing algorithm is used to prevent element distortion and to optimize element size and number. Numerical results are presented for flow into a complex domain in order to illustrate the versatility of the method.
Analysis of polymer membrane formation through spinodal decomposition
Authors: Caneba Gerard T.
Published: May 2005

A phenomenological model used in a previous work for spinodal decomposition of polymer‐solvent systems is further analyzed. From the dimensionless form of the nonlinear Cahn‐Hilliard equation, the dimensionless induction time is found to be a constant number for suddenly quenched systems. Computer simulation is carried out for prediction of early stage behavior with thermal history corresponding to a linear temperature drop followed by a constant temperature vs. time. In the areas of polymer membrane formation and phase separation studies, the universality of the constant dimensionless Induction time for suddenly quenched systems allows the determination of the minimum time needed for phase separation via spinodal decomposition. Also, simulation results for the double linear temperature history allows the convenient prediction of early stage spinodal decomposition behavior at every point of a membrane cross section undergoing thermal inversion phase separation.
Rheology, morphology, and mechanical characteristics of poly(etherether ketone)‐liquid crystal polymer blends
Authors: Mehta Atul , Isayev A. I.
Published: May 2005

This paper is in continuation of our previous paper on Poly(etherether ketone)‐liquid crystal polymer (PEEK‐LCP) composites. Rheological, morphological, and mechanical properties of polyetherether ketone and a thermotropic liquid crystalline polymer based on hydroxybenzoic acid/hydroxynaphthoic acid have been reported. Addition of LCP resulted in a marked reduction of viscosity and improved processability. Tensile properties improved with increase in LCP concentration. Synergistic effects have been observed at certain LCP concentrations. The elongation at break was found to reduce drastically above 10% of LCP content. This is a characteristic typical of chopped‐fiber‐filled composites. Morphology of injection molded and capillary extruded samples of the blends showed that the in‐situ formed fibrous LCP phase was preserved in a solidified form. The improvement in tensile properties is likely due to the reinforcement of the PEEK matrix by the fibrous LCP phase as observed by scanning electron microscopy. A distinct skin‐core morphology was found to develop in the injection molded samples of these blends. Mechanical properties measured in the flow and transverse direction indicated an increase in the degree of anisotropy with an increase in LCP content.
Thermal properties and morphology of hydrostatically extruded polypropylene
Authors: Ariyama Takashi , Takenaga Mitsuru
Published: May 2005

The melting point, specific heat, and morphology and hydrostatically extruded polypropylene (PP) were studied to clarify the plastic deformation of three different parts of the extrudates (periphery, intermediate, and core) parallel to the direction of hydrostatic extrusion. Differential scanning calorimeter (DSC) measurements showed that, for all the parts studied, the peak and the end‐of‐transition, temperatures had a minimum value at a percentage reduction in area, R, of 50% Similar behavior was observed for the specific heat evaluated at several temperatures below the melting point. The morphological structure observed by use of a polarizing microscope indicated that the shape‐ of spherulites above R = 50% changed from spherulitic to elliptic. It is suggested that the pronounced changes taking place around R = 50% are closely related to the marked bend in the extrusion pressure versus extrusion ratio curve which takes place at the same R value. The molecular chains in the coarse spherulites appear to be deformed below R = 50% in such a way that finer spherulites are formed; but at R values above 50% the presence of elliptic spherulites implies that non‐uniform deformation is present under higher hydrostatic pressure of extrusion.
Adaptive pressure control for melt spinning processes
Authors: Jang Yu‐Jen , Wu Wen‐Tend , Bai Chi‐Chung , Liu Shang‐Ren , Chuang Yun‐Yih
Published: May 2005

Indirect adaptive control of the pressure of an extruder for melt spinning processes was investigated. The controller was a proportional‐integral‐derivative. (PID) one. An identified model for the pressure system was determined by using weighted least‐squares estimation with an adjustable Identification interval. On‐line tuning of the PID controller based on the identified model was then carried out. Difficulties in determining the proper model and controller tuning were avoided. The experiment, carried out with a pilot‐type melt spinning machine, resulted in higher quality fiber production.
A 2‐d numerical study of intermeshing self‐wiping screws in biopolymer extrusion
Authors: Lai‐Fook R. A. , Li Y. , Smith A. C.
Published: May 2005

A knowledge of flow behavior is important in the study of laminar flow in twin‐screw extrusion processes to predict the velocity distribution and to understand the mixing process. The flow of a power law fluid in self‐wiping twin‐screw extruders is examined using a two‐dimensional finite element analysis of a mid‐channel section of intermeshing screws. Theory is compared with experiment using food biopolymer and plastic materials. Comparisons showing overprediction of throughputs, but similarities in behavior, suggest that this model could provide an upper limit for melt conveying. For most of the throughput range examined, pumping of intermeshing self‐wiping screws appears to be almost independent of the power law flow index of the melt extruded, but the value of the flow index determines the degree of influence intermeshing has on the overall pressure gradient generated in the extruder.
The effects of varied reactant ratios on the polymeric structures of stannous dicarboxylates
Authors: Ibidapo T. A. , McIntyre J. E. , East G. C.
Published: May 2005

Some polymeric Sn(II) dicarboxylates have been produced with good yields from aqueous solution via a double decomposition reaction using varied nonstoichiometric molar proportions of the reactants. They were obtained as highly viscous pale yellow liquids formed into separate denser phases in the precipitation bath. The highly viscous precipitates were drawn directly into fibers. Meltspun polymeric stannous dicarboxylates produced fibers which were only flexible above the glass transition temperature, Tg.

When the aliphatic dicarboxylic acids were replaced with their aromatic counterparts similar highly viscous liquids were obtained, but they solidified almost at the instant of formation.
Dielectric properties of a curing epoxy/amine system at microwave frequencies
Authors: Finzel Mark C. , Hawley Martin C. , Jow Jinder
Published: May 2005

Dielectric data collected at 2.45 × 109 Hz has been analyzed using a mean relaxation time model over the temperature range 50 to 100°C and at extents of cure from 0 to 57% for a stoichiometric DER 332 (Dow)/DDS (Aldrich) mixture. The relaxation times thus obtained obey the Arrhenius law and tend to increase with the extent of cure. This corresponds to the more rigid nature of the molecular structure as the network forms and the dipolar relaxations become more inhibited. Decreases in the activation energy of the relaxation along with a widening of the relaxation time distribution imply that the relaxations involve ever shorter chain segments as the extent of cure increases.
Microtexture and mechanical properties of carbon fibers: Relationship with the fiber‐matrix adhesion in a carbon‐epoxy composite
Authors: Guigon M.
Published: May 2005

The structure and the microtexture of carbon fibers are determined by transmission electron microscopy. All PAN‐based carbon fibers are made up of elemental microtextural units (EMU) whose microtexture governs their mechanical properties. EMU Carbon layers exhibit either their edge or their surface for outcropping the external surface of the fiber. Interfacial phenomena between fibers and matrix in a composite material depend on this outer microtexture.
Effects of air entrainment on the rheology of concentrated suspensions during continuous processing
Authors: Kalyon Dilhan M. , Yazici Rahmi , Jacob Cherian , Aral Birnur , Sinton Steve W.
Published: May 2005

Samples of a concentrated suspension were systematically collected from the mixing volume of a continuous processor. The large amplitude oscillatory shear behavior of the samples was found to be significantly affected by the screw configuration employed and the location. Microstructural analyses employing nuclear magnetic resonance imaging, wide‐angle X‐ray diffraction and X‐ray radioscopy revealed substantial entrainment of air into the suspension during continuous processing. The volume fraction of the entrained air increased with geometries and operating conditions leading to partially full channels. Overall, air entrainment is identified as a dominant factor in the development of the microstructure and the rheology of concentrated suspensions and should be considered in their optimum processing.
Dynamic mechanical response of model epoxy networks in the glassy state
Authors: Cukierman Serge , Halary Jean‐Louis , Monnerie Lucien
Published: May 2005

The dynamic mechanical properties of model epoxy‐amine networks are investigated in the glassy state over a wide range of frequencies, at temperatures between 123 K and 350 K. The effects of crosslink density and network chain flexibility on the β relaxation are examined. Motions responsible for the β process begin to develop at the same temperature, whatever the crosslink density. However, an increase in crosslink density is accompanied by an increase in amplitude and a broadening towards high temperatures of both damping tan δ and loss modulus E″. This effect is responsible for the decrease of elastic modulus E′ at room temperature with increasing crosslink density.
Examination of dimethacrylate inhomogeneity by solvent swelling techniques
Authors: Simon George P. , Allen Peter E. M. , Williams David R. G.
Published: May 2005

Dimethacrylate monomers polymerize to form highly crosslinked networks with an inhomogeneous distribution of regions of low and high crosslink density. The systems are probed in this work by observing the effects of solvents (nitrobenzene and water) on dynamic mechanical measurements, diffusion kinetics and fracture toughness experiments. Dynamic mechanical analysis showed that the addition of nitrobenzene is found to have little effect on the position of the glass transition or secondary relaxations for solvent levels of under 3.5 mass %. It is proposed that solvents initially diffuse into low crosslink density regions, impinging little on the methacrylate mainchains which reside largely in regions of high crosslink density. Only at higher solvent concentrations do these chains become plasticized. Confirmation of heterogeneity is provided by diffusion analysis of isothermal solvent uptake. This is also interpreted interpreted in terms of a two‐stage diffusion process due to differential rates of sorption which occur in different microregions. Weighing of the water uptake of samples suspended in water indicated that some 30% of water absorbed at equilibrium exists within void regions. Addition of water causes the fracture mechanism to change from a ‘stick‐slip’ mechanism characteristic of brittle polymers to stable crack growth with a lower fracture toughness. This is also attributed to differential swelling of the material causing internal stresses which aid material failure.
Fracture studies on a polyacetal—new thermoplastic polyurethane blend
Authors: John Reji , Neelakantan N. R. , Subramanian N. , Nair E. M. S.
Published: May 2005

Studies based on fracture mechanics have been made on polyacetal toughened with a synthesized thermoplastic polyurethane. The effects of elongation rate and defects like holes and notches on tensile properties have been investigated. Using three‐point bending specimens, fracture mechanics parameters such as strain energy release rate, G, Rice's contour integral, J, and fracture toughness, K have also been determined under plain stress conditions. The mechanical loss from the hysteresis curves, and ductile, brittle fractography using scanning electron microscopy have also been studied.
A method for predicting the useful life of moisture‐sensitive plastics
Authors: Dixon Robert R.
Published: May 2005

Arrhenius plots have long been used to allow predictions of the long‐term useful life for a variety of materials. These plots are generated by testing materials exposed to elevated temperatures for different intervals of time. Since such a technique eliminates moisture from consideration, a different technique should be employed for moisture‐sensitive materials used in humid ambients. A technique is described to allow for humidity in the prediction of useful life in moisture‐sensitive plastics. Modified Arrhenius curves are presented for a number of such plastics.
Predicting the behavior of nonlinear viscoelastic materials under spring loading
Authors: Brueller O. S.
Published: May 2005

Structural parts made of plastics are usually tested under creep loading conditions, i.e., the stress is applied almost suddenly and then kept constant, while defomation is measured. In practice, however it happens that such a structural part is loaded by an elastic member (for example, by a spring). In this case, the acting force is no longer constant; it decreases in the course of time, while the deformation of the specimen increases (and, obviously, that of the spring decreases). The present paper describes a numerical approach for the solution of this problem, based on the assumption that the creep behavior of the material is known. An example is presented.
Dielectric monitoring of the curing process in cyanoacrylate resin
Authors: Radhakrishnan S. , Saini D. R.
Published: May 2005

The cure monitoring of cyanoacrylate resin using a dielectric technique shows that in addition to the usual fast anionic polymerization step, there may be a secondary process involved over longer time scales. Two peaks are distinctly observed in the isothermal curing curves, and from the position of these at various temperatures, the activation energies of 0.4 eV and 0.17 eV could be derived. In cured cyanoacrylate resin, three relaxations were observed, viz., α, β, and γ, occurring at 152°c, 87°c, and 47°c, respectively (for 1 KHz measuring frequency), with activation energies of 1.3 eV, 0.56 eV, and 0.4 eV, respectively. The various results have been explained on the basis of secondary bond formation through the nitrile group, for which some evidence could be obtained from the infrared absorption spectra.
Optimization of the vulcanization process of rubber products
Authors: Steen J. , Aben W. J. , Wapenaar K. E. D.
Published: May 2005

Selection of the optimum conditions for the vulcanization of rubber products, particularly of bulky ones, often is quite difficult. Especially in cases of high demand, it is unavoidable to destruct expensive prototypes in order to check important properties of the rubber at various locations throughout the product. Finite element calculations can be used to predict the flow of heat during the vulcanization process. By converting the total heat input at a selected location during a certain time into a so‐called “effective vulcanization time” at a fixed reference temperature, it becomes possible to predict the properties of the rubber at that location. An example of such a procedure is given. However, to secure optimum conditions in this way would require repetitive (expensive) calculations. In this article a method is developed in which the vulcanization conditions are derived from the required properties of the rubber compound. The idea behind it is that optimal vulcanization is reached when at each location within the rubber product the effective vulcanization time at a selected reference temperature lies within predefined limits. The choice of the limits can be derived from the dependence of each of the properties chosen on the vulcanization time at the reference temperature.
The use of oven heat sag to determine heat resistance in polypropylenes
Authors: Kempthorn James T.
Published: May 2005

Heat deflection is often the only test used to determine a materials ability to withstand exposure to elevated temperatures under load. This test has its limitations, simply because not all materials operate under loads of 1820 kPa (264 psi) or 455 kPa (66 psi). Consequently, heat deflection cannot always give a true indication of a materials high temperature capabilities. The automotive industry has used the heat sag test to measure the deformation of elastomeric materials during the paint curing process. The heat sag test measures the sag of a molded bar. One end of the bar is clamped while the other end is free to sag or deflect. Samples are tested over a range of temperatures to determine the failure deflection point. This study examines the correlation of the heat sag to heat deflection and dynamic mechanical analysis (DMA) on polypropylene resins and compounds and polystyrene.
Percolation behavior in morphology and modulus of polymer blends
Authors: Hsu William Y. , Wu Souheng
Published: May 2005

The tensile property of a plastic/rubber blend depends critically on the morphology and connectivity of the two phases. At low plastic volume fractions, the plastic phase forms isolated domains in the matrix of rubber phase, and the tensile property of the blend is largely controlled by the continuous rubber phase. As the plastic volume fraction increases, the plastic phase gradually connects into a pervasive network that eventually dominates the tensile and shear properties of the blend. The transition of the blend from a rubber‐dominated to a plasticdominated behavior is a manifestation of percolation transition. The plastic volume concentration at which the transition takes place is the percolation threshold. Its dependence on morphology is discussed by contrasting the behaviors of anisotropic injection‐molded specimens vs. isotropic compression‐molded specimens of the two‐phase blends of an amorphous thermoplastic polyester, PETG, and an ethylene‐propylene‐diene rubber, EPDM. It is found that the tensile modulus just above the percolation threshold obeys a power law as a function of the plastic volume concentration in excess of the percolation threshold. By analyzing the longitudinal tensile modulus of injection‐molded PETG/EPDM specimens just above the threshold, it is shown that the scalar elastic percolation theory of de Gennes is at work here. For compression‐molded PETG/EPDM specimens, it is found that the isotropic tensile modulus over the entire composition range obeys the symmetric effective medium theory.
Comparison of “all trans” enzymatically prepared unsaturated polyesters with chemically synthesized and industrial polyesters
Authors: Geresh S. , Gilboa Y. , Abrahami S. , Bershadsky A.
Published: May 2005

The synthesis of unsaturated polyesters (UP) by high‐temperature polycondensation is accompanied by isomerization of the double bond from the cis to the trans configuration. The presence of the trans double bonds facilitates crosslinking and may have an important influence on rheological and mechanical properties of the UP and the cured end product. All‐trans polyesters are not available on the market. A study of “all‐trans” low‐temperature polycondensation based on chemical and enzymatic lipase catalysis was recently reported. This paper presents the characteristics of lipase‐synthesized UP vs. general‐purpose UP, as obtained by X‐ray, differential scanning calorimetry (DSC), and other methods. In contrast to the commercial amorphous UP, crystallinity was found in the “alltrans” enzymatically and chemically synthesized UP. The crystallinity of the enzymatically and chemically synthesized UP. The crystallinity of the enzymatically synthesized UP was confirmed by higher values of elasticity. DSC analyses complemented the results obtained by other methodologies.
On the tensile testing of high modulus polymers and the compliance correction
Authors: Turek Douglas E.
Published: May 2005

The application of a method to determine and correct for the influence of non‐specimen extension in tensile testing is reviewed and demonstrated using two different thermotropic liquid crystalline polymers. In the tensile testing of high modulus polymer extrudate, where the amount of specimen extension is inferred from the crosshead travel, the error associated with system compliance can be significant and parameters such as modulus and elongation will be in error. The need to apply the correction depends on the magnitude of the product of the sample modulus and cross‐sectional area, divided by the test gage length, relative to the system compliance value. Its application is not necessarily restricted to high modulus materials, and can be extended to samples of larger cross‐sectional area and lower modulus. Guidance to assist in the choice of a suitable gage length to avoid compliance correction and a method to quantify the error contribution is presented.
Gapwise density distributions in injection‐molded poly(methylmethacrylate)
Authors: Wimberger‐Friedl R. , de Bruin J. G.
Published: May 2005

Residual density distributions are determined in injection‐molded poly(methyl‐methacrylate) (PMMA) with the aid of a quantitative Schlieren optical technique. The gapwise distributions typically show a maximum beneath the surface. The height of the maximum as well as the level in the core vary with distance from the gate of the mold. The density distributions and the influence of the molding parameters are explained by the pressure course measured in the cavity and the process of vitrification of the sample during molding. The magnitudes of the variations of the gapwise distributions agree with the average density variations measured in a density gradient column. Residual stresses do not contribute significantly to the determined distributions. The density maximum is found closer to the surface than the maximum in birefringence that is induced by the shear flow during filling. The magnitude of the density variations is less than predicted by the pseudocompressibility, as determined in samples vitrified under constant pressure.
Coefficients of dynamic friction for low density polyethylene
Authors: Spalding Mark A. , Kirkpatrick Donald E. , Hyun Kun S.
Published: May 2005

The coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single‐screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperature. The coefficients of dynamic friction for a low‐density polyethylene resin are presented in this paper as a function of the surface temperature, pressure, and velocity.
Mechanical properties‐structure relationship in blends of polyamide 6 with γ‐irradiated LDPE
Authors: Valenza A. , Gallo L. , Spadaro G. , Calderaro E. , Acierno D.
Published: May 2005

Blends of γ‐irradiated and unirradiated low density polyethylene with polyamide 6 were made in order to study possible modifications induced by this irradiation. Blends with γ‐irradiated polyethylene show structure and properties significantly different with respect to blends made with the unirradiated polyethylene. In this paper data on mechanical properties (tensile and impact) of these blends are presented. Results are related to the different morphologies in the blends.
Stress relaxation behavior after cyclic preloading in polypropylene
Authors: Ariyama Takashi
Published: May 2005

The viscoelastic behavior of polypropylene before and after cyclic preloading was investigated by stress relaxation tests. The relaxation tests were performed after a simple uniaxial tension (number of cycles N = 0) and after the cyclic preloading (N = 50) by use of a closed loop, electrohydraulic, servocontrolled testing machine. The tests were conducted under different sets of strain rate, number of cycles, and strain amplitude. The experimental data were compared with theoretical results analyzed by use of a linear viscoelastic model. The three‐element model consists of a Maxwell unit and a Hookean spring in parallel. The calculated results agree well with the experimental ones; in particular, in the relaxation tests after the cyclic preloading (N = 50), the calculated results agree very well with the experimental ones at both the predetermined strain rates of 1,000 μ/s and 10,000 μ/s, at a strain amplitude of ±5%. It can be seen that the linear viscoelastic model explains the viscoelastic characteristics of polypropylene despite the solution of the constitutive equation constructed by the simple three‐element model.
Flow defects in linear low density polyethylene processing: Instrumental detection and molecular weight dependence
Authors: Ajji A. , Varennes S. , Schreiber H. P. , Duchesne D.
Published: May 2005

An elongational rheometer coupled with a primary extrusion device has been used for the detection of flow limitations in the extrusion of linear low density polyethylenes (LLDPE). The shear rate for the onset of flow defects (fd) was found to decrease with increasing branch length in the LLDPE copolymer, but the severity of fd was greater in butene‐ than in hexene‐ and octene‐copolymers. Studies of partially fractionated LLDPE showed that the critical shear rate for the onset of fd was closely related to the minimum molecular weight in the distribution of molecular weights. In addition, evaluations of bond strengths in LLDPE/metal joints showed that the same molecular weight parameter significantly affected that performance criterion. In combination, the experimental findings provided confirmation of sporadic adhesive failure (slip/stick effect) as the mechanism responsible for the occurrence of observed flow defects. Its manifestation is attributable to the thermodynamic drive that promotes the preferential localization of low molecular weight moieties at surfaces and at interfaces of polyolefins such as LLDPE.
Phase separation kinetics of rigid‐rod polymers during coagulation
Authors: Nelson Donald S. , Soane David S.
Published: May 2005

Kinetics of phase separation of poly(p‐phenylenebenzobisoxazole) (PBO) in methanesulfonic acid are examined by the time‐resolved small angle light scattering and turbidity measurements. Thin films of polymer solutions are spin‐coated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo a spinodal decomposition‐like phase separation, following Cahn‐Hilliard type phase separation kinetics upon exposure to water vapor. An exponential increase in the scattered light intensity at short times is found. Transmittance measurements are used to determine the effects of molecular weight and coagulation medium on the rate of coagulation.
Polyspirodilactam: A new family of high temperature polymers
Authors: Wang Pen‐Chung , Asbell William J. , Chuah Hoe H. , Gergen William P.
Published: May 2005

A new class of materials based on a spirodilactam structure has been recently synthesized as part of research into new polymeric materials. Not only is the spirodilactam structure novel, but it was not even the intended product in the synthesis as originally designed. The polymerization process discovered by the reaction of 4‐ketopimelic acid or its corresponding spirodilactone with primary amines opened a new field of polysprodilactam chemistry. This paper describes the chemistry leading to the discovery of spirodilactam‐based polymers and initial applications in the area of thermoplastics and thermosets. Most recent developments to be covered include aromatic spirodilactams and isomeric spirodilactams.
Characterization of ternary blends containing polycarbonate, tetramethyl polycarbonate, and poly (ϵ‐caprolactone)
Authors: Kim C. K. , Paul D. R.
Published: May 2005

The phase behavior of ternary blends of bisphenol‐A polycarbonate (PC), tetramethyl bisphenol‐A polycarbonate (TMPC), and poly (ϵ‐caprolactone) (PCL), where each binary pair forms completely miscible blends, was investigated. The ternary blends were found to be miscible for all compositions and do not phase separate prior to thermal decomposition. The melting point depression method based on both the Flory‐Huggins theory and the equation of state theory of Sanchez‐Lacombe was used to evaluate interaction parameters for each pair.