Download or read book On the Kinetics of Flow Induced Crystallization of Polyethylene Melt Above Its Normal Melting Point 8 written by Victor Tan and published by . This book was released on 1975 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advances in Material Forming written by Francisco Chinesta and published by Springer Science & Business Media. This book was released on 2007-04-19 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book groups the main advances in material forming, considering different processes, both conventional and non-conventional. It focuses on polymers, composites and metals, which are analyzed from the state of the art. Special emphasis is devoted to the contributions of the European Scientific Association for Material Forming (ESAFORM) during the last decade and in particular the ones coming from its annual international conference.
Download or read book Extensional flow induced Crystallization of Polypropylene written by Erica E. Bischoff White and published by . This book was released on 2011 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: A filament stretching extensional rheometer was used to investigate the effect of uniaxial flow on the crystallization of polypropylene. Samples were heated to a temperature above the melt temperature to erase their thermal and mechanical histories. The Janeschitz-Kriegl protocol was applied and samples were stretched at various extension rates to a final strain of e = 3.0. Differential scanning calorimetry was applied to crystallized samples to measure the degree of crystallinity. The results showed that a minimum extension rate, corresponding to a Weissenberg number of approximately Wi = 1, is required for an increase in percent crystallization to occur. Below this Weissenberg number, the flow is not strong enough to align the tubes of constrained polymer chains and as a result there is no change in the final percent crystallization. An extension rate was also found for which percent crystallization is maximized. The increase in crystallinity is likely due to flow-induced orientation and alignment of tubes of constrained polymer chains. Polarized-light microscopy verified an increase in number and decrease in size of spherulites with increasing extension rate. Small angle X-ray scattering showed a 7% decrease in inter-lamellar spacing at the transition to flow-induced increase in crystallization. Crystallization kinetics were examined by observing the time required for melts to crystallize under uniaxial flow. The crystallization time decreased with increasing extension rate, even for extension rates where no increase in percent crystallization was observed. These results demonstrate that the speed of crystallization kinetics is greatly enhanced by the application of extensional flow.
Download or read book Crystallization Modalities in Polymer Melt Processing written by Hermann Janeschitz-Kriegl and published by Springer. This book was released on 2018-03-27 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: In addition to structure formation in crystallizing polymers and semicrystalline polymers, this second edition completes the topic of transport phenomena. It also reviews solidification by crystallization during cooling and under flow or pressure, which all play an enormous role in polymer melt processing. Generally, there is an intensive interaction between three transport phenomena: heat transfer, momentum transfer (flow, rheology) and (flow induced) crystallization. The strong interaction between the three transport phenomena is a major challenge when it comes to experimentation, and advances in this area are detailed in the book, guiding further development of sound modeling. This book enables readers to follow an advanced course in polymer processing. It is a valuable resource for polymer chemists, applied physicists, rheologists, plastics engineers, mold makers and material scientists.
Download or read book Kinetics of Straininduced Crystallization of Polymers During Flow written by G. S. Y. Yeh and published by . This book was released on 1982 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from experimental studies of strain-crystallized polyethylenes, prepared in a simple shear couette rheometer, indicate a substantial increase in nucleation rate, a decrease in long period, as well as an increase in melting temperature with increasing shear. The changes appear to have the same thermodynamic origin in the reduction of the amount of melt entropy, Delta S', just prior to crystallization according to a strain-induced crystallization theory by Yeh and Hong. Consequently from the measured nucleation rate one can predict what the decrease in long period or the increase in melting temperature should be for a given strain-crystallized polyethylene. For example, the measured melting temperatures are indeed shown to be comparable to those predicted from nucleation rate measurements.
Download or read book Extensional Flow Induced Crystallization in Polyethylene Melt Spinning written by Vikas Madhusudan Nadkarni and published by . This book was released on 1974 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crystallization Studies on Deformed Polybutene 1 Melts written by Anthony Wereta (Jr) and published by . This book was released on 1970 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt: An apparatus was designed and built which allowed an investigation concerning the morphology and kinetics of crystallization of a deformed polybutene-1 melt. The polymer was quenched from a temperature above its melting point to one of two crystallization temperatures. The supercooled melt was then sheared and allowed to crystallize isothermally while the internal stress in the melt was continuously recorded. A polarizing microscope was employed for the simultaneous study of the resulting morphological changes. By properly accounting for thermal contractions within the apparatus caused by the quenching operation, as well as the imposed shear strain, a strain history of the polymer during crystallization was developed. From this strain history and the assumption that the volume contraction resulting from crystallization was isotropic, approximate kinetics of crystallization in a deformed polymer melt were determined. (Author).
Download or read book Maro Polymer Notes written by and published by . This book was released on 1996 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Flow induced Crystallization in Polymer Systems written by Robert L. Miller and published by Taylor & Francis. This book was released on 1979-01-01 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Science Technology Index written by and published by . This book was released on 1977 with total page 1532 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crystallization Kinetics of Poly ethylene Oxide written by Frances H. Segouin and published by . This book was released on 1994 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The three main goals of this project are to determine the molecular weight dependence of polyethylene oxide) on the 1) morphology of crystalline material, as seen with the polarizing light microscope, 2) nucleation of the crystalline phase, as demonstrated with an annealing study, and 3) parameters of a mathematical model for crystallization kinetics. Bulk crystallization kinetics of polyethylene oxide) from the melt have been studied for a large molecular weight range, 1500 g/mol to 7,000,000 g/mol. The effects of molecular weight and cooling rate on the width and degree of supercooling of DSC crystallization exotherms have been studied to determine the type of nucleation involved and to determine the relationship between the DSC signals and the morphology of a crystalline sample. As the molecular weight increases, at a cooling rate of twenty degrees per minute, the width-at-half- height of the exothermic DSC peak decreases from seven degrees to approximately three degrees for the low molecular weight samples and increases from three to seven degrees for the high molecular weight samples. The degree of supercooling at which the peaks reach a maximum generally increases from twelve degrees Celsius to above twenty degrees Celsius. The slower the cooling rate the narrower the width at half height of the crystallization peak and the lower the degree of supercooling at the maximum point of the crystallization exotherms. For all of the molecular weight samples, the crystallization peak temperatures increase in the range of one to ten degrees of supercooling from a one-degree-per-minute cooling rate to a twenty degrees-per-minute cooling rate. The average width-at-half-height increases from three to six- degrees Celsius from the one degree-per-minute cooling rate experiment to the twenty degreesper- minute cooling rate experiment. The morphology of the samples varied from a coarse non-interconnected lamellae formation below the critical molecular weight to an interconnected lamellae formation, also known as a spherulite, above the critical molecular weight. The critical molecular weight for polyethylene oxide) is 3400 g/mol. Based on the expression for the linear crystal growth rate, reported by Cheng et al.1, a mathematical model was created to model the DSC crystallization curves. This model, which incorporates heat transfer effects, can model the width and shape of the DSC curves, but the degree of supercooling that the model predicts is generally smaller than the experimental degree of supercooling. While modeling the DSC crystallization curves, it was found that the activation energy for reptation motion, U*, has less of an effect on the model crystallization curves than does the surface energy term, Kg, of the Cheng growth rate expression."--Abstract.
Download or read book A Study of Flow induced Crystallization of Polyethylene in the Four roll Mill Device written by Alexander Craig Bushman and published by . This book was released on 1993 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Study of Flow Induced Crystallization in Two phase Polymer Melts written by R. Kirk Guy and published by . This book was released on 1992 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of shearing and elongational flows on flow induced crystallization in polymer melts were investigated for the two-phase system of high molecular weight polyethylene suspended in a linear low density polyethylene carrier phase. Shearing flow was produced by a counter-rotating couette device and elongational flow was produced by means of a four roller mill device. Deformation and bursting of droplets were observed in both of these flows, however, shearing flow was found unsuitable for quantitative studies, since the orientation of the optical axes in the carrier and suspended phases were not coaxial. Hot stage and dichroism studies indicated that crystallization occurs in the suspended phase in the four roller mill, at temperatures above which quiescent crystallization would occur. In-situ birefringence measurements were made and initial crystallization rates were determined and found to depend upon both stress and strain in the deforming droplet. This was very suggestive of a viscoelastic phenomenon, not simply, a nucleation and growth controlled mechanism, thus the separability, of flow effects and nucleation and growth crystallization, is brought into question by this complex behavior. A first order approximation based on molecular rheology has been used to gain qualitative and quantitative insights on the observed trends.
Download or read book The Deformation Mechanisms in Branched Polyethylene Melts written by James C. Galt and published by . This book was released on 1963 with total page 1 pages. Available in PDF, EPUB and Kindle. Book excerpt: A program was undertaken to determine point to point response to stress of a high polymer above its crystalline melting point. From these observations, the actual velocity profiles for branched polyethylene melts in a capillary were obtained. Explanation for the unique character of the velocity profiles must be based on considerations of the molecular structure of each polymer. Velocity within the capillary depends not only on the location of the point of interest but also on which representative infinitesimal element of the melt is under consideration. A boundary annulus is next to the wall. It contains the stick-slip at the wall, zero velocities away from the wall, and pure translation (no rotation). The cause of the highly elastic, discontinuous flow of polymer in this region may be attributed to long-chain branching. A plug of elastically-strained structure is found at the centerline of the capillary. The plug flows at a uniform time-average velocity. The shear annulus is the region between the plug and the boundary annulus. Flow in this region is viscous or viscoelastic but shows structural breakdown and the thixotropic nature of polymer melts. (Author).
Download or read book A Study of Transient Flow induced Crystallization of Polymer Melts written by Alexander Craig Bushman and published by . This book was released on 1995 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flow-induced crystallization of several polymer systems has been studied using a four-roll mill device, coupled with optical polarimetry, to provide an in-situ technique for monitoring the transformation kinetics both during and following flow. The use of a crystallizable droplet phase, suspended within a non-crystallizable carrier phase, prevents die blockage and allows for direct measure of the droplet phase kinematics. Both birefringence and dichroism are used to investigate the crystallinity development within the deforming droplet. Birefringence studies suggest that the initial rate of crystallization is a function of both the induced stress and strain within the deformed material. Pre-crystallinity during the flow regime, prior to flow cessation, is required to achieve reproducible stress-strain behavior. Unlike birefringence studies, the dichroism studies allowed the study of the transient crystallization occurring during the flow regime. Induction times to crystallinity were found to correlate with the extension rate during the deformation. Rheological studies of the polymer systems were performed, wherein viscoelastic data and relaxation time constants were determined. A theoretical model for flow-induced crystallization was developed using a modified strain-induced crystallization model, coupled with the Hamiltonian Bracket formalism, to account for the dynamics of flow. A variety of flow kinematics and their effect on flow-induced crystallization are modeled. A non-linear force factor is incorporated to account for the finite extensibility of the molecule. The model is compared to experimental data and does predict qualitatively the effects of the flow field on crystallization.
Download or read book Flow Induced Crystallization by Surface Growth of Polyethylene Fibers written by Jeroen Rietveld and published by . This book was released on 1982 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Engineered Materials Abstracts written by and published by . This book was released on 1995-04 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt:
