摘要:

AbstractThe effect of hydrostatic pressure on molecular deformation of polypropylene extended under hydrostatic pressure is investigated by using internal friction measurements, wide angle X‐ray diffraction, and polarizing microscopy. A homogeneously transparent straight part is obtained by extending samples in the pressure range from 78 to 128 MPa. The overall mechanical properties of a sample extended underP= 102 MPa is significantly different from that of a sample extended underP= 128 MPa. The difference is related to the magnitude of hydrostatic pressure, the extension ratio, and the extent of transparency. The observed results on the β relaxation in the extended samples is found to be related to the morphological reorganization from a coarse spherulitic to a fine spherulitic structure. The cold‐drawn sample at atmospheric pressure has the γ‐peak at around °50°C, while the hydrostatically extruded samples and the extended samples have no γ‐peak. Consequently, the hydrostatic pressure suppresses the formation of the molecular structure relevant to the

ISSN:0032-3888    

DOI:10.1002/pen.760321102

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractFlow simulation to predict the position of the flow front during SMC and IMC compression molding, RIM, SRIM, and RTM, is very useful in obtaining better molded parts. We have derived criteria to determine when the filling stage for these processes can be decoupled and simulated without regard to heat transfer and chemical reaction. We discuss why a Generalized Hele‐Shaw model can be used to predict the flow front. Examples are given of the use of flow simulation in designing and locating SMC charges so as to reduce or eliminate knit lines, in locating IMC injection ports so as to avoid trapping air, in locating RIM injection gates to avoid trapping air and minimize knit‐lines, and in locating vents to avoid trapping air in RTM or SRIM mold

ISSN:0032-3888    

DOI:10.1002/pen.760321103

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA methodology is set forth for the numerical solution of the transient freezing problem of a viscous power‐law fluid flowing in a cold empty tube with a frozen layer forming on the inside tube surface. The fluid considered is the melt of a semicrystalline polymer with temperature dependent viscosity. The solution domain encompasses both the liquid and solid phases. Coordinate transformations are employed to immobilize and to straighten the moving, curved interface. An implicit finite difference method is employed to solve the governing equations. Numerical results are analyzed by examining the effects of the Peclet number, Nahme number, Stefen number, and the power law index on the profiles of the frozen layer. Variations of the thickness of the frozen layer as a function of time and axial coordinate are also presente

ISSN:0032-3888    

DOI:10.1002/pen.760321104

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractMethodologies are developed for studying the steady‐state operation of propylene polymerization in continuous‐flow stirred tank reactors (CFSTRs). The effect of several reactor operating variables and reaction variables (e.g., mean residence time, catalyst deactivation rate, multisite catalyst activity, etc.) on polymer properties is obtained. It is found that a compromise has to be made between the yield of the polymer and its polydispersity index, since they usually show opposing trends with the mean residence t

ISSN:0032-3888    

DOI:10.1002/pen.760321105

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe behavior of unplasticized poly(vinyl chloride) (UPVC) during single screw extrusion was studied. The melting and gelation mechanisms under a variety of operating conditions were identified using microscopy, density measurements, and thermal analysis. The compound followed the behavior of wall‐slipping materials, the melt forming a pool near the passive flight of the screw. Gelation involved the progressive destruction of the original powder morphology and the development, upon cooling, of an entanglement network with primary and secondary crystallinity. Both the breakdown and internal fusion of the grains were observed, depending on the location of the material around the screw. Tensile yield parameters were found to be independent of the gelation level. The values of the post‐yield parameters reached a maximum for gelation levels in the range of 70% to

ISSN:0032-3888    

DOI:10.1002/pen.760321106

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractMost industrial and laboratory blown film lines use an air ring with one or more lips to produce an annular air jet that cools the polymer extrudate. Experience in operating blown film lines indicates that the air flow around the bubble plays an important role in both heat transfer and momentum trasfer. The former has received some attention in the literature, but few investigations have been made on the latter. This paper deals with the aerodynamic aspect of the blown film process. An air flow field similar to that in the blown film process was produced by blowing air past a rigid model. Aerodynamic experiments were carried out to determine the velocity and pressure distributions, and the overall axial force on the rigid model. Theoretical predictions using the techniques of superposition of stream functions and macro‐balances of mass and energy were compared with experimental dat

ISSN:0032-3888    

DOI:10.1002/pen.760321107

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractMany twin screw extruders are operated in the starve‐fed mode with the majority of the extruder having partially‐filled channels. There will always be regions of totally filled channels due to the presence of the die or reverse elements. The authors experimentally show the effect of the change of percent drag flow on the rate of distributive mixing in the co‐rotating and counter‐rotating twin screw extruder. Optimum operating conditions for distributive mixing are identified experimentally and verified theore

ISSN:0032-3888    

DOI:10.1002/pen.760321108

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760321101

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY