Inspired by natural porous materials, such as wood, bamboo and spongy bone consisting of individual structural units that are hierarchically arranged to optimise mechanical properties such as strength and toughness, synthetic macroporous polymers with enhanced physical properties were created by emulsion templating. Hierarchical poly(merised) high internal phase emulsions (HIPE) were created from HIPEs stabilised simultaneously by particles and a surfactant. In these HIPEs, surfactant stabilised and particle stabilised water droplets coexist, which upon polymerisation of the minority oil phase gives rise to macroporous polymers with a hierarchical pore structure. An improvement of the mechanical properties of our hierarchically structured macroporous polymers at equal porosity was observed, due to a more efficient packing of pores in a configuration that improves mechanical strength despite the presence of interconnecting pore throats. Moreover, the permeability of the hierarchically structured polyHIPEs are exceeding those measured for conventional polyHIPEs made from surfactant only stabilised HIPEs.

High porosity, high performance macroporous biobased epoxy resins are produced by curing foam templates produced by mechanical frothing of a highly viscous epoxy resin.

In building construction, structural elements, such as lattice girders, are positioned specifically to support the mainframe of a building. This arrangement provides additional structural hierarchy, facilitating the transfer of load to its foundation while keeping the building weight down. We applied the same concept when synthesizing hierarchical open-celled macroporous polymers from high internal phase emulsion (HIPE) templates stabilized by varying concentrations of a polymeric non-ionic surfactant from 0.75 to 20 w/vol %. These hierarchical poly(merized)HIPEs have multimodally distributed pores, which are efficiently arranged to enhance the load transfer mechanism in the polymer foam. As a result, hierarchical polyHIPEs produced from HIPEs stabilized by 5 vol % surfactant showed a 93% improvement in Young's moduli compared to conventional polyHIPEs produced from HIPEs stabilized by 20 vol % of surfactant with the same porosity of 84%. The finite element method (FEM) was used to determine the effect of pore hierarchy on the mechanical performance of porous polymers under small periodic compressions. Results from the FEM showed a clear improvement in Young's moduli for simulated hierarchical porous geometries. This methodology could be further adapted as a predictive tool to determine the influence of hierarchy on the mechanical properties of a range of porous materials.

Mechanical frothing is one of the most commonly used methods to create gas-liquid foams. Until recently, the polymerisation of mechanically frothed gas-liquid foams was limited to quasi two-dimensional polymer structures, such as films. In this study we show that threedimensional bio-based polymer foams can be created by microwave curing of gas-soybean oil foams created by mechanical frothing using peroxide as the radical initiator. It was found that the introduction of air during the mechanical frothing was necessary to create the three-dimensional polymer foams. The potential of using bacterial cellulose nanofibrils (BC) simultaneously as stabilisers by obstructing the flow of liquid from the lamella region for these gas-soybean oil foams and nano-filler in the polymer foam is also demonstrated. It was found that the stability of the gas-soybean oil foam templates and the mechanical properties of the polymer nanocomposite foams are enhanced upon the addition of BC foams.

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