Drawing Behavior of Ultrahigh Molecular Weight Polyethylene (UHMWPE) Fibers in Supercritical CO2 PDF Download
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Languages : en
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The drawing behavior of Ultrahigh Molecular Weight Polyethylene (UHMWPE) fibers in supercritical CO2 (scCO2) is compared to that in air at different temperatures. Temperature substantially influences the drawing properties in air, while in scCO2 a constant draw stress and tensile strength are observed. Differential Scanning Calorimetry (DSC) shows an apparent development of a hexagonal phase along with significant improvements in crystallinity of air-drawn samples with increasing temperature. The existence of this phase is not confirmed by WIDE ANGLE X-RAY SCATTERING (WAXS) showing that air-drawn samples crystallize in an internally constrained manner. In contrast, scCO2 allows crystals to grow without constraints through a possible crystal-crystal transformation, increasing the processing temperature to 110 deg. C.
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Languages : en
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Book Description
The drawing behavior of Ultrahigh Molecular Weight Polyethylene (UHMWPE) fibers in supercritical CO2 (scCO2) is compared to that in air at different temperatures. Temperature substantially influences the drawing properties in air, while in scCO2 a constant draw stress and tensile strength are observed. Differential Scanning Calorimetry (DSC) shows an apparent development of a hexagonal phase along with significant improvements in crystallinity of air-drawn samples with increasing temperature. The existence of this phase is not confirmed by WIDE ANGLE X-RAY SCATTERING (WAXS) showing that air-drawn samples crystallize in an internally constrained manner. In contrast, scCO2 allows crystals to grow without constraints through a possible crystal-crystal transformation, increasing the processing temperature to 110 deg. C.
Author: Spe
Publisher: CRC Press
ISBN: 9781566768559
Category : Technology & Engineering
Languages : en
Pages : 1214
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Volume 2 of the conference proceedings of the SPE/Antac on 'Materials', held on the 711 May 2000 in Orlando, Florida, USA.
Author: Society of Plastics Engineers. Technical Conference
Publisher:
ISBN:
Category : Plastics
Languages : en
Pages : 1218
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Author: Vannessa Goodship
Publisher: iSmithers Rapra Publishing
ISBN: 9781859574942
Category : Science
Languages : en
Pages : 152
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Book Description
SCFs are currently the subjects of intense research and commercial interest. Applications such as the RESS (rapid expansion of supercritical fluid solutions) process are part of standard industrial practice. In view of their ever-growing importance in the polymer industry there is a need to fully comprehend how supercritical fluids interrelate with polymeric materials to realise the potential that can be gained from their use. The authors review the basic principles of SCFs and their application within the polymer industry: characteristics and properties, extraction of unwanted residual products, polymerisation solvents, and polymer impregnation. Processing applications such as plasticisation, foaming and blending are also considered. There is discussion of the potential within the polymer recycling industry for use of SCFs as cleaning agents or within supercritical oxidation processes. Around 400 references with abstracts from recent global literature accompany this review, sourced from the Polymer Library, to facilitate further reading. A subject index and a company index are included.
Author: Roberto Pantani
Publisher: MDPI
ISBN: 3039218808
Category : Science
Languages : en
Pages : 400
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Book Description
This collection of research and review papers is aimed at depicting the state of the art on the possible correlations between processing variables, obtained structure and special properties which this structure induces on the plastic part. The extraordinary capacity of plastics to modify their properties according to a particular structure is evidenced for several transformation processes and for many applications. The final common goal is to take profit of this peculiar capacity of plastics by inducing, through a suitable processing, a specific spatial organization.
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Languages : en
Pages : 0
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Enhancements in ballistic protective wear for soldiers rely heavily on the development of lightweight materials with increased moduli and strength. It is well established that an armors ballistic limit can be increased significantly by using materials with increased moduli and strength. The development of high performance fibers from flexible chain polymers has been a subject of intense interest over the past 30 years. However, to date the mechanical properties of commercial fibers are far below their theoretical values. This is due in large part to our inability to process the materials to achieve highly crystalline structures from highly extended chain conformations. In this STIR research program the feasibility of using subcritical and supercritical 002 in the processing of fibers with superior mechanical properties was investigated. The synergistic effects of 002 as both a pressurizing medium as well as a reversible plasticizer was shown to dramatically improve the mechanical stiffness and strength of both nylon6,6 and ultrahigh molecular weight polyethylene. In the case of Nylon6,6 fibers a greater than 30% increase in stiffness along with a 20% increase in strength was realized. Similarly, post treatment on UHMWPE fibers (Dyneema) showed an increase in modulus of greater than 50% of the commercial fibers. In both cases, the 002 treatment primarily increased the overall degree of crystallinity compared to air drawn fibers. It should be noted that, although the research has strong fundamental interests, it provides an environmentally benign approach to process fibers with superior mechanical properties. Once additional studies are conducted to isolate optimum process ranges, scale-up should be relatively quick since the polymeric materials and process equipment are all commercially available.
Author: Kan-nan Chen
Publisher:
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Category :
Languages : en
Pages :
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Author: Galip Yilmaz
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
In this work, the processing of a unique ultra-high molecular weight polyethylene (UHMWPE) polymer, in both powder and pellet form, using both regular and special injection molding techniques, was investigated in an effort to mass produce this high-grade specialty polymer. The goals of this study were to (i) improve the processability of UHMWPE, (ii) enhance the mechanical performance and overall quality of the molded parts, and (iii) develop an in-depth understanding of how the supercritical fluid (SCF), machine configuration, mold compression, mold insulating techniques, and process conditions affect the flow behavior and final quality of the injection molded UHMWPE. In the first study, two common atmospheric gases in their supercritical states-namely, nitrogen (scN2) and carbon dioxide (scCO2)-were used as processing aids in a special full-shot, high-pressure microcellular injection molding (MIM) process for processing UHMWPE pellets. The mechanical properties in terms of tensile strength, Young's modulus, and elongation-at break of the SCF-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were also analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. It was found that the processing of UHMWPE with both gases effectively reduced the thermal degradation of the material and the injection pressure, compared to regular injection molding, while still retaining the mechanical properties of the resin. In the second part, a follow-up study was conducted on conventional injection molding (IM), along with the special full-shot, high-pressure microcellular injection molding (MIM) using UHMWPE in pellet form. A relatively complicated and thin-walled mold design was used to produce box-shaped parts with varying wall thickness. Although different processing settings were tested in order to eliminate persistent short shot issues, only high-pressure MIM processing was able to fill parts completely. Furthermore, not only did high-pressure MIM processing effectively promote the processability of UHMWPE, it also reduced the very high injection pressure requirement and the high part shrinkage issues associated with the IM samples. In the third study, UHMWPE powder was processed using injection molding (IM) and injection-compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and to avoid damaging UHMWPE's molecular structure. Dynamic mechanical analysis (DMA) and Fourier-transform infrared spectroscopy (FTIR) tests confirmed that the thermal and oxidative degradation of the material was minimized but crosslinking was induced during molding. Tensile tests and impact tests showed that the ICM samples were superior to the IM samples. A delamination skin layer was formed on the IM sample surfaces, while it was absent in the ICM samples, thus suggesting two different flow behaviors between IM and ICM during the packing phase. The delamination layer defect was the subject of the fourth study as one of the main challenges of UHMWPE molding. The delamination layer hampers UHMWPE's two key properties: wear resistance and impact strength. A mold insulation method was employed to eliminate the formation of the delamination layer. The working principle of the method was to reduce the cooling rate and the shear stress of the polymer while improving polymer chain "interdiffusion" across the entangled chain bundles during the injection filling stage via a low thermal conductivity mold coating (e.g., epoxy coating). This method yielded molded parts free of delamination by delaying skin cooling during filling and packing. Therefore, it produced parts with enhanced mechanical properties, excellent impact strength, and improved surface quality.
Author: Japan The Society of Fiber Science and Techno
Publisher: Springer
ISBN: 4431552030
Category : Technology & Engineering
Languages : en
Pages : 451
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Book Description
This book reviews the key technologies and characteristics of the modern man-made specialty fibers mainly developed in Japan. Since the production of many low-cost man-made fibers shifted to China and other Asian countries, Japanese companies have focused on production of high-quality, high-performance super fibers as well as highly functionalized fibers so-called ‘Shin-gosen’. ZylonTM and DyneemaTM manufactured by Toyobo, TechnoraTM produced by Teijin, and VectranTM developed by Kuraray are those examples of super fibers. Carbon fibers ToraycaTM from Toray have occupied the most advanced high-performance application area. Various types of polyester fibers having design-shaped cross-sections and special fiber morphologies and those showing specific physico-chemical properties have also been developed to acquire a high-value textile market of the world. This book describes how these high-tech fibers have been developed and what aspects are the most important in each fiber based on its structure-property relationship. Famous specialists both in industry and academia are responsible for the contents, explaining the design concepts and the special technologies for the production of these special fibers. For university teachers and students, this volume is an excellent textbook that elucidates the basic concepts of modern fibers. At the same time, researchers, both in academia and industry, will find a comprehensive overview of recent man-made fibers. This publication, presenting the most easily understandable general survey of specialty man-made fibers to date, is dedicated to the 70th-anniversary of the Society of Fiber Science and Technology, Japan.
Author: Richard Gendron
Publisher: CRC Press
ISBN: 0203502167
Category : Technology & Engineering
Languages : en
Pages : 320
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Book Description
As researchers seek replacements for banned, ozone-depleting foaming agents, the authors of Thermoplastic Foam Processing: Principles and Development strive to develop a better understanding of foaming processes and find solutions for day-to-day practice. This book presents the latest research in foam extrusion and physical foaming agents with a st
