摘要:

AbstractThermotropic liquid crystal polymers have been modeled as an array of highly ordered polyhedric nematic domains immersed in a less‐ordered, nearly isotropic matrix. A function has been defined that expresses the elastic moduli of drawn fibers as a function of orientation and geometry of the nematic domains. When such a material is hot drawn in extension, the domains orient and elongate to produce an orthotropic fibrous phase. Equations are proposed to relate the elastic moduli of the fibers to the draw ratio and the extrusion conditions. Upon annealing of the hot drawn fibers, shrinkage occurs. It is proposed that the shrinkage is the result of a physical transformation from the fibrous state back to the nematic domain structure present before extrusion and drawing. The Avrami equation is used to describe the nucleation and growth processes controlling the shrinkage at constant annealing temperature. The model is shown to correlate experimental data on the elastic properties and the shrinkage of hot drawn PET/PHB60 liquid crystal polymer with the processing condition

ISSN:0032-3888    

DOI:10.1002/pen.760290302

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe development of molecular orientation and internal stresses in extruded sheet made of polypropylene was analyzed, and their correlations to operating conditions such as draw ratio, cooling rate, die temperature, melt temperature, and die gap opening were studied. Measurements of attenuated‐total‐reflectance infrared dichroic ratio for the surface molecular orientation, birefringence for the orientation stress distribution in the thickness direction, and free shrinkage ratio for the overall frozen‐in stresses were carried out to determine the amount of orientation stresses in the extruded samples. As expected, the overall orientation stress depends strongly on draw ratio, while higher melt temperature reduces the overall orientation. It was found that faster cooling rates and lower die temperatures cause surface orientation stresses to increase as the core orientation stresses remain almost unch

ISSN:0032-3888    

DOI:10.1002/pen.760290303

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA new method has been developed to measure the three‐dimensional temperature distribution of polymer melts in the reservoir of the heating barrel in the dynamic state. The procedure involves the use of a small‐sheathed thermocouple in the nozzle of the machine. The tip of the thermocouple can be varied in depth from the surface to the center of the nozzle. The polymer melt of a shot is found to have a three‐dimensional temperature distribution dependent on the geometry of the screw and the order of shot. These results reflect clearly the thermal histories of the polymer melt in the channel of the screw during plastication and conveyance, and indicate part of the dynamics of injection molding. Further, these measurements contribute to optimization of the design for the screw and the process condi

ISSN:0032-3888    

DOI:10.1002/pen.760290304

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractAn experimental study of polymer soluticn devolatilization in a counterrotating twin‐screw extruder has been undertaken. In an effort to ultimately predict mass transfer rates in such a process, this work analyzes the experimental results to determine the controlling mechanisms in the separation of volatile components from the polymer. The devolatilization process at hand encompasses the heavily foaming and nonfoaming regimes. Historically, the literature has centered primarily around the highly concentrated, bubble‐free diffusion‐controlled devolatilization regime. The analysis presented in this paper centers on the performance of the heavily foaming stages of the process. Recent and previously reported (1) data on the polystyrene/ethylbenzene (PS/EB) system, as well as newly collected data on the poly(methyl methacrylate)/methyl methacrylate (PMMA/MMA) system, are analyzed. In the foaming stages of the process, two regimes have been found. These regimes are differentiated by the availability of volume into which the foam can grow. Deformation and mixing effects appear to be secondary. Furthermore, temperature changes across the range of realistic operating conditions appear to affect mainly the thermodynamic driving force. It is only at extremely high temperatures that these effects are truly contro

ISSN:0032-3888    

DOI:10.1002/pen.760290305

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractInjection molding of polyethylene was carried out using molds that introduce axial elongational flow during the filling process, As compared with conventional injection‐molding methods, the present technique yields polyethylene materials having higher mechanical strengths (σ ≈ 150 MPa). The σ‐value of the moldings can be systematically monitored by adequately varying the elongational flow through modification of the mold geometry. Geometrical features of the volume containing the melt before injection as well as geometry of the die, the extruder, and the inlet influence the overall elongational flow, and thus, the mechanical strength of the m

ISSN:0032-3888    

DOI:10.1002/pen.760290306

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractIn the first part of this series, the influence of mold geometry was examined with reference to the improvement of the mechanical properties of elongational flow injection‐molded polyethylene. In the present study (Part 2), processing parameters have been investigated and the physical properties of the moldings examined. It is confirmed that mainly two parameters, the temperature of the melt and the pressure on the solidifying mold, govern the injection process. Results are discussed in terms of the molecular orientation that is developed during the filling process and depends on the temperature of the melt. The application of high pressures leads to a pressure‐induced crystallization effect that freezes in the molecular orientation within the m

ISSN:0032-3888    

DOI:10.1002/pen.760290307

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA thermocouple ring‐bar device located between the nozzle and screw‐tip was used to study the thermal homogeneity of a shot formed during injection molding. Axial and radial melt temperature profiles thus observed under various processing conditions illustrated the importance of screw channel volume‐to‐short‐size ratio on melt homogeneity, Several methods of improving melt quality, as measured by this device, are dem

ISSN:0032-3888    

DOI:10.1002/pen.760290308

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760290301

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY