The applicability of more than 70 semi‐crystalline polymer grades with different melting temperatures as phase change materials (PCM) is investigated. Their storage capacity (heat of fusion) and application temperature range (defined by the melting temperature range and the degradation behavior) are analyzed via differential scanning calorimetry (DSC). Application‐oriented stability investigations (thermal cycling and exposure to static thermal load above the polymer’s melting temperature) are applied on the most promising polymer types. The thermal and thermo‐oxidative degradation behavior is monitored via DSC and Fourier‐transform infrared spectroscopy. Different aging phenomena are identified. However, these have only little impact on the polymer’s storage capacity. Therefore, a great potential of polymers as PCM is revealed. Additionally, the economic efficiency of polymers as PCM is estimated and discussed.
The long-term stability of thermally conductive high-density polyethylene (HDPE)-based compounds as phase-change material (PCM) is investigated. For this purpose, the HDPE's thermal conductivity (TC) is first enhanced via compounding two different filler types (expanded graphite and aluminum) into the polymeric matrix. Bulky specimens of these compounds are then stored in air for up to 7289 h in the melt state to investigate the compounds' long-term stability as PCM. Their thermo-oxidative/thermal stability and their ability to maintain the isotropic material character (homogeneous distribution of the incorporated particles) is investigated. The compounds' degradation behavior is monitored via Fourier-transform infrared spectroscopy and the maintenance of the homogeneous filler distribution is examined via a combined differential scanning calorimetry/thermogravimetric analysis mapping of each exposed specimen. The storage capacity decreases minimally after 7289 h of exposure. Furthermore, the incorporated filler particles enhance the thermo-oxidative stability of HDPE as PCM. Consequently, thermally conductive HDPE is a highly interesting PCM.
or carbon black), [9][10][11][12][13][14][15][16][17][18] and mineral fillers (e.g., boron nitride, aluminum nitride, or talcum). [11,[19][20][21][22][23] Moreover, hybrid filler systems have been in the focus of investigations [22,24,25] trying to evoke synergistic effects by mixing the above mentioned filler types. Since the fillers are available in different geometries, sizes, and surface modifications, much work already covered the effect of varying filler size or shape [6][7][8][10][11][12]16,17,21,22] and specimen preparation (including filler and matrix pretreatment, blending procedure, and type of molding) [14][15][16]18,[20][21][22][23]25,26] on the TC. The TC of polymers can thereby be increased by several hundred percent. Nevertheless, the TC enhancements presented in the scientific literature differ significantly. The scientists apply different measurement instruments based on varying measurement principles to determine the TC. Only two studies were found that examine a possible impact of the applied measurement device on either the thermal diffusivity (proportional to TC) [27] or on the TC of the polymeric materials. [28] Both studies compare the results generated by the Laser Flash Analysis (LFA) and the Hot Wire technique. If available, also literature results were added to the comparative work. However, this was only done with unfilled polymers whereas compounds have not been tested in spite of their important role in thermal management as mentioned above. Zhao and coworkers [9] published a sound overview on TC of carbon additive-filled compounds based on their own results and on several other publications. In this overview, the utilized measurement system was indicated to the according result. This indicates that a possible impact of the applied measurement system on the detected TC was considered. However, to the best of our knowledge, this aspect has not been investigated systematically and comprehensively yet. Thus, the present study aims at examining the impact of the measurement system on the TC of unfilled polymers and of polymeric compounds. It specifically focuses on evaluating material-induced and measurement technology-induced effects on the TC. For this purpose, high-density polyethylene and linear low-density polyethylene were used as unfilled polymers and matrix materials for the compounds. Copper particles with different shapes were added to the polyethylene matrices with filler loadings of 10, 30, and 50 wt%. The applied TC measurement techniques cover four commercially available devices (Hot Disk, Transient Hot Bridge (THB), LFA, DTC-300). Filled Polymers The thermal conductivity (TC) of different polymeric materials is measured via four commercially available testing devices: TPS2500S by Hot Disk (Hot Disk), Transient Hot Bridge (THB) by Linseis, the Laser Flash Analysis (LFA) by NETZSCH, and the DTC-300 by TA Instruments. The investigated materials include high-density polyethylene (HDPE) and linear low-density poly ethylene (LLDPE) which are analyzed as received and after bein...
Back Cover: In article https://doi.org/10.1002/mame.201800355 by Katharina Resch‐Fauster and co‐workers, the melting process of semi‐crystalline polymers is used for storing thermal energy as it is converted to the heat of fusion, which is necessary to melt the crystalline structure. By cooling the polymer, it crystallizes again and releases the stored thermal energy which is then reused.
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