bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization and role of an elastomeric interphase on carbon fibers reinforcing an epoxy matrix
Authors: Gerard Jean‐Francois
Published: December 2004

Oxidized carbon fibers were coated using an on‐line filament winding process with an elastomeric adduct crosslinkable and compatible with an epoxy matrix. The coating and modifications of the epoxy network were studied by dynamic mechanical measurements. Assuming that apparent activation energies of the secondary relaxation βe of the epoxy network and main relaxation αa of adduct are very different, it is possible at low frequencies to separate the two peaks. The composite material can be described as a three phase system: an epoxy network as matrix, carbon fibers, and a soft interlayer. The mechanical behavior of unidirectional composite materials studied by impact and bending tests is strongly dependent on the presence and the thickness of the coating at the carbon fiber surface.
Fracture behavior of coated/uncoated graphite‐epoxy composites
Authors: Joseph R. , Bell J. P. , Rhee H.
Published: December 2004

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

End‐notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (GIC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (GIIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (KIC) of composites made with commercially treated fibers was also evaluated, using double side‐notched specimens.
Crack propagation modes in fiber and particulate composites in the microstructure
Authors: Theocaris P. S.
Published: December 2004

The influence of the hard or soft inclusions and the mesophase layers in either a soft‐hard‐soft or hard‐soft‐hard combination of biphase plates submitted to dynamic tensile loads on the fracture mode and bifurcation process in both phases was investigated in this paper. It was assumed that the soft or hard matrix is infolding the hard or soft inclusion of the plate, so that the plate constitutes a meridional section of the representative volume element of a unidirectional fiber composite, or a principal section of a particulate. The influence of the mechanical properties of either phase on the crack propagation velocity and the initiation of crack bifurcation was studied by using high‐speed photography and dynamic caustics. The results showed that the propagating crack tended to bifurcate either in the brittle or in the mesophase layer under certain conditions of propagation velocity. It was shown that bifurcation of a propagating crack depends on the elastic moduli and Poisson's ratios of the phases, as well as on the extent of the mesophase layer, which depended on the adhesion quality of phases.
Fluid sorption characterization of PEEK matrices and composites
Authors: Stober Eric J. , Seferis James C.
Published: December 2004

Neat poly(ether‐ether‐ketone) (PEEK) and carbon fiber reinforced PEEK (APC‐2) specimens were prepared using a variety of cooling rates to achieve a range of crystallinities. Amorphous specimens were exposed to a variety of fluids to determine the penetrant types which are able to strongly influence the material. This allowed the estimation of the solubility parameter and hydrogen bonding index for PEEK to be 9.5 and 3.1, respectively. Methylene chloride was used to investigate the kinetics of penetrant sorption. The data demonstrated Case II behavior, with the initial crystallinity having a pronounced effect on both the kinetic and equilibrium data. Accordingly, a model was proposed capable of describing the sorption level and penetration depth as a function of time given the sample crystallinity and sorption temperature. With Case II behavior there was no difference in the sorption kinetics of neat and fiber reinforced PEEK. Finally, the dynamic mechanical properties measured during sorption were found to be dependent on the sorption process.
Morphology and rheological properties of polypropylene‐linear low density polyethylene blends
Authors: Levij M. , Maurer F. H. J.
Published: December 2004

The dynamic shear viscosity and the morphology of polypropylene homopolymer and copolymer blended with linear low density polyethylene are studied. A maximum in the dynamic shear viscosity vs. blend composition is reported for the polypropylene copolymer, linear low density polyethylene system. The increasing dynamic shear viscosity is in accordance with the occurrence of a morphology of polyethylene inclusions in rubber surrounded by a polypropylene matrix. Comparing calculations of the dynamic shear viscosities—based on a shell model with interlayer—and experimental results supports this view.
A tensile flow stress model for oriented polypropylene
Authors: Tate K. R. , Perrin A. R. , Woodhams R. T.
Published: December 2004

Many solid‐phase processing and forming operations for polymers require tensile stretching forces to produce flow. To make forming operations practical, a knowledge of the flow stress of the polymer is required. This paper presents a simple formulation for predicting the flow stress of polypropylene In the oriented direction as a function of the controlling parameters, which are strain rate, temperature, and deformation ratio. It will be shown that the experimental flow stress data may be formulated in a way that is similar to the constitutive laws for metals. Equations for metals relating flow stress Lo strain rate, flow stress to strain, and flow stress to temperature are compared with an equivalent formulation for oriented polypropylene. The experimental conditions, chosen to develop the constitutive equations, reflect practical forming conditions, The deformation ratios (i.e., strains) were varied from 6 to 14. The strain rates imposed were between 10 and 1000% per min. Most of the tests were conducted in the temperature range 150 to 160°C, although a few were conducted at 130°C.
A study on the reactive extrusion process of polyurethane
Authors: Hyun M. E. , Kim S. C.
Published: December 2004

An engineering analysis of the reactive extrusion process of a thermoplastic polyurethane was made through numerical simulation and actual experiment. The reactants used in this system were 4,4′diphenylmethane diisocyanate, polycaprolactone diol (M.W., 824), and 1,4‐bu‐tanediol with equivalent weight ratio of 2:1:1. As a catalyst, dibutyltin dilaurate was used. The reaction kinetics and the viscosity function were obtained through experiments, and the mathematical model which includes the conservation equations of mass, momentum, energy, and chemical species was solved numerically to obtain the velocity, concentration, temperature, viscosity, and pressure profiles. The actual experiments were performed in the laboratory scale extruder to compare the experimental results with those of the numerical simulation.
Interpenetrating polymer network from blocked isocyanates. I. Structure and properties of polyurethane‐urea polyvinyl simultaneous interpenetrating networks
Authors: Michaud Philippe , Camberlin Yves , Mai Christian
Published: December 2004

A series of polyurethane‐urea/polyvinyl simultaneous interpenetrating polymer networks (SINs) were prepared starting from a mixture of isocyanate prepolymer blocked with N‐(1‐1′‐dimethyl‐3‐cxobutyl) acrylamide oxime, chain extender, vinyl monomers, and catalysts. Their physical properties and morphology were investigated using differential scanning calorimetry, dynamic mechanical measurements, and small‐angle X‐ray scattering. The polyurethane‐urea networks examined were two‐phase in nature. The vinyl network was formed with diacetone acrylamide oxime, trimethylolpropane trimethacrylate, and N‐vinyl‐pyrrolidone. Calorimetric analyses revealed that the polyether soft segment phase separated within the SINs. At higher temperature, dynamic mechanical measurements demonstrated the presence of only one glass transition temperature (Tg) intermediate in temperature to the Tg of the vinyl network and the Tg of the urethane hard phase. This is indicative of chain entanglement (interpenetration) between the vinyl network and the polyurethane hard segments resulting in a two‐phase morphology. Small‐angle X‐ray scattering analyses provided measurements of diffuse phase boundary thickness, phase mixing, and domain size distribution. Appreciable interfacial thickness was not observed and thus phase mixing occurred within the phases. Domain size distribution indicated that high network constraints hindered the development of domains and limited the phase segregation.
Mechanical property enhancement of semicrystalline polymers—A review
Authors: Bigg D. M.
Published: December 2004

Processing plastics below their melting points has been shown to be an effective way to significantly enhance the mechanical, chemical, and physical properties of semi‐crystalline thermoplastics. A number of techniques have been developed that are capable of producing highly oriented fibers, films, and shapes. In general, these techniques can be classified as drawing, extrusion, arid rolling, with some very specific modifications having been made to each, that affects the performance of the process. Of particular interest is the rate of production, the range of thicknesses achievable, the uniformity of properties in the product, and the extent, if any, of biaxiality in the product. In recent years, the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules. As an alternate to these orientation processes, techniques have been developed which rely on strain Induced crystallization to enhance the modulus of molded parts and extrudates from a melt. This paper constitutes a review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting materials.
Interpenetrating polymer networks from castor oil based polyurethanes, XI
Authors: Patel Prashant , Suthar Bhikhu
Published: December 2004

Under different experimental conditions, various liquid polyurethanes (PU) were synthesized from castor oil and isophorone diisocyanate varying NCO/OH ratio. These polyurethanes were then subsequently interpenetrated with n‐butyl acrylate (nBA) monomer and ethylene glycol di‐methacrylate as crosslinker by radical polymerization using benzoyl peroxide as an initiator. This leads to the formation of novel PU/PnBA interpenetrating polymer networks (IPNs) by transfer molding. These IPNs were characterized by their resistance to chemical reagents, thermal behavior (TGA), mechanical properties, namely; tensile strength, Young's modulus, elongation at break (%) and hardness (Shore A). The morphology of the IPNs was studied by Scanning Electron Microscopy. The dielectric behavior was computed in terms of electrical conductivities, dielectric constant (ε′), loss tangent (tan δ) and dielectric loss (ε″).
Thermodynamic miscibility of polymer‐liquid crystal blends
Authors: Patwardhan Ashutosh A. , Belfiore Laurence A.
Published: December 2004

The thermodynamic phase behavior of two polymer‐liquid crystal blends was investigated in both the solid and molten states. One of the blends (p‐hexyloxybenzoic acid and poly[ethylene glycol]) contains a semi‐crystalline polymer. The second example (p‐pentyloxycinnamic acid and bisphenol‐A polycarbonate) contains a high‐impact‐resistant amorphous thermoplastic. Whereas, the former system is almost completely immiscible at ambient temperature, yet advantageous for applications in the microelectronics industry, the latter blend exhibits partial (concentration‐dependent) miscibility. Our multi‐technique assessment of miscibility/phase separation includes high‐resolution carbon‐13 solid state NMR spectroscopy, differential scanning calorimetry (DSC), and group‐contribution thermodynamics (Universal Quasi‐Chemical Functional‐Group Activity Coefficient formalism including a Free Volume correction for the small molecule activity, UNIFAC‐FV). Approximate temperature‐composition (equilibrium) phase diagrams are constructed for both blends in light of the results from NMR, DSC, and UNIFAC‐FV.
Molecular orientation in drawn smectic and crystalline isotactic polypropylene
Authors: De Candia F. , Russo R. , Vittoria V. , Iannelli P.
Published: December 2004

The drawing behavior of two polypropylene films of different structures was analyzed. The two films differ as a consequence of different quenching conditions. At low temperature, a biphasic smectic‐amorphous system was obtained, while quenching at 100°C produced a biphasic crystalline‐amorphous system. The drawing of samples was carried out at 110°C at which temperature the smectic phase is not stable and is transformed into the crystalline α‐form. The initial structure affects the drawing behavior and the properties of the drawn samples. The mechanical, optical, and X‐ray analyses clearly show that high molecular orientation is achieved at lower deformations in the initially smectic sample. In particular, the amorphous phase is highly oriented, inducing higher axial elastic modulus.
Application of a concept of distributed damage to creep induced buckling of high density polyethylene specimens
Authors: Cohen A. , Arends C. B.
Published: December 2004

In this work, a concept of distributed damage, including its inception and propagation, was applied to creep induced buckling of specimens prepared from high density polyethylene (HDPE). Using a kinetic relationship for damage accumulation, an integral equation for the front of the damage zone was derived. A time parameter associated with the inception of the damage front was obtained. The motion of the front was approximated for small times. Long time estimation was obtained using an assumption for a shape of the damage distribution. These results enabled us to review reported experimental results on creep induced buckling using a new insight into the relationship between applied load and time to buckle.
Thermal behavior, morphology, and some melt properties of blends of polycarbonate with poly(styrene‐co‐acrylonitrile) and poly(acrylonitrile‐butadiene‐styrene)
Authors: Kim W. N. , Burn C. M.
Published: December 2004

Blends of bisphenol‐A polycarbonate (PC) with poly‐ (styrene‐co‐acrylonitrile) (SAN) and poly (acrylonitrile‐butadiene‐styrene) (ABS) prepared by screw extrusion and solution‐casting were investigated by differential scanning calorimetry and scanning electron microscopy. From the measured glass‐transition temperatures (Tg) and specific heat increments (ΔCp) at the Tg, SAN appears to dissolve more in the PC‐rich phase than does PC in the SAN‐rich phase. Also, the decrease of Tg (PC) in PC/ABS blends is larger than in the PC/SAN blends. From the Tg behavior and the electron microscopy study, it is suggested that the compatibility increases more in the SAN‐rich compositions than in the PC‐rich compositions of the blends. In the study of extrudate swell of the PC/SAN blends and the PC/ABS blends, the maximum level of extrudate swell is reached at 0.5 weight fraction of PC for both blend systems. The Flory‐Huggins polymer‐polymer interaction parameter (χ12) between PC and SAN was calculated and found to be 0.034 ± 0.004. A similar value of χ for PC and SAN was found with the PC/ABS blends.
A thermodynamic base for the stress activated phase transition deformation model
Authors: Liu Tuomin , Harrison I. R.
Published: December 2004

The three essential factors of the Juska–Harrison stress activated phase transition (SAPT) deformation model are analyzed. Based on the concept of “mechanical melting”, a formula for the theoretical melting stress is derived from thermodynamics. A comparison of experimental and calculated results for a number of polymers shows that the strain energy is high enough to induce isothermal “mechanical melting” during extension, and the observed yield stress has the same order of magnitude as the theoretical melting stress.
Chlorinated high density polyethylene. II. Solid state structure
Authors: Chang B. H. , Dai J. W. , Siegmann A. , Hiltner A.
Published: December 2004

Chlorination of high density; polyethylene results in polymers which consist of unmodified methylene units and chlorinated methylene co‐units. The effect of the concentration and distribution of chlorinated units on the solid state structure has been examined by thermal, wide angle X‐ray diffraction and dynamic mechanical analysis. As the substitution becomes more random, the crystallinity, crystallite size, and crystalline perfection decrease for a given chlorine content. The chlorinated units are shown to be capable of co‐crystallizing, and the concentration of chlorine in the crystalline phase increases as the distribution is made more random. Concurrently, the chlorine concentration of the amorphous phase decreases. Segregation of chlorine into the amorphous regions is most efficient when the substitution is blocky.
Application of the parallel Avrami model to crystallization of poly(etheretherketone)
Authors: Cebe Peggy
Published: December 2004

We have reexamined the parallel Avrami model recently proposed by Velisaris and Seferis (1) to describe the non‐Isothermal crystallization of poly(etheretherketone), PEEK. We show that, based on considerations of morphology development, the crystallization process with the larger Avrami exponent has the higher melting point, whereas the process with the smaller Avrami exponent has the lower melting point. This assignment differs from that of Velisaris and Seferis. In addition, we have used the infinite crystal melting point, as required by crystallization theory, to determine the Avrami rate parameters for the two processes. With this revision of the parallel Avrami model, we have applied the model to non‐isothermal crystallization of APC‐2 PEEK composite. Under the assumption that the linear growth rate determines the Avrami rate parameter, both the transport activation energy, U, and the kinetic parameter, Kg, are found to compare favorably with the values previously determined from isothermal crystallization of neat resin PEEK.
Microstructure in injection molded samples of liquid crystalline poly(P‐hydroxy‐benzoic acid‐Co‐ethylene terephthalate)
Authors: Hedmark Per G. , Lopez J. Manuel Rego , Westdahl Marianne , Werner Per‐Erik , Jansson Jan‐Fredrik , Gedde Ulf W.
Published: December 2004

The microstructure of injection molded bars (2.9 and 5.8 mm thick) of thermotropic liquid crystalline poly(p‐hydroxy‐benzoic acid‐co‐ethylene terephthalate) has been studied by SEM on samples etched with n‐propylamine, SEM fractography, DSC, IR, ESCA, WAXS and polarized microscopy. The 2.9 mm bar consists of three different layers: a highly oriented surface skin, an oriented intermediate layer and a non‐oriented core. The 5.8 mm bar has a more complex microstructure and is composed of five different layers: a highly oriented surface skin, an oriented layer just beneath, a non‐oriented layer, another oriented layer and a non‐oriented core. The thicknesses of the different layers vary, significantly, with distance from the mold gate. The thickness of the core increases, significantly, with increasing distance from the mold gate at the expense of the oriented layers. The structure within the different morphological layers is not perfectly uniform. Tensile testing demonstrated the mechanical anisotropy of the surface material (a ratio of almost 20 between the longitudinal and transverse moduli) and the isotropy of the central core material.
A study of miscibility of blends of polybutadienes of varying microstructure
Authors: Shah Ketan , Min Kyonsuku , White James L.
Published: December 2004

The miscibility of various amorphous polybutadienes with mixed microstructures of 1,4 addition units (cis, 1,4 and trans 1,4) and 1,2 addition units have been investigated. The studies here involved optical transparency, differential scanning calorimetry, and small angle light scattering. It was found that a 90 percent (cis) 1, 4 addition polybutadiene was immiscible with high (91 percent) 1,2 addition polybutadiene. Reduction of the 1,2 content to 71 percent induced an upper critical solution temperature (UCST) with the cis 1,4 polymer. Polybutadienes with 50 percent and 10 percent 1,2 contents were miscible above the crystalline melting temperature of the cis 1,4 polybutadiene. Immiscibility of the 91 percent 1,2 addition polymer was also found with a 10 percent 1,2 polybutadiene. The latter polymer also exhibits an UCST with the 71 percent 1,2 polymer. The results are used to interpret the characteristics of blends of polybutadienes of varying microstructure.
Processing‐morphology relationships of compatibilized polyolefin/polyamide blends. Part I: The effect of an lonomer compatibilizer on blend morphology
Authors: Willis J. M. , Favis B. D.
Published: December 2004

The morphology of compatibilized polyolef in/polyamide blends was found to be significantly dependent on the concentration of an ionomer compatibilizer (polyethylene‐methacrylic acid‐isobutyl acrylate terpolymer) in the blend. For a dispersed phase content of 10% by weight, a maximum reduction in phase size was observed when only 0.5% by weight of ionomer was added to the blend, A more significant reduction of the dispersed phase size was observed when the minor phase was nylon, due to interactions which exist between the ionomer and the polyamide. These interactions have been confirmed by Fourier transform infrared spectroscopy. At high concentrations of the ionomer, flocculation of the nylon dispersed phase was observed. In comparison to one‐step mixing, blends prepared by two‐step or batch mixing were characterized by a smaller dispersed phase when nylon was the matrix, and a larger particle size when nylon was the minor phase. The results observed are explained in terms of a speculative model of the interactions occurring across the nylon‐polvolefin interface.
Rubber toughening of polystyrene through reactive blending
Authors: Fowler M. W. , Baker W. E.
Published: December 2004

Acrylonitrile‐butadiene rubber having carboxylic acid groups (XNBR) and polystyrene having oxazoline groups, were melt blended in a Rheomix mixer under optimized conditions, The ratio of rubber to polystyrene phase was kept constant at 1:4 by weight. The concentration of the reactive oxazoline groups in the polystyrene phase was varied by mixing polystyrene (PS) with a copolymer of styrene and vinyl oxazoline (OPS). A torque rise observed during blending was found to be related to the concentration of oxazoline‐carboxylic acid pairs. This torque rise, and independently measured increases in viscosity, both indicate inter‐polymer crosslinkihg. Scanning electron microscopy was used to observe the morphology of the blends. Improved rubber phase dispersion was observed with increasing oxazoline concentration. Instrumented impact strength measurements were made using an unnotched Charpy technique. The plastic yielding was then quantified with the use of a ductility ratio. The impact strengths and ductility of the reactive blends are found to be up to 73% greater than those of the corresponding non‐reactive blends. Increasing the OPS concentration beyond 5% results in decreasing impact strength, for as the compatibility increases, the rubber particle size decreases below an effective size for rubber toughening. Similar impact improvement is observed when the major PS phase is substituted with high impact polystyrene (HIPS) containing some OPS.
Reactive extrusion of polystyrene/polyethylene blends
Authors: van Ballegooie Peter , Rudin Alfred
Published: December 2004

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho‐vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter‐rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre‐treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.
Determination of the nature and content of antioxidant and antioxidant synergist in polyethylene and crosslinked polyethylene used in cables
Authors: Crine J.‐P. , Haridoss S. , Cole K. C.
Published: December 2004

It is shown that polyethylene and crossllnked polyethylene resins used for cable applications contain an antioxidant synergist in addition to an antioxidant. Their nature and content have been determined by a combination of ultraviolet and Fourier transform infrared spectroscopy and neutron activation analysis measurements. The results thus obtained suggest that part of the antioxidant compound is grafted to polymer chains during crosslinking.
Dielectric analysis of epoxy/amine resins using microwave cavity technique
Authors: Jow J. , Hawley M. C. , Finzel M. , Kern T.
Published: December 2004

Dielectric properties (permittivity and dielectric loss factor) of stoichiometric mixtures of DGEBA (diglycidylether of bisphenol A) epoxy (DER 332) and amine (diaminodiphenyl sulfone; DDS) as a function of temperature and extent of cure have been measured at a microwave frequency of 2.45 GHz. Permittivity and dielectric loss factor of this resin increase with increasing temperature and decrease with increasing extent of cure. Dielectric loss factor is more dependent on temperature in the early stages of cure but becomes less dependent on temperature as the cure proceeds. Dielectric loss data can be related to extent of cure in order to monitor the cure process. Online measurements of temperature‐ and cure‐dependent dielectric loss factor show three material structure stages and significant changes in dielectric loss factor during the microwave cure process. Dielectric Joss factor is also found to be the same for both thermal and microwave cured samples.
A process for the simultaneous oligomerization and copolymerization of ethylene
Authors: Benham E. A. , Smith P. D. , McDaniel M. P.
Published: December 2004

High density polyethylene becomes more flexible and tough by adding short branches onto the otherwise linear backbone. Commercially, this is achieved by adding 1‐butene or 1‐hexene comonomer to reactor and copolymerizing it with ethylene. A process has now been developed which uses low pressure to produce new forms of branched polyethylene without addition of comonomer to the reaction mixture.
Computer‐aided analysis of a linearly tapered coat‐hanger die
Authors: Liu Ta‐Jo , Hong Chin‐Nan , Chen Kun‐Chou
Published: December 2004

We describe the computer‐aided engineering analysis of a linearly tapered coat‐hanger die in this paper. The general governing equation for flow distribution inside the die was derived first. On the basis of this equation, we have developed the design formula for a die to deliver uniform flow. In addition, we have also examined the variations of lateral flow uniformities and residence time distributions of polymeric liquids under several different design and operating conditions: (1) using manifolds with non‐circular cross‐sections, (2) adjusting production widths, (3) delivering fluids with different viscosities, and (4) enlarging manifolds for practical production considerations.
On the role of coupling agents in zirconia‐polypropylene suspensions for ceramic injection molding
Authors: Hunt K. N. , Evans J. R. G. , Woodthorpe J.
Published: December 2004

The effect of titanate, zirconate, and zircoaluminate coupling agents on the viscosity of zirconia‐polypropylene injection molding blends was investigated. The zircoaluminate did not influence viscosity while the two former additives effected a considerable reduction. The titanate coupling agent also reduced the viscosity of the polymer in the absence of ceramic powder, and was more efficient in this respect, as a flow modifier than dioctyl phthalate. A comparable effect on the ceramic suspension was obtained by adding a species similar in molecular structure to the titanate coupling agent but without coupling ability.
Memory effects in polymers. II. Processing history vs. crystallization rate of nylon 6—observation of phenomenon and product behavior
Authors: Khanna Y. P. , Reimschuessel A. C. , Banerjie A. , Altman C.
Published: December 2004

The observation of a novel phenomenon is reported whereby the processing history of a nylon 6 leads to a memory effect which in turn affects its crystallization rate from the molten state. Differential scanning calorimetry (DSC) and optical microscopy are the primary techniques used to demonstrate that the melt‐crystallization behavior of nylon 6 can be controlled by processing variables. Characterization data is presented to show that obvious parameters such as molecular weight, impurities, monomer and oligomers, etc. are not responsible for the observed changes in crystallization behavior upon processing. It is shown that the mechanical properties and/or morphology of a nylon 6 article can depend upon the processing technique (e.g., compression or injection molding) as well as the processing history of the nylon 6 resin itself.
A study of bubble nucleation in a mixture of molten polymer and volatile liquid in a shear flow field
Authors: Han James H. , Han Chang Dae
Published: December 2004

Bubble nucleation in a mixture of volatile liquid and polymer melt under shear flow conditions was investigated, using a light scattering technique. In the study, a mixture of polystyrene and trichlorofluoromethane was extruded through a slit die having glass windows and bubble nucleation in the flow channel was observed optically. A He‐Ne laser was used to illuminate the nucleating and growing bubbles. The light flux scattered by the growing bubbles at a fixed angle was detected by a photomultiplier with the aid of a high‐voltage power supply. The bubble nucleating site in the flow channel was located using a computer controlled tracking system, which was designed to move the entire optical system automatically in the three dimensional space, and also had the ability to follow the software control command and cooperate with the data acquisition system. When the site of bubble nucleation was located, the coordinates of this site in the flow channel and the experimental conditions were automatically recorded on a floppy diskette by entering a software command. The pressure profile along the flow channel was measured by pressure transducers, with the aid of a microprocessor‐based pressure reading system. It has been found that the site of bubble nucleation varies with the position in the direction perpendicular to the flow direction, which is attributed to the nonuniform velocity and stress distributions in the slit flow channel. The present investigation suggests that bubble nucleation can be induced either by flow and/or shear stress; specifically, flow‐induced bubble nucleation is the dominant mechanism at positions near the center of the die opening, and shear‐induced bubble nucleation is the dominant mechanism at positions near the die wall. It should be mentioned that the bubble near the die wall may also be generated by cavitation brought about by the surface roughness of the wall and also by thermal fluctuations due to the heat transfer between the metal (die wall) and the mixture of polymer and volatile component. The present study indicates that bubble nucleation in a shear flow field can occur at an unsaturated condition. This is in contrast to bubble nucleation under static conditions, where supersaturation is necessary.
Laboratory simulation of space and salt water environmental effects on polymers
Authors: Garton Andrew , Henry Jacqueline L. , McLean Paul D. , Stevenson William T. K.
Published: December 2004

Most polymers are eroded rapidly (>0.1 μm/h) in the low earth orbit (LEO) environment when facing the direction of flight. The rate of erosion varies little with the polymer type, except for fluoropolymers and silicones. Methods for simulating such an environment are reviewed. Secondly, the oxidation lifetime of stabilized and unstabilized polyolefins can be reduced 50 to 90 percent, with a, high yield of carboxylic acid (i.e. chain scission) oxidation products, when thermal oxidation at 70 to 90°C takes place in 0.01 to 0.1 molar sodium chloride solutions, as compared to thermal oxidation in air. Both sets of observations illustrate the need for detailed mechanistic investigations before accelerated test procedures can be developed to predict material lifetime.
Effect of mixing history on phase morphology of a polyalloy and a polyblend
Authors: Plochocki A. P. , Dagli S. S. , Curry J. E. , Starita J.
Published: December 2004

This paper details some of the immediate findings for phase morphology formation and persistence in an industrial melt mixing of a polyblend/alloy (‘PB’/‘PBA’). Estimation of the minor phase domain size in a polyblend is feasible if the viscoelasticity functions, interfacial tension of the component‐polymers, and the mixing process shear stress level are available. Clusters of domains are formed in the mixer (following streamlines). During steady flow in capillaries the clusters are forming rings which result from the flow velocity profile. Quantitative description of the clusters requires an expansion of image analysis software to account for the interdomain spacing in the clusters, as well as for their pattern. The on‐line rheometry was found useful for monitoring coalescence and the effectiveness of the compatibilizer: higher “stiffness” of the PAB melt compared with that of PB shows up in measurements of complex viscosity and modulus. Further study is required, however, for correlating domain spacing and the real time rheometry data (esp. the relaxation spectrum plateau [13]). Finally, the study of phase morphology for the “model” polyblend provides an insight into the melt deformation history in an industrial mixer. It is expected that the distribution of domain sizes would correlate with the pass frequency in the mixing blocks [41], stress distribution in the extruder, and coalescence of the dispersed (“minor”) phase.
Sheet molding compound compression‐molding flow
Authors: Castro J. M. , Griffith R. M.
Published: December 2004

Most available descriptions of sheet molding compound (SMC) flow are based on a generalized Hele‐Shaw type model. These analyses have several deficiencies. SMC slip at the wall is neglected, and unrealistic rheological models are used. Consequently, molding pressures are incorrectly predicted but, nonetheless, the fill patterns for thin, large area charges typical of exterior automotive body panels are reasonably well predicted as is shown here by comparison with experiment. Recently, a model has been developed that allows for slip at the wall and assumes extensional resistance controls in the interior of the SMC. The model contains the Hele‐Shaw approximation as an extreme case. The predicted molding forces during fill are compared with experiment for some commercial moldings. A dimensionless group to predict when the Hele‐Shaw type models fail in predicting the charge shape is developed and its applicability demonstrated.
Molecular weight distributions of tetrafluoroethylene‐hexafluoropropylene copolymers
Authors: Tuminello W. H.
Published: December 2004

A new methodology has been developed to determine molecular weight distributions (MWD) from dynamic rheometry data. The present work extends and modifies previous results and illustrates that the MWDs of tetrafluoroethylenehexafluoropropylene copolymers (FEP) are broader than previously thought. The major change in methodology involves the relationship between a reduced form of the elastic shear modulus as a function of frequency, G′(ω), and the cumulative weight fraction as a function of molecular weight. The new method uses a square root versus the former linear relationship. Spectroscopic analysis of the end group concentration was used to determine the number‐average molecular weight. These data were used to reference the MWDs determined by dynamic rheometry and indicate that the molecular weights of these polymers are 20% lower than previously found.
Measurement of polymer viscoelastic response during an impact experiment
Authors: Nairn J. A.
Published: December 2004

Instrumented impact data on polymers typically show high frequency oscillations that decay in amplitude during the impact event. By undertaking a complete impact analysis including effects of inertial loading, external damping (friction), and internal damping (viscoelastic relaxations), we have been able to predict all the details of the high frequency oscillations. The most consistent analysis of impact data on Delrin® 100 polyacetal is one that ignores friction and attributes the decay of the high frequency oscillations to the effect of viscoelastic relaxations in the polymer. The impact analysis therefore allows us to extract viscoelastic relaxation information from Instrumented impact data. It is further suggested that this direct observation of viscoelastic relaxations during impact testing should make it possible to make a quantitative assessment of the role that viscoelastic relaxations play in influencing the impact toughness of polymers.
Fracture toughness of impact‐modified polymers based on the J‐integral
Authors: Narisawa I. , Takemori M. T.
Published: December 2004

The fracture toughness characterization of four impact‐modified polymers based on the J‐integral concept was studied. We have discovered that the use of the “crack blunting line” concept needs revision. Direct measurements of the crack growth can be made (as opposed to indirect readings from the fracture surface) that test the applicability of the crack blunting concept. Our results indicate that for rubber‐toughened polymers the use of the blunting line fails to specify properly the critical J‐integral value for crack initiation.
Stress development in plastic sheet extrusion
Authors: Chan T. W. David , Lee L. James
Published: December 2004

The development of flow‐induced stresses in extruded sheet made of polypropylene was analyzed. A theoretical model was developed to simulate velocity, temperature, and stress profiles for polymeric materials flowing inside a slit die. The output of this simulation was then used to compute temperature and stress profiles as the extrudate emerged from the die, cooled, and relaxed under no draw conditions. Simulated surface stresses and stress profile across the extruded sheet agreed well with the experimental data for the die temperature effect and the die gap effect at low draw ratios.
A semi‐empirical algorithm for flow balancing in multi‐cavity transfer molding
Authors: Manzione L. T. , Osinski J. S. , Poelzing G. W. , Crouthamel D. L. , Thierfelder W. G.
Published: December 2004

Multi‐cavity transfer molding is an important process step in several electronic and photonic technologies. In some applications, uniform filling of the cavities of the mold, or mold balancing, is required. A semi‐empirical flow model to predict mold filling patterns was developed. The algorithm is a one‐dimensional network flow simulation that uses experimental pressure drop data to determine the volumetric flow rate through the gates and runners. A comprehensive experimental program was undertaken to determine these hydraulic resistances for different flow rates and mold geometries. A theoretical treatment is also described to compute hydraulic resistance from gate geometry. Uniform gate resistances provide unbalanced filling and higher velocities in the cavities. Balanced filling can significantly reduce the molding compound velocity and the flow induced stresses, but imperfect balancing compromises the benefits. Experimental filling patterns were obtained for two sets of gates. The agreement between the model and the experiments was satisfactory, and the discrepancies were attributed to correctable phenomena.
The effects of blending small amounts of homopolystyrene on the mechanical properties of a low styrene content styrene‐butadiene‐styrene block copolymer
Authors: Flosenzier Linda S. , Rohlfing John H. , Schwark Alodia M. , Torkelson John M.
Published: December 2004

Tensile, cyclic, and tear properties were compared for several styrene‐butadiene‐styrene (SBS) triblock copolymers, KRATON D2104, D1101 and D1102, and blends of D2104 with monodisperse polystyrene of various molecular weights. D2104 is expected to have a morphology of polystyrene spheres in a polybutadiene continuous matrix. The mechanical properties of D2104 were compared to the properties of SBS materials which have higher styrene contents and exhibit cylindrical or lamellar morphologies. Blending the D2104 with polystyrene (molecular weights ranging from 2000 to 51,000) to 24 and 28 wt % total styrene content showed that the tensile strength obtained for a blend was dependent on the molecular weight of the polystyrene added. Cycle testing of the D2104‐polystyrene blends showed that with increasing polystyrene content the softening effect increases with increasing strain. This indicates that the degree of phase continuity of the polystyrene domains may be changing from a spherical morphology to a cylindrical morphology similar to that of pure SBS with 28 wt % styrene content. Tear test results for the blends were also observed to be similar to the results for pure SBS of the same total polystyrene content.
Characterization of polyester/polycarbonate blends by size exclusion chromatography and melt rheometry
Authors: Miller R. L. , Brooks R. V. , Briddell J. E.
Published: December 2004

A major obstacle to the study of polymer blends has been the lack of a convenient technique for measurement of molecular weight. Melt rheometry, while giving useful information related to processing and end‐use performance, is incapable of providing detailed information on the individual components. This work describes the use of size exclusion chromatography (SEC) to study the molecular‐weight distributions of polycarbonates and aromatic polyesters in blends of the two. SEC of the polycarbonate is achieved in a solvent which dissolves the polycarbonate, but not the polyester, while SEC is performed in a solvent which dissolves both components, but using selective detection. Thus, SEC is used to examine the individual components of the blend, while rheometry can be used to study the blend as a whole. This combination of techniques has been successfully used to analyze the effect of moisture, processing conditions, and recycling on blend properties.
On gradual dosage of the initiator in the suspension polymerization of vinyl chloride
Authors: Mrázek Zdeněk , Lukáš Rudolf , Ševčík Stanislav
Published: December 2004

Initiator dosage in the solid phase during the suspension polymerization of vinyl chloride has been investigated with the use of a special apparatus developed for this purpose. Results arc reported on a series of polymerizations in which the initiator was divided in various ratios between the starting and additional quantities, added either in one dose or repeatedly to the reaction mixture at various reaction times. Discussed is the kinetic course of polymerization and the effect of dosage on the rate of reaction heat release. It is found for the system used that a suitable dosage regime allows the total amount of the initiator to be reduced by as much as 15 percent, while the yield and the reaction time corresponding to the standard polymerization procedure remain unchanged.
Dynamics of a cascade of two continuous stirred tank polymerization reactors with a binary initiator mixture
Authors: Kim Kee Jeong , Choi Kyu Yong , Alexander James C.
Published: December 2004

The dynamic behavior of two continuous stirred tank reactors in series has been investigated for free radical solution polymerization of styrene with a binary mixture of two initiators having different thermal decomposition activities. For a wide range of initiator feed composition, both reactors exhibit quite complex nonlinear steady state and transient behavior. When the reactor residence time is used as a bifurcation parameter, the second reactor can have up to five steady states. For certain range of reactor operating conditions, bifurcations to various types of periodic solutions have been observed, such as Hopf bifurcation, isolas, period doubling, period‐doubling cascade, and homoclinics. The effects of other reactor variables, such as total initiator concentration, coolant temperature, and reactor volume ratio on the reactor dynamics, are illustrated to show the complex dynamic behavior of the two‐reactor system catalyzed by a mixture of t‐butyl perbenzoate and benzoyl peroxide.
Viscosity buildup in condensation reactions: Reaction conditions and reactor size effects
Authors: Dairanieh I. S.
Published: December 2004

The viscosity of sulfonated melamine‐formaldehyde resins prepared in batch receptors of different sizes is shown to be a function of the reaction time, temperature, and pH. A formula relating these variables to viscosity buildup is presented. It shows that the pH is more influential than the temperature in increasing viscosity. The reactor mixing patterns are also shown to have a profound influence on resin viscosity. The agitator geometry, and not its tip speed, was found to affect considerably the viscosity buildup. Implications of these observations on the scale‐up of condensation reactions are discussed.
Numerical prediction of fiber orientation in injection molding
Authors: De Frahan H. Henry , Verleye V. , Dupret F. , Crochet M. J.
Published: December 2004

We develop a numerical method for calculating fiber orientation in the midsurface of a molded part of small thickness. Two‐dimensional fiber orientation is predicted on the basis of either Jeffery's equation or a constitutive equation for the orientation tensor. The calculation is fully transient; it is performed on a time‐dependent flow domain. The method is based on finite elements. Updated finite element meshes are generated at every instant of filling and allow one to perform an accurate calculation of the orientation even along the boundary of the flow domain. The method is applied to several examples in plane and three‐dimensional geometries.