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      Characterization of Anisotropic Properties of Hot Compacted Self-Reinforced Composites (SRCs) via Thermal Diffusivity Measurement

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          The mechanical properties of self-reinforced composites (SRCs) produced in a hot compaction process significantly depend on the process parameters. Only a little deviation of the process temperature or pressure causes the component to act differently under mechanical load. This is a chance and a challenge at the same time, since this process is difficult to handle but by properly controlling the process parameters, the mechanical properties can be adjusted, even locally for one component. In this research SRC are manufactured in a hot compaction process. A correlation between process parameters and density is found. Density increased from 0,8 to 0,91 g/cm³ by increasing temperature and pressure in the hot compaction process. The different thermal properties in the direction of orientation (IP) and transverse to orientation (TP) are measured with a laser flash device. It was found that, due to a change in density and molecular orientation, diffusivity and conductivity are influenced in different degrees in IP and TP directions. For interpretation of thermal measurement results, microstructures are analysed with a confocal laser scanning microscope after preparing the specimen with a permanganate etching. A schematic model of conductive path is worked out and discussed. With measurement data the anisotropy of IP and TP diffusivity is calculated, and a model is built to describe relative density related to anisotropy. The highest anisotropy between IP and TP diffusivity was calculated with a ratio of 6 at a relative density of approximately 0,82 g/cm³. Since mechanical properties in correlation to process parameters have already been investigated, results of this investigation, in combination with previous research on mechanical properties, will enable the development of a non-destructive testing method for SRCs by measuring the thermal diffusivity.

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          Most cited references 28

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          A permanganic etchant for polyolefines

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            Impact of molecular orientation on thermal conduction in spin-coated polyimide films

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              Novel Polyethylene Fibers of Very High Thermal Conductivity Enabled by Amorphous Restructuring

              High-thermal-conductivity polymers are very sought after for applications in various thermal management systems. Although improving crystallinity is a common way for increasing the thermal conductivity (k) of polymers, it has very limited capacity when the crystallinity is already high. In this work, by heat-stretching a highly crystalline microfiber, a significant k enhancement is observed. More interestingly, it coincides with a reduction in crystallinity. The sample is a Spectra S-900 ultrahigh-molecular-weight polyethylene (UHMW-PE) microfiber of 92% crystallinity and high degree of orientation. The optimum stretching condition is 131.5 °C, with a strain rate of 0.0129 s–1 to a low strain ratio (∼6.6) followed by air quenching. The k enhancement is from 21 to 51 W/(m·K), the highest value for UHMW-PE microfibers reported to date. X-ray diffraction study finds that the crystallinity reduces to 83% after stretching, whereas the crystallite size and crystallite orientation are not changed. Cryogenic thermal characterization shows a reduced level of phonon-defect scattering near 30 K. Polarization Raman spectroscopy finds enhanced alignment of amorphous chains, which could be the main reason for the k enhancement. A possible relocation of amorphous phase is also discussed and indirectly supported by a bending test.

                Author and article information

                International Polymer Processing
                Carl Hanser Verlag
                21 November 2019
                : 34
                : 5
                : 532-540
                1 IfW Plastics Technology, University of Kassel, Kassel, Germany
                Author notes
                [] Correspondence address, Mail address: Fabian Jakob, IfW Plastics Technology, University of Kassel, Mönchebergstrasse 3, 34125 Kassel, Germany, E-mail: jakob@ 123456uni-kassel.de
                © 2019, Carl Hanser Verlag, Munich
                Page count
                References: 33, Pages: 9
                Self URI (journal page): http://www.hanser-elibrary.com/loi/ipp
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