bluuebunny/crossref_metadata_2025 huggingface dataset:
The mechanical properties of styrene‐butadiene‐styrene (SBS) triblock copolymer blends with polystyrene (PS) and styrene‐butadiene copolymer (SBR)
Authors: Diamant Joram , Soong David , Williams Michael C.
Published: December 2004

Measurements were made of linear viscoelastic properties and nonlinear stress‐strain properties of phase‐separated styrene‐butadiene‐styrene (SBS) copolymers and their blends with several homopolymer polystyrenes (PS) and one random copolymer (SBR). Torsion pendulum testing yielded shear moduliG′,G″, and Rheovibron experiments produced tensile moduliE′,E″, over a 220°K range of temperature, both at low frequencies. For pure copolymers and their PS blends,G′ andE′ correlated quite well with the total PS content, butG″ andE″ were more sensitive to how the additive was distributed. Results suggest that a PS additive whose molecular weight (M) is less than that of the copolymer PS‐block (Ms) causes expansion of both the interphase and the homogeneous PS‐rich phase, while an additive withM>Msmixes less well with these phases (probably forming separate domains of pure PS) and is less effective in enhancing the linear moduli. The blending with SBB produced reduction inG′ but a broad midrange peak inG″, suggesting that SBR was localized almost entirely within an expanded interphase. Tensile stress‐strain data were obtained with an Material Testing System at room temperature. For PS blends, properties did not correlate well with the total PS content, the blends being always weaker than the SBS of the same overall composition. The amount of set also increased with PS content in the blends. Cyclic tests to increasing strain showed progressive structural alterations (as for the host SBS), with blend behavior resembling host properties more closely with each new cycle. When SBR was the additive, amounts as small as 1 percent reduced the curves by 15 percent. The yield stress was eliminated entirely with an addition of 10 percent SBR, but for all cases the set was the same. Results are discussed in terms of interphase force barriers to chain flow.
Relationship between rheological properties and impact strength in high impact polystyrene
Authors: Dalal Mukund D. , Armstrong Robert C.
Published: December 2004

Two batches of a commercially available high‐impact polystyrene having different impact strengths were investigated. The steady‐shear flow properties, dynamic shear properties, and elongational flow properties of the two were measured. Transmission electron microscopy (TEM) was used to study the microstructure. It is suggested that melt rheology can be a sensitive tool in the characterization of final product properties of rubber‐modified polymers: the zero‐shear‐rate viscosity and the dynamic storage modulus G′, at low frequencies, were experimentally shown to correlate directly with the impact strength, despite the fact that TEM revealed no gross differences in the morphology of the two batches.
Fatigue fracture of polycarbonate
Authors: Takemori Michael T.
Published: December 2004

The fatigue fracture process in polycarbonate can be different for cracks grown from notches and from surface crazes. During the discontinuous crack growth process (which occurs during the very slow crack growth regime), full‐width cracks grown from notches have a very different crack tip plastic zone when compared to that observed in localized cracks grown from surface crazes. These localized surface cracks have a pair of sharply defined shear bands at the crack tip (forming the “epsilon” plastic zone) that are absent from notched‐grown cracks, The presence of the shear band pair in this plastic zone produces two major modifications. The discontinuous crack growth is extended to higher stress intensity ranges due to the (crack tip) craze stabilization by the shear band pair. Moreover, a shear fatigue fracture mode, absent in the notched specimens, occurs upon termination of the discontinuous growth process. The implications of this comparison are that estimates of fatigue lifetimes of smooth samples based on fatigue crack growth data (on notched specimens) may be erroneous.
The effect of moisture on the fatigue resistance of an aramid/epoxy composite
Authors: Roylance Margaret E.
Published: December 2004

An investigation has been carried out concerning the effects of moisture on the mechanical properties of a unidirectionally reinforced aramid/epoxy composite; specifically, Kevlar 49‐Fiberite 934. (Fiberite 934 is a 350°F‐cure epoxy composed primarily of tetraglycidyl methylene dianaline and hardened by diaminodiphenyl sulfone.) Absorption of water has been found to plasticize the resin so as to produce a decrease in the glass transition temperature from, 210°C to 150°C, and this plasticization serves to increase substantially the room‐temperature ductility of the resin. Moisture also serves to increase the static tensile strength, of the laminate, presumably by enhancing resin ductility and making the composite more forgiving of local flaws and fiber misalignments. The moisture‐induced enhancement of static strength is observed to carry over to an increase in fatigue lifetime at a given stress, although the fraction of ultimate tensile strength lost per decade of fatigue loading is the same in wet and dry materials. It is concluded that the mechanism of fatigue damage—probably a form of fiber abrasion—is unaffected by moisture, but the fatigue resistance of the wet composite is improved by virtue of its increased static strength.
Tensile yield in poly(4‐methyl pentene‐1)
Authors: Hartmann B. , Cole R. F.
Published: December 2004

Uniaxial tension tests to the yield point were performed on a crystalline polymer, poly(4‐methyl pentene‐1) (PMP) as a function of temperature from 21° to 200°C at a strain rate of 2 min−1. After testing, the specimens showed considerable stress whitening as a result of microvoid formation. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (240°C). Thus, the behavior of this crystalline polymer is similar to that of glassy polymers, but with the melting temperature, rather than the glass transition temperature, as the reference point. The ratio of thermal to mechanical energy input to produce yielding is an order of magnitude smaller for PMP than it is for glassy polymers. The ratio of yield stress to Young's modulus is about 0.02, which is typical for polymers. Yield stress is a linear function of log strain rate, which implies that yielding can be described as a segmental flow rate process in which the applied stress biases the activation energy. The activation volume is on the order of 20 monomer unit volumes and increases as the temperature increases. The activation energy is 19 kcal/mol.
A model of compression mold filling
Authors: Tucker C. L. , Folgar F.
Published: December 2004

A model is proposed for the flow, reaction, and heat transfer during compression molding of thin, flat parts. The isothermal Newtonian version of the model is implemented using the finite element method, and is capable of handling arbitrary planar geometries. Automated mesh expansion and boundary condition modification allow the simulation to run without operator interaction. The model accurately predicts mold filling pattern for non‐Newtonian and non‐isothermal flows.
Characterizing photoresists by thermal analysis
Authors: Appelt B. K.
Published: December 2004

Photoresists and solder masks are used extensively for manufacturing printed circuit boards to define and protect the circuits, respectively. These systems exhibit exothermic polymerization and crosslinking reactions upon exposure to UV light or to elevated temperatures. Differential scanning calorimetry (i.e., the heat of reaction) was, therefore, employed to characterize batch‐to‐batch variations and to characterize the photoreaction in these photosensitive materials. This technique allows unambiguous evaluation of the photoreaction independent of other parameters such as developer reactivity, temperature, and other variables that commonly interfere with functional tests.
Aspects of dispersion and flow in thermoplastic‐elastomer blends
Authors: Schreiber H. P. , Olguin A.
Published: December 2004

Polypropylene, polystyrene, EP (ethylene/propylene) rubber, and bromobutyl rubber were blended under standardized conditions and the sizes of minor phase domains determined by Quantimet analysis. Dispersion effectiveness was found to depend on the melt viscosities of components under mixing conditions and on their “compatibilty” as inferred here from surface‐tension data. Dispersion was optimized when components wet readily at contact surfaces and when melt viscosities were similar. Shear heating during dispersion appeared to offer an empirical index of component compatibilty. Apparent melt viscosities of the blends further reflected the component compatibility factor.
The effect of storage temperature on the mobile water content and the fracture toughness of a filled‐polymeric system
Authors: Cahill R. W.
Published: December 2004

Charpy specimens of a filled‐polymeric system from two partially cured and two completely cured lots obtained from one supplier were stored at selected temperature and relative humidity (RH) conditions to determine the relationship between mobile water content and the fracture toughness of the material. The fracture data showed that specimens from three of the structures exhibited similar ductile‐to‐brittle transition temperatures (DBTT) as a result of exposure to these environments even though samples from one of the three units were subjected to only part of the pure cycle. Samples from the other partially cured structure consistently displayed a more ductile fracture behavior throughout the conditioning range studied. Exposure to 100°F/75 percent RH environments, the highest temperature and RH of this study, appeared to enhance the fracture toughness of the material from all four units, and no evidence of deleterious chemical aging was found. Mobile water contents were measured on Charpy fracture residues, and these results correlate well with DBTTs of the filled polymer, as does RH. Charpy specimens from the partially cured structure with the best fracture performance have essentially the same water concentrations as the others, suggesting that the lower DBTTs associated with this unit may be due to a lesser degree of crosslinking.
Stress corrosion cracking of poly(vinylidene fluoride) in sodium hydroxide
Authors: Hoa S. V. , Ouellette P.
Published: December 2004

Stress corrosion cracking of poly(vinylidene fluoride) in sodium hydroxide solution is investigated. Poly(vinylidene fluoride) (PVDF) is embrittled in the presence of solutions of sodium hydroxide. Cracks developed in specimens of PVDF subjected to load and solution of NaOH. Reddish‐brown deposits appear before cracks can be seen. Straining the material slightly above its yield point retards the cracking activity. An explanation for this behavior is provided.
Effects of strain rate and temperature upon tensile properties of acetal copolymers
Authors: Wissbrun K. F.
Published: December 2004

The strength and elongation to break of an acetal copolymer were measured at four elongation rates, from 0.2 to 20 in./min, at temperatures from 239 K to 339 K. Both strength and elongation results could be reduced to master curves by means of time‐temperature superposition. The temperature dependence of the shift factors was given by an equation of the WLF form, with parameters close to those found for most amorphous polymers, at a reference temperature equal to the γ‐transition temperature of the polymer. Extrapolation to much higher testing rates and to much slower creep rates was satisfactory. Similar but less extensive tests were run on two other samples with different molecular weights. The yield stress was independent of molecular weight, but elongation increased with increasing molecular weight at all conditions.
The specification of orientation and its development in polymer processing
Authors: White James L. , Spruiell Joseph E.
Published: December 2004

A critical review of the specification of orientation and its development in polymer‐processing operations is presented. Orientation may in general be specified by orientation distribution functions, but is most conveniently expressed in terms of orientation factors which are second moments of the distribution. The Hermans orientation factor represents polymer‐chain orientation for systems with fiber symmetry (uniaxial orientation) and the Hermans‐Stein orientation factors express uniaxial orientation for each of the crystallographic axes of crystalline polymers. Biaxial orientation is, however, developed in tubular film extrusion, blowmolding and, indeed, all processing operations other than fiber formation. Orientation factors developed previously by the authors express biaxial orientation in terms of the angles between the machine and transverse directions and the polymer chain axis or crystallographic axes. In flowing polymer melts, the Rheo‐Optical Law, which relates birefringence and stress, represents a relationship between polymer‐chain orientation and stress. In vitrified polymeric glasses (e.g. polystyrene), the orientation factors are related linearly to the stress field at vitrification. This has been shown experimentally for melt spinning and tubular film extrusion. The results of studies of blowmolding and injection molding are consistent with this. The crystalline orientation factors have also been found to be determined by the stress field at solidification in melt spinning and tubular film extrusion.
New techniques for the characterization of orientation in semicrystalline polymer moldings
Authors: Samuels Robert Joel
Published: December 2004

This paper describes new techniques for evaluating orientation in polymer moldings. Injection moldings of isotactic polypropylene, a semicrystalline polymer, have been used to demonstrate the analytical procedures.
Super strong polymers in planar directions
Authors: Zachariades Anagnostis E. , Economy James
Published: December 2004

A novel approach for producing multiaxially oriented polymers with ultrahigh mechanical properties in more than one direction is discussed. According to the approach, which is adaptable to conventional commercial processes, the polymer is processed in a contained geometry at a temperature near to but below the isotropic crystalline melting point under curvilinear flow conditions generated by the combined effects of a compressive force and a rotational force perpendicular to the compressive force. The process is demonstrated with thermoplastic and thermotropic polymers using simple torsional flow. The general features of the process and the properties of the multiaxially oriented polymers are discussed in view of the different flow conditions.
Thermal conductivity of plastic foams
Authors: Williams R. J. J. , Aldao C. M.
Published: December 2004

A simple equation enabling the prediction of the thermal conductivity of plastic foams, without the aid of adjustable parameters, is proposed. The equation is based on a recurrent method, previously developed, that showed reasonable agreement with experimental results. Ways of decreasing the thermal radiation contribution are shown. In particular, the influence of cell size, radiation transmission through solid membranes, and low‐emissivity boundary surfaces are analyzed. Errors involved in steady techniques of measuring the thermal conductivity associated with radiation are discussed.
Design of two‐stage extractor screws
Authors: Squires P. H.
Published: December 2004

A basis for design of two‐stage extractor screws is developed with special focus on determining optimum design of the final pumping section in order to maximize pressure‐generating capability. Departure from the conventional square‐pitch helix angle of 17.7° appears justified in this section of the screw where pressure‐development capability is critical to successful performance. Optimization can produce gains of 5 to 30 percent in pressure (or in corresponding length reductions), the exact benefits depending on the non‐Newtonian behavior of the melt and on the optimization strategy selected.
Process control of injection molding
Authors: Sanschagrin Bernard
Published: December 2004

This paper discusses the most important input parameters affecting the conventional injection‐molding process and describes a closed‐loop control system for determining the interaction between ten process inputs and three output parameters. The input parameters are: back pressure, holding pressure, injection time, open mold time, shot size, clamping pressure, injection pressure, screw speed, and boost cut‐off. The output parameters studied are: part weight, maximum cavity pressure, and maximum mold deflection.
Moldability studies in reactive polymer processing
Authors: Manzione L. T. , Osinski J. S.
Published: December 2004

Reactive polymer processing is the combined polymerization and processing of reactive prepolymers in a single operation. It encompasses a wide variety of processing methods including Reaction Injection Molding (RIM), a relatively new and growing fabrication method. Reaction Injection Molding utilizes impingement mixing of low viscosity fluids, injection of the reactive mixture into a mold, and polymerization therein to enable the molding of large plastic items. Polyurethane is currently the most commercially utilized RIM material although a number of other systems such as epoxy, nylon, and polyester are also suitable. Non‐urethane systems such as epoxy are often not as amenable to the process, however, since they are slower reactions and have a potentially damaging exotherm. A comprehensive analysis was developed to determine if a molding system is processable by RIM. Criteria for processability were established and include the ability to mix on impingement, fill large molds characteristic of the process, and provide a short cycle time without promoting a damaging exotherm. The treatment, consisting of both experimental and numerical techniques, was applied to identify potential epoxy molding systems, establish their processing window, and conduct an optimization of the process parameters to evaluate productivity. The analysis and its conclusions are applicable to most reactive polymer processing operations that employ a rapid, exothermic, polymerization reaction.
Determination of time independent component of the complex modulus during cure of thermosetting systems
Authors: Farris Richard J. , Lee Charles
Published: December 2004

A recent development suggests an approach to measure the equilibrium modulus through an impulse method. This paper is to report an attempt to apply such methods in measuring the changes of the equilibrium modulus of a thermosetting system during isothermal cures. Dynamic modulus changes were also measured and the results were correlated with that from the impulse method. At two different temperatures of cure, the equilibrium modulus values measured were very similar when the dynamic measurements showed tan δ = 1. At this point, it is not certain if the measured modulus is the real time independent portion of the elastic modulus, or contains the long relaxation time constant portion of the relaxation spectrum which appears to be pseudo‐time independent at the time scale and the instrumental sensitivity of the present experimental set‐up. This paper demonstrates the ease with which the impulse technique can be applied and suggests possible limitations or refinements.
Head to head polymers. XXV: Properties of head to head polyisobutylene
Authors: Malanga Michael , Vogl Otto
Published: December 2004

Head‐to‐head polyisobutylene, prepared by the Grignard coupling reaction of 2,2,3,3‐tetramethyl‐1,4‐dibromobutane had molecular weight of 3,000 to 10,000 and was characterized by wide angle x‐ray diffraction, optical microscopy and thermal behavior. Head‐to‐head polyisobutylene is crystalline, with a crystalline melting point of 187°C and a glass transition temperature of 87°C (measured by DSC at a scan rate of 20°/min.); these values compare to a glass transition temperature of head‐to‐tail polyisobutylene of similar molecular weight of −61°C and a crystalline melting point of 5°C, which can only be observed when the sample was stretched. The maximum rate of degradation of head‐to‐head polyisobutylene (20°/min. programmed temperature increase) is at 315°C, 70°C lower than that of head‐to‐tail polyisobutylene.
A phenomenological master curve for viscosity—structure data for two phase polymer systems in simple shear flow
Authors: Lyngaae‐Jorgensen J.
Published: December 2004

A master curve hypothesis is established based on a mass balance and an assumption of continuous stress through interfaces for well dispersed two phase systems with “defined” zero shear viscosity. The master curve, which is in reasonable accordance with experimental data is represented in a double logarithmic plot of log (ηT/T,0) against log \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{\eta _{T,0} M_C H\rho}}{{c^2 RT}}\dot \gamma _T} \right) $\end{document}. Mc is the molecular weight between entanglements, H = M̄w/M̄n, ρ is the density, c is the polymer concentration, all defined for the continuous phase. ηT and ηT,0 are the viscosity and zero shear viscosity of the blend, ηT is the apparent shear rate, R the gas constant, and T is absolute temperature.
A survey of dual phase continuity and miscibility in interpenetrating polymer networks, making use of selective decrosslinking and dissolution of one component: Poly(n‐butyl acrylate)/polystyrene
Authors: Sperling L. H. , Widmaier J. M.
Published: December 2004

A sequential interpenetrating polymer network, IPN, may be defined as a combination of two polymers in network form, at least one of which was polymerized or crosslinked in the presence of the other. Two major problems of interest to sequential IPN's relate to phase continuity and extent of mixing within each phase. A first attempt to define the molar volume of a network is made in terms of the molar volume of the polymer between crosslinks. This permits a thermodynamic calculation of the changes in molecular mixing expected as a function of crosslink density. The experimental system was poly(n‐butyl acrylate)/polystyrene IPN's, where the PnBA was crosslinked with acrylic acid anhydride. This last may be selectively hydrolyzed, forming a semi‐IPN, and then the PnBA can be extracted. Scanning electron microscopy and dynamic mechanical spectroscopy were carried out at each stage.
Heating and bonding mechanisms in ultrasonic welding of thermoplastics
Authors: Tolunay M. N. , Dawson P. R. , Wang K. K.
Published: December 2004

An experimental study of the heating and bonding mechanisms in ultrasonic welding is described. Polystyrene specimens were joined under a variety of welding conditions while the temperatures at the interface and within the interior of these specimens were measured. The power input, amplitude of vibrations, and amount of deformation during welding were measured concurrently. In general, the rate of heating at the interface is greatest at the beginning of the weld cycle, but slows markedly after the interface temperature reaches approximately 250°C. The interface temperature peaks well before the weld is completed. Temperatures within the body increase most rapidly at temperatures near the glass transition temperature. Welded specimens were broken on a special testing apparatus under combined torsional and compressional loads to determine the weld strength. The results show that weld strength is dependent on the amount of energy input and the degree to which material flows out of the interface region. Possible mechanisms for heating and bonding during ultrasonic welding are discussed in light of the observed behavior.
Fiber fracture in reinforced thermoplastic processing
Authors: von Turkovich Richard , Erwin Lewis
Published: December 2004

The length reduction of reinforcing fibers in short‐fiber reinforced plastics during processing has been studied experimentally. It has been shown that fiber volume fraction, initial length, and initial state of dispersion have little effect on the final fiber length. In dilute suspension theory based on shearing flow conditions and fiber properties the flow stresses are found to be compatible with the experimental results and results which are found in the literature.
Poly (butyleneterephthalate)‐ethylenevinylacetate polymer blends
Authors: Pilati Francesco
Published: December 2004

Polymerization of dimethylterephthalate (DMT) and 1,4‐butanediol (4G) carried out in the presence of about 15 weight percent of ethylene‐co‐vinylacetate copolymers (EVA), gave blends with average dimensions of the “soft domains” of a few microns. During polymerization, reaction between EVA and poly(butyleneterepthalate) (PBTP) takes place leading to the formation of macromolecules of PBTP‐g‐EVA and crosslinked EVA in addition to unreacted EVA and linear PBTP. These different chemical structures can be fractionated by selective solubility and quantitatively measured. Their relative amounts depend particularly on the percentage of vinylacetate (VA) in the initial EVA and on the time of reaction. During polymerization there is a retarding effect on the increasing of the molecular weight of linear PBTP which can be ascribed to the lower volatility of the acetate by‐products, derived from the reaction with EVA, which act as monofunctional impurities.
Solution processing and properties of molecular composite fibers and films
Authors: Hwang W‐F. , Wiff D. R. , Verschoore C. , Price G. E. , Helminiak T. E. , Adams W. W.
Published: December 2004

Experimental studies of fiber wet‐spinning and solution processing of films of molecular composites are presented. The rigid rod polymer was poly (p‐phenylenebenzobisthiazole) (PPBT) and the flexible polymers were poly (2,5(6′)‐benzimidazole) (ABPBI) and poly (2,5(6′)‐benzothiazole) (ABPBT). Effects of the flexible polymer molecular entanglements in solution on the processing are discussed. These fibers and films have very high modulus and strength, which improve upon heat treatment. The uniaxial modulus of highly oriented molecular composites follows the linear rule of mixtures.
The preparation of oriented morphologies of the thermotropic aromatic copolyester of poly(ethylene terephthalate) and 80 mole percent p‐acetoxybenzoic acid
Authors: Zachariades Anagnostis E. , Logan John A.
Published: December 2004

Highly oriented morphologies of poly(ethylene terephthalate) and 80 mole percent p‐acetoxybenzoic acid were prepared by shearing in an optical plate‐plate rheometer and by melt fiber drawing in a temperature range at which the copolyester was either in the semicrystalline state or liquid crystalline phase. The optical, thermal, and mechanical properties of the oriented films and drawn fibers depended significantly on the processing temperature.
The flow of a polymerizing liquid in a cylindrical pipe
Authors: Malkin A. Ya. , Sherysheva L. I. , Kulichikhin S. G. , Zhirkov P. V.
Published: December 2004

This work concerns the flow of a polymerizing liquid (a monomer) in a cylindrical pipe, which simulates the flow‐through reactor. A general formulation of the hydrodynamics of the rheokinetic problem in the non‐isothermal case of flow is given. The problem is solved with account taken of the existence of a radial distribution of velocity, residence time, and degree of conversion in the duct. The shape of the velocity profile undergoes change as the flow moves along the duct: it is originally parabolic (prior to reaction), then becomes strongly extended (at the intermediate stages of the reaction), and finally (upon completion of the reaction) assumes the parabolic shape again. It has been shown that in isothermal or nearly isothermal cases, it is possible to work out sufficiently simple scale‐up laws capable of establishing the dependence of the total degree of conversion and pressure drop on the time of polymerization and the geometric size of the reactor.
Recent advances in the theory of polymeric alloys
Authors: Noolandi Jaan
Published: December 2004

The theory of multicomponent polymeric systems, termed “polymeric alloys”, composed of block copolymers, homopolymers and solvents is discussed. We first review the microscopic interfacial properties of polymeric mixtures, highlighting the interfacial activity of block copolymers as emulsifying agents in incompatible homopolymer blends. We then turn to some interesting features of the phase diagrams, such as homopolymer‐induced mesophase formation and the existence of eutectic points, similar to those for metallurgical alloys. Finally, we address problems in polymer dynamics and present some recent new theoretical results based on the tube model.
Analysis of transient sorption and permeation of small molecules in multiphase polymer systems
Authors: Ottino J. M. , Shah N.
Published: December 2004

The transport of small molecules (gases) in incompatible polymer blends, semi‐crystalline polymers, and filled polymer systems is usually examined in terms of transient sorption and permeation experiments which yield effective values of diffusivity and permeability. From a modeling standpoint these complex systems can be regarded as composites with complex morphology whereas the gas can be considered as a molecular probe of the morphology and especially its connectedness. In this paper we present a brief review of transport descriptions in prototype ordered and disordered systems with special emphasis on simulation of transient measurements. The simulations presented are selected in such a way as to aid in the interpretation of experimental results obtained by sorption and permeation and in the construction and evaluation of morphologies with desired effective transport properties.
Thermal expansion of oriented glassy polymers
Authors: Smith K. J.
Published: December 2004

A phenomenological model of entanglement networks is developed and applied to deformed glassy polymers. Thermal expansivities and birefringence are analyzed. The model assumes a stable network of entanglements up to draw ratios of about 5. Beyond that range the entanglement structure breaks down to maintain a nearly constant drawing stress. The results are used to determine the ultimate linear expansivities of atactic polystyrene.
Torsional braid analysis of bitumen‐liquid rubber mixtures
Authors: Kortschot M. , Woodhams R. T.
Published: December 2004

The performance of liquid rubbers as low‐temperature plastcizers for bitumen was evaluated by the torsional braid technique developed by Gillham. The low‐temperature dynamic mechanical properties of bitumen‐liquid rubber mixtures were measured from ambient to −100°C and compared with the corresponding fracture behavior using a modified Fraass test. Microscopic observation of the mixture revealed that the liquid rubber was partially soluble in the bitumen at 23°C and at concentrations greater than 10 percent tended to form colloidal dispersions of rubber particles having mean diameters of approximately 10 μm. The loss tangent maxima shifted to lower temperatures and became less pronounced as the concentration of liquid polybutadiene increased. The colloidal rubber dispersion further contributed to the ductility and reduced the brittle temperature of the bitumen at −30°C at 20 percent liquid rubber concentration. The reduction in the brittle temperature of the bitumen is related to the glass‐transition temperature of the added rubber, those rubbers having, the lowest glass‐transition temperatures being most efficient. Such modifications are necessary to reduce the tendency of asphaltic paving materials to crack in cold climates.
Positional small angle X‐ray scattering from flaws
Authors: LeGrand D. G.
Published: December 2004

A simple theory of PSAXS (positional small angle X‐ray scattering) has been developed and used to aid in the interpretation of PSAXS data from flaws. The importance of the various experimental parameters has been studied and an explanation offered for apparent magnification. A comparison between images created by assumed flaw structures and from actual flaws has been made. It is proposed that three dimensional imaging of flaws can be performed.
Influence of composition, crystallization conditions and melt phase structure on solid morphology, kinetics of crystallization and thermal behavior of binary polymer/polymer blends
Authors: Martuscelli Ezio
Published: December 2004

Results of an investigation on the morphology, the crystallization and the thermal behavior of several binary crystallizable blends are reported. The composition, molecular mass and crystallization conditions strongly influence the crystallization and the thermal behavior as well as the overall morphology of crystallizable binary blends. Quantities such as nucleation density (N), radial growth rate (G) of spherulites, overall rate of crystallization (K), and equilibrium melting temperature (Tm) are strongly dependent upon composition, crystallization conditions, and molecular mass of components. The type of dependence is to be related to the physical state of the melt, which, at the crystallization temperature, is in equilibrium with or coexists with the developing solid phase. In the ease of compatible blends such as poly(ethylene oxide)/poly(methyl methacrylate) the depression observed for G and Tm is mainly to be attributed to the diluent effect of the non‐crystallizable component. For such a blend it is found that, after crystallization, the non‐crystallizable component is trapped in intralamellar regions increasing the distance between adjacent lamellae. Depression of G, in the case of incompatible blends such as isotactic polypropylene/rubbers is mainly accounted for by rejection and deformation of rubber drops. The coexistence during crystallization of different processes such as molecular fractionation and segregation, preferential inclusion or dissolution of molecules with lower molecular mass and/or high degree of steric disorder of the crystallizable component in the phase rich in non‐crystallizable component and vice versa may explain some minima observed in the plots of T and Tm, vs. composition in the case of blends semicompatible in the melt. It was found that the addition of a second non‐crystallizable component causes drastic variations on some morphological and structural quantities of the semicrystalline matrix (isotactic polypropylene or nylon 6) such as the shape, dimensions, and regularity of spherulites and interspherulite boundary regions and lamella and interlamella thickness. In some cases the formation of new boundary lines connecting occluded particles are also observed. Such phenomena may have great importance on crack propagation and on impact behavior as well as on the tensile mechanical properties of binary blends characterized by a semicrystalline polymer component with a relatively high Tg and a rubber‐like component with a lower Tg.
Applications of polymer blends: Emphasis on recent advances
Authors: Robeson L. M.
Published: December 2004

In the past decade, polymer blend technology has achieved an important position in the field of polymer science. With increased academic and industrial research interest, the application of polymer blend technology to commercial utility has grown significantly. This review on the applications of polymer blends will cover the major commercial blends in the categories of styrene‐based polymer blends, poly(vinyl chloride) blends, polyacrylate blends, polyester and polycarbonate blends, polyolefin blends, elastomer blends, polyelectrolyte complexes, and interpenetrating polymer networks. New developments in polymer blend applications will be discussed in more detail. These systems include linear low‐density polyethylene blends with either low‐ or high‐density polyethylene, styrenemaleic anhydride terpolymer/ABS (acrylonitrile‐butadiene‐styrene) blends, polycarbonate/poly(butylene tetephthalate) blends, new PPO/polystyrene blends, and tetramethyl bisphenol A polycarbonate/impact polystyrene blends. Areas for future research to enhance the potential for polymer blend applications will be presented. The need for improved methods for predicting miscibility in polymer blends is discussed. Weldline strength is a major property deficiency of two‐phase systems (even those with mechanical compatibility), and future research effort appears warranted to resolve this deficiency. The use of polymeric compatibilization additives to polymer blends has shown promise as a method to improve mechanical compatibility in phase‐separated blends, and will be expected to be the subject of future research programs. Finally, the reuse of polymer scrap is discussed as a future application area for polymer blends. Unique applications recently proposed for polymer blends include immobilization of enzymes, permselective membranes, reverse osmosis membranes, selective ion‐exchange systems, and medical applications using polyelectrolyte complexes.
Preliminary results on toughening a linear‐low‐density polyethylene using thermoplastic elastomers
Authors: Baker W. E. , Catani A. M.
Published: December 2004

The effects of several commercially available thermoplastic elastomers (TPE) on a gas‐phase linear‐low‐density polyethylene (LLDPE) were studied using small‐scale commercial‐compounding techniques. The properties of blown films of these compositions were evaluated as a function of TPE type and composition and compared to unmodified LLDPE films. Ethylene/propylene elastomers had modest effects on the falling dart impact strength and machine‐direction tear propagation resistance while polyisobutylene and styrene block copolymers had more significant effects on these properties.
Laminar shear mixing in reaction injection molding
Authors: Bourne J. R. , Garcia‐Rosas J.
Published: December 2004

Turbulent flow in the impingement mixing head of a reactions injection molding machine produces a laminated mixture, whose striations are mostly so thick that any subsequent copolymerization would be hindered by diffusion. However, further reduction in striation thickness occurs during laminar flow through the runner. This is calculated here and is a function of the radial position in the runner and of its length/diameter ratio. So, for example, when L/D = 10, it is predicted that at least 79 percent of, the reagent striations would be thin enough to permit reaction under kinetically controlled conditions.
Synthesis of poly(oxyethylene‐styrene‐oxyethylene) triblock copolymers and their phase behavior
Authors: Xie Hongquan , Zhou Peiguang
Published: December 2004

Interesting phenomena were observed in the polymerization of styrene and ethylene oxide into PEO‐PSt‐PEO triblock copolymers using potassium naphthalene as initiator and tolusene as a solvent. The relationship between the phenomena and molecular weight of the blocks was studied. The purified and characterized triblock copolymer showed mesomorphic behavior in toluene solution which depolarized polarized light increasingly as the concentration was increased. The structure of the triblock copolymer was also studied by small‐angle laser light scattering and by electron microscopy.
The unique properties of silicone and fluorosilicone elastomers
Authors: Cornelius D. J. , Monroe C. M.
Published: December 2004

In this paper a brief description of the synthesis of silicone polymers and their compounding is given, and the wide range of properties available in Silastic®

Registered trademark of Dow Corning Corporation.

silicone rubber is discussed. Some of the key properties are related to several applications. These include mechanical properties, chemical and environmental resistance, thermal stability; electrical properties, flame resistance, and surface characteristics. Silicone rubber parts are currently used in the automotive, electronic, dairy, medical, construction, and aerospace industries. Among the applications discussed are axle seals, hose, milk inflations, wire and cable insulation, and elastomeric keyboard springs. In addition, improved silicone rubber materials are being developed for new applications.
Permeability barriers by controlled morphology of polymer blends
Authors: Subramanian P. M.
Published: December 2004

Melt fabricated plastic articles with improved solvent and vapor barrier properties are of great need in the packaging industry. Various techniques, such as coextrusion, surface treatments, and coatings, are being employed currently towards this objective. Present work has identified a unique polymer blend approach to impart solvent and gas barrier properties to a polyolefin material. This involves incorporation of small amounts of a modified nylon barrier material, and processing under controlled conditions, in single step blowmolding or other extrusion processes. The unusual barrier effects obtained at small concentrations of the barrier material are obtained by the controlled morphology of the dispersed phase and optimum formulation of the ingredients.
Impact energy absorption of unidirectional glass fiber‐epoxy composites
Authors: Golovoy A. , Van Oene H.
Published: December 2004

The influence of resin and fiber properties on the impact behavior of composites can be assessed in a three‐point drop‐weight impact test by varying the length‐to‐thickness ratio of the specimen. The fracture initiation energy per unit deformed volume,wi, can be described by the expression:where τ11is the tensile stress, τ12is shear stress;E11is tensile modulus; andG12is shear modulus. A unidirectional glass fiberepoxy composite was tested at impact velocities of 2.2 m/s (5 mph) and 4.5 m/s (10 mph). The energy to initiate fracture,wi, was in the range of 2 to 3.5 MJ/m3, apparently independent of impact velocity. The total energy absorbed by the impacted composite was also found to be independent of impact rate but very sensitive to the length to thickness ratio: about 13 and 3.5 MJ/m3 at the corresponding ratios of 4.6 and 23. It was generally observed that high fracture energy is associated with extensive specimen delamination, i.e. failure in shear.
Studies on the melt flow behavior of thermoplastic elastomers from polypropylene—Natural rubber blends
Authors: Kuriakose Baby , De S. K.
Published: December 2004

The melt flow behavior of thermoplastic polypropylenenatural rubber blends has been evaluated with specific reference to the effects of blend ratio, extent of dynamic crosslinking of the rubber phase and temperature, on viscosity, flow behavior index, and deformation of the extrudate. The proportion of rubber in the blend and the extent of dynamic crosslinking of the rubber phase were found to have profound influence on the viscosity of the blends at lower shear stresses. But at higher shear stresses, the effect of blend ratio on viscosity was comparatively less for the uncrosslinked blends than that for the crosslinked blends. At lower shear stress, the viscosity of the blend increased with increase in degree of crosslinking but at higher shear stress, the effect of crosslinking on viscosity was found to vary depending on the ratio of the plastic and rubber components in the blend. The deformation of the extrudates was also very much dependent on both blend ratio and degree of crosslinking.
An engineering study of the film embossing process
Authors: Kamal M. R. , Haber A. , Ryan M. E.
Published: December 2004

A mathematical model of the dynamics and heat transfer of the film embossing process has been developed. The thermal analysis around the preheat roll is determined from an unsteady, two‐dimensional heat conduction equation along with appropriate boundary conditions by neglecting the curvature of the preheat roll and choosing a Lagrangian reference frame. The heat transfer occurring between the preheat roll and the embossing rolls is based on a one‐dimensional analysis, including both convective and radiative effects. The deformation occurring in the nip region is analyzed for two different situations. For the case where the surface features are small in comparison with the film thickness, a modified one‐dimennsional calendering analysis is given, accounting for the irregular geometry of the embossing roll surface. For the case where the polymer does not make complete contact with the surface of the engraved channel, the local deformation is determined by means of a simple one‐dimensional cavity filling model. The required pressure distribution is determined by means of a simple one‐dimensional cavity filling model, The required pressure distribution is determined by means of a conventional calendering analysis. The analysis for the case of a Newtonian and power‐law model is presented in detail. The model yields qualitatively correct results and is computationally simple.
Evaluation of simple dynamic models and controllers for hydraulic and nozzle pressure in injection molding
Authors: Fara Dib Abu , Kamal M. R. , Patterson W. I.
Published: December 2004

Simple pseudo‐steady state relations between the hydraulic and nozzle pressures of an injection molding machine were presented and verified experimentally. A simulation study was performed to evaluate the performance of simple controllers using dynamic models developed for the hydraulic and nozzle pressures. The controllers chosen were the discrete proportional, proportional‐integral (PI), and proportional‐integral‐derivative (PID) types, tuned according to the ITAE criterion. The control of hydraulic pressure simulation showed that the PI controller had the best overall performance, whereas the result of nozzle pressure control loop simulation showed that the PID controller performance was better than that of the PI controller. All the controllers, in both loops, gave responses that were about an order of magnitude more rapid than the open loop response.
Experimental study and analysis of a slit die viscometer
Authors: Rauwendaal Chris , Fernandez Franco
Published: December 2004

A slit die viscometer (SDV) was built and evaluated extensively. A major advantage of the SDV is the ability to measure in‐line rheological data in a continuous fashion, using a setup that most closely approximates the conditions encountered in a real extrusion process. Comparisons will be presented of viscosity data of the SDV to data from a capillary rheometer (CR) and a Rheometrics Mechanical Spectrometer (RMS). Viscosity values as measured on the SDV tend to be lower than those measured on the CR and RMS. Possible reasons for this disagreement will be discussed. The effect of temperature on viscosity, the effect of pressure on viscosity, and the effect of compressibility will be analyzed in detail. It will be shown that these effects can be substantial, particularly with certain types of polymers. Finally, the feasibility of using the slit die viscometer to determine first normal stress differences will be explored.
Pressure build‐up during the packing stage of injection molding
Authors: Chung Tai‐Shung
Published: December 2004

A thorough study of an isothermal fluid motion within the mold cavity during the packing stage is presented. The fluid is considered Newtonian, and its compressible behavior is assumed to obey the Spencer‐Gilmore equation of state. Mathematical results indicate that the pressure built up during the packing stage is strongly dependent on the melt viscosity and the boundary of the cavity. The effects of pressure gradient and distribution, during this stage, on the shrinkage of the final products are also discussed.
Viscosity of copolymers containing carbon black
Authors: Lakdawala K. , Salovey R.
Published: December 2004

The flow behavior of random copolymers of styrene and butyl methacrylate containing specific carbon blacks varying in surface area were studied at various temperatures and shear rates. Master curves of reduced viscosity as a function of shear rate were prepared for the pure copolymers at 150°C. The superposition required vertical and horizontal shifts, proportional to (aT)−1 and (aT).53, respectively, where aT is the shift factor. With the incorporation of carbon black, the viscous response is non‐Newtonian exhibiting a yield stress at increasing filler concentration and surface area. Master curves of viscosity against shear rate were generated at fixed filler loadings and surface areas by using a single horizontal shift factor.