摘要:

AbstractIn order to obtain explicit information about the influence of different low density polyethylene (LDPE) quality parameters on extrusion coating processability, a test run was made with an autoclave reactor and the products were investigated. All the grades manufactured had melt indices (MI), densities, molecular weight distributions (MWD), and degrees of long chain branching(LCB) typical of commercial extrusion coating grades. The processability characteristics studied were maximum line speed and neck‐in. The influence of MI, density, and extrusion melt temperature were systematically investigated. It was found that the maximum line speed rose with increasing MI, density, and extrusion melt temperature, and that an increasing extrusion melt temperature led to a growing difference between the maximum line speed at a constant coating thickness and the maximum line speed at a constant screw speed. Neck‐in was found to increase with increasing MI, increasing density, and increasing coating thickness. These effects were more pronounced at higher extrusion melt temperatures. When using the extrusion temperature needed to achieve a certain line speed for each grade, the influence of MI on neck‐in was practically non‐e

ISSN:0032-3888    

DOI:10.1002/pen.760181302

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAn empirical model suggested earlier by B. H. Bersted predicting the rheological properties of linear polyethylene from the molecular weight distribution is modified to account for the rheological properties in steady shear flow of branched polyethylene as well. The shear dependent viscosity, the steady shear compliance, and extrudate swell could be calculated from the distributions of molecular weight and long‐chain branching in good agreement with experimental data for eight commercial low density polyethylenes. Tanner's equation was used to calculated die‐swell from the modified Bersted model. The steady shear compliance was found to be related to\documentclass{article}\pagestyle{empty}\begin{document}$(\overline {gM} )_z .(\overline {gM} )_{z + 1} /(\overline {gM} )_w^2 .$\end{docume

ISSN:0032-3888    

DOI:10.1002/pen.760181303

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractPractical ways of processing thermoset materials by injection molding have been developed. These methods have been used particularly in the automotive and electrical industries. The tensile behavior is discussed for specimens which were injection molded from reinforced and filled phenolic unsaturated polyester and epoxy resin. This behavior aids the layout of flow paths. Under static loads the materials show less creep than most thermoplastics. “Post shrinkage” was observed as a shortening of specimens under prolonged heating. Because of brittleness, the materials failed under dynamic load at low strain. The first microcracks directly initiate the final failure. Before the final failure, the materials craze at a certain strain. By means of different testing methods these strain values were determined. For practical applications, these values should be considered in the designing of thermoset pa

ISSN:0032-3888    

DOI:10.1002/pen.760181304

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractSwelling and hygroelasticity of polymers are discussed in terms of a coefficient of hygroelasticity defined here by analogy with the coefficient of thermal expansion. The relationship between the proposed coefficient and the mechanical properties of the material and the stresses which develop in it is established. The relationship provides means for predicting the lifetime of the polymer under conditions similar to those used for measuring the coefficient of hygroelasticity. The experimentally examined behaviors of two systems, polyester‐boiling water and epoxy‐methylene chloride at 18°C, are in reasonable agreement with the predict

ISSN:0032-3888    

DOI:10.1002/pen.760181305

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760181306

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe effects of thermal treatment, residual solvent, and preswelling on the thermal properties and swelling behavior of solution cast polyblend films of poly(2,6‐dimethyl,1,4‐phenylene oxide) (PPO) and polystyrene (PS) were determined. Repeated cycling in the DSC analysis of the “as cast” films suggested that the original films contained residual casting solvent and that solvent‐induced crystallization occurred in the PPO‐rich compositions. Crystallinity was, apparently, eliminated by the first heating cycle in the differential scanning calorimeter. Sorption kinetics and apparent equilibria, characterizing the penetration of these films by n‐hexane from the vapor phase, indicated that both the sorption rate and apparent equilibria are significantly affected by the prior history of the film samples. The sorption results presented here are quantitatively consistent with earlier studies of the PPO‐PS system. The increased rate and amount of sorption observed in preswollen samples, and the reduced rate and amount of sorption observed in annealed samples are consistent with recent descriptions of sorption behavior in diverse glassy homo

ISSN:0032-3888    

DOI:10.1002/pen.760181307

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe kinetics of the dibutyltin dilaurate catalyzed bulk polymerization of 4,4′‐diphenylmethane diisocyanate (MDI) with poly‐ϵ‐caprolactone were studied by infared spectroscopy and adiabatic temperature rise. The overall reaction order was found to change from 3/2 to 2 with increasing temperature. At temperatures above 80°C, the order with respect to catalyst was found to decrease with concentration from 1 to 1/2. The results were consistent with a Michaelis Menten type kinet

ISSN:0032-3888    

DOI:10.1002/pen.760181308

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractWire coating extrusion was studied, both experimentally and theoretically, using a pressure‐type die. For the experimental study, a wire coating apparatus of laboratory scale was constructed, consisting of a pay‐off device, extruder, cross‐head and pressure‐type die, cooling trough, and take‐up device. The materials used were low‐ and high‐density polyethylenes and thermoplastic rubber. The following measurements were taken during the experiments: (1) the axial pressure profiles in the die, (2) melt flow rate, and (3) take‐up speed. The measurements were then used to determine the effect of the rheological properties of the polymers on the performance of the wire coating operation. It was found that a reduction in axial pressure gradient and a reduction in the recoverable elastic strain of a molten polymer at the die exit can be realized as the speed of the wire is increased. 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 polymer being extruded. Solution of the system equations permitted us to predict the velocity profile and shear stress distributions of a molten polymer inside a pressure‐ty

ISSN:0032-3888    

DOI:10.1002/pen.760181309

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe cooling of a crystallizing polymer is analyzed taking into account the effect of pressure drop on the energy balance. Thermal conductivity and diffusivity of a low density polyethylene are determined at pressures between 0.1 and 150 MPa (1 and 1500 bars). Using a pressure, volume, temperature‐diagram, a complete set of material functions could be obtained. A numerical cooling model based on these material functions was established and tested experimentally. Good agreement between the model and experiment was obtained. The numerical algorithm of the model can be adapted easily to plastics processing operations, e.g., injection molding, blow molding, and extrusio

ISSN:0032-3888    

DOI:10.1002/pen.760181310

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractShear stress and first normal stress difference data are presented for materials which exhibit a constant viscosity and yet at the same time exhibit elasticity levels of the same order as polymer melts. Flow pattern observations in circular die entry flows in conjunction with independent shear and normal stress measurement strongly suggest that these fluids would make excellent model fluids for melt studies. Studies in which the influence of elasticity in the absence of shear thinning and fluid inertia can easily be made. Furthermore it is clearly shown that a realistic solution to the die entry flow problem is not obtained using second order flow theory. In the second order region the secondary cell is observed to be almost identical in size to the cell observed for an inelastic Newtonian fluid in creeping flow. Marked growth in the secondary cell as a function of elasticity is not observed until the shear rates exceed the region of second order behavior. This growth in cell size as a result of elasticity is followed at higher shear rates by a spiraling flow instability like that observed for some polymer melts.

ISSN:0032-3888    

DOI:10.1002/pen.760181311

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY