摘要:

AbstractA noncontacting experimental procedure is used for characterizing lateral strain effects during the large‐strain uniaxial stretching of flat sheet‐like specimens of polycarbonate, polyetherimide, and poly(butylene terephthalate), both at room and elevated temperatures. It is shown that the in‐plane lateral stretch, λ2, is related to the longitudinal stretch, λ1, through the relation λ2= λ 1−n. Depending on the temperature, the “Poisson's ratio” for incremental strains,n, is shown to lie betweenn= 0.4 andn= 0.5. While the lateral stretch in the thickness direction, λ3, is smaller than λ2at room temperature, it is shown that λ3= λ2at higher temperatures. Stretch data have been used to infer the volumetric strai

ISSN:0032-3888    

DOI:10.1002/pen.760281902

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA trial and error approach reflects the state of the art in reaction injection molding. Material and process parameters determine the “moldability” of a specific system in a particular application. The concept of “molding areas” on the critical parameters plane can be extended form thermoplastic injection molding (TIM) to reaction injection molding (RIM).In this work moldability diagrams for the filling and curing stages of a RIM process are obtained based on a simplified engineering approach. The key process parameters chosen for the filling stage are initial material temperature and filling time. In the curing stage, the critical parameters are considered to be mold wall temperature and demold time. Experimental results obtained on a laboratory‐scale RIM machine on a Crosslinking polyurethane system are used to check the validity of the predicted molding areas. The agreement obtained is satisfactory considering the broad range of processing parame

ISSN:0032-3888    

DOI:10.1002/pen.760281903

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe performance of cooling extruders widely used in thermoplastic foam extrusion was analyzed, by numerically solving the equations of motion and heat transfer. Analysis of cooling extruders does not require a consideration of the melting behavior of polymers, thus simplifying the system equations considerably. The flow geometry analyzed was an unwound screw channel of a single‐screw extruder, i.e., a rectangular channel of uniform height followed by diverging and converging sections. Due to the cooling of both the extruder barrel and the screw, the heat transfer equation considered includes the terms describing the convective heat transfer in the down‐channel direction and the conductive heat transfer in the cross‐channel direction, in addition to the terms describing the viscous shear heating. For the analysis, a power‐law model was used as the constitutive rheologlcal equation, describing the viscosities of a mixture of a fluorocarbon blowing agent and a low‐density polyethylene melt (or polystyrene melt). The parameters in the Theological model were determined using the data of Han and Ma (13). In obtaining numerical solutions of the equations of motion, an integration method was employed to overcome the problem of numerical instabilities. The present analysis predicts the profiles of developing temperature and velocity in the down‐channel direction, and the profiles of temperature, velocity, shear rate, and viscosity in the cross‐channel direction. In presenting the results of computer simulation, emphasis is placed on the effects of cooling the extruder barrel and screw on the performance of cooling extruders, in terms of the pressure drops along the extruder axis and the mechanical power consumption. This study provides a rational basis for the design of cooling extruders widely used in thermoplastic foam extrusion and for the selection of optimum extrusion conditions in producing thermo

ISSN:0032-3888    

DOI:10.1002/pen.760281904

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe reversible step growth polymerization in homogeneous continuous flow stirred tank reactors (HCSTRs), in which the condensation product (W) leaves the reactor through flashing, has been analyzed. The molecular weight distribution (MWD) of the polymer formed is governed by nonlinear coupled algebraic relations to be solved simultaneously. To find the MWD numerically a large number of these are normally solved simultaneously using a suitable iterative procedure. In this paper, these have been decoupled using the technique proposed in our earlier works (1, 2) and the MWD can now be obtained sequentially without any trial and error. This leads to considerable saving in computation time compared to methods currently used. To demonstrate the efficacy of the algorithm, the polycondensation step of the poly(ethylene terephthal‐ate) (PET) formed in HCSTRs has been analyzed. The MWD, the average chain length and the polydispersity index of the polymer have been computed and it takes 0.1 CPU seconds on a DEC 1090 as opposed to the earlier method which would take seventy minutes for similar computations. The simple model of the HCSTR for the PET formation gives the effect of reactor temperature and pressure and the quantitative results have been presented in this pape

ISSN:0032-3888    

DOI:10.1002/pen.760281905

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe microstructure of injection molded bars (2.9 and 5.8 mm thick) of thermotropic liquid crystalline poly(p‐hydroxy‐benzoic acid‐co‐ethylene terephthalate) has been studied by SEM on samples etched with n‐propylamine, SEM fractography, DSC, IR, ESCA, WAXS and polarized microscopy. The 2.9 mm bar consists of three different layers: a highly oriented surface skin, an oriented intermediate layer and a non‐oriented core. The 5.8 mm bar has a more complex microstructure and is composed of five different layers: a highly oriented surface skin, an oriented layer just beneath, a non‐oriented layer, another oriented layer and a non‐oriented core. The thicknesses of the different layers vary, significantly, with distance from the mold gate. The thickness of the core increases, significantly, with increasing distance from the mold gate at the expense of the oriented layers. The structure within the different morphological layers is not perfectly uniform. Tensile testing demonstrated the mechanical anisotropy of the surface material (a ratio of almost 20 between the longitudinal and transverse moduli) and the isotropy of the centra

ISSN:0032-3888    

DOI:10.1002/pen.760281906

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMeasurements of shrinkage stress and birefringence have been undertaken on drawn samples of a copolyterephthalate based on ethylene glycol and 1,4 cyclohexane‐dimethanol. The temperature location and the peak value of the maximum shrinkage stress have been related to the drawing conditions (temperature, strain rate and draw ratio), comparing the results with those reported for poly (ethylene terephthalate). Moreover, a value of the stress optical coefficient of the copolymer equal to 14.5 × 10−9m2N−lhas been ob

ISSN:0032-3888    

DOI:10.1002/pen.760281907

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractRolling‐drawing is a simple, effective, solid state processing technique for manufacturing high strength and high modulus oriented polymer sheet products. The process is capable of increasing the tensile modulus and strength of polypropylene by more, than an order of magnitude with inexpensive equipment and straight forward controllable techniques. This paper gives an overview of the rolling‐drawing of polypropylene. It is intended to answer the following questions. What is rolling‐drawing? What changes in tensile properties can be expected as a result of this process? What deformation processes occur during rolling‐drawing? What are the processing variables and how do these variables relate to the deformation ratio achieved by rolling‐drawing? A tensile flow stress relationship was formulated from experimental data for oriented polypropylene. This constitutive equation, estimates the flow stress (or yield stress) of the polymer as a function of deformation ratio, strain rate and temperature. Since stretching was found to provide a significant portion of the deformation during the rolling‐drawing process a Hoffman‐Sachs computer analysis was written to predict plastic deformation and drawing forces in the stretch zone. The results of experimentation and the analysis are briefly compared

ISSN:0032-3888    

DOI:10.1002/pen.760281908

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA mathematical model is presented which describes the degree of cure in a thermosetting adhesive used to bond sheet molding compound (SMC) components. The model allows computer aided optimization of the thermosetting process for any type of electromagnetic heating of the various layers of the structure (e.g. dielectric, microwave or induction), arbitrary material properties and arbitrary layer thickness. Computer simulated results are given for the particular case when the cure of the thermosetting material is initiated by its exposure to a high‐power radio‐frequency electric field (dielectric heating). These results indicate a strong sensitivity of the process to the thickness of the adhesive layer and the degree of coupling with the electromagnetic field. The analysis demonstrates that substantial heat losses from the relatively thin adhesive layer to the structural members of the joint by diffusive heat flow can be counterbalanced by additional electric power dissipated either in the adhesive or the structural members of the joint. Although derived for dielectric heating, those results are general, being independent of the type of electromagnetic heating emplo

ISSN:0032-3888    

DOI:10.1002/pen.760281909

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractLinearly tapered coat hanger dies or T‐dies are widely accepted. Nevertheless a newly proposed curvilinearly tapered coat hanger die has been shown to perform much better. It costs about the same as the other types of dies. This contribution is considered in terms of the recent literatur

ISSN:0032-3888    

DOI:10.1002/pen.760281910

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760281901

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY