Thermal Energy Storage Capability of Polyurethane Foams Incorporated with Microencapsulated Phase Change Material

Phase-Change Materials as Cryo-Shock Absorbers in Rigid Polyurethane Cryogenic Insulation Foams

This study investigates the effects of microencapsulated phase-change materials (PCMs) on the density and thermal conductivity of rigid polyurethane (PU) foams, alongside their mechanical properties. Introducing PCMs into the foam composition results in increased viscosity, complicating the mixing of polyol and isocyanate components. This viscosity increase can slow the foaming rate and subsequently raise the foam density, as observed in both poured and sprayed rigid PU foams containing 5% and 10% PCM, leading to density increases of up to 9%. Despite these slight density changes, the thermal conductivity remained relatively stable due to the preservation of the foam's closed-cell structure. The mechanical evaluation revealed a decrease in compressive and tensile strength with a higher PCM content attributed to defects arising in the foam's cellular architecture. However, adhesive strength to aluminum substrates improved, particularly with 5% PCM, possibly due to a more consistent foam structure during the slower foaming process. Differential scanning calorimetry and a dynamic mechanical analysis indicated that the incorporation of PCM increased the glass transition temperature and affected the foam's mechanical properties. This research underscores the potential of microencapsulated PCMs to enhance the functionality of rigid PU foams while needing careful consideration of their concentration to avoid compromising the structural integrity.

Foamed Phase Change Materials Based on Recycled Polyethylene/Paraffin Wax Blends

Foamed phase-change materials (FPCMs) were prepared using recycled linear low-density polyethylene (LLDPE) blended with 30 wt.% of paraffin wax (PW) and foamed by 1,1'-azobiscarbamide. The protection of pores' collapse during foaming process was insured through chemical cross-linking by organic peroxide prior foaming. This work represents one of very few attempts for a preparation of polymeric phase change foams without a use of micro-encapsulated phase change component leading to the enhancement of the real PCM component (PW) within a final product. The porous structure of fabricated foams was analyzed using micro-computed tomography, and direct observation, and reconstruction of the internal structure was investigated. The porosity of FPCMs was about 85-87 vol.% and resulting thermal conductivity 0.054-0.086 W/m·K. Differential Scanning Calorimetry was used to determine the specific enthalpies of melting (22.4-25.1 J/g) what is the latent heat of materials utilized during a heat absorption. A stability of samples during 10 heating/cooling cycles was demonstrated. The phase change changes were also investigated using the dynamic mechanical analysis from 0° to 65 °C during the 10 cycles, and the mechanical stability of the system and phase-change transition were clearly confirmed, as proved by DSC. Leaching test revealed a long-term release of PW (around 7% of its original content) from samples which were long term stored at temperatures over PW melting point. This is the usual problem concerning polymer/wax blends. The most common, industrially feasible solution is a lamination of products, for instance by aluminum foils. Finally, the measurement of the heat flow simulating the real conditions shows that samples containing PW decrease the energy passing through the sample from 68.56 to 34.88 kJ·m^-2. In this respect, FPCMs provide very effective double functionality, firstly common thermal insulators, and second, as the heat absorbers acting through melting of the PW and absorbing the excessive thermal energy during melting. This improves the heat protection of buildings and reduces temperature fluctuations within indoor spaces.