Excellent Specific Mechanical and Electrical Properties of Anisotropic Freeze‐Cast Native and Carbonized Bacterial Cellulose‐Alginate Foams

Abstract

Native and carbonized freeze-cast bacterial cellulose-alginate (BC-ALG) foams possess an ice-templated honeycomb-like architecture with remarkable properties. Their unique pore morphology consists of two levels of porosity: 20-50 µm diameter pores between, and 0.01-10 µm diameter pores within the cell-walls. The mechanical properties of the BC-ALG foams, a Young's modulus of up to 646.2 ± 90.4 kPa and a compressive yield strength of up to 37.1 ± 7.9 kPa, are high for their density and scale as predicted by the Gibson-Ashby model for cellular materials. Carbonizing the BC-ALG foams in an inert atmosphere at 1000-1200 °C in a second processing step, both pore morphology and mechanical properties of the BC-ALG remain well preserved with specific mechanical properties that are higher than those reported in the literature for similar foams. Also the electrical conductivity of the BC-ALG foams is high at 1.68 ± 0.04 S cm −1 at a density of only 0.055 g cm −3 , and is found to increase with density as predicted, and as a function of the degree of carbonization determined by both carbonization temperature and atmosphere. The property profile makes freeze-cast BC-ALG foams and their carbonized foams attractive for energy applications and as a sorbent.

Insights into Hierarchical Structure–Property–Application Relationships of Advanced Bacterial Cellulose Materials

“…[ 86 ] This carbonization process endows BC with excellent electrical and thermal conductivity as well as good chemical resistance without destroying its 3D structure. [ 47 ] Carbonized BC shows great potential in conductive materials, [ 87 ] oxygen reduction catalysts, [ 88 ] sensors, [ 89 ] supercapacitors, [ 90 ] ion batteries, [ 91 ] and water treatment. [ 92 ]…”

“…Carbonization processes result in the retention of the 3D nanofiber network structure of BC. [47] In contrast to biosynthetic or chemical modification, physical modification includes processes such as stretching, [48] ultrasonication, [49] compression, [50] high-speed shearing, [51] and extrusion. [52] These processes can lead to the collapse of the 3D structure or the disappearance of micron-sized macropores.…”

Cellulose Nanocrystal Embedded Composite Foam and Its Carbonization for Energy Application

“…For example, since nano-fibrillated cellulose (NFC) is a cellulosic nanomaterial with good crystallinity and sizeable specific surface due to the cellulose I structure, it can serve as a structural material for the aerogel [ 13 , 14 ]. Although cellulose can extend its applications, its relatively low mechanical property must be improved significantly [ 15 , 16 ]. On the other hand, much effort has been made to construct a form-stable cellulose compound for energy-related applications by carbonizing cellulosic materials [ 17 , 18 ].…”

Freeze-derived heterogeneous structural color films

“…With the structural characteristics, diverse building elements 29 , such as ceramics 30 , 31 , carbon nanotubes 32 , graphene 33 , 34 , polymers 35 , and boron nitride 36 , have been integrated into mass complex composites possessing nacre-like morphology via ice-templating 37 – 41 . In addition, benefitting from the porous nature of ice-template materials, the freeze-casting method is creatively used to prepare aerogel 42 , smart sponges 43 , 44 , polymeric woods 45 , and multifunctional cellular plastics 46 . Remarkably, strong tough hydrogels 47 , 48 and fatigue-resistant hydrogels 49 , which are difficult to prepare by other methods, are successfully fabricated through the ice-template strategy 50 .…”