摘要:

AbstractThe current state of the art on polymer devolatilization is reviewed. After a brief description of existing processes, two aspects of the problem are taken into consideration: modeling and optimization of actual processes, and physicochemical data needed for analysis. It is shown that, while many of the available models concentrate on the fluid mechanics involved and on mass transfer, heat transfer may well be the rate determining phenomenon. Values of the relevant physicochemical parameters may range over several orders of magnitude within any given process, and the availability of reliable data over the ranges of interest is in general significantly less good than would be needed for reliable analysis.

ISSN:0258-0322    

DOI:10.1002/masy.19930680103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA novel device to fit on the exit of the ACER capillary extrusion rheometer has been designed to allow the controlled application of hydrostatic pressure to the body of the fluid under test. The rheological properties of the fluid can be examined over a wide range, ambient to 200MPa. This paper will describe the equipment and the effect of hydrostatic pressure and temperature on the flow properties to the various polymer melts, PC, ABS, PP and HDPE.

ISSN:0258-0322    

DOI:10.1002/masy.19930680104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report an evaluation of the use of Binding's method (Ref 11) for determining extensional viscosity values from capillary die rheometry entrance pressure drop data. A constitutive relation defining the fluid's rheological behaviour is first postulated, from which the pressure drop in a contraction region is calculated by numerical simulation for a range of flow rates. Extensional viscosity estimates are then made from the simulated pressure drop data using Binding's method, and these estimates are compared with the exact extensional viscosity determined from the constitutive relation. A highly accurate augmented spectral method is used to perform the numerical simulation. The Binding estimates obtained are good for certain types of fluid, but poor for others. A simple empirical correction of the Binding method, however, is found to give good agreement in all the cases studied.

ISSN:0258-0322    

DOI:10.1002/masy.19930680105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rheological and kinetic behavior of a new commercial toughened epoxy matrix is characterized through a complete experimental program. The kinetic behavior of the thermosetting resin is described by applying a new empirical model, accounting for autocatalytic and difussion control effects. The rheological model uses the kinetic information and describes the matrix viscosity as a function of temperature and degree of reaction using only three fitting parameters. The complete model is verified through calorimetric and rheological tests performed at different temperatures (isotherms) or heating rates (dynamic tests); or under more complex conditions simulating the processing conditions during autoclave lamination. Finally the chemo‐rheological model is considered as a part of a master model describing the complete processing behavior of thermoset matrix composites. The use of the master model in control and optimization algorithms is also illustrate

ISSN:0258-0322    

DOI:10.1002/masy.19930680106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe determination of residual stresses in thin polymer coatings is important for the prediction of failure due to delamination and cracking. If the internal tensile stresses exceed the cohesive strength of the solid coating, cracking may occur which can result in coating ‐ substrate delamination. This is especially important in the coatings and electronics industries in which coating reliability is central to the performance of a product. There are three primary causes of residual stresses in coatings, 1.) Chemical reactions in which a condensation molecule is evolved and given off during processing, 2.) Evaporation of solvent or carrier solution during drying, and 3.) Mismatch in coefficients of thermal expansion between the substate and the coatin

ISSN:0258-0322    

DOI:10.1002/masy.19930680107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA similarity rule due to Markovitz is used for the correlation of the relaxation modulus for different polymeric materials. This rule has long been employed implicitly in the empirical shifting rules for the reduction to common curves of viscoelastic data measured on the same polymer over a range of temperatures and concentrations. It is shown here for the rubbery regime of polydisperse polymers that when relaxation moduli are scaled with the steady‐state compliance and the time with the mean relaxation time, data for a variety of amorphous polymeric materials tend to plot on a common curve. This suggests that the dimensionless rubber modulus is, to first order, a common function of dimensionless time for materials which include whole polymers and polymer solutions, the effects of temperature and concentration being automatically incorporated into the two scaling parameters. For materials with sufficient polydispersity the correlation appears to be valid over a wide range of the available experimental data. These amorphous materials appear to share only one feature, flexible molecules with broadly distributed molecular weights. For narrowly dispersed polymers the modulus in the terminal zone is also correlated according to the above rule, but the influence of other parameters appears as the transition to the glassy regime is approached. An additional application of the similarity rule allows the relaxation modulus computed from molecular dynamics simulations of idealized polymers to be compared with experimental moduli for real materials even though the characteristic times for these systems differ by more than ten orders of magnitud

ISSN:0258-0322    

DOI:10.1002/masy.19930680108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractUniaxial elongation and compression data of linear and branched polymer melts as well as of rubbers are analyzed with respect to their nonlinear strain measure. This is found to be the result of two contributions: (1) affine orientation of network strands, and (2) isotropic strand extension. Network strand extension is caused by an increasing restriction of lateral movement of polymer chains due to deformation, and is modelled by a molecular stress function f, which in the tube concept of Doi and Edwards is the inverse of the relative tube diameter. At small strains, f2is found to be linear in the average stretch for melts as well as for rubbers, which corresponds to an affine deformation of the tube. At large strains, melts show maximum molecular tension depending on the degree of long‐chain branching, while rubbers show maximum extensibilit

ISSN:0258-0322    

DOI:10.1002/masy.19930680109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThermoplastic matrix composites are of increasing technical interest. This new generation of materials is not only comparable to conventional thermosetting systems in terms of performance and durability, but also affords considerable incentive in weight reduction and cost‐effective manufacturing. A careful description of the different intermediate material forms is presented in this paper along with their advantages and inherent drawbacks in processing and the manufacturing steps which follow. The micro‐mechanics of flow and deformation which, however, have to occur are partly different from that known from thermosetting composites and metallic materials. Therefore, the flow and micro‐deformation mechanisms, such as resin percolation, transverse flow and inter as well as intra‐ply slip will be discussed in detail along with their importance to get optimum consolidation of the final com

ISSN:0258-0322    

DOI:10.1002/masy.19930680110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractExperimental developments in different areas of polymer melt rheology and recent results are reviewed: Shear oscillations were performed with mixtures of polyisobutylenes (PIB) of relatively small molecular mass distributions and with blends of polystyrene (PS) and polymethylmethacrylate (PMMA). For the latter, the interfacial tension between the melts of PS and PMMA can be derived from the results. ‐ In constant shear rate flow, the measurement of the first normal stress difference N1in a commercial cone‐and‐plate rotational rheometer is simple if the test temperature is kept extremely constant. By a further modification a partial integral of the pressure distribution is measured from which the second normal stress difference N2can be determined. ‐ The molecular orientation in shear flow results in a rheological anisotropy that can be studied in a parallel‐plate shear rheometer in which the polymer melt sample can arbitrarily be sheared in two perpendicular directions. ‐ For melt elongation by rotary clamps constant, arbitrary ratios of the strain rate components can be applied. Planar elongations of the PIB samples indicate an influence of the width of the molecular mass distribution. More general elongations with a change of the strain rate ratio during the test are of especial interest as is documented by the comparison of the resulting stresses with predictions from different network theories. ‐ In a rheometer for simple elongation at 170°C, recovery after melt extension of the PS/PMMA blends reveals a value of the interfacial tension equal to the one obtained from shea

ISSN:0258-0322    

DOI:10.1002/masy.19930680111

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe present paper considers the problem of predicting extrudate shapes from asymmetrical dies for Newtonian and non‐Newtonian fluids. The flow is fully three‐dimensional and an exploration of finite elements and boundary elements is made with a view to finding accurate, stable and economical schemes. A number of finite elements are compared and we conclude that some of the Fortin elements are most useful on the grounds of computational overhead and solution accuracy. These have been used to investigate some symmetrical (square dies) and asymmetrical (unequal lip) planar and general L‐shaped die flows for Newtonian fluids. The question of predicting regions of plug flow is addressed for materials with a yield stress in the three‐dimensional case. Finally, we show that an unconstrained extrudate may, in absence of gravity, describe a helix in space as the most general

ISSN:0258-0322    

DOI:10.1002/masy.19930680112

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY