摘要:

AbstractTo study the energy dissipation in the different zones of an extruder, a special barrel has been designed where local torquesTqcan be measured at the beginning of the conveying, the transition, and the metering zone. Experiments carried out for a commercial polyethylene and poly(vinyl chloride) at different processing conditions show that in some cases negativeTqin the metering zone may occur. A very basic analytical treatment of the flow situation in the metering zone shows that for a given drag flowTqis dependent on the pressure gradient and particularly on its sign.Tqdecreases with decreasing positive pressure gradient until there is pure drag flow. It further decreases with increasing negative pressure gradient until it becomes zero and even negative. A comparison of theoretical and experimental results for the metering zone shows good quantitative agreement though the main aim of the paper is to provide a better general understanding of the complex situations inside an extruder.

ISSN:0032-3888    

DOI:10.1002/pen.760270302

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAn analysis of flow of a power law fluid in a spiral mandrel die is presented. The analysis is applied to study the effect of various die design parameters on the flow distribution at the end of the spiral mandrel section. Three variables that have a very strong effect on the flow distribution are the number of grooves, the initial clearance, and the groove helix angle. The distribution is improved by increasing the number of grooves, by using a non‐zero initial clearance, and a relatively small helix angle. Two more variables that have a significant effect on the flow distribution are the taper angle and the initial groove depth. The optimum taper angle was found to be between 1 and 3 degrees. The distribution uniformity improves with the initial groove depth, while the pressure drop reduces at the same tim

ISSN:0032-3888    

DOI:10.1002/pen.760270303

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAn attempt is made to gain better physical insight on the draw resonance phenomenon occurring during melt spinning of polypropylene (PP). An experimental study is first carried ouit to determine effects of spinning variables and material parameters on draw resonance, using two PRO‐FAX PP resins and one PRO‐FAX/LDPE blend. Based on the experimental observations, our view on the cause of draw resonance is presented. With this new concept, we are able to explain various aspects of the draw resonance phenomenon observed experimentally during melt spinning of PRO‐FAX PP resins. It is concluded that the extensional viscosity versus strain relationship, as determined by an extensional rheometer, is one of the most valuable rheological measurements in analyzing flow instability occurring during polymer processing operations that utilize extensional

ISSN:0032-3888    

DOI:10.1002/pen.760270304

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractVarious blends of ultra‐high molecular weight polyethylene (UHMWPE) with linear low‐density polyethylene (LLDPE) were prepared in an internal (Banbury type) mixer, a static mixer, and by solvent blending. Two mixing techniques, namely simultaneous and sequential loading methods, were employed with the internal mixer. In the former case, the two polymer components were simultaneously loaded at 180°C and mixed. The latter method allowed the UHMWPE component to diffuse at 250°C and cooled it down to 180°C, then the LLDPE component was added subsequently and mixed. Rheological and mechanical properties of these blends are profoundly affected by the mixing techniques used. Rheological results shows yield characteristics of UHMWPE/LLDPE blends, in particular in blends of high UHMWPE contents. Tensile properties of sequentially loaded blends vary more or less linearly with blend compositions. However, negative or positive deviations are seen in the simultaneously prepared blends. Differential scanning calorimetry (DSC) studies indicate that co‐crystallization takes place between UHMWPE and LLDPE components in sequentially mixed blends. DSC and small‐angle light scattering (SALS) studies show that separate crystallization takes place in simultaneously blended compounds as a result of poor mixing. It seems that the sequential loading method provides more homogeneous compounds than those of simultaneou

ISSN:0032-3888    

DOI:10.1002/pen.760270305

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractCarbon dioxide and methane gas permeabilities, solubilities and diffusivities for poly [N, N′‐(phenoxyphenyl)‐pyromellitimide] films synthesized in our laboratory are contrasted with values measured for a chemically identical commercial polyimide film, Kapton H. The synthesized samples exhibited greater permeabilities, solubilities, and diffusivitles than those of the commercial sample. At the same time, the higher carbon dioxide permeability is associated with only a moderate reduction in permselectivity for the CO2/CH4system. The increased sorption and transport coefficients for the synthesized sample are attributed to a lower degree of aggregation and orientation of this film as compared to the Kapton H s

ISSN:0032-3888    

DOI:10.1002/pen.760270306

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractSheet molding compound (SMC) compression molding growth will benefit from faster cycles and more uniform cure so as to reduce in‐plane thermal residual stress and resulting warpage in the molded part. These improvements require an in‐depth study of the mold thermal design. Here we use a finite element model to analyze the quasi‐steady temperature distribution in a plane perpendicular to the heating channels of a representative mold, and a finite difference model to investigate the cure dynamics at critical regions. Several changes in the mold heating system and operating conditions were considered and their effects on the temperature distribution and cure time were studied. It was assumed that the steam condensate is well drained and enough steam is supplied so that the steam tube walls are kept at a constant temperature. An important conclusion of the present study is that better insulation of the mold from the press does not help much in improving the uniformity of cavity surface temperature or cure. It was also found that reducing the distance between two consecutive steam tubes beyond the distance from the steam tube to cavity surface will not yield a significant change. The most practical way to give both more uniform cavity surface temperature and faster cure is to have higher steam temperature for the region where the charge is initially p

ISSN:0032-3888    

DOI:10.1002/pen.760270307

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractMultilayer composite films consisting of polyolefins, either polypropylene, linear low density or medium density polyethylene, a thin adhesive layer, and a polyamide in various ratios were prepared using two basically different processes. The first, a conventional blown film process in which the extrudate is stretched while in the molten state; and the second, a two‐stage process in which the quenched extrudate is stretched at a temperature below the polymers' melting point. The films so prepared, having identical composition and similar extents of stretching, were compared on the basis of their tensile properties, thermoelastic shrinkage, oxygen transmission rate, and thermal behavior. The effects of stretching temperature, rate, and extent on the behavior of the composite films and control single layer films were investigated. The stretching temperature was found to be the dominating single process parameter in determining the films' behavior. The overall performance including tensile properties, barrier, and shrink properties of the “cold” stretched films was found markedly superior to that of the conventionally blown films. The stretched composite films possess physical properties that cannot be attained by the conventional pr

ISSN:0032-3888    

DOI:10.1002/pen.760270308

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760270301

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY