Scalable Fabrication of Thermally Insulating Mechanically Resilient Hierarchically Porous Polymer Foams

Abstract

The requirement of energy efficiency demands materials with superior thermal insulation properties. Inorganic aerogels are excellent thermal insulators, but are difficult to produce on a large-scale, are mechanically brittle, and their structural properties depend strongly on their density. Here, we report the scalable generation of low-density, hierarchically porous, polypropylene foams using industrial-scale foam-processing equipment, with thermal conductivity lower than that of commercially available high-performance thermal insulators such as superinsulating Styrofoam. The reduction in thermal conductivity is attributed to the restriction of air flow caused by the porous nanostructure in the cell walls of the foam. In contrast to inorganic aerogels, the mechanical properties of the foams are less sensitive to density, suggesting efficient load transfer through the skeletal structure. The scalable fabrication of hierarchically porous polymer foams opens up new perspectives for the scalable design and development of novel superinsulating materials.

Thermal Transport in 3D Nanostructures

“…Extensive results have shown an ultralow thermal conductivity of the polymer nanocellular foam with pore sizes down to 100 nm. For instance, Rizvi et al successfully fabricated polypropylene foams using industrial‐scale foam molding technique to achieve a low thermal conductivity of 29 mW m −1 K −1 (for air) at a density of 0.074 g cm −3 …”

“…For instance, Rizvi et al successfully fabricated polypropylene foams using industrial-scale foam molding technique to achieve a low thermal conductivity of 29 mW m −1 K −1 (for air) at a density of 0.074 g cm −3 . [56] Overall, researchers have investigated the thermal transport of the polymer nanocellular foams with various constituent polymer matrices, different pore sizes, and different densities. Since there are already several recent reviews devoted to the thermal conductivity of nanocellular foams, [51] we will not focus on this group of structures in this review.…”

Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

“…However, the thermal insulation applications of pure MOFs have rarely been exploited, probably because of the difficulty in shaping and processing of the brittle and insoluble MOF crystals [4,11]. Apart from their low thermal conductivity, thermal insulation materials are required to be fire-retardant, lightweight, and mechanically resilient or flexible from an application perspective [12][13][14][15]. Inorganic thermal insulation materials such as silica aerogels are usually mechanically brittle and difficult to prepare in larger sizes, making them challenging to use in, for example, building or packaging materials [16,17].…”

Hierarchical Cellular Poly(m‐phenylene isophthalamide) with High Flame Retardancy, Mechanical Robustness, and Heat Resistance at Extreme Situation

“…Heat transfer in foams is composed of three parts of contributions, i.e., thermal radiation (λr), thermal conductivity of solid phase (λs), and gas phase (λg). [ 44 ] The thermal conductivity of PMIA foams mainly depended on their bulk density, as seen in Figure 5c. Lower bulk density generated a lower contribution of λs and a higher λg.…”