Showing papers in "Polymer Engineering and Science in 1974"
TL;DR: In this paper, an indirect method of estimating the solubility parameter of high molecular weight polymers is proposed, which is based on group additive constants, but is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of structural formula of the compound.
Abstract: Development of an indirect method of estimating the solubility parameter of high molecular weight polymers. The proposed method of estimating the solubility parameter, like Small's method, is based on group additive constants, but is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of structural formula of the compound.
1,590 citations
TL;DR: In this article, the authors summarized the status of work in this area with emphasis on recent results relating to kinetic, thermal, and rheological characterization of thermosetting molding compounds.
Abstract: The injection molding of thermosetting compounds involves complex interactions between material parameters and molding conditions, on one hand, and moldability and the ultimate properties of molded parts, on the other hand. The main role of the molding variables may be related to their effects on the cure time and temperature and on the flow and thermal phenomena that affect orientation and residual stresses. These effects are manifested in the ultimate mechanical properties and shrinkage of the molded articles. Only scattered empirical data are available on the effects of material parameters, like the basic kinetic, thermal, rheological, and pressure-volume-temperature properties of thermosetting compounds. The lack of useful information in this area may be related to the unavailability of sufficient, satisfactory data on the above properties. This situation has also resulted in limitations on meaningful work towards the mathematical modelling of the molding process, which would be useful for the optimization of production rates and product quality. The paper summarizes the status of work in this area with emphasis on recent results relating to kinetic, thermal, and rheological characterization of thermosetting molding compounds.
541 citations
TL;DR: In this article, the influence of surface properties on the flow of fluids, including epoxy resin, through aligned glass and other fiber beds has been examined, and the observed flow rates were higher than those predicted from the Kozeny-Carman equation, and were influenced by the surface properties of the fluid used.
Abstract: The influence of surface properties on the flow of fluids, including epoxy resin, through aligned glass and other fiber beds has been examined. The observed flow rates were higher than those predicted from the Kozeny-Carman equation, and were influenced by the surface properties of the fluid used. This is attributed to variations in the distribution of porosities and to the presence of air bubbles trapped during the initial wetting of the bed. The implications of these findings to the preparation of composites are discussed.
201 citations
TL;DR: In this paper, a study of materials which are positive-temperature-coefficient resistors has been conducted, where the authors found that on repeated cycling through the anomaly temperature or on extensive heating at or above the anomalous temperature, the room temperature resistivity rises and the anomaly height falls to zero.
Abstract: This is a study of materials which are positive-temperature-coefficient resistors. Such materials, composed of conductive particles dispersed in a crystalline polymeric matrix, have been found to be of limited stability. An example is carbon black in high-density polyethylene. On repeated cycling through the anomaly temperature or on extensive heating at or above the anomaly temperature, the room temperature resistivity rises and the anomaly height falls to zero. This phenomenon has been shown to be caused by the absorption of oxygen by the polymer matrix which alters the structure, reduces the crystallinity, and induces an unusual form of crosslinking of a reversible nature.
195 citations
TL;DR: In this article, a theoretical analysis using finite element methods has been applied to oriented short-fiber composites and spherical particle composites in order to predict the influence of a finite layer at the interface on mechanical properties.
Abstract: A theoretical analysis using finite element methods has been applied to oriented short-fiber composites and spherical particle composites in order to predict the influence of a finite layer at the interface on mechanical properties. In this study the interfacial layer has been modeled by assuming that a layer surrounds the interface and that this layer has a modulus of elasticity different than both the fiber and the matrix. The stress distribution near the interface has been determined as a function of the elastic constants of the interface layer and the interface layer volume fraction. This analysis has also been performed for two volume fractions of fibers and two fiber length to diameter ratios. From this stress distribution, the composite modulus and toughness have been determined as a function of interface modulus. It is theoretically shown that the toughness, measured by amount of strain energy absorbed, can be maximized by controlling the interface modulus. Furthermore, recent experimental results appear to verify the theory.
185 citations
TL;DR: In this paper, a finite element method is proposed for solving two dimensional flow problems in complex geometrical configurations commonly encountered in polymer processing, which is applicable to flow in relatively narrow gaps of variable thickness and any desired shape.
Abstract: A finite element method is proposed for solving two dimensional flow problems in complex geometrical configurations commonly encountered in polymer processing. The method is applicable to flow in relatively narrow gaps of variable thickness and any desired shape. It was developed for analyzing flow in injection molding dies and certain extrusion dies. The fluid can be any non-Newtonian fluid which is incompressible, inelastic, and time independent. The flow field is divided into an Eulerian mesh of cells. Around each node, located at the center of the cell, a local flow analysis is made. The analysis around all nodes results in a set of linear algebraic equations with the pressures at the nodes as unknowns. The simultaneous solution of these equations results in the required pressure distribution, from which the flow rate distribution is obtained. Solution for the isothermal Newtonian flow problem is obtained by a one-time solution of the equations, whereas solution of a non-Newtonian problem requires iterative solution of the equations.
131 citations
TL;DR: A new kind of acetal fiber has been discovered which has a tensile strength of 1.7 GPa (250,000 psi) and an elastic modulus of 35 GPa(5 × 106 psi) as mentioned in this paper.
Abstract: A new kind of acetal fiber has been discovered which has a tensile strength of 1.7 GPa (250,000 psi) and an elastic modulus of 35 GPa (5 × 106 psi). This fiber is produced by a special two-stage drawing process in the solid state which requires careful control of deformation rate and temperature. Previously known drawn fibers are reported to consist of folded-chain blocks joined by a limited number of tie-molecules. It is hypothesized that the second stage of the novel drawing process eliminates the lamella (block) surfaces which act as strength-limiting stress concentrators. A new type of fiber is created in which any remaining chain-folds are distributed as defects in a continuous crystal matrix. It is the continuity of the crystal matrix which is believed responsible for the remarkable properties of the fiber.
107 citations
89 citations
TL;DR: In this paper, a mold with interchangeable cavity plates was built and used with an Instron capillary rheometer, type MCR, to investigate the injection molding process.
Abstract: A specially-designed mold with interchangeable cavity plates was built and used with an Instron capillary rheometer, type MCR, to investigate the injection molding process. Flow patterns in the mold cavity were illustrated with a visual tracer technique. The complete deformation history of the tracers was recorded on a motion picture for several runs. The flow patterns provide data for computing the components of the rate-of-deformation tensor which is used to identify specific shear and extensional flows. The tracer marks in the cross section of a molding offer information on the skin thickness and the dimensions of the core channel.
76 citations
TL;DR: In this paper, flow patterns have been observed during the injection molding of low-density polyethylene and polystyrene melts under various molding conditions, including isothermal and cold cavity wall conditions.
Abstract: Flow patterns have been observed during the injection molding of rheologically characterized low-density polyethylene and polystyrene melts under various molding conditions. Some studies of high-density polyethylene were also carried out. Various mold designs were included in the study and the flow patterns investigated under both isothermal and cold cavity wall conditions. In addition to investigating injection molding of single polymer melts, flow patterns in the sandwich molding of polyethylene and polystyrene were studied.
70 citations
TL;DR: In this paper, two component topologically-interpenetrating polymer networks were made of the SIN type composed of two polyurethanes (a polyether-based and a polyester-based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters.
Abstract: Two component topologically-interpenetrating polymer networks were made of the SIN type (simultaneous interpenetrating network) composed of two polyurethanes (a polyether-based and a polyester-based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters. The linear polymers and/or prepolymers were combined in solution and in bulk together with the necessary crosslinking agents and catalysts. Films were cast and chains extended and crosslinked in situ. All of the IPN's exhibited one glass transition (Tg) intermediate in temperature to the Tg's of the component networks, and as sharp as the Tg's of the components. This suggests that phase separation may not occur and thus some chain entanglement (interpenetration) of the two networks is involved. The observed Tg's are always several degrees lower than the arithmetic means of the component Tg's. A theory based on interpenetration is developed to account for this.
TL;DR: In this paper, a simple method for predicting the primary normal stress function, θ, from viscosity data is proposed, based on the Goddard-Miller rheological equation of state.
Abstract: A simple method for predicting the primary normal stress function, θ, from viscosity data is proposed. A relation between θ and the viscosity function, θ, based on the Goddard-Miller rheological equation of state, is given. An easy-to-use generalized chart for estimating θ from θ is presented; in order to use this chart, viscosity data must be available from the zero-shear-rate value of the “power law region.” The method was applied to six polymer melts, three polymer solutions, and an aluminum soap solution for which θ had been measured experimentally. Even though θ varied by a factor of 103 over the examined range of shear rate, the theory and experiment seldom differed by more than a factor of 2. The generalized chart for θ was combined with Tanner's theory to prepare a graph which may be used to estimate jet swell from viscosity data. Comparison with experimental data of jet swell for 4 polymer melts shows good agreement.
TL;DR: In this paper, the transport equations for a power law fluid are used to solve the transient and non-isothermal problem of filling a disk-shaped cavity, using the results obtained it is possible to predict gate pressures, fill times and short shots.
Abstract: The transport equations for a power law fluid are used to solve the transient and non-isothermal problem of filling a disk-shaped cavity. Using the results obtained it is possible to predict gate pressures, fill times and short shots. Furthermore, the velocity and temperature fields can be obtained throughout the filling process. This information specifies the formation of a frozen surface layer during filling. Rigid PVC was primarily used in the simulations, but some results are also given for linear polyethylene, nylon 6–6, ABS and polystyrene.
TL;DR: In this paper, the equilibrium penetrant content of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature.
Abstract: The equilibrium sorption of n-hexane vapor and n-hexane liquid in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature. These equilibrium sorption measurements were supplemented by density determinations, refractive index measurements, differential scanning calorimetry and differential thermal analysis. A seemingly complicated pattern of results emerged when the equilibrium penetrant content was plotted as a function of blend composition. At relatively low activity and temperature the equilibrium concentration of n-hexane in these films monotonically increased with poly(phenylene oxide) content in the blend. Conversely, at high activities and in unit activity liquid, the equilibrium penetrant concentration exhibited a distinct minimum when plotted as a function of blend composition. At higher activities, solvent induced crazing accompanied the sorption of penetrant. These results were explained consistently by considering the nature of the sorption isotherm over an activity range sufficient to lower the glass transition temperature, of the equilibrated and swollen blend, below the temperature of the sorption experiment. Most importantly, the interpretation and explanation of these data are based upon phenomena common to all glassy polymer-organic penetrant systems and no special properties of this blend system were included in the analysis. The results, therefore, reflect the apparent homogeneity of polystyrene-poly (phenylene oxide) blends and are useful in considering the equilibrium of penetrant sorption in glassy polymers as a general class of materials.
TL;DR: In this paper, a rheological analysis of a wire-coating die is presented, in which lateral forces related to the secondary normal stress function acting on the wire are considered.
Abstract: A rheological analysis of a wire-coating die is presented. The rheological forces which might play a role in the stability of the wire are estimated. In particular, consideration is given to lateral forces related to the secondary normal stress function acting on the wire which is in an eccentric position, and the hydrodynamic force related to the viscosity function acting on the wire which moves at an angle to the die axis. For the former a simple, yet general, expression was derived by solving the flow problem (without axial pressure gradient) with the Ericksen equation in bipolar coordinates. Results indicate that normal stresses stabilize the wire, i.e., tend to restore it to the central location, provided the secondary normal stress function is negative. The hydrodynamic effect tends to reduce the angle between wire and die axes, thus drawing attention to the need of perfect mechanical centering of the guider tip, since in this case this effect also reduces eccentricity. The need is stressed for further work, in particular, experimental measurement of the secondary normal stress function.
TL;DR: In this article, the development of impact polystyrene and types of processes used are traced from its inception, and the prior art and patent picture, before and after the issue of the Dow basic patent, is discussed.
Abstract: The development of impact polystyrene and types of processes used is traced from its inception. Our accidental discovery of the process has resulted in the process being termed unique in that no other commercial polymerization has a like phenomenon that occurs in the shearing agitation step. The prior art and patent picture, before and after the issue of the Dow basic patent, is discussed. The litigation that has centered around the patent is reviewed. Information presented shows that this basic process for impact polystyrene has experienced an unusual degree of commercial success and has led to this family of plastics becoming of major commercial importance. These impact plastics have been accepted and used on a global basis.
TL;DR: In this article, the mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported and a number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density.
Abstract: The mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported. Both organic and inorganic fiber reinforcements were used in fiber volume fractions of 0.10 to 0.50. A number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density. The dependence of composite properties on the properties of the constituent materials is discussed. Fiber efficiency factors for strength and modulus are presented and models for predicting composite mechanical behavior are reviewed.
TL;DR: In this paper, a concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers, and several samples of polyethylene oxide (Carbowax 4000, Carbowax 20-M, and WSR-205) were used.
Abstract: A concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers. This instrument allows crystallization to be followed at both constant temperature and shear rate. Several samples of polyethylene oxide (Carbowax 4000, Carbowax 20-M, and WSR-205) were used. A low molecular weight fraction of the Carbowax 20-M, as well as the unfractionated material, was crystallized under shear. The WSR-205 was studied only in a mixture with Carbowax 4000. It was shown that the kinetics of crystallization of uncrosslinked melts of polyethylene oxide are altered by shear. The induction times for the appearance of crystallinity are shorter in the sheared systems than in the quiescent melts. The Avrami exponents are also higher for crystallization in sheared melts than in quiescent systems and increase with decreasing supercooling. The high values of the Avrami exponent are attributed to the disruption of crystalline aggregates into particles larger than the critical sized nucleus. These particles will persist in the melt and continue to grow spontaneously. A continuous infusion of growing particles into the melt occurs.
At constant temperature and shear rate, the induction time of the crystallization curve is influenced by polymer molecular weight. In moderate to high molecular weight samples, the effect of shear becomes saturated at very low shear rates. Decreasing the molecular weight separates the crystallization curves. The curves from the higher shear rates appear at the shorter induction times. However, decreasing the molecular weight below that at the critical entanglement molecular weight allows the nucleation rate, strongly dependent upon the supercooling, to influence the relative positions of the sheared crystallization curves.
TL;DR: In this paper, the authors evaluated the susceptibility of styrene-acrylonitrile copolymers according to the factors which effect craze initiation and those which limit the rates of flaw propagation.
Abstract: Glassy, amorphous thermoplastics experience a nearly universal susceptibility to crack and craze formation in the combined presence of stress and a chemical environment. This susceptibility has been evaluated for styrene-acrylonitrile copolymers according to the factors which effect craze initiation and those which limit the rates of flaw propagation. Molecular weight, styrene-acrylonitrile ratio, rubber content, and rubber phase morphology are variables which were found to affect flaw initiation and propagation. Fundamental characterization of the chemical parameters which control the initiation of craze formation in polysulfone and polycarbonate is also presented. In particular, “3-dimensional” solubility parameters have been observed to be a reasonable means of characterizing susceptibility to environmental stress cracking.
TL;DR: In this paper, the spiral mold method was used in a study of phase separation occurring in glass-containing polyethylene and polyamide melts, and the results showed a decrease in glass concentration near the center of the spiral.
Abstract: The spiral mold method (moldability test) was used in a study of phase separation occurring in glass-containing polyethylene and polyamide melts. Pronounced separation effects were recorded for low density polyethylene containing 25 percent glass spheres with diameters ranging approximately from 50 to 100 μm, the glass concentration at the tip of the spiral exceeding 40 percent by weight. For melts containing smaller spheres or fibers the effect was of the order of a few percent. There was a decrease in glass concentration near the center of the spiral.
TL;DR: In this article, a theoretical model for the simulation of dynamic operation of a plasticating extruder is proposed, which can be used as a tool to study various dynamic situations of interest in the operation of an extruder.
Abstract: A theoretical model for the simulation of dynamic operation of a plasticating extruder is proposed. The model can be recommended as a tool to study various dynamic situations of interest in the operation of an extruder. Several responses to changes in operating conditions are discussed. They indicate the occurrence of transient maximas and occasional oscillations. The controlling of flow rate by adjusting a valve at the die seems to cause temporary local high peaks in pressure, whereas its control through screw speed seems to be satisfactory.
TL;DR: In this paper, the effects of mold temperature and flow on the size and orientation of spherulitic and transcrystalline regions are discussed, and deformation at the weld line under uniaxial tensile stress is analyzed by optical microscopy.
Abstract: The morphology of isotactic polypropylene in molded plaques containing a knit line is described in detail. The effects of mold temperature and flow on the size and orientation of spherulitic and transcrystalline regions are discussed. Deformation at the weld line under uniaxial tensile stress is analyzed by optical microscopy.
TL;DR: In this article, simultaneous interpenetrating polyacrylate and polyurethane networks were made by mixing several concentrations of the linear polymer and prepolymer in solution, together with their respective chain extending and cross linking agents and catalysts, casting films and curing them in situ.
Abstract: Interpenetrating polymer networks of the SIN type (simultaneous interpenetrating networks) composed of a polyacrylate and a polyurethane were prepared. They were made by mixing several concentrations of the linear polymer and prepolymer in solution, together with their respective chain extending and crosslinking agents and catalysts, casting films and curing them in situ. The morphology was studied by differential scanning calorimetry and electron microscopy in order to determine the extent of chain entanglement of the two networks (interpenetration). It was found that little or no phase separation occurred, thus implying extensive interpenetration.
TL;DR: In this paper, the temperature dependence of the mechanical properties of a 50/50 blend of PVAC and lightly crosslinked PMMA has been examined using the data of Kawai et al. The shift distances, log aT, were generated by bringing the experimental data into coincidence on master curves calculated from a Takayanagi model whose parameters were varied in different regions of temperature.
Abstract: The temperature dependence of the mechanical properties of a 50/50 blend of PVAC and lightly crosslinked PMMA has been examined using the data of Kawai et al. The shift distances, log aT, were generated by bringing the experimental data into coincidence on master curves calculated from a Takayanagi model whose parameters were varied in different regions of temperature. This method allows one to construct a master curve for a thermorheologically complex two-phase material if the model and the mechanical properties of the constituent phases and their temperature dependence is known. The shift distances then provide insight into the intricate relations between the time and temperature dependence of the mechanical properties of the composite.
TL;DR: In this paper, the Boltzmann superposition principle was used to predict the creep of polyethylene and polypropylene for approximately 132 000 hr. with a reasonable accuracy.
Abstract: : Creep tests at constant stress, temperature and relative humidity for two thermoplastics were conducted for approximately 132 000 hr. The strains for the first 2000 hrs were described by an equation. This equation was found to predict the creep of PVC for approx-imately 132 000 hr. with reasonable accuracy. The predicted strains for polyethylene were somewhat low. Strains during unloading and reloading after 90 000 hr. of creep were pre-dicted reasonably well by the Boltzmann superposition principle. (Author, modified-PL)
TL;DR: In this paper, the spectroscopic techniques of reflection-absorption and internal reflection in the infrared region were used to define and characterize overall chemical changes occurring at a metal-polymer interface.
Abstract: By incorporating the spectroscopic techniques of reflection-absorption and internal reflection in the infrared region, we have been able to define and characterize overall chemical changes occurring at a metal-polymer interface. Our initial studies have concentrated on the oxidative degradation of metal-polymer systems. These systems are of particular importance because of the common need to retard the metal-catalyzed degradation of the polymer. Preliminary results for copper-polyethylene interfaces, models for polyolefin-insulated cable, have shown the copper surface to be the site of the initial catalysis in the oxidation of the polyethylene. When copper deactivators are added to inhibit the oxidation, initial reactions between the copper surface and the inhibitor can be seen. The importance of these surface reactions highlights the necessity for studying the interface.
TL;DR: In this paper, a modified Larson-Miller master rupture curve is proposed which can predict the long-term strength of particulate-filled thermosetting composites as functions of rupture time, temperature, filler size, and content.
Abstract: Particulate-filled thermosetting composites are widely used, yet little systematic work has been done on their long-term strength characteristics. In this study short-term tensile, flexural, and impact tests as well as tensile creep-rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short-term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson-Miller master rupture curve is proposed which can predict the long-term strength of particulate-filled thermosetting composites as functions of rupture time, temperature, filler size, and content.
TL;DR: In this article, the chemo-rheological behavior of three high temperature epoxy resins, Ferro E-293, 3M PR-286 and PR-288, was elucidated using a modified Weissenberg Rheogoniometer.
Abstract: The chemo-rheological behavior has been elucidated for three high temperature epoxy resins. Constant temperature and shear stress measurements were made on a modified Weissenberg Rheogoniometer. Curing behavior of various temperatures is unified by a time-temperature superposition method. The curing rate of one resin, Ferro E-293, is limited by the chemical reaction. The other resins, 3M PR-286 and PR-288, each have consecutively occurring reactions, both of which are diffusion limited. The chemo-rheological information obtained for these materials is used to model viscosity for compression molding of hand-laidup composites.
TL;DR: A class of negative electron-beam resist copolymers of glycidyl methacrylate and ethyl acrylate is described in this paper, which have excellent lithographic characteristics.
Abstract: A class of negative electron-beam resists is described which have excellent lithographic characteristics. The resists are copolymers of glycidyl methacrylate and ethyl acrylate. Their molecular weights, epoxy contents, and polydispersivities can be controlled to give an adjustable range of electron sensitivity and contrast. The copolymers are compared to other epoxy containing, negative electron-beam resists.
Micrography of resist profiles generated from a single line scan of the electron beam have been used to illustrate the complex interaction of accelerating voltage of the electron beam and resist contrast on resolution. Optical gratings made from single line scans of the beam have feature sizes less than 300 nm in the resist, etched metals, and dielectrics.
TL;DR: In this article, the dynamics of blade-coating of a viscoelstic fluid onto a moving sheet is described by an empirical constitutive equation which shows non-Newtonian viscosity and finite normal stress behavior consistent with typical observations of polymeric fluids.
Abstract: A theory is presented which describes the dynamics of blade-coating of a viscoelstic fluid onto a moving sheet. The method begins with the usual “lubrication” approximation, and develops the solution as a perturbation about the Newtonian case. Viscoelasticity is described by an empirical constitutive equation which shows non-Newtonian viscosity and finite normal stress behavior consistent with typical observations of polymeric fluids. Theoretical results indicate a small increase in coating thickness due to departure from Newtonian behavior, and a significant decrease in the magnitude of the pressure developed under the blade. Consequently, the blade loading can be reduced significantly by viscoelastic effects. The results for the loading may be an artifact of the specific constitutive model, since it can be shown that some viscoelastic fluids, specifically an “elastic Newtonian” fluid, would exhibit increased loading relative to the inelastic Newtonian case.