bluuebunny/crossref_metadata_2025 huggingface dataset:
Oligomer distribution for interfacial step growth polycondensation
Authors: Munjal S.
Published: May 2005

Low levels of oligomer molecules are generally desirable in polymeric materials. It is known that several reactor variables can affect the oligomer distribution, and therefore it is useful to have predictive models for molecular weight distribution. The normal approach of a differential equation–based model is very complex to set up if it is applied rigorously to include all the non‐Flory aspects of the step growth polycondensation and in particular the interfacial polycarbonate polymerization. In this paper, simple methods based on the Monte Carlo method and Stockmayer distribution are applied to simulate the effects of mass‐transfer, unequal reactivity, and the starting stoichiometry of the polycondensing functional groups on the oligomer distribution. It is shown that these parameters can have a significant effect on the oligomer weight distribution and polydispersity of the final polymer.
A novel approach to a truly dynamic thermodynamics
Authors: Lindenmeyer Paul H. , Astarita G.
Published: May 2005

A novel approach to a truly dynamic thermodynamics is proposed in which equilibrium is defined in terms of explicit time, distance, and acceptable error scales. This approach involves reformulating the second law of thermodynamics in terms of an excess energy that vanishes at equilibrium instead of an entropy that assumes some unknown maximum value. Excess energy is defined mathematically as the total Legendre transform of energy with respect to an independent set of extensive variables. Excess energy is effectively the free energy functional of a nonequilibrium system and is a function of the time, distance, and acceptable error scales. Elimination of entropy from thermodynamics requires recognizing temperature as a thermal stress, proportional to the antimetric component of the stress tensor that is neglected when one assumes the validity of Cauchy's second law of motion. The inclusion of temperature as part of the stress‐strain couple completes the science of thermomechanics and opens the way for a practical unification of chemistry and physics in strictly mechanical terms.

The last sentence of the abstract shows how high the goals that Lindem meyer set for himself were. I personally do not agree with the idea that mechanics is the queen of all sciences, and that given deep enough probing one could achieve “a practical unification of chemistxy and physics in strictly mechanical terms”; for instance, electromagnetism has full citizenship's rights in physics, and it is hard to conceive that it could be reduced to mechanics.
The oxidative degradation of imide polymers. I: Ozonolysis of a model compound, N‐phenylphthalimide
Authors: Barman S. , Newhouse E. I. , Neely W. C.
Published: May 2005

The reactions of N‐phenylphthalimide films with ozone have been studied under a variety of conditions: dry ozone, moist ozone, ozone plus ultraviolet light, as well as ozone plus water vapor plus ultraviolet light. This compound is a conveniently available model for imide polymers. These reaction conditions represent simulation of certain aspects of the space environment. For each set of reaction conditions the reaction products were determined by combined gas chromatography/mass spectrometry. Semiempirical molecular orbital computations were made of the relative energetics of possible reaction pathways consistent with the generation of the observed products. The reaction products found indicate fragmentation of the imidic moiety for which the energetics are favorable.
Properties of electropolymerized polycarboxyphenylmethacrylamide matrices/graphite fiber composites: Crosslinking effect
Authors: Liang Jeng‐Li , Bell James P. , Scola Daniel A.
Published: May 2005

Imide formation from ‐CONH and ‐COOH functional groups of 2‐carboxyphenylmethacrylamide (2‐CPM), 4‐carboxyphenylmethacrylamide (4‐CPM), 4‐carboxyphenyl methacrylamide/methylmethacrylate (4‐CPM/MMA) and 4‐carboxyphenylmethacrylamide/N‐phenylmalemide (4‐CPM/NPMI) electropolymerized matrices was investigated. It was found that 2‐CPM polymers undergo intramolecular imidization and anhydride formation, which result in a small amount of crosslinked network. On the other hand, the thermally cured 4‐CPM polymer demonstrates a significant increase in gel fraction. Tg and dynamic storage modulus, owing to crosslinked network formation. Tgs of 4‐CPM/MMA and 4‐CPM/NPMI composites measured by thermomechanical analysis after thermal heating were increased and were correlated very well with the preheating time. The 4‐CPM/MMA composites with a particle crosslinking (Tg increased to 245°C) maintained a higher Izod impact strength than a typical epoxy composite (200 kJ/m2 vs. 100 kJ/m2). Upon heating to promote crosslinking, a lower shear strength (65 MPa) of a 4‐CPM/MMA composite increased to a strength of 78 MPa, close to the 80 MPa of an epoxy composite at 67% fiber volume fraction. A lower water absorption of around 1% was associated with the increased crosslinking. The mechanical properties of the 4‐CPM/NPMI composites showed a similar trend upon preheating.
Orientation parameters for the specification of effective properties of heterogeneous materials
Authors: Munson‐Mcgee S. H. , McCullough R. L.
Published: May 2005

A general formulation is presented for the orientation averaging of the properties of representative volume elements of heterogeneous materials. Approximations are introduced that result in the identification of four independent orientation parameters that are required to specify a general state of three‐dimensional orientation. The general relationships are reduced further for the special case of “planar” and “axial” distribution and applied to an aggregate averaging scheme for short‐fiber composites.
Shear test for thermoplastic polymers
Authors: Hedner Gert , Seldén Ragnar , Lagercrantz Per
Published: May 2005

A shear test is proposed as a complement to the tensile test in order to characterize the short time mechanical behavior of thermoplastic polymers. The proposed test geometry makes the test easy to perform and to evaluate and gives relevant information about anisotropy, plastic deformation, crack initiation, and propagation properties. Three different materials have been tested and the results are discussed.
Radical terpolymerization of zincacrylate, acrylonitrile, and styrene initiated by As2S3‐styrene complex
Authors: Agrawal B. P. , Srivastava A. K.
Published: May 2005

Terpolymerization was investigated by dilatometry for zincacrylate (ZnA2), acrylonitrile (AN), and styrene (St), radically initiated by a As2S3‐styrene complex (I) in dimethyl sulphoxide (DMSO), at 90 ± 0.1°C for 1 h under inert atmosphere. The system follows non‐ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is Rpα(I)0.27 (St)0.31 (AN) 0.22[ZnA2]0.12. The value for the activation energy and k/kt are 55 kJ mol−1 and 1.87 × 10−7 1 mol−1 s−1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.
Multilayer extrusion: Experiments and computer simulation
Authors: Mavridis H. , Shroff R. N.
Published: May 2005

A mathematical model is presented for the computer simulation of multilayer flow of polymer melts in coexitrusion. The proposed model can handle an arbitrary number of layers. The viscosity of each layer is shear‐rate and temperature dependent. Given the material properties, die dimensions, and process conditions, the model determines the flow field throughout the die gap. Computer simulations and experimental data are presented for a three‐layer polyester/EVA/polyester film coextrusion, with emphasis on the interfacial instability and its effects on optical properties of the film. The rsults are discussed in the context of the critical interfacial shear stress criterion that has been proposed by Schrenk, et al. (1) for the onset of interfacial instability. It appears that elasticity differences between layers contribute to the interfacial instability. It is conjectured that minimizing interfacial shear stress and matching elasticities of adjacent layers is an appropriate criterion in coextrusion analysis.
A sliding plate normal thrust rheometer for molten plastics
Authors: Oakley J. G. , Giacomin A. J.
Published: May 2005

A sliding plate rheometer has been developed to measure the normal thrust of a molten plastic in large amplitude oscillatory shear. The normal thrust of a molten plastic in large amplitude oscillatory shear is a significant nonlinear effect that has previously been unobtainable. Normal thrust measurements may now be used to help understand and characterize nonlinear viscoelastic behavior inherent in most molten plastics. The new rhemoeter incorporates a piezoelectric pressure transducer in a very stiff plate that minimizes compliance. Normal thrust measurements with cone and plate rheometers are made by measuring the total force on the plate (or cone) and are subject to error due to edge effects. The new rheometer measures the local pressure in the sample and is therefore unaffected by sample size or edge effects. Normal thrust measurements in large amplitude oscillatory shear are reported for both molten Phillips TR480 high density polyethylene pipe resin which contains 2% by weight of carbon black filler and IUPAC LDPE X. Crosstalk due to shear stress on the active face of the pressure transducer causes signal error which for oscillatory shear is filtered out using a discrete Fourier transform.
Spectra composite that withstands torch flame test
Authors: Lem K. W. , Kwon Y. D. , Chin H. B. , Li H. L. , Prevorsek D. C.
Published: May 2005

In recent years, the development of high performance Spectra® fibers has received increasing attention in industry. Because of the outstanding capability to absorb energy, these polyethylene fibers are frequently used in damage tolerant composite materials to protect equipment, apparatus, and/or people against blast and debris of explosion or projectiles. Since the fiber is thermally stable, it is possible to design composite structures that are suitable for use in applications where prolonged exposure to flame is anticipated. In this paper, we report the findings obtained in a recent flammability evaluation of a Spectra composite subjected to a torch flame, and to hot metal balls. The Spectra composite structures that will be discussed were found to withstand these exposures without burning and the smoke generation and toxic gas emission were far below the limits set in the standard for current aircraft interior materials.
Numerical simulation of the post‐filling stage in injection molding with a two‐phase model
Authors: Chen B. S. , Liu W. H.
Published: May 2005

A two‐phase model is presented for simulating the post‐filling stage of injection molding of amorphous and semicrystalline materials. A finite‐element scheme with quadratic shape function for the pressure is proposed. The melt is considered in terms of Hele‐Shaw flow for a non‐Newtonian fluid using a modified‐Cross model with either an Arrhenius‐type or WLF‐type functional form to describe the viscosity under nonisothermal conditions; the compressible behavior of the polymer is assumed to obey either a double‐domain Tait or single‐domain Spencer Gilmore equation of state. The interfacial energy balance equation including the latent‐heat effect for semicrystalline materials is coupled with the transient energy equation for the solid and melt phases in order to predict the solidified layer and temperature profile. Two well‐characterized materials, namely a commercial‐grade PP and PS, were used in the present work. Good agreement is obtained between the present simulation and experimental pressure traces from this study and from previous investigation in the literature. The effects of compressibility, viscosity model, and thermal properties upon the predicted pressure field are also considered.
Deformation and energy absorption of polymer foams as a function of 2‐D indenter and absorber geometries
Authors: Stupak P. R. , Donovan J. A.
Published: May 2005

Two‐dimensional indenters (flat plate and cylinder) were used to compress rectangular and trapezoidal foam energy absorbers as a function of polymer, foam density, and thickness. An increased deformation volume formed when the indenter contact area was less than the foam absorber area, resulting in both increased energy absorption and stress transmitted to the indenter (i.e., “load spreading”). The deformation volume was trapezoidal, not prismatic, and was characterized by the indenter geometry, dimensions, and foam thickness. Conservative energy absorber design can be achieved by using “energy absorption diagrams” that account for the indenter (i.e., product) and absorber geometry and degree of load spreading.
Rheological and mechanical properties of thermotropic polyesters with long flexible spacers in the main chain
Authors: Shin Boo Young , Chung In Jae , Kim Bong Shik
Published: May 2005

Linear thermotropic liquid crystalline polymers based on two bisphenol monomers and terephthaloyldichloride were prepared via melt polymerization. Fibers from liquid crystalline polymers were spun above the mesophase transition temperature. In this work, the mechanical and morphological properties of fibers based on such polymers were studied. High values of tensile strength and tensile modulus were obtained, and we tried to prove these high mechanical properties quantitavely by using rheological properties of these polymers and morphology of their fibers. These values were varied by the take‐up speed.
The morphology of rigid‐rod polymers and molecular composites resulting from coagulation processing
Authors: Nelson Donald S. , Soane David S.
Published: May 2005

The effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid‐rod polymer, such as poly(p‐phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations.
The production and properties of oriented polypropylene laminates
Authors: Chen H. J. , Kortschot M. T. , Leewis K. G.
Published: May 2005

The mechanical properties of isotactic polypropylene can be enhanced in one direction by a combination of rolling and drawing in a rolling mill. The longitudinal strength and modulus of the oriented polypropylene (OPP) increases with an increase in draw ratio; however, the transverse properties remain relatively unchanged. In this study, multidirectional OPP laminates [with (0)2, (0/90)s and (0/±45)s lay‐ups] were made to obtain sheet materials with improved properties in more than one direction in the plane. A hot‐plate welding technique was used to produce these translucent and recyclable laminates. The in‐plane properties of the laminates were successfully predicted with classical laminate theory (CLT), which is commonly used to predict the properties of fiber reinforced materials. These laminates can be quasi‐isotropic and were found to have improved modulus [up to 6 GPa for (0/90)s laminates] and strength [up to 150 MPa for (0/90)s laminates] as well as exceptionally good impact toughness.
Fiberoptic intrinsic fluorescence for in‐situ cure monitoring of amine cured epoxy and composites
Authors: Paik Hyung‐Joon , Sung Nak‐Ho
Published: May 2005

The cure reactions of epoxy‐diamine and its composites are monitored in‐situ using the intrinsic fluorescence of the aromatic diamine, diaminodiphenyl sulfone (DDS). With a fiberoptic fluorimeter, in‐situ cure monitoring was performed via a single fiber, distal‐end probe, in neat epoxy as well as in commercial grade prepregs containing graphite fibers and DDS curing agent. The prepregs were investigated during multiply lamination in an oven. The fluorescence excitation spectra were obtained by emitting at 420 nm with a scan range of 320 to 400 nm, and the DDS peak position was determined as a function of cure time and temperature. The DDS spectra show a progressive red shift up to 24 nm when the primary amine is reacted with epoxide to become the secondary and the tertiary amines. The spectral shift of the DDS is also correlated with the extent of epoxide reaction determined by the Fourier transform infrared (FTIR) spectroscopy. Both data exhibit a linear relation, consistent with the behavior of the DDS peak shift, which increases linearly with the amine reaction. The excitation spectra also show a temperature dependency such that the amount of red shift increases with the measurement temperature in a manner that can be described by an exponential function. The temperature effects also depend on the state of cure in the sample. The temperature correction can be made by the application of an empirically developed equation. Thus, a direct comparison can be made among the on‐line data obtained under varying conditions of cure, by reducing the spectral data to any reference temperature. This intrinsic fluorescence technique is much simpler than the previously reported extrinsic fluorophore technique, which requires the addition of an extrinsic fluorophore and an internal dye, and can be applied to any commercial prepregs containing DDS, thus making it a very powerful and widely applicable monitoring tool for composite processing.
Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation
Authors: Goel Satish K. , Beckman Eric J.
Published: May 2005

Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. We have employed a pressure quench in a CO2‐swollen PMMA sample to generate a microcellular core structure encased by a nonporous skin. Further, we have demonstrated that classical nucleation theory can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials, provided that the effects of the CO2‐diluent on the surface tension of PMMA are adequately taken into account. This is because our system is in a homogeneous liquid state at our operating conditions because of the plasticization. Both model predictions and data indicate that cell density rises sharply at a saturation pressure of approximately 14 MPa (at 40°C), leveling out above 27 MPa. By contrast, the effect of temperature on cell density in the range 40°C to 80°C is minimal.
Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends
Authors: Brahimi B. , Ait‐Kadi A. , Ajji A.
Published: May 2005

In this article, we investigate the effect of weld lines on the tensile mechanical properties of unmodified and copolymer modified high density polyethylene (HDPE) and polystyrene (PS) blends. The homopolymers were melt blended in the proportion of 20 wt% HDPE and 80 wt% PS using a twin screw extruder at a temperature of 200°C. The results show that the mechanical properties are generally lower when weld lines are present. The decrease of the mechanical properties is much more pronounced for the blends. The addition of small amounts of a commercial styrene/butadiene copolymer significantly improves the strength and the elongation at break of this blend. An optimum copolymer concentration was observed at 3 wt%. This value coincides with the interphase saturation concentration of the copolymer obtained from the analysis of the DMTA (dynamic mechanical and thermal) properties of the blends. The copolymer was also found to induce important changes in the morphology of the blend. The interdiffusion of the polymer fronts in the weld region was also improved by the presence of the copolymer. It is believed that these two aspects contribute to the enhanced properties obtained with copolymer modified blends in presence of weld lines. An important effect of the injection temperature on the tensile strength and the elongation at break of welded samples with copolymer modified blends was observed. The effect of mold temperature on these properties was less important mainly at low injection temperatures. Only a slight effect of these two parameters was observed for the tensile modulus in the range of mold and injection temperatures considered in this study.
Crystallinities of poly(chlorotrifluoroethylene) and its copolymers by differential scanning calorimetry, X‐ray diffraction, and density measurements
Authors: Murthy N. S. , Khanna Y. P. , Signorelli A. J.
Published: May 2005

Crystallinities of films of copolymers of chlorotrifluoroethylene with 0 to 4% vinylidene fluoride, different molecular weights and thermal histories were calculated from differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and density measurements. The crystallinities for these films range between 16 to 58%, 11 to 71%, and 13 to 77% as determined by DSC, XRD, and density, respectively. Although the numerical value of the DSC, XRD, and density crystallinities obtained by each of the techniques are different, they correlate well with each other. The primary source of error in DSC is the uncertainty in drawing the baseline for separating the heat of fusion and heat of crystallization. In XRD, the ambiguities in the separation of the amorphous and crystalline peaks reduce the precision of the results. Calculation of crystallinity from density values requires that the distribution of the VF2 between the amorphous and crystalline regions be known. In addition, the density technique is not sensitive to variations in the crystalline and amorphous densities.
An extension of the Painter‐Coleman miscibility guide to ternary polymer blends
Authors: Espi E. , Fernandez‐Berridi M. J. , Iruin J. J.
Published: May 2005

The idea of separating the free energy of mixing into two contributions (corresponding to the “physical” or “nonspecific” and to the “specific” interactions, respectively) proposed by Painter and Coleman has been extended to ternary polymer/polymer/polymer blends. In this paper experimental phase diagrams of three ternary blends have been reproduced by estimating both contributions for the interaction energy density (Bij) which characterizes each polymer pair. In contrast to the Painter‐Coleman Miscibility Guide rules, we have found that, in some cases, “specific” contributions positive and unfavorable to the mixing, due to the self‐association of one of the components, can describe more adequately the experimental trends.
Water soluble copolymers. 55: N‐isopropylacrylamide‐co‐acrylamide copolymers in drag reduction: Effect of molecular structure, hydration, and flow geometry on drag reduction performance
Authors: Mumick Pavneet S. , Hester Roger D. , McCormick Charles L.
Published: May 2005

Non‐ionic, hydrophobically associating, water soluble N‐isopropylacrylamide‐co‐acrylamide (IPAM) copolymers have been synthesized and characterized specifically for the study of drag reduction. The drag reduction (DR) performance has been measured with a rotating disk rheometer and a capillary flow apparatus. The DR studies were performed in deionized water, 0.514 M NaCl and 1 M urea. DR efficiency is dependent on copolymer structure, composition, and solvation. Copolymers showing intermediate values of hydrophobic character are found to be the most effective drag reducers. For this copolymer series, IPAM‐70 (the copolymer synthesized with 70 mole% N‐isopropylacrylamide in the feed) is the most efficient drag reducer. The DR properties of the IPAM copolymers are influenced by hydrophobic associations as well as hydrogen bonding. The effects of salts from the Hofmeister series, cosolvents such as dioxane, and temperature are also examined. Drag reduction performance of the various copolymers is correlated to empirical relationships involving degree of polymerization, second virial coefficient or other solvation parameters, and concentration.
Shear and elongational behavior of linear low‐density and low‐density polyethylene blends from capillary rheometry
Authors: Müller A. J. , Balsamo V. , Silva F. Da , Rosales C. M. , Sáez A. E.
Published: May 2005

In this work we present an experimental study of shear and apparent elongational behavior of linear low‐density (LLDPE) and low‐density (LDPE) polyethylene blends by means of capillary rheometry. The characterization of these rheological properties is crucial in the design of a blend that combines the ease of processing of LDPE with the mechanical advantages of the LLDPE. Two different low‐density polyethylenes and one common linear low‐density polyethylene were used to prepare the blends. The results obtained indicate a strong sensitivity of the rheology of the blend to changes in the molecular weight of the LDPE employed. For the higher molecular weight LDPE, the shear viscosity of the blend was essentially equal to that of the LDPE homopolymer up to a concentration of 25% of LLDPE, whereas the apparent extensional viscosity was appreciably lower. For the lower molecular weight LDPE, the same trend was obtained regarding the shear viscosity, but in this case the apparent extensional viscosity of the blend was somewhat higher than that of the LDPE homopolymer.
Dynamic rheological properties of polyetherimide/polyetheretherketone/liquid crystalline polymer ternary blends
Authors: Bretas R. E. S. , Collias D. , Baird D. G.
Published: May 2005

The dynamic rheological properties of poly(etherimide)/poly(etheretherketone)/liquid crystalline polymer (LCP) ternary blends were measured in order to correlate these properties with the morphology obtained after extrusion. The viscosity radio, ηd/ηm, where ηd = disperse phase viscosity and ηm = matrix viscosity, had to be redefined. Below 50 wt% LCP, ηd = ηLCP, ηm = ηPEEK+PEI and ηd/ηm < 1. Above 50 wt% LCP, ηd = ηPEEK+PEI, ηm = ηLCP and ηd/ηm > 1. Fibrillar morphologies were obtained in both cases, except below a concentration of 20 wt% LCP. At low concentrations of LCP the ternary blends had lower viscosities than the component polymers, showing a flow promotion effect of the LCP on the PEI‐ and PEEK‐rich phases.
Design of electrofusion joints and evaluation of fusion strength using fusion simulation technology
Authors: Nishimura Hiroyuki , Inoue Fumio , Nakashiba Akio , Ishikawa Testuo
Published: May 2005

Fusion simulation is one of the key techniques in designing and producing electrofusion (EF) joints for gas distribution and in evaluating fusion joint integrity. This paper describes the result of a numerical simulation of a thermal fusion process, using the finite element method. A nonlinear heat transfer computer program was used to obtain the temperature profile of a large electrofusion joint at fusion. The effects of applied voltage, heating time, wire pitch, and ambient temperature were examined for designing a 150‐mm EF joint. A method to shorten the cooling time was also investigated. The fusion condition range suitable for a 150‐mm EF joint was found to be slightly narrower than that suitable for a 50‐mm EF joint. Examination of the effect of wire pitch revealed that if the pitch is extremely large, thermal degradation starts in the resin close to the wire before the fusion‐interface strength reaches the maximum value. We have developed a program to simulate the process of closing the gap between the pipe and the joint due to resin expansion and melting after the power is supplied.
Rubber toughening of poly(lactide) by blending and block copolymerization
Authors: Grijpma D. W. , Van Hofslot R. D. A. , Supèr H. , Nijenhuis A. J. , Pennings A. J.
Published: May 2005

Copolymers of L‐lactide with 15 or more mole % D‐lactide are amorphous, noncrystallizable hydrolytically degradable materials. These glassy materials are brittle in tension and bending. To make these materials suitable for use as load‐bearing devices in biomedical applications, toughness has to be enhanced. This is effectively accomplished by introducing a separate degradable rubber phase in the amorphous matrix. Several approaches have been explored: solution blending and coprecipitation of trimethylene carbonate and ϵ‐caprolactone rubbers and poly(lactide), preparation of ABA triblock copolymers and blending of ABA block copolymers with the amorphous poly(lactide) matrix. In all cases very tough materials could be prepared. These materials are easily processable by compression molding at relatively low temperatures.
The effect of particles on failure modes of filled polymers
Authors: Bazhenov S.
Published: May 2005

The effect of rigid particles on the fracture mode of polymers that yield with necking was analyzed theoretically with a model of regularly arrayed spherical particles. The adhesion between a polymer and particles was assumed to be weak, and particles were assumed to debond from the polymer before necking. A linear decrease in engineering draw stress with an increase in the filler content was derived. An increase in filler content leads to a transition in deformation mechanism. The transition depends on the ability of the polymer to strain‐harden. If the ability to strain‐harden is insignificant and the engineering fracture stress (strenght) of the polymer is lower than its yield stress, the transition is from ductile to brittle fracture. If the ability to strain‐harden is essential and the strength of the unfilled polymer is higher than its yield stress, the transition (ductile‐to‐ductile) is from neck propagation to uniform ductile yield. The critical filler contents were determined for both transitions from the properties of an unfilled polymer. The ductile‐to‐ductile transition without embrittlement is possible if the strength of the unfilled polymer is higher than its yield stress. Results for polymers filled by weakly bonded particles were compared with polymers filled by particles that debond after the yield stress.
Weldline strength in glass fiber reinforced polyamide 66
Authors: Meddad A. , Fisa B.
Published: May 2005

Presence of weldlines introduces an element of uncertainty to the performance of injection molded parts. Weldlines are particularly problematic in reinforced plastics because, unlike molecular orientation in neat polymers, the flow induced fiber orientation does not relax. This paper deals with the structure and mechanical behavior of weldlines in glass fiber reinforced nylon 66, a plastic known for excellent fiber‐matrix adhesion. Two molds were used to generate weldlines: a double gated tensile sample shaped cavity in which the weldline is formed by a head‐on collision of melt fronts flowing in opposite directions and a film gated rectangular plaque with a circular insert in which the weldline formation behind the insert is followed by additional flow. In both cases the weldline zone is several millimetres wide: in the plane where the melts fronts have met fibers are oriented parallel to this plane (random‐in‐plane in the double‐gated cavity and unidirectional in the cavity with insert). The transition zone between the weldline plane and the rest of the sample is characterized by an increased presence of microvoids. Weldline tensile depends little on the fiber concentration and on the sample shape or thickness: values close to the matrix strength are found: in samples without weldlines strength increases with the fiber content. However, in instrumented impact penetration test during which the material is subjected to multiaxial loading, the weldline effect appears negligible.
Wall thickness uniformity in plastic pipes: Computer simulations of the effectiveness of die mandrel offsetting and pipe rotation in combatting sag
Authors: Pittman J. F. T. , Whitham G. P. , Farah I. A.
Published: May 2005

A computer simulation, based on a thermoviscous model of cooling and gravity induced flow (sag) in plastic pipe manufacture, which has previously been described in detail and validated against experimental results, is here used to investigate the effectiveness of die mandrel offsetting and pipe rotation in combatting sag. SDR11 MDPE pipes of 315, 560, 800, and 1000 mm diameter are considered. Results are examined in terms of a waste percentage, representing polymer used in excess of that corresponding to the minimum wall thickness. With a concentric mandrel, waste is predicted to be 4.3, 14.0, 17.9, and 18.7% for the four sizes, respectively. Optimum offsets and minimum waste percentages are found to be: 2 mm, 0.8%; 15 mm, 4.6%; 42 m, 9.8%; 63 mm, 12.7%, respectively. For the largest pipe this corresponds to a wall thickness variation of 19.6 mm. Simulations of rotation of the 800 mm pipe show waste falling rapidly to 5% at 1 revolution/4800s, then a slower decrease, reaching 1.6% at 1 revolution/600s. The simulation is equally applicable to all grades and sizes of pipe, and provides a valuable computer aid for the design and operation of pipe cooling lines.
Chaotic mixing in the enhanced mixing simulator
Authors: Ling F. H.
Published: May 2005

The mixing performance of an experimental device—the enhanced mixing simulator (EMS)—is studied in this paper. In this device, the Couette flow is perturbed laterally, so that uniform and quick mixing can be achieved. Numerical simulation of the mixing in EMS flows is performed, which shows good agreement with the experimental results. Spline interpolation and advanced integration techniques are used in particle tracking, so that accurate results are obtained at low costs. Poincaré sections are used to study the long‐term mixing behavior. The uniformity of the simulated mixture is evaluated using statistical approaches—the variation coefficient and the Kolmogorov test. The Kolmogorov test is adequately implemented for our purpose and incorporated with efficient sorting algorithms. The mixing rate is determined from the time evolution of uniformity during mixing. It is also shown that although the Lyapunov exponent can identify chaos, it does not measure the mixing rate. Optimal design of the EMS is discussed.
Fracture toughness of injection molded glass fiber reinforced polypropylene
Authors: Hashemi S. , Koohgilani M.
Published: May 2005

The fracture behavior of polypropylene reinforced with 30% by weight of short glass fibers was studied using single and double feed plaque moldings. Plaques were injection molded using several gate types and gate positions. Fracture toughness Kc, was calculated at different positions in the plaque moldings using single edge notched tension specimens. Fracture toughness was assessed in the directions parallel and perpendicular to the mold fill direction through measurements of the load to produce complete fracture. Results indicated that the value of fracture toughness is affected by the type of gate as well by size of gate. Position of the specimen also affected fracture toughness. Generally, specimens taken from positions near cavity walls gave higher toughness values than those taken from the center of the moldings. Furthermore, fracture toughness in the transverse direction was consistently higher than in the melt flow direction. Finally, in the case o double feed moldings, a much higher fracture toughness was obtained when the initial crack was perpendicular to the weld line than when it was placed inside the weld line.
Discrete strength levels in modified polypropylene tapes
Authors: Dmitorva D. , Kostov G. , Garova G.
Published: May 2005

A statistical study of the strength of unmodified and modified uniaxially drawn polypropylene tapes was carried out. The results show that the curve representing the distribution of strength for unmodified tapes reveals seven discrete levels corresponding to microdefects in the form of microcrazes and submicrocrazes. On introduction of modifying additive, three discrete strength levels were observed, corresponding to submicrocrazes. The strength of the modified polypropylene tape increase approximately twice compared to the strength of the initial material. The polyfunctional effect of the additives as artificial nucleators and regulators of the structure leads to an increase of the degree of crystallinity which in turn restrains the submicrocrazes development into microcrazes. The method used could be applied for objective analysis of the tensile characteristics of polymeric materials.
Radiation crosslinking of polyethylene with electron beam at different temperatures
Authors: Qu Baojun , Rårby Bengt
Published: May 2005

The effect of temperature over the range −196 to 150°C on the crosslinking of polyethylenes irradiated by electron beam has been investigated on the basis of gel content determination and Fourier transform infra‐red (FTIR) spectroscopy. The crosslinking efficiency increases significantly with increasing irradiation does and at elevated irradiation temperature. The crosslinking rates of high density polyethylene (HDPE) and low density polyethylene (LDPE) samples above the melting point (TM) are much higher than those below Tm. The FTIR data give positive evidence: (i) that trans‐vinylene double bonds in cross linked HDPE and LDPE samples increase with increasing irradiation dose temperature (ii) that vinyl double bonds in HDPE decrease rapidly with increasing irradiation dose and temperature, and (iii) vinylidene groups in LDPE decrease slowly with increasing temperature at the lower dose and are almost independent of the irradiation temperature at above room temperature and the higher dose of more than 100 kGy. Gas bubbles are observed in LDPE samples irradiated at 100 and 150°C with high dose (200 to 250 kGy). The size of the bubbles increases gradually at high temperatures.
Water sorption and diffusion in starch/polyolefin blends
Authors: Willett J. L.
Published: May 2005

The kinetics of water sorption by starch filled polyolefins has been investigated using blends of commercial starch masterbatch with low density polyethylene (LDPE), high density PE (HDPE), and copolymers of ethylene with methyl acrylate (EMA), ethyl (EEA), AND n‐butyl acrylate (EBA). Transient state diffusion coefficients (D) of water in the blends were determined using Fickian analysis of the initial stages of the sorption isotherms. Measured D values were several orders of magnitude lower than values reported for either pure starch of LIDPE by various investigators. Resin effects on D were on the order DHDPE < DLDPE ≪ DEBA < DEEA < DEMA. The resin effects diminished as the starch content increased. The lower magnitude of D in the blends relative to pure LDPE was attributed to the sorption of water by the dry starch particles, in a manner similar to dual‐mode sorption in glassy polymers. Copolymer effects were consistent with reduction in crystallinity caused by the comonomers. The dependence of the diffusion coefficient on starch content was not described by mixing models of heterogeneous systems of percolation theory.
Numerical simulation of fluid flow and heat transfer in twin‐screw extruders for non‐Newtonian materials
Authors: Sastrohartono Trihono , Jaluria Yogesh , Karwe Mukund V.
Published: May 2005

A new simplified approach has been proposed for the numerical simulation of the thermal transport in corotating, tangential, and self‐wiping twin‐screw extruders. It is assumed that the flow domain in a twin‐screw extruder can be divided into (i) the translation region (T‐region), which represents a flow similar to that in a single‐screw channel and (ii) the intermeshing region (I‐region), which is located between the two screws. The two regions are simulated separately and then coupled for each screw section to model the overall transport in tangential and self‐wiping twin‐screw extruders. A finite difference method is employed for the developing flow and temperature fields in the T‐region, in order to minimize the computing effort, while a finite element method is employed for determining the interchannel flow mixing and the thermal transport in the I‐region. Results are obtained in terms of temperature, velocity, and pressure variations along the screw channels and mixing between the two screws.
Model filled polymers. XV: The effects of chemical interactions and matrix molecular weight on rheology
Authors: Agarwal Shishir , Salovey Ronald
Published: May 2005

In order to explore the effects of chemical composition on the rheological behavior o filled polymeric systems, we prepared polystyrene (9PS) and poly(methyl methacrylate) (PMMA) particles crosslinked with either ethylene glycol dimethacrylate (EGDMA) or divinyl benzene (DVB), and mixed these particles in a PMMA matrix. PS particles crosslinked with 10% EGDMA are better dispersed in a PMMA matrix, compared to PS particles, crosslinked with 10% DVB, due to the compatibilizing effect of EGDMA. For PMMA particles crosslinked with DVB, particle‐matrix interactions in a PMMA matrix are smaller than in EGDMA‐PMMA filled PMMA. Therefore, particles tend to agglomerate in PMMA composites filled with DVB‐PMMA particles, especially in a low molecular weight matrix. We compared PMMA matrices of molecular weights 35,000 and 75,000. Higher particle‐matrix interaction in the higher molecular weight matrix resulted in lower relative viscosities for DVB‐PS filled systems, due to better dispersion of the particles. Composites filled with EGDMA‐PS particles behave similarly to those filled with DVB‐PS particles. PMMA composites filled with DVB‐PMMA particles have a lower relative viscosity in the higher molecular weight PMMA matrix at low shear rates, due to better dispersion in the higher molecular weight matrix. However at high shear rates, particles are well dispersed in both PMMA matrices and, then, the relative viscosity is higher due to better bonding in the higher molecular weight matrix.
A model for nonlinear creep and physical aging in poly(vinyl chloride)
Authors: Dean G. D. , Tomlins P. E. , Read B. E.
Published: May 2005

The creep behavior of polymers depends on the physical age of the material at the time of stress application. Creep curves shift to longer times for more highly aged material and, in poly(vinyl chloride), (PVC), this can be modeled by an empirical equation in which the magnitude of an effective mean retardation time parameter is dependent upon, and increases with, the age of the polymer. Creep compliances for PVC also depend on the magnitude of the applied stress when this exceeds about 4 MPa. This nonlinear behavior is caused, at short creep times, by a reduction in the value for the retardation time parameter on application of the creep stress. Specimens appear therefore to be initially de‐aged by elevated stresses. Subsequently, this parameter increases with creep time implying that physical aging has been reactivated, but the rate of increase also depends on the stress level. These influences of elevated stresses can be described by an extension of the creep model, and parametric expressions have been derived which relate creep compliance values to time, stress, and the age of the polymer. It is shown how the parameters can be determined from a short series of creep experiments and thus how creep deformations can be calculated over wide ranges of time, stress, and age.
An integral constitutive equation for nonlinear plasto‐viscoelastic behavior of high‐density polyethylene
Authors: Lai J. , Bakker A.
Published: May 2005

In the present paper an effort is made to model the time‐dependent behavior of high‐density polyethylene (HDPE) with a one‐dimensional integral representation. Owing to the plasto‐viscoelastic behavior of the material, we assume that the total strain can be decomposed into a recoverable viscoelastic strain and an irrecoverable plastic strain. The viscoelastic deformation is represented by the Schapery thermodynamic theory. The plastic deformation is assumed to be accumulated during the loading history. An effective time concept is introduced for the plastic deformation, so that the response due to complex loading can be accounted for. The present representation gives a very good prediction of the responses of creep and recovery, two‐step creep, and constant stress rate loading and unloading. It is also applied successfully to describe the process of preconditioning of semicrystalline polymers.
Cure behavior and properties of an epoxy resin modified with a bismaleimide resin
Authors: Kim Dae Su , Han Mi Jeong , Lee Jae Rock
Published: May 2005

A bismaleimide (BMI) resin was added to an epoxy system composed of N,N′‐tetraglycidyldiaminodiphenyl methane (TGDDM) and diaminodiphenyl methane (DDM). Cure behavior of the BMI modified epoxy resins was studied by a dynamic differential scanning calorimetry (DSC) method. Dynamic DSC thermograms of the BMI modified epoxy resins indicated unimodal reaction exothermic peaks. The overall heat of reaction per unit mass decreased with BMI composition. The residual heat of reactions of the epoxy blends cured at 180°C for 3 h increased with BMI composition. Thermal stability of the epoxy system improved by incorporating BMI resin. Flexural strength and modulus increased with BMI composition.
Rubber‐modified thermosets cured in heated molds: Experimental study of phase separation profiles
Authors: Fang Dong Pu , Frontini Patricia M. , Riccardi Carmen C. , Williams Roberto J. J.
Published: May 2005

An epoxy‐amine thermosetting polymer, modified by 15 wt% castor oil (CO) or by a commercial rubber (epoxy‐terminated butadiene‐acrylonitrile copolymer, ETBN), was cured in a mold at different heating rates. CO‐modified materials cured at high heating rates exhibited a nonuniform phase separation profile, i.e. a single‐phase transparent core surrounded by opaque layers containing dispersed domains. The resulting structure was explained by simulating conversion vs. temperature trajectories taking place during the cure. Thermal and mechanical properties of uniform and nonuniform materials were compared. These include glass transition temperature, microhardness, yield stress and yield strain in uniaxial compression, and fracture toughness. Some possibilities for further research in this area are discussed.
Step‐growth polymerization of maleic anhydride and 1,2‐propylene glycol
Authors: Jedlovčnik R. , Šebenik A. , Golob J. , Korbar J.
Published: May 2005

The NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography) studies of the polymerization of maleic anhydride and 1,2‐propylen glycol are reported. Assignment of individual groups was made and their concentration dependence on reaction time was established. The first step of the reaction is the formation of monoesters, which, immediately after the temperature increased, reacted to diesters. The reactivity ratio between the primary and the secondary hydroxyl group of 1,2‐propylene glycol was 2.6:1. The concentration of water formed was followed as a function of reaction time by the Karl–Fischer method.