Characterisation of multifunctional composites exhibiting mechanical and thermal management capabilities
Creators: name: Yoo, Sanghyun
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401602
subject: Composite and hybrid materials

description: Thermal storage systems based on latent heat are among the efficient energy saving solutions. Unlike the sensible heat, much higher storage densities and narrow operating temperatures can be achieved using latent heat. To utilise these advantages, Phase Change Materials (PCMs) have been integrated into load- and non-load-bearing components to enhance their thermal storage capacity. PCMs are capable of absorbing, storing and releasing a large amount of thermal energy so-called latent heat. Thermal energy is absorbed and released during the phase change without changing the temperature itself. In this regard, multifunctional composite exhibiting both structural properties and thermal storage capability can be a viable solution to reduce energy consumption in engineering applications.<br><br>In order to develop PCM-incorporated multifunctional composites, it is necessary to characterise the inclusion effect of PCMs on the host composite laminates. In particular, micro-PCMs are integrated into traditional Fibre Reinforced Polymer (FRP) composite and its influence was investigated. Furthermore, thermal management capabilities are strongly influenced by not only the filler but also thermo-mechanical properties of the matrix. The characterisation of viscoelastic properties is important due to the viscoelastic nature of the polymer matrix. As a result, the micro-PCMs inclusion effect on mechanical, thermophysical and viscoelastic properties of composites was experimentally investigated.<br><br>It was found that the tensile, compressive, and flexural properties of multifunctional composites were reduced by increasing the weight fraction of micro-PCMs. The failure mechanism changed from matrix to interfacial failure after incorporating 12 wt.% of microencapsulated PCMs. Using short-beam-strength (SBS) tests and SEM analysis, it was identified that a significant reduction in the interfacial shear strength is contributing towards the degradation of mechanical properties. The interfacial adhesion between micro-PCMs and matrix was deteriorated due to the poor wetting of the fillers during manufacturing. On the other hand, the embedded micro-PCMs improved Mode Ι interlaminar fracture toughness due to the particle toughening mechanisms (i.e. crack pinning and debonding). The effect of solid ↔ liquid phase transition of micro-PCMs on the mechanical properties of composites was also studied through SBS tests, at temperatures below and above the melting temperature of PCM.<br><br>The influence of micro-PCMs on the thermophysical properties of multifunctional laminates was also examined. While the thermal storage capacity (heat of fusion) of the composites was directly proportional to the weight fraction of micro-PCMs, the thermal and dimensional stability of the multifunctional composites were significantly affected by increasing microencapsulated PCMs concentration. The thermal decomposition temperature was reduced and the coefficient of thermal expansion (CTE) was increased due to the inclusion of micro-PCMs. These observations indicate that the interfacial properties between micro-PCMs and matrix play a crucial role in determining the thermal and dimensional stability of the composites.<br><br>Finally, by investigating the viscoelastic properties, it was revealed that the glass transition temperature of the composites was also affected since incorporating micro-PCMs promotes segmental motions of epoxy. The viscoelasticity of micro-PCMs-enhanced FRP composites was investigated using multi-frequency scans through the concept of activation energy and free volume. In addition, an unusual transition in the storage and loss moduli of composites was observed at lower temperature ranges, which was attributed to phase transition of micro-PCMs (solid → liquid phase) and confirmed by the correlation between DMA and DSC analysis of micro-PCMs capsules.