This paper presents the formation and use of a novel composite nanostructured calcium silicate phase change material with significant thermal buffering capacity for use in thermally responsive packaging and construction materials. Phase change materials (PCMs) provide the opportunity for passive heat storage and release across a liquid-solid phase transition, due to the associated latent heat. The energy required to melt the PCM can be absorbed from the warmer surroundings, stored in the liquid phase and released when the liquid solidifies. The ice-water phase change can store and release 330 kJ kg-1 of thermal energy at 0oC. Alkane (paraffin wax) materials have latent heats of about 160-200 kJ kg-1 with the melting point determined by the hydrocarbon chain length, typically 0-100oC. The technical challenge in using PCMs is containing the liquid phase after melting. One method is to contain the liquid PCM in a micro polymer capsules which are incorporated into the end use material. Nanostructured calcium silicate (NCS) is a proprietary material comprising nanosize platelets stacked together in a unique open framework structure forming discrete particles of about 1-5 microns in size. The material has a high pore volume giving a high liquid absorbency of up to 500-600 g oil 100g-1 solid, and a high surface area of up to 500 m2 g-1. This technical problem of containing the liquid paraffin wax following melting, has been overcome by incorporating it into the porous matrix of the nanostructured calcium silicate. Typically 300-400 wt% PCM can be accommodated. Above the melting point the liquid PCM phase is fully contained in the pores of the silicate with the overall NCS-PCM composite remaining as a solid powder. This powder can be incorporated into packaging and construction materials to provide heat buffering properties of about 110 kJ kg-1. The effective temperature range for the thermal buffering is determined by the melting point of the PCM used. The NCS-PCM composites utilising Rubitherm RT paraffin PCMs with melting points of about 6, 20 and 25oC have been prepared and incorporated as a filler into fluted paperboard, sandwich board, sealed plastic bags and sealed bubblewrap plastic bags to provide various configurations of thermal buffering liners. The thermal buffering properties, and the thermal conductivities have been measured. The practical thermal performance of packages with these liners was characterised by recording the temperature at various points inside and outside the packages as they were cooled from ambient temperature to about 2oC and then warmed up again. The results show that ordinary paperboard packages had little thermal buffering capacity and the contents of the package quickly equilibrated with the outside temperature. When liners containing the NCS-PCM composite were introduced into the package, significant thermal buffering capacity was achieved. Using a NCS-PCM liner with a buffering temperature of 6oC, the inside temperature of the package remained below 10oC for 100 minutes longer as it was warmed to ambient temperature. These new NCS-PCM heat storage materials provide further opportunities to develop new thermal buffered packages and construction materials.
Journal: TechConnect Briefs
Volume: 2, Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2018
Published: May 13, 2018
Pages: 227 - 230
Industry sectors: Advanced Materials & Manufacturing | Energy & Sustainability
Topics: Materials for Sustainable Building, Sustainable Materials