Abstract
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.
Highlights
It is estimated that roughly 30–40% of the world’s total energy produced from fossil fuels is consumed by the construction industry, what results in one-third of the world’s greenhouse gas emissions
This work focused on the preparation of foamed phase-change materials using recycled linear low-density polyethylene blended with 30 wt.% of paraffin wax (PW)
The concentration of 30 wt.% of PW was selected according to previous optimization to get materials with appropriate latent heat, high porosity, low thermal conductivity, and acceptable leakage of PW from final materials
Summary
It is estimated that roughly 30–40% of the world’s total energy produced from fossil fuels is consumed by the construction industry, what results in one-third of the world’s greenhouse gas emissions. In Qatar, 65% of produced electricity is consumed by cooling systems in all types of buildings [1] From this reason, it is important to develop materials which effectively absorb and release an excess thermal energy to insure thermal indoor comfort, minimizing the need of electrical energy for heating in winter and cooling in summer. It is important to develop materials which effectively absorb and release an excess thermal energy to insure thermal indoor comfort, minimizing the need of electrical energy for heating in winter and cooling in summer These materials can reduce variations in temperature of buildings when outside temperature changes over day. Polymeric foams, such as polyurethane, polyethylene, and polystyrene are the most commonly applied materials for insulation because of their low thermal conductivity, low density, acceptable mechanical properties, and an appropriate price [2,3]
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