ISSN:0032-3888    

DOI:10.1002/pen.760181002

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe parison extrusion and the effects of post‐extrusion swelling and sagging in the blow molding process have been studied by several authors and some qualitative relationships with rheological parameters have been attempted. The aim of this work is to show that, under some simplifying assumptions, the relevant rheological parameters—the swelling of the parison and its tensile compliance—can be directly determined from the viscoelastic analysis of the process. The reliability of the model has been tested by experiments carried out by the pinch‐off mold technique which provides the parison weight profile as a function of both previous extrusion history and mold closing delay. First of all it has been shown that the proposed model is suitable to represent the data. The swelling behavior shows the expected dependence on time and shear rate and the long‐time swelling data compare well with those determined by capillary extrusion experiments. It has also been found that the measured tensile compliance is of the same order of magnitude as that determined by conversion of tensile relaxation experiments; however, in the blow molding experiments the compliance of the parison decreases with increasing extrusion shear rate, i.e., by increasing the induced anisotropy of the polymer. As rheological examples, the performance displayed on both industrial and laboratory machines is discussed for three high density poly

ISSN:0032-3888    

DOI:10.1002/pen.760181003

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractWhen 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 t

ISSN:0032-3888    

DOI:10.1002/pen.760181004

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe empirical equation proposed by Lyons and Tobolsky (1) to describe the concentration dependence of zero‐shear viscosity in polymer solutions was tested on a variety of data taken from the literature, covering different polymer‐solvent systems, molecular weight, temperature, and the whole concentration range. This equation was fitted to each set of experimental viscosity‐concentration data by a least squares method. The validity of this equation is verified. The dependence of the optimal values obtained for the three parameters intrinsic viscosity, [η], Huggins constant,k, and new empirical constant,b, on molecular weight, temperature, and solvent is also dis

ISSN:0032-3888    

DOI:10.1002/pen.760181005

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA rheological model of solid polymers is proposed. Its mechanical analog is a parallel of a linear spring and a Maxwell element with variable viscosity. The viscosity of the dashpot is allowed to change with stress both directly, by an Eyring‐type mechanism, and through free volume changes according to the Doolittle equation. Predictions of the model reproduce many of the features shown, especially after yielding, by constant velocity stress‐strain, stress‐relaxation and creep data taken at room temperature on biaxially‐oriented poly(ethylene terephthalate) over a wide range of loadin

ISSN:0032-3888    

DOI:10.1002/pen.760181006

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractParticulate‐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 particl

ISSN:0032-3888    

DOI:10.1002/pen.760181007

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAn important parameter in the various molding techniques used in polymer processing is the rate of cooling the object. The effect of the thermal history on the linear viscoelastic properties was studied, mainly by means of stress relaxation experiments on ABS samples in which the influence of other process variables was eliminated. In agreement with recent literature data, it appeared that the time dependence of the stress can be represented by a universal formula, provided that no perceptible change in temperature or relaxation of volume takes place during the experiment. The position of the momentary relaxation curve along the time scale can therefore be described by one characteristic mechanical relaxation timetr. The value oftris affected by the temperatureT, but even more by the thermal history, i.e., by the rate of cooling,q, and the annealing time,ta, at the measuring temperature previous to recording of the relaxation curve. In the case of very rapidly quenched samples, exact proportionality was found to exist betweentrandtaat temperatures belowTg−15°C. In slowly cooled samplestrcan be longer by a factor of ten than in quenched samples, at the sameTand at annealing times of about 1 h. The difference decreases with increasingta, but remains substantial up totavalues much longer than the total cooling ti

ISSN:0032-3888    

DOI:10.1002/pen.760181008

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe dependence on frequency of the limiting value of strain, ψL, for which linear Viscoelastic response occurs in eccentric rotating disks (ERD) flow is studied theoretically and experimentally. The theoretical investigations are based upon the general simple‐fluid theory of Coleman and Noll. It is shown that according to this theory ψLbecomes independent of angular velocity, ω, at relatively high frequencies, whereas ψLbecomes inversely proportional to ω at sufficiently low frequencies. The results of previous investigations, based upon some special rheological models, are discussed. The behavior predicted by the simple‐fluid theory is confirmed by experiments on polyisobutylene s

ISSN:0032-3888    

DOI:10.1002/pen.760181009

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThis paper describes the use of the Rheovibron visco‐elastometer in the shear mode. A new self‐centering sample holder was designed allowing the evaluation of the real and imaginary parts of the shear modulus on low modulus materials such as polymer melts, uncrosslinked and slightly crosslinked elastomers, and elastoplast

ISSN:0032-3888    

DOI:10.1002/pen.760181010

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThis paper deals with two kinds of internal stresses in amorphous polymers. First, the internal stresses connected with molecular orientation are discussed. A framework is presented that describes the interrelations of the various orientation effects (anisotropy, birefringence, etc.) and their dependence on the thermomechanical history of the material. The second part of the paper deals with the residual thermal stresses generated by rapid inhomogeneous cooling through the glass transition range. These so‐called cooling stresses are well‐known in glass technology. The theory of the quenching of flat glass plates is described, generalized to objects of arbitrary geometry, and shown to be applicable to polymers. The practical importance of cooling stresses is discus

ISSN:0032-3888    

DOI:10.1002/pen.760181011

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY