Macrostructures with hierarchical porosity produced from alumina–aluminum hydroxide–chitosan wet-spun fibers

This paper reports on the development of macrostructures with hierarchical porosity produced from Al2O3–Al(OH)3–chitosan wet-spun fibers. Aqueous suspensions (13 vol% of solids, 1.3 vol% of chitosan, 0.1 M acetic acid, pH–4) containing different Al2O3–Al(OH)3 ratios were extruded through a 500 μm diameter syringe needle into a 2 M NaOH coagulation bath. After washing and drying, these continuous fibers were controllably chopped into 5 mm long staples and shaped under vacuum into 40×40 mm2 cylindrical macroelements, using 2 wt% chitosan solution as binder. By varying the Al2O3–Al(OH)3 content (100–0, 50–50 and 0–100 vol%) and sintering temperature (1100–1500 °C), structures with different levels of porosity (up to 84%), specific surface area (up to 7 m2 g−1) and mechanical strength (up to 9 MPa in uniaxial compression) were obtained. The ratio between the porosity inside the solid part of the structure and the interfilament space was also affected by these parameters and was adjusted according to the numerous potential applications of this system.