Efficient energy use in buildings is one of the main challenges for the next decades. More than one-third of global energy consumption is spent in this sector, from which more than a 50% is needed to heat indoor spaces (1). Proper insulation is then mandatory to prevent heat losses and save energy, money, and reduce CO2 emissions. Therefore, the study of materials with enhanced insulation properties becomes an urgent task for the scientific community. Current trends to reduce the thermal conductivity of insulating materials are to replace the air inside them with vacuum (2) or to reduce the pore size below the mean free path of air molecules (3), that is, producing nanocellular materials.
Nanocellular materials are characterized by cell sizes in the range of tens to hundreds of nanometers and present a reduced thermal conductivity thanks to the Knudsen effect (3). To fully take advantage of this effect, low-density nanocellular materials are required (4). However, the production of such materials is still a challenge for the scientific community, and novel systems and processes are needed to reach low densities (below 0.2) and at the same time cell sizes clearly below 1 micron. This paper is focused on this topic, analysing a promising system (PMMA/TPU blends) that allows reaching the desired densities.
In this work, low-density nanocellular polymers (relative density under 0.2) are produced via the gas dissolution foaming method. The materials used for this study are blends of poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU). These two polymers are immiscible, and during the melt blending process in the extruder, the minority component (TPU) is dispersed in nanometric domains. As a result, the PMMA/TPU blends are nanostructured, and these nanometric TPU domains act as preferable nucleation areas in the foaming process, allowing the appearance of nanometric cells. The effect of different TPU contents, PMMA grades, and foaming conditions are also studied and discussed in this work.
1. International Energy Agency (IEA). 2013.
2. Alam, M., Singh, H., Limbachiya, M. C. Applied Energy 2011, 88 (11), 3592–3602.
3. Notario, B., Pinto, J., Solorzano, E., de Saja, J. A., Dumon, M., Rodriguez-Perez, M. A. Polymer 2015, 56, 57–67.
4. Li, Z., Zhu, C., Zhao, X. International Journal of Heat and Mass Transfer 2017, 108, 1982–1990.