bluuebunny/crossref_metadata_2025 huggingface dataset:
Line‐Profile resist development simulation techniques
Authors: Jewett R. E. , Hagouel P. I. , Neureuther A. R. , Van Duzer T.
Published: December 2004

The relative advantages and disadvantages of three different algorithms are compared for simulating the time evolution of two‐dimensional line‐edge profiles produced by a locally rate dependent surface etching phenomenon. Simulated profiles typical of optical projection printing and electron‐beam and X‐ray lithography of micron‐sized lines in resist and etching of ion‐implanted SiO2 are used as a basis of comparison. One of the algorithms is a cell‐by‐cell removal model used earlier by Neureuther and Dill. One of the newly developed algorithms employs ray tracing; it can be shown that the path followed by a point on a front between the developed and undeveloped regions can be calculated using ray‐optic equations. The other new algorithm uses a string of points initially on the surface of the exposed resist. The points on the string advance perpendicular to the local direction of the string; with time the string of points moves down into the resist, replicating the action of a developer. We compare the computing cost, convenience, and accuracy of the algorithms.
X‐ray lithography
Authors: Feder R. , Spiller E. , Topalian J.
Published: December 2004

The advent of X‐ray lithography as a natural compliment to electron beam pattern generation and photolithography seems to be filling a need in the fabrication of submicron devices. The X‐ray technique, which is simple for single level devices, lags behind other lithographies in registration techniques. However, its proven high resolution capabilities is responsible for the increased interest in further development. At present a, variety of mask substrates are being evaluated with no one material exhibiting an overwhelming advantage. The type of substrate used is closely coupled to the permissable wavelength of the X‐ray source. The X‐rays used for lithography to date vary from Rh L (4Å) up to CK (44Å). Each wavelength shows a distinct advantage and disadvantage. For example, at short wavelengths substrates can be relatively massive but resists are less sensitive and high resolution masks have low contrasts. At longer wavelengths, resists are more sensitive and masks have higher contrast, but defects due to dust are more probable. The use of more than one X‐ray source could fulfill the requirements imposed by mask making and device fabrication. High throughput for both masks and device require both foster resists and higher intensity X‐ray sources.
Differential dissolution and electron‐beam lithographic sensitivity of poly(methyl methacrylate)
Authors: Helbert J. N. , Cook C. F. , Poindexter E. H. , Wagner B. E.
Published: December 2004

Photolithographic and electron‐beam integrated circuit fabrication techniques rely heavily upon differences in polymer resist dissolution (development) rates to produce circuit patterns. We have applied the wide‐line NMR, technique, augmented by dynamic nuclear polarization, to the measurement of polymer dissolution rates of poly(methyl methacrylate), (PMMA). At high gamma‐ray exposures, we find PMMA to have dissolution rates from 2X to 1000X those of unirradiated material. The highest radiation‐enhanced dissolution rates are obtained with carbon tetrachloride‐based developer solutions, whereas generally lower enhanced rates are observed with 1:3 acetone or methylethylketone/isopropanol standard developer. E‐beam line exposures are developed in PMMA and poly(ethyl methacrylate), PEMA, resists using similar developers for comparison. Using straight CCl4 as a developer, e‐beam lines 1‐2 μ wide were developed in 3800 Å thick PEMA resist at 1 × 10−5 C/cm2 with ≤200 Å loss in unexposed resist thickness. The higher differential dissolution with CCl4, a poorer solvent for unirradiated PMMA than acetone or MEK, is explained by decline in polarity of PMMA by radiationinduced decarboxylation.
Oligomeric fluorinated additives as surface modifiers for solid polymers
Authors: Berneit Marianne K.
Published: December 2004

Successful modification of the surface properties of solid polymers was obtained by the adsorption of appropriate partially fluorinated oligomers at polymer/air and polymer/substrate inter faces during the formation of these interfaces. These additives, in concentrations of 0.25 percent, effectively lowered the critical surface tension of wetting, γc, of such polymers as polystyrene, poly(methylmethacrylate), and poly(vinylidene chloride) copolymers by as much as 26 dyn/cm. The obtained low γc values of 14 dyn/cm correspond to surfaces containing closely packed CF3 and CF2 groups. Adhesion of additive‐containing polymer films to various substrates was demonstrated to be a function of additive diffusion to the polymer/substrate interface, its subsequent adsorption and molecular orientation at that interface, and the surface energy of the substrate. The fluorinated additive molecules also have the advantage of being sufficiently mobile in the solidified polymer to reach and repair the interfaces.
The role of the interface in adhesion phenomena
Authors: Mittal K. L.
Published: December 2004

The role of the interface in adherend‐adherate combinations and in the strength of adhesive joints has been examined. For the former systems, practical adhesion (as determined experimentally, for example, by peel, tensile, or shear strengths) is a function of basic adhesion (determined by intermolecular, interactions such as van der Waals, electrostatic, or valence type forces) and many other factors. Adhesive joint strength depends pends upon the mechanical response of the various phases involved; however, the data in the literature on such strengths suggest the importance of surface chemical and energetic factors. Various such criteria, including, wetting, thermodynamic work of adhesion WA, and interfacial tension, ySL, for maximum joint strengths and the conditions which optimize these criteria are discussed. The testing of these factors against the literature data on adhesive joint strengths shows that the interfacial tension between the substrate and the adhesive (ysL) is the most important criterion; the lower the ySL, the higher the joint strength. In the case of adherend‐adherate systems, (e.g., metallized polymers), basic adhesion can be improved by chemical bonding or electrostatic contributions, and this improvement may or may not be reflected in improved practical adhesion. Examples are cited where an increase in basic adhesion does culminate in improved practical adhesion. On the other hand, practical adhesion does not always correlate with basic adhesion due to the influence of other factors.
Structure and properties of microcomposites and macrocomposites from block polymers
Authors: Aggarwal S. L. , Livigni R. A.
Published: December 2004

The incorporation of a rubber phase in glassy polymers, as is well known in the case of high impact polystyrene, leads‐to an increase in their impact strength. Block polymers offer three principal approaches for obtaining multiphase glassy polymers in which an elastorner phase is present in the matrix of the glassy polymer. They are: (1) control ofblock polymer composition, (2) blending of block polymer with homopolymers, and (3) polymerization of a solution.of a block polymer in the monomer corresponding to one of the blocks. The observed properties, such as impact strength, modulus, and heat distortion temperature, desired in rubber modified glassy polymers are discussed for block polymer systems prepared using the above approaches.
Structure of AB block copolymers with a polypeptide block: Effect of the chain conformation
Authors: Douy André , Gallot Bernard
Published: December 2004

The structure of AB copolymers with a polypeptide block has been studied by X‐ray diffraction, electron microscopy, infrared spectroscopy, and circular dichroism. Copolymers with a polyvinyl block (polybutadiene or polystyrene) and a hydrophobic polypeptide block (polybenzyl‐L‐glutamate or polycarbobenzoxy‐L‐lysine) exhibit a lamellar structure in the dry state and in solution in dioxane or in different chlorinated solvents. This lamellar structure consists of plane, parallel, equidistant sheets. Each sheet results from the superposition of two layers: one formed by the polyvinyl chains in amore or less random coil conformation, the other formed by the polypeptide chains in an α‐helix conformation, arranged in a hexagonal array and generally folded. Copolymers with a polyvinyl block and a hydrophilic polypeptide block (poly‐Llysine or poly‐L‐glutamic acid) exhibit a larnellar structure in water solution and in the dry state. The difference between this lamellar structure and the preceding one consists in the conformation of the polypeptide chains: an intramolecular mixture of coiled chains, α‐helices, and β chains. Copolymers with a polysaccharide block and a hydrophobic polypeptide block exhibit in DMSO solution and in the dry state a lamellar structure similar to that of copolymers with a polyvinyl block and a hydrophobic polypeptide block.
Thermodynamics of plasticized triblock copolymers. Part II: Model verification by light transmittance and rheology
Authors: Pico Efrain R. , Williams Michael C.
Published: December 2004

An earlier paper proposed a theoretical model for the thermodynamics of microphase separation in a plasticized triblock copolymer. Data on laser light transmission through plasticized films and on dynamic viscosity: of these films are presented in support of model predictions. Two styrenebutadiene‐styrene copolymers were tested: Kraton 1101 with block weights (12.5‐75‐12.5) × 103 and TR‐41‐1467 with weights (9.6‐47.5‐9.4) × 103 using the solvent dipentene (p‐mentha 1, 8 diene), which is favorable for both blocks. The role of such solvents is to depress the temperature of microphase separation, Ts. Optical and rheological measurements of Ts agreed with each other arid, in most cases, with the theory; discrepancies with theory were noted only when Ts was less than Ts for polystyrene. These data along with electron microscopy also support the prediction that the favored morphology for these systems is a mixture of planar and inverted (middle‐block) cylinders and spheres.
Statistical thermodynamics of microdomain structures in block copolymer systems
Authors: Helfand Eugene , Wasserman Z. R.
Published: December 2004

A statistical thermodynamic theory of the microdomain structure of block copolymers is presented in qualitative physical terms. Special emphasis is placed on a presentation of the final algebraic formula which may be used to determine lamellar domain sizes as a function of block length and physical parameters. Calculations on lamellar domains and preliminary results for spherical domains are compared with experiments. Other topics discussed are: width of the interphases, results of a more exact theory, and thermodynamic., stability of the domain structure.
Monte Carlo studies of isolated AB block copolymer molecules
Authors: Bendler John , Šolc Karel
Published: December 2004

Recent theoretical progress in understanding conformations of AB block copolymer molecules in dilute solution is reviewed. The results of the authors' own biellipsoidal smooth density model (BEM) are compared to the findings recently reported by two independent groups, for the more rigorous self‐avoiding walk models with nearest neighbor interactions (SAW). The SAW results confirm the BEM conclusions for the size and shape behavior of individual blocks under changing solvent‐temperature conditions. The relative orientation and separation of the blocks depend strongly, on the magnitude of AB interactions, while the individual, block parameters are much less sensitive in this respect. Parfial segregation (or partial block mixing) is the general rule rather than the exception, and is aided by the low polymer concentrations which are, found in the overlap region in dilute solutions. A unified view of homopolymers and block copolymers emerges from these models, with homopolymers being a special case of the latter group. Inherent to BEM is the arrowhead‐like overall shape of the molecules, which appears to survive under most conditions.
Emulsifying properties, of block copolymers. Oil‐water emulsions and microemulsions
Authors: Riess G. , Nervo J. , Rogez D.
Published: December 2004

The emulsifying effect of poly(styrene‐b‐ethylene oxide) block copolymers (Cop PS‐PEO) has been studied for the toluene‐water system as a function of the molecular characteristics of the copolymer (composition, molecular weight, and structure). To demonstrate the surfactive properties of Cop PS‐PEO, we determined the interfacial tension γi for the toluene‐water system in the presence of these block copolymers. For oil/water (O/W) and water/oil (W/O) emulsions, prepared in the presence of Cop PS‐PEO, we determined the phase inversion point, the particle size of the dispersed phase, the stability and the viscosity as a function of the PEO content, the molecular weight, and the structure of the block copolymers. It appeared that the best results for the emulsification are obtained with Cop PS‐PEO having molecular weights less than 100, 000. Stable O/W emulsions of small particle size are preferentially prepared with di‐ or triblock copolymers having a PEO content of 60‐80 percent. In contrast, stable W/O emulsions are obtained with diblock copolymers having a PS content of 60‐80 percent. The difference in behavior between diand triblock copolymers also showed the importance of the chain conformation at the toluene‐water interface. As an extension, we have shown that microemulsions can be obtained with such polymeric surfactants. Isopropanol and butylamine appeared to be efficient cosurfactants for the system water/toluene/Cop PS‐PEO.
Some comments on post extrusion swelling phenomena: Die entrance or die passage
Authors: Chapoy L. L. , Pedersen S.
Published: December 2004

The mechanistic origins of the post extrusion swelling phenomenon have been the subject of considerable debate. Conflicting theories have postulated that it is caused either by (1) deformations at the die entrance which are recovered upon die exit as a consequence of viscoelastic memory or (2) elastic enorgy, which is stored during capillary flow by the action of normal stress, and subsequently released upon die exit or by both (1) and (2). We have described these situations by mathematical models and show that the resulting equations are similar despite different origins. The difficulties in interpreting the results mechanistically are discussed. Empirically, the results can be described as being exponential in capillary residence irrespective of cause.
A study of the flow properties of rubbers using the rheometrics mechanical spectrometer
Authors: Mukherjee Debi P.
Published: December 2004

The dynamic shear properties of a natural rubber and several commercial synthetic polyisoprenes were measured in a Rheometrics mechanical spectrometer. The dynamic viscosity vs angular velocity curve was fitted to the three‐constant Car, reau model. The rheological parameters were correlated with molecular characteristics such as gel content and weight average molecular weight. The viscosity measurements at high shear rate were obtained from capillary rheometry. The viscosity vs shear rate curve at the low shear rate end was found to be superimposible on the plot of dynamic shear viscosity vs twice the angular velocity.
Viscoelastic parameters of characterized branched polyethylenes
Authors: Ram Arie
Published: December 2004

Certain steady state viscoelastic parameters, including melt viscosities, normal stress coefficients, and shear compliances, are determined for a series of well‐characterized low, density polyethylene samples, and the results are analyzed. The effects of shear rate, temperature, molecular weight, molecular weight distribution, and the degree of long chain branching are demonstrated. The agreement observed between steady state shear compliance values derived from normal stresses and those obtained from die swell measurements is significant.
Swelling and hygroelasticiiy of polymeric composites
Authors: Marom Gad
Published: December 2004

Investigated are the swelling and hygroelasticity of a unidirectional glass fiber‐reinforced epoxy composite subjected to boiling water for 24 hrs. By analogy with thermoelasticity, a coefficient of hygroelasticity is defined and shown to be predictable from the coefficients of the constituent materials by Schapery's equations. A mechanism for water penetration into the composite which combines capillarity and diffusion is proposed on the basis of the results of the water take‐up as a function of the composite specimen width (fiber length).
Adhesive properties of star‐shaped block copolymers
Authors: Meyer G. C. , Widmaier J. M.
Published: December 2004

Star‐shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene‐b‐isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.
Thermal load in the processing of thermoplastics
Authors: Ingen Housz Jan F.
Published: December 2004

By manipulation of residence time and temperature distributions along a streamline, a reduced residence time may be formed which is a quantitative measure of the thermal load to which the material being processed is subjected in any part of the process. This method is applied in two examples. In the metering zone of a single screw extruder the highest thermal load is found at 2/3 of the channel height. For a case of pipe cool ing it is shown that a much higher extrusion temperature is possible without increasing the danger of degradation by the addition of an internal cooling system to the conventional sizing method.
Degradation and enhancement of the fatigue behavior of glass/graphite/epoxy hybrid composites after accelerated aging
Authors: Hofer K. E. , Stander M. , Bennett L. C.
Published: December 2004

The tensile fatigue characteristics of graphite/glass/epoxy hybrid composites were investigated before and after exposure to various high humidity environments. Accelerated aging treatments of 98 percent RH and 120°F were applied both continuously for 500 and 1000 h and coupled with a 350°F thermal shock after −67°F low temperature exposure. This latter thermohumidity cycle was applied for 500 h total exposure time. Cyclic loading tests showed that degradation due to the moisture and thermohumidity conditioning treatments was in‐most cases small. Some bereficial behavior of the humidity exposure was also noted. The hybrid fatigue characteristics both before and after exposure were a blend of the nearly flat advanced fiber composite S‐N behavior and the highly curved glass fiber composite S‐N behavior. This was attributed to a mixture of failure modes for the hybrid system.
Morphological and physical property effects for solvent cast films of poly‐2, 5(6) benzimidazole
Authors: Wereta Anthony , Gehatia Matatjahu T. , Wiff Donald R.
Published: December 2004

A polybenzimidazole having the structural repeat unit magnified image and designated AB‐PBI was formed into films by casting or precipitating from dilute solutions. Selected films were swollen in a plasticizing medium arid drawn about 2X. All films were dried in a vacuum oven to aid in the removal of residual solvent and moisture. Wide angle X‐ray scattering (WAXS) was used to show the type of ordering found in this material and to indicate the extent of molecular orientation. Neither a glass transition nor a crystalline melting point has been observed for this polymer, A Perkin‐Elmer DSC was used to scan the temperature range from −150 to H‐400°C in search of secondary transitions. The rheovibron proved more sensitive and a transition was located in the vicinity of −60°C. An activation energy‐was determined. The morphology of this polymer is subject to speculation. The ability of the chain to adopt a linear conformation leads to the possibility of a liquid‐crystalline nature in solution. A model based on the data in hand is suggested. Stress‐strain data was used to compare the mechanical properties of films prepared by several methods as well as to demonstrate the effect of orientation on strength.
A study of viscous dissipation in the calendering of power‐law fluids
Authors: Kiparissides C. , Vlachopoulos J.
Published: December 2004

A finite difference procedure was used to solve the equation of conservation of energy with the lubrication approximation. The temperature profiles due to viscous dissipation in the gap formed by a pair of equal sized rolls rotating at the same speed exhibit two maxima in the vicinity of the roll surfaces. The maximum temperatures also exhibit two local maxima and a minimum in the direction of flow. The calculated temperature distributions across and along the flow field reveal the possibility of excessive local heating which might be detrimental for certain temperature sensitive materials such as poly(vinyl chloride) and rubbers.
Orientation development and relaxation in injection molding of amorphous polymers
Authors: Dietz Wolfgang , White James L. , Clark Edward S.
Published: December 2004

Orientation development in amorphous polymer melts being vitrified in an injection molding process is described. Predictions of orientation development are based on the argument that the stress‐optical laws are valid in the molten stare and birefringence values appropriate to the stress levels at the time of vitrification remain. This theory is compared to birefringence distributions determined in injection molded parts.
Viscosity, modulus, and die swell of glass bead filled polystyrene‐acrylonitrile copolymer
Authors: Agarwal Pawan K. , Bagley Edward B. , Hill Christopher T.
Published: December 2004

Flow curves were obtained at 190°C over the shear rate range 0.1 to 100 sec−1 for polystyrene‐acrylonitrile copolymer containing up to 36 percent by volume glass beads, using a capillary extrusion rheometer. The addition of glass beads always increased shear stress and viscosity at a given shear rate, with the increase being more pronounced at low shear rates. The addition of glass beads decreased die swell, which also depended on shear‐stress and capillary length‐to‐radius ratio. At low shear rates a lower limiting value of die swell ratio of about 1.1 was achieved. Values of recoverable shear derived from end correction data by the technique of Philippoff and Gaskins and from die‐swell data by the method of Bagley and Duffey are compared. A fairly good agreement was found for low concentration blends at low shear, However, the values differed by a factor of up to 3 at higher shear stresses. In all cases, recoverable shear was found to increase with shear stress at a fixed filler loading and to decrease with increased filler loading at a fixed shear stress. Values of shear modulus calculated from the recoverable shear measurements decreased rapidly with increasing shear stress.
A study on the dissolution rate of irradiated poly(methyl methacrylate)
Authors: Ouano A. C.
Published: December 2004

A detailed study of the factors affecting the dissolution rate of poly(methyl methacrylate), PMMA, showed that the magnitude of the increase in the dissolution rate of irradiated PMMA could not be entirely attributed to the reduction in the molecular weight, MW. The formation of non‐polymeric volatile fragments by radiation exposure, i.e., CO, CO2H2, CH3OH and CH4 causes a large increase in the solvent flux into the polymer matrix, thereby causing a large increase in the dissolution rate of exposed PMMA. The volatilization of these low molecular weight fragments cause an increase in the “excess free volume” (microporosity) of the glassy PMMA. The relative magnitudes of the contribution of the MW reduction and the formation of volatile matter on the increase in the solubility rate of the irradiated polymer were found to depend on the molecular size of the solvent, and also on the enthalpy of mixing.
Effect of long‐term water exposure on properties of carbon and graphite fiber reinforced epoxies
Authors: Mazor Avraham , Broutman Lawrence J. , Eckstein Bernard H.
Published: December 2004

The effects of long term exposure to dry and humid environments on carbon‐epoxy and graphite‐epoxy composites have been studied. Filament wound Naval Ordnance Laboratory rings were fabricated in 1965 and were placed in dry, distilled water and sea water for 11 years. Moisture desorption tests were conducted in order to determine the water content of specimens exposed to the water environments, The effect of the history on moisture absorption characteristics was investigated by re‐exposure of partially and completely dried specimens to two different environments: distilled water at 60°C and 98% relative humidity at 60°C. The weight gain was measured and diffusion coefficients were calculated. Horizontal shear tests and flexural tests were performed on “wet” specimens (current properties) and on partially and completely dried specimens (residual properties). The shear strength of the carbon‐epoxy composites is degraded by the exposure while that of the graphite‐epoxy composite is slightly increased. The composite flexural strengths are not degraded by the exposure. These results are discussed in terms of failure modes.
Block copolymer deformation
Authors: Gaylord Richard J. , Lohse David J.
Published: December 2004

The deformation behavior of block copolymers is examined. Interdomain bridges, loops, cilia and floating chains in spherical, cylindrical and lamellar domain morphologies are considered. In the theoretical model, which is analogous to the “three‐chain” model in classical rubber elasticity theory, interdomain chains are confined between pairs of infinite, parallel impenetrable walls constructed at the surfaces of nearest neighbor domains. The domains are taken as undeformable. The quantities which are calculated are: the Young's modulus; the partial molar elastic free energy of swelling; and the stress‐strain relation for simple extension.
Rheoiogical studies of compaction for polystyrene powder
Authors: Umeya Kaoru , Kara Ryuichi
Published: December 2004

Polystyrene powder was compacted in a cylindrical die at constant compaction speed. Compaction was found to be influenced by test temperature, compaction speed and void fraction of the powder bed. The stress reduction behavior of an axial stress σ1 and a radial stress σ2 was observed at constant void fraction after compaction. The stress reduction thus obtained was interpretable by adopting an octahedral normal stress σoct and an octahedral shear stress τoct which were converted from σ1 and σ2. This behavior was attributable to the deformation of polystyrene around contact points and to a sliding mechanism between particles. It was ascertained that the relation between a shear stress τ and a normal stress σ obtained on compaction differed from that obtained in shear by a mechanism involving movement between polystyrene particles.
Applications of differential scanning calorimetry to photocurable polymer systems
Authors: Wight Frederick R. , Hicks George W.
Published: December 2004

Modification of a standard differential scanning calorimeter to allow irradiation of the sample material with ultraviolet light allows one to follow the course of polymerization of photocurable polymer systems. The rate and heat of polymerization are readily determined by this technique which gives it a number of very useful applications. As a quality control tool, one can use the heat of polymerization to monitor the number of reactive sites present in the prepolymer thus achieving a degree of control on the ultimate properties of the cured film. Similarly, analysis of a cured film will indicate the presence of any uncured material, thus allowing one to adjust curing conditions accordingly. The technique has numerous other applications in the study of photocurable resins, such as evaluation of initiator efficiencies, optimization of curing parameters (initiator concentration, lamp design), and the sensitivity of prepolymers to oxygen and wavelength.
Softening rates for polystyrene under shear conditions
Authors: Sundstrom D. W. , Lo J. R.
Published: December 2004

The processing of thermoplastics often requires conversion of a solid to a viscous fluid under shear conditions. In this study, solid blocks of polystyrene were softened on a hot, moving surface over a range of surface temperatures and velocities. The conservation equations for mass, momentum, and energy were applied to the fluid layer and simplified by an order of magnitude analysis. An integral method of solution was developed which predicted rates of softening that agreed closely with the measured rates.
Equilibrium melting of flexible linear macromolecules
Authors: Wunderlich Bernhard
Published: December 2004

The extensive literature on equilibrium melting of flexible linear macromolecules has been reviewed during the last year. The discussion in this paper is based on experiments on actual, large, extended chain crystals and extrapolations on metastable crystals. A series of 32 complete sets of melting temperatures, heats of fusion, volume changes on fusion, and entropies of fusion have been collected. These data are compared to melting data on rigid macromolecules and small macromolecules. Only a relatively simple model of rotational isomerism is needed to understand the entropy of fusion of flexible linear macromolecules which is 8‐12 J/K/mole of rigid backbone units whenever there is no mobility in the crystal at the time of melting. This is much less information on detailed conformational analysis than is generally assumed to be necessary to interpret melting. Instead, it is of importance to consider for the discussion of melting also the change in packing fraction on fusion, which is high for crystals with planar zig‐zag conformation, and low for helices. Both types of crystals lead to similar packing fractions in the melt. Higher packing fractions, both in the melt and crystal, are found for polyesters, polyamides, and polyoxides. The heats of fusion which make up the third group of melting parameters considered are more connected with molecular size (surface area) and cohesive energy density than mobility, so that larger mobile backbone units and higher cohesive energy densities lead to higher melting temperatures. A further addition to the heat of fusion comes from the presence of high energy rotational isomers in the melt, which again increases the melting temperature. Further refinement of this initial discussion is possible, but all aspects of melting must be taken into account rather than concentrating on single aspects as has been done in the past.
Solidification of poly(ethylene terephthalate) with incomplete crystallization
Authors: Muzzy J. D. , Bright D. G. , Hoyos G. H.
Published: December 2004

Cooling is a critical step in any crystalline polymer molding or extrusion process. A simulation is proposed which will predict the transient temperature and crystallinity profiles developed when a finite polymeric slab comes in contact with a cooling fluid. A generalized, phenomenological model of the crystallization kinetics of polymers is incorporated to account for the effect of the latent heat of crystallization on the thermal history as well as on the crystalline structure at any point in the slab. The model assumes heterogeneous nucleation and temperature‐dependent radial growth of spherulites. DSC cooling thermograms for the polymer are used to verify the kinetic model for comparing experimental measurements against simulated results. Observed spherulite sizes should also be matched by the simulation. Kinetic data have been obtained for two grades of poly(ethylene terephthalate) which have the same growth rate expression but different nucleation characteristics. Crystallinity of these two polymers decreases rapidly as either quench temperatures or nucleation densities are decreased independently. Calculations have been carried out for 1/16 in. thick sheets of polymer exposed to a cooling medium with a heat transfer coefficient of 100 Btu/hr/ft2/°F. Temperature gradients are also presented. The simulation can be used for optimizing quench conditions in polyester film extrusion.
Effect of molecular weight on high pressure crystallization of linear polyethylene. II. Physical and chemical characterizations of crystallinity and morphology
Authors: Ferguson Raymond C. , Hoehn Harvey H.
Published: December 2004

The high pressure crystallized specimens described in the preceding paper (1) were characterized by X‐ray diffraction, density, and differential scanning calorimetry, Nitric acid etching, followed by gel permeation chromatography and DSC on the residues provided further characterization of the morphology. The crystallinity decreased from 100 to 80 percent with increasing molecular weight, over the rangeMw= 4.9 × 104to 4.6 × 106. The crystallites were predominately in extended chain morphology, but the percent in extended chain form decreased from 98 to 85 percent over the indicated molecular weight range. In all cases, there was a wide, bimodal or multi‐modal, distribution of lamellar thickness. The physical characterization results were consistent with and complementary to the results from electron microscopy. The large differences in crystallinity and gross morphology readily account for observed molecular weight dependent differences in mechanical properties.
Strength of discontinuous reinforced composites: II. Isotropic crystalline polymers
Authors: Kardos J. L. , Piccarolo S. , Halpin J. C.
Published: December 2004

Crystalline polymers are heterogeneous materials consisting of two distinct phases. They may therefore be treated as molecular versions of engineering composite materials. This paper summarizes the physical model which, when used in conjunction with composite theory, yields a complete calculational format for stiffness, expansion strain, and yield strength. The important input parameters to the calculation are the mechanical properties of the individual constituent phases (crystalline and amorphous), the crystallite aspect ratios, the volume fraction crystallinity, allowable failure strains for a continuous crystal system, and a measure of stress concentrations and strength reduction caused by the discontinuous nature of the actual crystalline reinforcing phase. An expression for the strength reduction factor is developed and details of the stiffness and yield strength calculations are presented for high density polyethylene (HDPE). Comparison with experiment for HDPE yields excellent agreement well within the necessary design accuracy. Agreement with experiment in the case of low density polyethylene (LDPE) is not as good, but within expectations considering the degree of theory refinement and the poorer morphological data base for LDPE.
The amorphous contribution to the modulus of a semi‐crystalline polymer
Authors: Lohse David J. , Gaylord Richard J.
Published: December 2004

The amorphous contribution to the Young's modulus of a semi‐crystalline polymer is calculated for two morphologies: the spherulite and the stacked lamellae structure. Four types of amorphous chains are considered: bridges (or tie molecules); cilia; loops; and floating, unattached chains. The statistics of a polymer chain between two, infinite, impenetrable, parallel walls are used in the modulus calculation. It is found that for each type of amorphous chain, the Young's modulus is greater in the stacked lamellae structure than in the spherulite. The Young's modulus of a cilium, loop and floating chain all increase with increasing chain contour length while the Young's modulus of a bridge passes through a minimum value. The behavior of the Young's modulus as a function of temperature is analogous. These results are discussed in terms of the relative importance of crystalline lamellar impenetrability and the inherent elastic nature of the amorphous chains, in the Young's modulus behavior.
Preparation of ultradrawn polyethylene by a novel radial‐compression method
Authors: Griswold Phillip D. , Porter Roger S. , Desper C. Richard , Farris R. J.
Published: December 2004

High density polyethylene has been ultradrawn at 80°C by a novel radial–compression method which involves the gradual buildup of highly‐stretched elastic (spandex) filaments around the circumference of a solid polymer cylinder. The sheath of tightly‐wound filaments generates a high‐radial pressure which forces the polyethylene cylinder to neck down, uniaxially extend, and ultradraw. The physical and mechanical properties of radially‐compressed polyethylene of maximum draw ratio, 40‐45X, were evaluated and compared with the same polymer ultradrawn in other stress fields. In most physical property categories, the radially‐compressed samples are virtually indistinguishable from samples prepared by solid‐state extrusion at higher temperature and pressure. The transparency and the maximum tensile modulus, 62 GPa, further confirm the effectiveness of radial compression in achieving ultradraw. An experimental technique for measuring the radial pressure generated by the winding of the highly‐stretched elastic filament is presented. The upper‐bound pressure in the radial‐compression experiments was less than 100 MPa.
Metal‐containing cured resins based on divalent metal salts of ethylene glycol‐methacrylate‐maleate
Authors: Matsuda Hideaki , Okamoto Takanori
Published: December 2004

Divalent metal salts of ethylene glycol‐methacrylate‐maleate in the amorphous state were easily soluble in styrene, methyl methacrylate and ethyl acrylate, to give homogeneous, curable mixtures with high metal content. The viscosities of the mixtures varied depending on the metal present. The mixtures were copolymerized to give metal‐containing cured resins of increased compressive strength and Rockwell hardness. Moreover, heat distortion temperature could be improved by introducing Mg or Ca. Of the cured resins studied, the Mg‐containing resin showed the best physical properties. Resistance of the metal‐containing resins to attack by organic solvents was generally high, whereas greater degradation by aqueous reagents was noted. The thermal behavior of the resins is discussed.
Electrical properties of carbon black filled polyethylene
Authors: Narkis M. , Ram A. , Flashner F.
Published: December 2004

Resistivity and dielectric constant of polyethylene/carbon black compounds were measured from room temperature to 140°C. Within the polyethylene melting region a PTC/NTC (positive followed by negative temperature coefficients) phenomenon is observed, whose intensity depends on the type of carbon black, its concentration and other parameters. Reproducibility of the PTC phenomenon in polyethylene compounds containing a single type of carbon black is rather low. However, by using mixtures of carbon blacks differing appreciably in their particle size, remarkable reproducibility improvements can be achieved. Several other aspects are also discussed in the present paper covering current‐voltage relationships in these materials, comparison of PTC curves with DSC thermograms upon heating and cooling, and dielectric constant‐temperature relations. The carbon black concentration giving the optimum PTC intensity can be predicted approximately from room temperature data.
Polymer blends containing poly(vinylidene fluoride). Part II: Poly(vinyl esters)
Authors: Bernstein R. E. , Paul D. R. , Barlow J. W.
Published: December 2004

Blends of poly(vinylidene fluoride) PVF2, with poly(vinyl acetate), PVAc; with poly(vinyl propionate), PVPr; and with poly(vinyl butyrate), PVBu, were prepared by solution blending. Solutions containing PVF2 with either PVPr or PVBu exhibited phase separation, and it was concluded that neither of these polymers are miscible with PVF2. Phase separation did not occur with solutions containing PVF2 and PVAc. Dried samples of this blend system were subjected to differential thermal analysis, dynamical mechanical testing, and visual observations of their melts. From these results, it was concluded that PVF2 and PVAc are miscible. The detailed results and the structural implications of these observations are discussed.
Melting behavior of solid polymers on a metal surface at processing conditions
Authors: Mount Eldridge M. , Chung Chan I.
Published: December 2004

The melting or plasticating behavior of seven commercial polymers (high density polyethylene, low density polyethylene, polypropylene, polyoxymethylene copolymer, polystyrene, poly(methyl methacrylate), and polycarbonate (PC) was investigated using an experimental apparatus specifically designed to measure the melting rate and the viscous shear stress of a solid polymer on a steel surface under precisely controlled conditions of temperature, velocity, pressure and sample width comparable to actual processing. The melting rate (per unit polymer solid/metal contact area) was found to increase with increasing temperature for all polymers except PC, to decrease with increasing sample width and to increase less than proportionally to velocity. Pressure increased the melting rate somewhat for most of the polymers. The viscous shear stress decreased with increasing temperature for all polymers except PC, decreased with increasing sample width and increased with increasing velocity. Pressure generally increased the viscous shear stress. PC showed an unusual behavior with a maximum in the melting rate near 4200°F(215.5°C) and also a maximum in the viscous shear stress near 445°F (229.4°C). The present melting model could be examined unequivocally for the first time using our experimental results. Comparison of our experimental results with the predictions of the present melting model clearly indicates the inadequacy of the present melting model, Our experimental results will provide a basis for rational development of a reliable melting model.
Dynamic modulus of rubber by impact and rebound measurements
Authors: Bassi A. C.
Published: December 2004

When rubber is deformed an energy input is involved which is released in part when the rubber returns to its original shape. The part which is not returned as mechanical energy is dissipated as heat. The “rebound resilience” is defined as the ratio of the energy returned to the energy applied for deformation by an indentation due to a single impact. In this experiment, a pendulum mass and a test piece, as long as they are in contact, may be considered an oscillating system having one degree of freedom in which the rubber is a Voigt model. The correlation between rebound resilience and loss angle of the rubber may thus be derived. The measurement of the contact time between pendulum indentor tip and rubber surface, in addition to the rebound resilience, allows calculation of deformation, speed and acceleration of the damped sinusoidal motion. The penetration of the spherical indentor under a constant force depends on Young's modulus. Scott found an empirical relationship among force applied, depth of indentation, radius of the indentor tip and the modulus. This relationship has been recently improved by Stiehler and coworkers, The Stiehler formula has been used here for evaluating the storage modulus of rubber vulcanizates by using the maximum force transmitted by the impacting mass and the indentation depth of the test piece at the same time.
Use of a gas chromatograph for measurement of the rate of monomer desorption from poly (vinyl chloride) resins
Authors: Berens A. R.
Published: December 2004

Previous studies by a gravimetric technique have established that the sorption and desorption of small quantities of vinyl chloride monomer (VCM) by poly (vinyl chloride) (PVC) resin powders obeys Fickian diffusion kinetics. Consequently, the rate of sorption or desorption is very sensitive to the size and structure distribution of the resin particles and is a useful measure of these properties. To facilitate the measurement of desorption rates, an “inverse GC” technique has been developed, with the PVC powder taking the place of the usual gas Chromatograph column. The detector and electronics of the GC are used to follow the VCM content of a carrier gas stream passing through a PVC resin sample initially equilibrated to a uniform VCM content. This method yields results consistent with the gravimetric data and provides a convenient means of characterizing PVC particle structure.
Hardness testing of plastics
Authors: Phillips P. J. , Ramakrishnan N. R. , Oxlade P. L. S.
Published: December 2004

The effect of time of indentation and time of recovery on the Rockwell hardness, of a series of glassy and crystalline polymers has been determined. An analytical technique, based on conventional viscoelastic approaches, has been developed. This technique permits the resolution of the hardness number into its components of permanent deformation, retarded elastic compression, and retarded elastic recovery. Subtraction of components due to retarded elastic response results in hardness numbers dependent only the time‐dependent permanent deformation. Extrapolation of this data to zero time results in an absolute or time‐independent value of Rockwell hardness, designated Ro.
Head to head polymers IX: The rheological behavior of H‐H and H‐T atactic polystyrenes
Authors: Jacovic M. , Vogl O.
Published: December 2004

The rheological behavior of a sample of H‐H polystyrene of Mn of 41,000 and a Mw/Mn of 2 was compared at 160 and 190°C with a sample of H‐T atactic polystyrene of similar molecular weight. The melt viscosity of H‐H polymer (unlike the H‐T polymer) was non‐Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H‐H polystyrene. The flow activation energy (E*) of H‐H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H‐H polymer has a smaller increase of G′ with ω than that of the H‐T polystyrene.
The impact behavior of ABS over a range of temperatures
Authors: Newmann L. V. , Williams J. G.
Published: December 2004

Charpy type tests have been conducted on a typical grade of aerylonitrile‐butadiene‐styrene (ABS) over the temperature range +60 to −80°C. At the higher temperatures, the fractures were fully ductile and have been explained in terms of a constant energy density necessary to produce craze‐whitened material. Below −40°C, the results were analyzed using a linear elastic fracture mechanics approach and values of Gc, the critical strain energy release rate, were obtained. The intermediate temperatures produced partially‐ductile behavior and these data were also analyzed to yield effective values of Gc.
Infrared laser ablation of polymers
Authors: Cozzens Robert F. , Fox Robert B.
Published: December 2004

Ablation produced by 10.6 μm laser irradiation of eleven polymers is reported. Polymers which formed a carbonaceous residue were found to have much higher ablation energies than cleanly ablating polymers. All non‐char forming polymers studied had observed laser ablation energies in the range 3.4‐3.9 KJ/g except for poly (α‐methylstyrene) which had a value of 2.4 KJ/g. The low value forpoly (α‐methylstyrene) is attributed to an exceptionally efficient depolymerization. The observed ablation energy of poly (methyl methacrylate) was found to decrease with increasing irradiance up to about 15 watts/cm2, reaching a constant value of 3.5 KJ/g at irradiances between 20 and 2600 watts/cm2. The proposed process of laser ablation is one that involves random fragmentation resulting from the accumulation of vibronic energy.