摘要:

AbstractCapillary viscometers have been used extensively, because of their simplicity and reliability, to measure the viscosity of fluids over a wide range of shear rates. However, in capillary flow, the shear rate is not uniform throughout the capillary, a pressure gradient is established in the direction of flow, and the temperature of the fluid is nonuniform due to viscous dissipation. In the present work, a general, simple and practical method is proposed for correcting for the effects of pressure variation and viscous dissipation in determining the viscosity of polymer melts at high pressures. The method essentially involves the estimation of temperature, pressure, shear rate, and shear stress under a variety of experimental conditions at a predetermined point in the capillary. As such, it may be considered as a generalized extension of the classical Rabinowitsch‐Mooney method for estimating true viscosity in capillary flo

ISSN:0032-3888    

DOI:10.1002/pen.760200202

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe problem of the migration of impurities from plastic containers has been analyzed, and the effect of the outward diffusion of the container contents on the impurity migration has been considered. The system of equations describing the coupled diffusion problem has been solved using finite‐difference methods, and an analytical solution has been developed for the initial stages of the mass transfer process. It was found that the outward diffusion of the container contents can exhibit a large effect on the migration of impurity if the ratio of the diffusivity of the container contents to the diffusivity of the impurity exceeds 100. Sufficiently large values of this diffusivity ratio and of the impurity partition coefficient can minimize the buildup of undesirable impurities in the contents of a plastic containe

ISSN:0032-3888    

DOI:10.1002/pen.760200203

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAn experimental and theoretical study of wire coating coextrusion through a pressure‐type die was carried out. For the experimental study, the wire coating apparatus employed was the same as that described in Part I of this series (14), except for the newly constructed coextrusion die. The die was provided with three melt pressure transducers along the axial direction, which permitted us to determine the pressure gradient in the die. It was found that a reduction in pressure gradient was realized when a lower viscosity polymer was coextruded with a high viscosity polymer. The materials used for the coextrusion were combinations of low‐density polyethylene, high‐density polyethylene, polystyrene, and two different commercially available thermoplastic rubbers (UniRoyal TPR‐1900 and Shell Kraton G 2701). The use of a high shrinking (crystalline) polymer inside a low shrinking (amorphous) polymer was found to give rise to distorted coatings (non‐circular cross section of the coated wire). The interface between the coextruded layers was examined under a magnifying lens, and it was found that under certain processing conditions, the interface was highly irregular. Experimental correlations were obtained to explain the onset of an unstable interface in terms of the rheological properties of the individual components being coextruded, and of the processing variables. It was found that interfacial instability occurs when the shear stress and the viscosity ratio (also elasticity ratio) of the two components at the interface exceed certain critical values. 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 polymers being coextruded. Solution of the system of equations permitted us to predict the velocity profile and shear stress distributions of two molten polymers inside a pressure‐type wire coating coextrusion die. Comparisons were made between the experimental and theoretically predicted volumetric flow rates. The comparison was found to be reasonably good with certain systems. The discrepancy between the experimentally obtained and the theoretically predicted volumetric flow rates was attributed to interface migration and interfacia

ISSN:0032-3888    

DOI:10.1002/pen.760200204

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractFiber spinning experiments were carried out with an α‐methyl styrene/silicone block copolymer under various sets of spinning conditions. The behavior observed was very sensitive to the ambient axial temperature profile employed along the spinline and to the initial melt temperature at the die. By optimizing these parameters, very high draw ratios (>400 to 1) could be achieved. Under less optimum conditions, filament rupture and instabilities such as draw resonance, accompanied by periodic diameter and spinline tension fluctuations, were noted. Tensile stress and axial velocity gradient profiles were obtained along the spinline under a variety of spinning conditions. These profiles, together with an independent: rheological characterization of the polymer, provide insights into the mechanisms giving rise to the various types of behavior observ

ISSN:0032-3888    

DOI:10.1002/pen.760200205

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA mathematical model for polymer flow in the clearance between high‐resistance filter elements is developed. An analytical solution is obtained for pressure and velocity profiles for Newtonian fluids. A numerical solution is obtained for elastic fluids displaying power‐law behavior in viscosity and entrance pressure loss. Elasticity of the polymer melt or solution is shown to be a significant factor in, determining these profiles. An example of the model's application, using rheological data for a commercial polyethylene, is given, and the impact of clearance flow pressure losses on the mechanical side loading of the filter elements is discus

ISSN:0032-3888    

DOI:10.1002/pen.760200206

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractSuspension polymerized poly (vinyl chloride) (PVC) is made up of 150 μm grains. Within these grains are 2 μm primary particles which apparently become the flow units under low melt temperature (175°C) extrusion conditions. The 2 μm particles are visible by light transmission microscopy by shearing the extruded product between glass slides after swelling in acetone or by electron transmission microscopy of ultrathin microtomed samples. This product, made up of 2 μm flow units, is brittle and has poor toughness retention upon weathering. At higher melt temperatures (185–190°C), agglomeration of the 2 μm particles occurs, giving a rough surface but tougher product. At higher melt temperatures, a continuous melt occurs, leading to a smooth surface and tough product with excellent toughness retention upon we

ISSN:0032-3888    

DOI:10.1002/pen.760200207

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA critical angle illumination microscopy technique was used to study thein situdissolution dynamics of polystyrene, poly (α‐methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α‐methylstyrene showed the cracking phenomena exhibited by atacti

ISSN:0032-3888    

DOI:10.1002/pen.760200208

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA two stage drawing procedure is described for producing highly oriented polymeric materials. The high orientation of both the crystalline and amorphous phase in the semi‐crystalline materials studied resulted in the materials possessing high mechanical properties. The ability to obtain high amorphous orientation is critical. Tensile strengths of 16 g/denier for polyethylene are determined, for example. The results suggest that the existence of a prominent crystalline dispersion mechanism (as observed in dynamical mechanical studies) is not necessary for the attainment of high mechanical properties. Thus a method was devised for the determination of the optimum drawing temperatur

ISSN:0032-3888    

DOI:10.1002/pen.760200209

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760200201

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY