bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface degradation processes and durability
Authors: Kaelble D. H.
Published: December 2004

This paper discusses a recently developed surface energetics criterion for adhesive bonding and fracture and its applications in such diverse areas as structural adhesive bonding, fiber reinforced composites, biomaterials development, and lithographic printing. The theoretical relations describe systematic methods for the surface energy analysis of solid adhesive and adherend surfaces. The surface tension properties for the adhesive and adherend can then be introduced into a modified Griffith fracture mechanics relation to obtain predictions of bond strength under varied conditions of liquid or gas phase immersion such as water and dry air.
Linear dynamic mechanical properties of an SBS block copolymer
Authors: Gouinlock Edward V. , Porter Roger S.
Published: December 2004

Dynamic viscosity and elastic modulus for a low molecular weight styrene‐butadiene‐styrene (SBS) block copolymer ate measured as a function of temperature (80‐170°C) and frequency using the eccentric rotating disc geometry. These linear properties are superimposed to yield master curves each of which exhibits two branches below different (critical) reduced frequencies. At lower temperatures, the non‐Newtonian behavior characteristic of SBS block copolymers is observed. In contrast, Newtonian response occurs at higher temperatures. As a consequence, plots of the viscoelastic properties vs temperature exhibit discontinuities below the critical frequencies, reflecting a narrow transition at about 142°C. Above this temperature, it is inferred, consistent with the equality of dynamic and steady state viscosities, that the polystyrene (S) blocks, existent in dispersed domains at low temperatures, exceed a critical degree of compatibility with the continuous polybutadiene phase. The activation energies indicate that the S blocks affect the temperature dependence of the dynamic properties in proportion to their presence in an interphase which is assumed to continuously grow in size as temperature is raised to the transition temperature. Below the critical reduced frequencies, it is inferred that S domain disruption may increasingly occur in conjunction with the observed property enhancement due to these domains, relative to the miscible blocks, as reduced frequency is lowered. However, above these frequencies, the presence of frequency‐temperature superposition implies that the S domains and the miscible blocks are equivalent in their effects on properties. At still higher reduced frequencies, the domains present at the low temperatures studied are assumed to remain intact, but plateau behavior similar to the response characteristic of homopolymers is observed.
Deformation behavior of an S‐B‐S copolymer
Authors: Odell J. A. , Keller A.
Published: December 2004

In accordance with previous studies, ‘single crystal’ tyr samples were prepared from the polystyrene‐polybutadien‐ polystyrene (S‐B‐S) three block copolymer Kraton 102 consist ing of a hexagonally packed parallel array of glassy S cylinder within a rubbery B matrix. Following earlier investigations o the pronounced anisotropy of the modulus, the actual deformation mechanism is examined in terms of the microstructures on straining perpendicular and parallel to the cylinder direction up to and beyond yielding. On perpendicular straining, a one to‐one relation is observed between ‘lattice’ and sample stray up to about 10 percent, coupled with complete recovery. For higher strains, the deformation becomes increasingly irreversible dependent on the time of stressing, a behavior which is found to be caused by cracks forming along crys tallographically defined directions of the hexagonal macrolai tice. On parallel straining, the stress‐strain curves display yield behavior at ∼3 percent strain, the yielded material be coming more compliant even at small strains on repeated test ing. However, on storage, the sample rehardens, a proces accelerated by heat treatment. This behavior is explained in terms of a breaking up and reformation of the cylinders and is supported by the subsequent experiments. These includ measurement of birefringence, which in the reversible small strain region corresponds to expectations from uniform strain in both S and B phases, but which beyond the yielded region displays behavior such as expected from deformation of the B phase alone. The postulated break‐up of cylinders on yielding is directly confirmed by electron microscopy on Iongitudinal sections thin enough to contain a single layer of cylinders. The yield behavior itself is treated theoretically using the composite mechanics approach. Two treatments are applied, the trad itional shear lag theory and a new random rod breaking theory In the latter case, in particular, very good agreement with experiment is found in that both the observed stress to yield and the electronmicroscopically seen fractured rod length in the yielded product are predicted.
Small angle X‐ray scattering from block polymers. II. The bulk state
Authors: Legrand A. D. , Vitale G. G. , Legrand D. G.
Published: December 2004

The basic theory of X‐ray scattering is applied to various hypothetical models for the bulk state of block polymers in order to explain the angular dependent scattering. The intensity of scattering is calculated for a rnicellar model, a zone model, and a molecular dumbbell model. The molecular dumbbell model, in contrast to the micellar and zone models, assumes that a block copolymer containing domains may be treated as one giant molecule and that, therefore, the locations of the domains are not random but are governed by the statistics of the segments which interconnect them. Experimental and calculated scattering curves are compared for several different types of block polymers.
Pulsed nuclear magnetic resonance for studying phase separation in block and segmented copolymers
Authors: Assink R. A. , Wilkes G. L.
Published: December 2004

Pulsed nuclear magnetic resonance measurements have shown that segmented polyurethanes as well as block copolymers segregate into domains with distinct mobilities. The usefulness of this technique for investigating the importance of the domain interface and for studying the mixing/ demixing of domains has been demonstrated. By examining the percent rigid material as a function of temperature, a polystyrene/butadiene block copolymer showed little evidence of domain interface effects, while in a series of segmented polyurethanes, the interface was seen to be important. The domains of a polyester soft segment and diphenylmethane diisocyanate hard segment polyurethane were mixed by annealing at 170°C. Examination of the demixing process as a function of storage temperature enabled an activation energy for domain formation of 36 ± 5 kcal/mole to be calculated. In a series of polyurethanes with varying amounts of hard segments, the material with the least amount of hard segments showed evidence of soft segment crystallinity. The mixing proces in this series was interpreted in terms of shifting correlation frequency distributions.
The influence of diblock copolymers on the structure and properties of polybutadiene‐polyisoprene blends
Authors: Ramos A. R. , Cohen R. E.
Published: December 2004

The structure and properties of a ternary polymer system comprised of 1, 4 polybutadiene, cis 1, 4 polyisoprene, and the corresponding 1, 4 polybutadiene/cis 1, 4 polyisoprene diblock copolymer have been investigated. Dynamic mechanical properties were measured as a function of frequency (3.5 to 110 Hz) and temperature (−135 to 40°C). Thermomechanical analysis and transmission electron microscopy provided additional information on the, phase relationships in the various specimens. The blends studied covered the entire triangular composition diagram; both slow solvent evaporation and rapid spin casting techniques were employed in the sample preparation. Results indicate that the BI diblock is a single phase material whereas binary blends of the two homopolymers are two‐phase in nature. Ternary blends of the two homopolymers with diblock and binary blends of a single homopolymer with diblock can be one or two phase materials depending on the sample composition and the ratio of B to I units in the diblock. All evidence From the dynamic, thermomechanical and microscopic experiments is used to elucidate the influence of the diblock in these polymer blends.
Chiorosulfonated block copolymers
Authors: Rogers C. E. , Covitch M. J.
Published: December 2004

Rubber‐phase chlorosulforiated polystyrene‐poly‐(ethylene‐butene‐1)‐polystyrene block copolymers were prepared by reaction of the block copolymer in solution with SO2 and C12. Sample compositions ranged up to 7 weight percent sulfur and 29 weight percent chlorine contents as determined by X‐ray fluorescence and infrared spectroscopy. A series of chlorosulfonated derivatives of an analogue of the elastomeric midblock were prepared and analyzed in similar fashion. A comparison of dynamic mechanical and dielectric behavior of solvent cast films of the block copolymer and midblock polymer materials indicates the existence of sulfonyl chloride dipole‐dipole complexes in the solid state. Further evidence for the presence of such aggregates was obtained from analysis by Fourier‐transform infrared spectroscopy. It appears that polystyrene domains in the block copolymer materials hinder this aggregation up to moderate concentrations of the sulfonyl chloride group as compared with the relatively unrestrained aggregate formation in the analogue midblock materials. At high levels of substitution, the formation of dipole aggregates disrupts the integrity of the polystyrene domain structure in the block copolymer materials, resulting in a reduction in mechanical strength.
Effects of coupling agents on the mechanical and rheologica properties and mica‐reinforced polypropylene
Authors: Boaira M. S. , Chaffey C. E.
Published: December 2004

Dimethylaminoethyl methacrylate (DMAEMA) was investigated as a prospective coupling agent for mica‐reinforced polypropylene. Composites prepared with the widely‐used silane coupling agent, N‐(4‐vinylphenyl) methyl‐N′‐(3‐trimethoxysilylpropyl)ethylenediamine monohydroehloride (Z‐6032), were compared with the amino‐coupled composite. Improvements in the flexural properties at room temperature were observed with the two coupling agents: a 22 percent increase in the strength with the silane compared to a. 16 percent increase with DMAEMA. Cone‐and‐plate viscometry at 220°C showed that the addition of coupling agents greatly, reduces the viscosity of the composite: a 50 percent decease was obtained with the silane‐treated composite and a 20 percent decrease with DMAEMA.
Evaluation of processing factors on turning of thermoplastics
Authors: Roy P. K. , Basu S. K.
Published: December 2004

Experiments were carried out to study the effects of cutting speed, feed, depth‐of‐cut and tool‐nose‐radius on the cutting force and surface roughness produced during turning of the thermoplastics Nylon‐6 and Teflon. Generalized equations for the cutting force and surface roughness in terms of processing factors have been established using the statistical technique of multiple regression analysis. The equations have been tested for acceptability by the F‐test and the degree of significance of various factors has been assessed by the t‐test.
Correlations for zero‐shear and shear‐rate dependent viscosity of polymeric solutions
Authors: Chitrangad B. , Osmers H. R. , Middleman S.
Published: December 2004

Solution viscosity is known to be sensitive to the nature of solvent and the polymer concentration. The magnitude of such effects, however, is not quantitatively understood. Correlations to predict zero‐shear and shear‐rate dependent viscosity of polymer solutions from polymer solution parameters are presented. Polymer domain volume is found to be the controlling parameter for the zero‐shear viscosity of dilute polymer solutions, that is solutions with insignificant entanglements. At higher concentrations, where polymer‐polymer interactions become significant, it is found that, except for the magnitude of the solvent viscosity, the nature of the solvent is of no consequence. In this region zero‐shear viscosity is correlated as a function of the parameter cM5/8, where C and M represent concentration and molecular weight, respectively. A relaxation time such as Bueche's time constant satisfactorily represents the solvent effects on the non‐Newtonian behavior of polymer solutions by incorporating the measured zero‐shear and solvent viscosities.
Flow and heat transfer in the nozzle of an injection molding machine
Authors: Nunn R. E. , Fenner R. T.
Published: December 2004

When a polymer melt is forced through the nozzle of an injection molding machine, the material temperature increases significantly. This increase, which is very difficult to measure, is not uniform and local temperature peaks may cause thermal degradation. A method is described for the analysis of timedependent heat transfer and flow in such nozzles. Melts are treated as being inelastic but with viscosities which are nonNewtonian and dependent on both temperature and pressure. Distributions of velocity, temperature and pressure are obtained with the aid of a finite difference method for solving the differential conservation equations' of continuum mechanics. Typical results show that the times required to reach steady flow conditions are small compared with total injection times. Heat transfer is predominantly convective, and flows leaving injection nozzles and entering molds are very far from being thermally fully‐developed.
Effect of cross‐linking on hydrostatic creep of epoxy
Authors: Findley W. N. , Reed R. M.
Published: December 2004

Samples of epoxy having three different degrees of crosslinking were subjected to several constant values of hydrostatic pressure ranging from 1000 psi to 80 ksi. Each period of constant pressure was followed by a period at atmospheric pressure. A continuing decrease in volume (creep), as measured by axial strain at constant pressure, was observed for pressures of 10 ksi and greater. The creep strain was recovered immediately upon pressure removal. Reapplication of pressure after a short period at atmospheric pressure resulted in the same creep behavior as that resulting from the first pressure. The least cross‐linked epoxy had the smallest creep rate and the smallest compressibility. These observations are consistent with the view that the leapt cross‐linked epoxy would be the most compact and have the least voids at points of cross‐linking.
Experimental characterization of the alignment of short fibers during flow
Authors: Murty Karra N. , Modlen G. F.
Published: December 2004

An experimental approach has been made to investigate and characterize the alignment of short fibers contained in a suspension, during flow of the suspension through a convergent channel. Flow patterns have been obtained and analyzed for suspensions of various fiber concentrations. The influence of parameters such as fiber length, volume fraction and viscosity of the carrier medium on the degree of fiber alignment, has been examined. In order to minimize jamming, the viscosity of the carrier medium must be larger than a certain critical viscosity that is dependent on fiber length and volume fraction.
Correlation of normal stresses in polystyrene melts and its implications
Authors: Oda Kunio , White James L , Clark Edward S.
Published: December 2004

It is found that the principal normal stress difference, N1, in commercial polystyrene melts is a unique function of shear stress σ12, independent of temperature and molecular weight, An empirical expression representing this relationship is developed. The functional dependence reported does not represent data for narrow molecular weight distribution polystyrenes, generally significantly overpredicting N1 values. The basis for this behavior is discussed. The implications of the N1 − σ12 relationship to some rheological and processing problems are described.
Properties of a polyamide thermoplastic based on 2,2‐bis‐(4‐aminocyclohexyl)propane
Authors: Hill H. Wayne , Campbell Robert W. , Shuk Robert S.
Published: December 2004

The structure and properties of an unusual new polyamide copolymer derived from 2,2‐bis‐(4‐aminoeyclohexyl)propane and a 60/40 molar mixture of azelaic and adipic acids are described. The alicyclic diamine structure, with its cyclohexyl rings and central gem‐dimethyl group, contribute to chain stiffness and amorphous character in the polyamide, and sets it apart from more common polyamides (e.g., nylon 6–6) with their relatively flexible polymer chains, low glass transition temperatures and high levels of crystallinity. The particular combination of dicarboxylic acids employed yields a resin with a high glass transition temperature (185°C). This amorphous, colorless material is exceptionally transparent, with a high luminous transmission (92 percent) and low haze (0.5 percent). The polymer is tough and resistant to scratching and abrasion and to attack by chemicals and solvents. Its high glass transition temperature leads to a high heat deflection temperature (160°C) and excellent retention of its mechanical properties at elevated temperatures. It is an atypical nylon in that its dimensions, mechanical properties and electrical properties are relatively unaffected by changing moisture content.
The effect of glass‐resin interface strength on the impact strength of fiber reinforced plastics
Authors: Yeung Peter , Broutman Lawrence J.
Published: December 2004

The effect of glass‐resin interface strength on the impact energy of glass fabric (style 181) reinforced epoxy and polyester laminates has been determined. The interface strength was altered by surface treatment of the fabrics with silane coupling agents and with a silicone fluid mold release and the interlaminar shear strength was determined as a means to evaluate the interface strength. An instrumented Charpy impact test was used on unnotehed specimens and thus both initiation and propagation energies could be determined as well as dynamic strength. It was found that the initiation energy for both polyester and epoxy laminates increased with increasing interlaminar shear strength, The propagation energy and thus the total energy for polyester laminates displays a minimum at a critical value of interlaminar shear strength (ILSS). Below this critical value, the total impact energy increases with decreasing shear strength and the dominant energy absorption mode appears to be delamination. Above the critical value, the impact energy increases with increasing values of ILSS and the fracture mode is predominantly one of fiber failure. In all cases, even with mold release applied, the shear strength of epoxy laminates was above this critical value and‐thus the total impact energy increases with Increasing values of ILSS. The maximum energy absorbed for the epoxy laminate and the polyester laminate is nearly identical. However, the maximum for the epoxy laminate occurs when the shear strength is maximized while for the polyester laminate the shear strength must be minimized. For the polyester laminate when delamination is predominant, it was found that the glass surface treatment affects the amount of delamination as opposed to the specific value of delamination fracture work.
Improving the crack resistance of bulk molding compounds and sheet molding compounds
Authors: McGarry E. J. , Rowe E. H. , Riew C. K.
Published: December 2004

Fiber‐reinforced plastics exhibit two types of mechanical failure: gross fracture and microcracking. Gross fracture involves both matrix and fiber failures. Principal resistance to crack propagation derives from partial decoupling of fibers and then stressing, remove finite volumes of them to fracture. Classical concepts of fracture mechanics can be applied to such composites, though modifications of methodology to treat anisotropy and other special effects are required. Microcracking occurs principally in the matrix phase and usually accompanies cyclic fatigue, drop impact, bending, or rapid cooling from molding temperatures. It lowers composite stiffness, environmental resistance and may reduce strength. Matrix resins require high fracture toughness to minimize or eliminate microcracking. This paper discusses cracking in bulk molding compounds and sheet molding compounds, complex materials containing high percentages of glass fibers and calcium carbonate filler. Microcracking can be greatly reduced by tire addition of small amounts of a rubber to the polyester matrix. Various tests such as impact, bending, acoustic emission and crack propagation demonstrate the improved toughness properties which result. No sacrifice of original strength characteristics occurs, and markedly improved resistance to damage has been noted with rubber modified epoxy and polyester matrix resins.
The use of coupling agents to enhance the performance of aramid reinforced composites
Authors: Vaughan D. J.
Published: December 2004

In view of the organic nature of aramid fiber and its ability to be combined with a number of polymer systems, fabric woven from that fiber has previously been used in an unfinished or scoured stale. However, this has resulted in a marked lack of adherence at the fiber‐resin interface that has considerably reduced compressive values in the composite; this is particularly evident when the composite is exposed to adverse aqueous environments. In order to overcome what appears to be the major deficiency in this fiber, a series of coupling agents has been developed which, when used in conjunction with a number of commercial resin systems, shows a marked improvement in interlaminar adhesion. The paper outlines the problem of using untreated fiber and establishes the area of responsibility for initial failure. It then shows how the correct use of coupling agents has overcome the interfacial adhesion problem and has enhanced the performance of aramid fiber reinforced composites.
Studies on multilayer film coextrusion II. Interfacial instability in flat film coextrusion
Authors: Han Chang Dae , Shetty R.
Published: December 2004

An experimental study was carried out to investigate the phenomenon of interfacial instability in multilayer flat‐film coextrusion. For the study, a sheet‐forming die with a feed block was used to coextrude three‐and five‐layer flat films. Polymers coextruded were: (a) low‐density polyethylene with polystyrene, and (b) high‐density polyethylene with polystyrene. It was observed that, for a given polymer system, there is a critical value of wall shear stress at which an irregular (i.e., unstable) interface between the layers sets in, giving rise to a pattern similar to that usually found in a wood panel. Once the instability sets in, the severity of interfacial instability is found to depend on both the total volumetric flow rate (hence wall shear stress) of the combined streams and the ratio of the individual layer thicknesses. An attempt is made to correlate the critical conditions for the onset of interfacial instability in terms of the layer thickness ratio, and the viscosity and elasticity ratios of the two polymers being coextruded.
Studies on multilayer film coextrusion III. The rheology of blown film coextrusion
Authors: Han Chang Dae , Shetty R.
Published: December 2004

Multilayer blown film coextrusion was studied, both experimentally and theoretically. For the experimental study, an annular die with a feed‐port system was designed and multilayer blown films were produced by rotating the inner mandrel with a one horsepower variable‐speed drive at speeds from nearly 2 to 6 rpm, and by inflating the tubular molten film with air. The die has 16 feed slots and melt pressure transducers are mounted along the axial direction of the outer wall of the annular flow channel. The transducers were used to determine the pressure gradient in the annular flow channel, which then permitted determination of the reduction in pressure drop when different combinations of two polymer systems were coextruded. Polymers used for b own film coextrusion were: (1) low‐density polyethylene with ethylene‐vinyl acetate; (2) low‐density polyethylene with high‐density polyethylene; (3) low‐density polyethylene with polypropylene; (4) high‐density polyethylene with ethylene‐vinyl acetate. For the theoretical study, stratified helical flow was analyzed using a power‐law non‐Newtonian model. A computational procedure was developed to predict the number of layers, layer thickness, and the volumetric flow rate as functions of certain processing variables (namely, the pressure drop in the die, and the angular speed of rotation of the inner mandrel of the die) and the rheological parameters of the individual polymers concerned. Comparison was made of the theoretical prediction of volumetric flow rate with experimental ones. Some representative results are presented of the theoretically predicted axial and angular velocity distributions, shear stress profiles, and shear rate profiles.
Simultaneous interpenetrating networks based on castor oil polyesters and polystyrene
Authors: Devia‐Manjarres N. , Manson J. A. , Sperling L. H. , Conde A.
Published: December 2004

Simultaneous interpenetrating networks (SIN's) have been synthesized by simultaneous polymerization of a rubbery polymer based on castor oil and a second plastic forming monomer plus initiator and crosslinking agent. According to the overall composition and synthetic details, SIN's of elastomeric, leathery, or plastic behavior have been obtained. Polymers employed were the crosslinked polyester from castor oil and sebacyl chloride (a castor oil derivative) and polystyrene crosslinked with 1 percent divinyl benzene, simultaneously polymerized. Electron microscopy revealed a complex two phase morphology strongly depending on the relative gelation times of the two polymers, the polymer gelling first becoming the more continuous phase. Stress‐strain curves show a SIN plastic with a well developed yield point, as well us highly toughened elastomers. Both the plastic and the elastomeric SIN's are tougher than the corresponding homopolymers. Modulus‐temperature curves show a glass transition temperature around −60°C for the elastomer component, and +100°C for the polystyrene in the SIN's.
Weathering of fiber‐reinforced epoxy composites
Authors: Roylance David , Roylance Margaret
Published: December 2004

Unless suitably stabilized and coated, fiber‐reinforced composites are subject to photoinitiated oxidation which results in a degradation of the resin surface and an eventual reduction in the composite's mechanical properties. The photo‐oxidation, which is initiated by UV‐absorbing oxidation products created during cure, is relatively amenable to detection by techniques of analytical chemistry. Mechanical test results, which reflect a wide range of material properties, are more subject to variability and misinterpretation.
Twin screw reinforced plastics compounding
Authors: Todd D. B. , Baumann D. K.
Published: December 2004

Co‐rotating, self‐wiping twin‐screw equipment has been developed which incorporates fiber glass or fillers into various plastics to form compounds with superior mechanical properties. Fiber glass bundles are folded into the plastic melt in such a fashion that each glass strand is wetted out with minimum breakage of the strand. The intensity of compounding is controlled externally to condition the basic polymer for optimum filler incorporation. The external control permits compounding a wide variety of plastics over a range of throughputs. The degree of mixing can be varied while the machine is in operation. The fiber resin blend passes through an independently controlled extruder for pelletizing with a hot die face cutter. Either air or water quench systems can be used for cooling the pellets. The gentle handling of the fiber resin blend through compounding and extrusion not only minimizes glass breakage, but also minimizes wear on the equipment. Retention of glass fiber length and good strand bonding impart superior properties to the fiber resin product.
Curing and heat transfer in polyurethane reaction molding
Authors: Broyer Ephraim , Macosko Christopher W. , Critchfield Frank E. , Lawler Lee F.
Published: December 2004

Temperature measurements were made on the adiabatic polymerization of three urethane systems; two casting formulations, one thermoplastic and the other thermosetting, and a commercial reaction injection molding (RIM) formulation with a 10 second gel time. The data were found to fit a simple nth order overall kinetic expression. These kinetic and heat of reaction results were used to model heat transfer in a 3.8 cm diameter cylinder with an isothermal wall. Experimental temperature profiles for the two casting urethanes were in good agreement with predictions. The kinetic data on the RIM material was used to model temperature profiles1 in 3 and 6 mm thick plaque molds. Experimental measurements of temperature near the mold center agreed with the model. Temperatures measured near the wall were higher due to failure of the isothermal wall assumption.
A method to evaluate the effect of compounding technology on the stress transfer interface in short fiber reinforced thermoplastics
Authors: McNally D. , Freed W. T. , Shaner J. R. , Sell W.
Published: December 2004

The strength and impact resistance of short fiber reinforced thermoplastics are greatly affected by the nature of the stress transfer interface which in turn is influenced by physico‐chemical and geometric factors. The geometric factors are controlled by the compounding technology used to manufacture the composite. This paper describes the use of several compounding technologies and a method used to infer the effectiveness of those technologies from studies of molded part mechanical properties and glass fiber length distributions. Resin systems studied were acetal copolymer, polybutylene terephalate, and nylon 6,6.
Wirecoating die design using finite element methods
Authors: Caswell Bruce , Tanner Roger I.
Published: December 2004

The design of wire‐coating dies is described using finite element numerical analysis as a guide. Finite elements are able to accommodate awkward geometries and non‐Newtonian fluid properties in a realistic manner, and produce streamline and stress patterns within the die. Two basic die geometries are examined and a new design which eliminates recirculation within the die is proposed.
A rigid poly(vinyl chloride) compound with improved combustion characteristics
Authors: Hartitz J. E. , Yount R. A.
Published: December 2004

By means of compounding, we have developed a rigid poly(vinyl chloride) (PVC) formulation with improved overall combustion properties. Newly developed analytical methods indicate a considerable reduction in the level of gases released during combustion, in addition to excellent flammability characteristics and low visible smoke emission levels. The analytical methods discussed are expected to aid in the selection of a feasible protocol for biological testing and in the interpretation of results obtained from such testing. The under‐lying compounding technology is currently restricted to normal impact rigid PVC cube compounds but expected to be expanded into high impact PVC, flexible PVC, PVC powder compounds and cellular PVC.
Draw resonance involving rheological transitions
Authors: Matsumoto Takayoshi , Bogue Donald C.
Published: December 2004

The periodic diameter variations in melt spinning known as draw resonance have been extensively studied, both theoretically and experimentally. The theory has evolved from analyses for isothermal, Newtonian spinning in which the critical draw ratio was found to be 20.21. Compared with this, recent theories have shown that elasticity and cooling are stabilizing (with certain qualifications on the range of variables) and that non‐linear rheological response is destabilizing. The present work presents systematic data on two polymers, one that is always amorphous (polystyrene) and one that solidifies into a semi‐crystalline state (polypropylene). Isothermal and non‐isothermal data are available for the former; non‐isothermal data, for the latter. The melt temperature, the cooling environment, the die length, the spinning length, the mass flow rate and the draw ratio were varied. Certain observations cannot be explained within the existing theoretical framework, specifically the destabilizing effect of certain cooling histories in the case of polystyrene and the destabilizing effect of short dies, presumably a die swell effect, in the case of polypropylene. Very highly oriented polystyrene can be produced under certain conditions when the fiber temperature is held above Tg.
Electropolymerization on graphite fibers
Authors: Subramanian R. V. , Jakubowski James J.
Published: December 2004

The electrodic polymerization on graphite fibers of a variety of monomers having different types of functional groups has been investigated. In addition to vinyl polymerization, some novel polymerizations of cyclic functional groups have been conducted under appropriate polymerization conditions. In many instances, the grafting of the surface polymer to the fiber has been confirmed. The stereochemical configuration of poly(methyl methacrylate) resulting from electropolymerization was measured, but conclusive evidence could not be obtained for the occurrence of stereo‐regulation in electrochemical polymerization on graphite fiber surface; Composite specimens were prepared by the incorporation of the coated fibers in an epoxy matrix. It was demonstrated that the effect of electropolymerization on the interfacial properties of the resulting composite was manifested in variations of the measured interlaminar shear and impact strengths of the composite specimens. The increase or decrease in interlaminar shear was accompanied by the usually observed reverse change in impact strength. In exception to this general trend, it was also indicated that the shear and impact strengths could simultaneously be increased. Implicit in these findings is the contribution of the electrochemically formed interlayer to one or more of the toughening mechanisms that are available to fiber reinforced composites. The potential value of interphase modification by electrochemical polymerization is thus clearly indicated.
Interfacial flow instability in multilayer coextrusion
Authors: Schrenk W. J. , Bradley N. L. , Alfrey T. , Maack H.
Published: December 2004

In coextrusion of multilayer film and sheet, one type of flow instability which can occur is a wavelike distortion of the interface under certain coextrusion conditions. Severe instability can cause intermixing of the layers, particularly in thin skin coextrusion. Observations have shown that the onset of instability is associated with a “critical interfacial shear stress”. This paper describes a mathematical model of non‐Newtonian multilayer flow which was used to correlate experimental observations.
Relative toxicity of the pyrolysis products from some thermoplastic and thermoset polymers
Authors: Kourtides Demetrius A. , Gilwee William J. , Hilado Carlos J.
Published: December 2004

Relative toxicity data on the pyrolysis products of a variety of thermoplastic and thermoset polymers are presented. The data are presented in terms of time to incapacitation and time to death with a fixed sample weight of 1.0 g, and in terms of the apparent lethal concentration required to produce 50 percent mortality within a fixed exposure period of 30 min.
Value recovery from polymer wastes by pyrolysis
Authors: Roy M. , Rollin A. L. , Schreiber H. P.
Published: December 2004

Pyrolysis of polymer wastes appears to be a suitable means of dealing with an increasingly important environmental problem. To provide background on the pyrolytic behavior of wastes, model mixtures of polyethylene and polystyrene have been pyrolyzed in various gas phases including nitrogen and carbon monoxide, at atmospheric and at reduced pressures and at temperatures from about 300–900°C. When the pyrolyzing temperature is attained by gradual heating, and when pyrolysis occurs at pressures in excess of about 200 torr, the process occurs as if each component were present alone—that is, no evidence for component interaction was noted. In these cases, the known mechanisms for pyrolysis of the pure polymers can be applied to the behavior of mixtures. Complicating effects due to interactions between the starting polymers, or among the pyrolysis products, were observed in low pressure pyrolysis (≲20 torr); further, it was shown that the balance of pyrolysis products depends on rates of attaining the pyrolyzing temperature, more rapid rates favoring the production of carbon‐rich solid residues of possible use as carbon blacks. More detailed understanding of pyrolytic processes in polymer mixtures is needed to permit selection of conditions producing the optimum balance of useful products.
Micromechanical analysis of a model for particulate composite materials with composite particles—survey of craze initiation
Authors: Riccò T. , Pavan A. , Danusso F.
Published: December 2004

Particulate‐filled materials consisting of a continuous matrix phase and a discontinuous filler phase made up of discrete heterogeneous particles are simulated by an elementary model consisting of a single spherical particle embedded in an infinite matrix, the particle being constituted by a spherical core within a concentric spherical shell. The specific case studied is one in which the particle core and matrix are of the same glassy polymer, and particle shell is a rubbery material. The distributions of six suggested craze initiation factors in the region surrounding the single particle are calculated when the material is subjected to a uniform uniaxial tension at infinity. Results indicate that the critical regions for craze formation are located either at the pole or at the equator of the particle (the polar axis being parallel to the applied tension), depending on the criterion considered and on the relative size of the glassy core in the particle.
Assessment of relative flammability and thermochemical properties of some thermoplastic materials
Authors: Kourtides Demetrius A. , Parker John A.
Published: December 2004

The thermochemical and flammability characteristics of some typical thermoplastic materials currently in use and others being considered for use in aircraft interiors are described. The properties studied included (a) thermal mechanical properties such as glass transition and melt temperature, (b) changes in polymer enthalpy by differential scanning calorimetry, (c) thermogravimetric analysis in an anaerobic and oxidative environment, (d) oxygen index, (e) smoke evolution, (f) relative toxicity of the volatile products of pyrolysis, and (g) selected physical properties. The generic polymers which were evaluated included: acrylonitrile‐butadiene‐styrene, bisphenol A polycarbonate, bisphenol fluorenone carbonate‐dimethylsiloxane block polymer, phenolphthalein‐bisphenol A polycarbonate, phenolphthalein polycarbonate, polyelher sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone; chlorinated poly vinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters including molding characteristics of some of the advanced polymers are described. Test results and relative rankings of some of the flam inability, smoke and toxicity properties are presented. Under these test conditions, some of the advanced polymers evaluated were significantly less flammable and toxic or equivalent to polymers in current use. A relationship of the anaerobic char yield of the polymers to their relative flammability properties is shown.
Solid state coextrusion: A new technique for ultradrawing thermoplastics illustrated with high density polyethylene
Authors: Griswold Phillip D. , Zachariades Anagnostis E. , Porte Roger S.
Published: December 2004

Ultraoriented films of high density polyethylene (HDPE) have been prepared in continuous lengths by a new method, solid state coextrusion, through conical dies of extrusion draw ratios up to 36. Preformed HDPE billets ∽7 cm long and ∽1 cm in diameter of duPont Alathon 7050R, Mw = 59,000, Mn = 19,900, were split longitudinally into halves and then one or more wafers of the same polymer were inserted between the two sheath halves. Thereafter, the whole assembly was extruded through a conical die of 20° included entrance angle in the absence of lubricant and at temperatures substantially below the melting range yielding continuous and transparent films. The physical and mechanical properties of the HDPE films so produced were evaluated and compared with the properties of the same polymer extruded through a slit die. The high melt transition, tensile modulus and transparency confirm the effectiveness of the new method in continuously attaining ultradrawn films.
Heat transfer to a plastic tape traveling over heated rolls
Authors: Brazinsky I. , Davis H. L.
Published: December 2004

Temperature was calculated as a function of lateral and axial position within a thin poly(ethylene terephthalate) (PET) tape traveling alternately over a heated roll and through air. The system consists of a pair of rolls which are internally heated and located in an oven. The centers of the rolls are ten inches apart and the tape makes eight wraps around the roll pair. Three sources of heat transfer to the tape are considered: convection and radiation from the heated rolls, convection from the air, and radiation from the hot oven walls. Calculations were carried out for oven wall temperatures of 100 and 1000°C, air temperatures of 100 and 205°C, and roll surface temperatures of 180 and 235°C. The computations generally indicate that after several wraps the temperature of the outside surface of the tape (i.e., the surface that does not contact the rolls) is essentially the same each time the tape leaves the roll. However, this temperature changes us the tape then travels through the adjacent, downstream air space. Although there is a temperature gradient across the tape, the temperature of the inside surface (i.e., the side that contacts the rolls) exhibits behavior similar to that of the outside surface.
Studies on wire coating extrusion. I. The rheology of wire coating extrusion
Authors: Han Chang Dae , Rao D.
Published: December 2004

Wire coating extrusion was studied, both experimentally and theoretically, using a pressure‐type die. For the experimental study, a wire coating apparatus of laboratory scale was constructed, consisting of a pay‐off device, extruder, cross‐head and pressure‐type die, cooling trough, and take‐up device. The materials used were low‐ and high‐density polyethylenes and thermoplastic rubber. The following measurements were taken during the experiments: (1) the axial pressure profiles in the die, (2) melt flow rate, and (3) take‐up speed. The measurements were then used to determine the effect of the rheological properties of the polymers on the performance of the wire coating operation. It was found that a reduction in axial pressure gradient and a reduction in the recoverable elastic strain of a molten polymer at the die exit can be realized as the speed of the wire is increased. For the theoretical study, using a power‐law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymer being extruded. Solution of the system equations permitted us to predict the velocity profile and shear stress distributions of a molten polymer inside a pressure‐type wire coating die.
Penetration mechanics of textile structures: Influence of non‐linear viscoelastic relaxation
Authors: Roylance David , Wang Su Su
Published: December 2004

A numerical simulation of ballistic impact and penetration on woven textile panels is described which can easily incorporate a wide variety of realistic constitutive and fracture models. The use of this model in assessing Viscoelastic relaxation effects is illustrated, and is further extended to include non‐linear Viscoelastic effects. Since a variety of non‐linear models is presently available and there is insufficient evidence to indicate the superiority of any single one in this instance, the Eyring non‐linear model was chosen arbitrarily to indicate the ease with which these models may be implemented into the numerical treatment. The results obtained using the non‐linear model are compared with comparable computer experiments using linear elastic and linear Viscoelastic models.
Analysis of non‐linear stress relaxation in polymeric glasses
Authors: Matsuoka S. , Bair H. E. , Bearder S. S. , Kern H. E. , Ryan J. T.
Published: December 2004

Non‐linear stress relaxation data were obtained for polycarbonate and polystyrene as a function of temperature, strain magnitude and thermal history. Data were analyzed according to the previously proposed free volume model to account for the shift of relaxation times with strain and thermal history. The result of the analysis is shown to be in close agreement with the tensile stress‐strain data. The yield phenomenon is analyzed as a rate dependent strain‐induced glass to rubber transition.
Linear and non‐linear viscoelastic behavior of poly(methyl methacrylate) in the hard region
Authors: Koppelman J. , Hirnböck R.
Published: December 2004

The relaxation behavior of poly(methyl methacrylate) in the hard region is caused by hindered rotations of the methoxycarbonyl side groups of the molecules. Measurements of the Young's modulus and the shear modulus at different frequencies, temperatures and strains lead to the following conclusions: each moving side group is surrounded by the elastic matrix of mean chains, The elasticity of this matrix depends on volume and temperature. Also the activation energy of the moving side group depends on volume and temperature, because the activation energy is the sum of an intramolecular and an intermolecular component. Due to the statistical entanglement of the molecules, the intermolecular contribution to the activation energy has a statistical distribution depending on volume. The reaction rate theory is of value for interpreting the viscoelastic behavior in the linear and non‐linear range if several considerations are followed.
Structural heterogeneity of suspension poly(vinyl chloride) resins
Authors: Krzewki Rudolf J , Sieglaff Charles L.
Published: December 2004

Morphology of poly(vinyl chloride) resin particles formed by suspension polymerization was investigated by a combination of several techniques. Significant differences were found in the internal structure of resins obtained under different polymerization conditions. Five main types of resin particles with different porosity and absorptivity were identified by scanning electron microscopy. Three methods were employed to characterize porosity and structural heterogeneity of resin particles: density fractionation of resin particles in mixtures of methanol and carbon tetrachloride; absorption of silicone oil and dioctyl phthalate by resin particles; and examination of fractured particles embedded in epoxy resins. All three methods gave consistent results and can be used for semiquantitative characterization of resin structural heterogeneity. Different particle structure and degree of resin heterogeneity: can profoundly affect compounding and processing operations.
Relationship of poly(vinyl chloride) stability to flow
Authors: Collins Edward A.
Published: December 2004

The effect of molecular weight and polymerization temperature on thermal stability is critically examined. The concept of flow‐stability is introduced as a new method of evaluating the thermal stability of poly(vinyl chloride). In the processing temperature range 200 to 220°C, the viscosity decreases by a factor of two while the thermal stability decreases by a factor greater than three.