Excellent Specific Mechanical and Electrical Properties of Anisotropic Freeze‐Cast Native and Carbonized Bacterial Cellulose‐Alginate Foams
Kaiyan Qiu, Ulrike G. K. Wegst
Abstract
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.