摘要:

AbstractThe cure monitoring of cyanoacrylate resin using a dielectric technique shows that in addition to the usual fast anionic polymerization step, there may be a secondary process involved over longer time scales. Two peaks are distinctly observed in the isothermal curing curves, and from the position of these at various temperatures, the activation energies of 0.4 eV and 0.17 eV could be derived. In cured cyanoacrylate resin, three relaxations were observed, viz., α, β, and γ, occurring at 152°c, 87°c, and 47°c, respectively (for 1 KHz measuring frequency), with activation energies of 1.3 eV, 0.56 eV, and 0.4 eV, respectively. The various results have been explained on the basis of secondary bond formation through the nitrile group, for which some evidence could be obtained from the infrared absorption sp

ISSN:0032-3888    

DOI:10.1002/pen.760330302

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIn rotational molding, shortening the cycle time is one of the most important requirements for increasing production rates and reducing product cost. A characteristic feature of the process is that the mold and plastic powder are heated from room temperature to the melting temperature of the plastic and then back to room temperature. In addition, in the vast majority of cases the heat input and subsequent heat extraction occur at the outside surface. In order to improve the heat transfer, this paper considers the effects of internal heating and cooling. A mathematical model has been developed in which an internal heating term can be incorporated. The experiments with rotomolding powders show that the predictions made by the model are accurate. In particular, it is found that the introduction of internal heating is very effective in shortening the cycle time and that the introduction of internal cooling in rotational molding provides a more uniform structure and less likelihood of warpage.

ISSN:0032-3888    

DOI:10.1002/pen.760330303

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis study attempts to investigate the kinematics of the mixing occurring in the lenticular kneading disc section of the co‐rotating twin screw extruder, employing the tools of dynamics. The Eulerian velocity field distributions, generated by a two‐dimensional isothermal and creeping flow of Newtonian fluid under the periodic co‐rotation of the kneading discs, were obtained by Finite Element Method. A simple and novel particle tracking technique based on the FEM solution of the velocity field was employed to follow individual particles, and to produce the Poincare section mapping. Furthermore, fingerprints of chaotic motion were revealed essentially through the Lyapunov exponents, which were positive. The results suggest that the dynamics in the two‐dimensional kneading disc section of the twin screw extruder can be characterized as capable of imparting chaotic motion. The tools developed in this study should facilitate a better understanding of the mixing capabilities of the twin screw extrusion

ISSN:0032-3888    

DOI:10.1002/pen.760330304

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA finite difference solution for an isothermal viscoelastic liquid flowing through a film forming die is investigated. The fluid is described by a Maxwell model in which the time derivative has been replaced by an Oldroyd's convective derivative and the numerical technique used combines features of the Solution Algorithm (SOLA), Simplified Marker and Cell method (SMAC), and SOLASMAC. The numerical scheme was tested with a Newtonian fluid and high density polyethylene (HDPE). Two slit dies with gap‐to‐length ratios 4 and 16 were used. In the two cases, die swell has occurred: A maximum of 4.5% swell was observed for the Newtonian fluid, while up to 77% swell was attained with HDPE. The simulated flow behavior of HDPE exhibited high amplitude oscillations at dimensionless time greater than 0.18. These oscillations are thought to be related to the nature of sheet flow, which can be unstable. This study shows that with some improvement the finite difference method can be used for studying the extrusion of polymer through slit and capillary d

ISSN:0032-3888    

DOI:10.1002/pen.760330305

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIsothermal melt‐spinning of two thermotropic liquid crystalline polymers (TLCPs), a wholly aromatic copolyester KU‐9211 (also named K161 from Bayer AG) and an aliphatic containing TLCP, PET/PHB60 (Tennessee Eastman), was studied to analyze the effect of processing conditions on fiber properties. Fibers were melt‐spun from a capillary rheometer equipped with an isothermal chamber in which cross‐flowed air was used as the cooling medium. The processing variables studied included the extrusion temperature, the extrusion rate, the cooling conditions, and the draw ratio. As‐spun fibers were characterized by measuring storage moduli and molecular orientation parameters as a function of draw ratio under various processing conditions. Among the processing variables studied, the draw ratio was the primary factor in determining both the fiber modulus and the molecular orientation. The extrusion rate did not appear to affect the fiber properties within the range studied. The properties of K161 fibers were also dependent on the extrusion and cooling temperatures, while PET/PHB60 fibers were rather insensitive to the processing temperatures within data scatter and temperatures studied. A composite model based on a rigid‐rod rotation mechanism and the deformation of nematic domains in an elongational flow field was used to model the experimental results and was compared with other theories available. Conformance of data to the composite model was obtained by use of a single temperature dependent parametern, suggesting that the rigid‐rod rotation mechanism could be used to predict the orientation development of TLCPs. The Halpin‐Tsai equations and the orthotropic equation for angular dependence were used to describe the elastic properties of

ISSN:0032-3888    

DOI:10.1002/pen.760330306

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene‐acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composite

ISSN:0032-3888    

DOI:10.1002/pen.760330307

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe change in morphology and interface quantities have been analyzed for an immiscible polymer blend during reactive processing. A model polymer/polymer combination, hydroxy‐terminated poly(ε‐caprolactone)/liquid rubber with α, ω‐carboxy groups, was employed. The blend was subjected to light scattering measurements, ellipsometry, and gel permeation chromatography (GPC). Size reduction of the dispersed phase during processing was followed by a systematic decrease in the correlation distance ζ and an increase in the specific interfacial area Ssp, both by the Debye‐Bueche plot of light scattering profiles. Also observed was the time variation of the volume fraction of interfaceVλestimated as a product of the Ssp and the interfacial thickness by ellipsometry. The changes in ζ, Ssp, andVλwith processing were accelerated when a coupling agent,γ‐aminopropyltriethoxysilane (APS), was added. The amount of block copolymer formedin‐situin the APS‐loaded system was estimated by GPC with RI and UV detectors. For the size reduction kinetics in both APS‐loaded and ‐unloaded systems, Rittinger's law w

ISSN:0032-3888    

DOI:10.1002/pen.760330308

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractSelection of the optimum conditions for the vulcanization of rubber products, particularly of bulky ones, often is quite difficult. Especially in cases of high demand, it is unavoidable to destruct expensive prototypes in order to check important properties of the rubber at various locations throughout the product. Finite element calculations can be used to predict the flow of heat during the vulcanization process. By converting the total heat input at a selected location during a certain time into a so‐called “effective vulcanization time” at a fixed reference temperature, it becomes possible to predict the properties of the rubber at that location. An example of such a procedure is given. However, to secure optimum conditions in this way would require repetitive (expensive) calculations. In this article a method is developed in which the vulcanization conditions are derived from the required properties of the rubber compound. The idea behind it is that optimal vulcanization is reached when at each location within the rubber product the effective vulcanization time at a selected reference temperature lies within predefined limits. The choice of the limits can be derived from the dependence of each of the properties chosen on the vulcanization time at the reference temper

ISSN:0032-3888    

DOI:10.1002/pen.760330309

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760330301

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY