Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules
Thermal energy storage offers a viable solution for managing intermediate energy availability challenges. Phase change materials (PCMs) have been extensively studied for their capacity to store thermal energy when available and release it when needed, maintaining a narrow temperature range. However,...
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MDPI AG
2025-04-01
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| author | Refat Al-Shannaq Monzer Daoud Mohammed Farid Md Wasi Ahmad Shaheen A. Al-Muhtaseb Mazhar Ul-Islam Abdullah Al Saidi Imran Zahid |
| author_facet | Refat Al-Shannaq Monzer Daoud Mohammed Farid Md Wasi Ahmad Shaheen A. Al-Muhtaseb Mazhar Ul-Islam Abdullah Al Saidi Imran Zahid |
| author_sort | Refat Al-Shannaq |
| collection | DOAJ |
| description | Thermal energy storage offers a viable solution for managing intermediate energy availability challenges. Phase change materials (PCMs) have been extensively studied for their capacity to store thermal energy when available and release it when needed, maintaining a narrow temperature range. However, effective utilization of PCMs requires its proper encapsulation in most applications. In this study, microcapsules containing Rubitherm<sup>®</sup>(RT) 21 PCM (Tpeak = 21 °C, ΔH = 140 kJ/kg), which is suitable for buildings, were synthesized using a suspension polymerization technique at different operating temperatures (45–75 °C). Two different water-insoluble thermal initiators were evaluated: 2,2-Azobis (2,4-dimethyl valeronitrile) (Azo-65) and benzoyl peroxide (BPO). The prepared microcapsules were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), particle size distribution (PSD), scanning electron microscope (SEM), and optical microscopy (OM). Additionally, the microcapsules were subjected to multiple melting and freezing cycles to assess their thermal reliability and performance stability. DSC results revealed that the microcapsules using BPO exhibited a latent heat of melting comparable to those produced with Azo-65 at an operating temperature of 75 °C. However, the onset crystallization temperature for the BPO-encapsulated PCMs was approximately 2 °C lower than that of the Azo-65-encapsulated PCMs. The greatest latent heat of melting, 107.76 J/g, was exhibited by microcapsules produced at 45 °C, representing a PCM content of 82 wt. %. On the other hand, microcapsules synthesized at 55 °C and 75 °C showed latent heats of 96.02 J/g and 95.66 J/g, respectively. The degree of supercooling for PCM microcapsules was reduced by decreasing the polymerization temperature, with the lowest supercooling observed for microcapsules synthesized at 45 °C. All microcapsules exhibited a monodisperse and narrow PSD of ~10 µm, indicating uniformity in microcapsule size and demonstrating that temperature variations had no significant impact on the particle size distribution. Future research should focus on low-temperature polymerization with extended polymerization times. |
| format | Article |
| id | doaj-art-b83a2894cfc048f890338cf558ce5ed5 |
| institution | Kabale University |
| issn | 2673-8023 |
| language | English |
| publishDate | 2025-04-01 |
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| spelling | doaj-art-b83a2894cfc048f890338cf558ce5ed52025-08-20T03:29:43ZengMDPI AGMicro2673-80232025-04-01521910.3390/micro5020019Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM MicrocapsulesRefat Al-Shannaq0Monzer Daoud1Mohammed Farid2Md Wasi Ahmad3Shaheen A. Al-Muhtaseb4Mazhar Ul-Islam5Abdullah Al Saidi6Imran Zahid7Department of Chemical Engineering, Dhofar University, Salalah P.O. Box 2509, OmanDepartment of Mechanical Engineering, Dhofar University, Salalah P.O. Box 2509, OmanDepartment of Chemical and Materials Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New ZealandDepartment of Chemical Engineering, Dhofar University, Salalah P.O. Box 2509, OmanDepartment of Chemical Engineering, College of Engineering, Qatar University, Doha P.O. Box 2713, QatarDepartment of Chemical Engineering, Dhofar University, Salalah P.O. Box 2509, OmanDepartment of Chemical Engineering, Dhofar University, Salalah P.O. Box 2509, OmanMechanical Engineering and Technology Department, Government College University Faisalabad, Faisalabad 38000, PakistanThermal energy storage offers a viable solution for managing intermediate energy availability challenges. Phase change materials (PCMs) have been extensively studied for their capacity to store thermal energy when available and release it when needed, maintaining a narrow temperature range. However, effective utilization of PCMs requires its proper encapsulation in most applications. In this study, microcapsules containing Rubitherm<sup>®</sup>(RT) 21 PCM (Tpeak = 21 °C, ΔH = 140 kJ/kg), which is suitable for buildings, were synthesized using a suspension polymerization technique at different operating temperatures (45–75 °C). Two different water-insoluble thermal initiators were evaluated: 2,2-Azobis (2,4-dimethyl valeronitrile) (Azo-65) and benzoyl peroxide (BPO). The prepared microcapsules were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), particle size distribution (PSD), scanning electron microscope (SEM), and optical microscopy (OM). Additionally, the microcapsules were subjected to multiple melting and freezing cycles to assess their thermal reliability and performance stability. DSC results revealed that the microcapsules using BPO exhibited a latent heat of melting comparable to those produced with Azo-65 at an operating temperature of 75 °C. However, the onset crystallization temperature for the BPO-encapsulated PCMs was approximately 2 °C lower than that of the Azo-65-encapsulated PCMs. The greatest latent heat of melting, 107.76 J/g, was exhibited by microcapsules produced at 45 °C, representing a PCM content of 82 wt. %. On the other hand, microcapsules synthesized at 55 °C and 75 °C showed latent heats of 96.02 J/g and 95.66 J/g, respectively. The degree of supercooling for PCM microcapsules was reduced by decreasing the polymerization temperature, with the lowest supercooling observed for microcapsules synthesized at 45 °C. All microcapsules exhibited a monodisperse and narrow PSD of ~10 µm, indicating uniformity in microcapsule size and demonstrating that temperature variations had no significant impact on the particle size distribution. Future research should focus on low-temperature polymerization with extended polymerization times.https://www.mdpi.com/2673-8023/5/2/19phase change materials (PCMs)microencapsulationsuspension polymerizationthermal energy storage |
| spellingShingle | Refat Al-Shannaq Monzer Daoud Mohammed Farid Md Wasi Ahmad Shaheen A. Al-Muhtaseb Mazhar Ul-Islam Abdullah Al Saidi Imran Zahid Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules Micro phase change materials (PCMs) microencapsulation suspension polymerization thermal energy storage |
| title | Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules |
| title_full | Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules |
| title_fullStr | Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules |
| title_full_unstemmed | Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules |
| title_short | Roles of Polymerization Temperature and Initiator Type on Thermal Properties of Rubitherm<sup>®</sup> 21 PCM Microcapsules |
| title_sort | roles of polymerization temperature and initiator type on thermal properties of rubitherm sup r sup 21 pcm microcapsules |
| topic | phase change materials (PCMs) microencapsulation suspension polymerization thermal energy storage |
| url | https://www.mdpi.com/2673-8023/5/2/19 |
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