Valorization of Kraft black liquor and tannins via porous material production

Macroporous polymeric monoliths were prepared using, as main raw material, mixtures of hydrolysable and condensed tannins and Kraft black liquor from pulp industry. The process consists of mechanical frothing of aqueous solutions constituted with the different polyphenols, a hardener, and in the presence of a surfactant that maintains the foam stable before curing. The aim of this work was to study the contribution in the formulations of Kraft black liquor on physical properties for the foams. This objective was justified by the significantly lower cost of black liquor as compared with that of tannins. The target application is the thermal and sound insulation in the building industry. The materials obtained were characterized by scanning electronic microscopy, mercury porosimetry and mechanical, thermal and acoustical measurements. Solid, self-standing foams with an average porosity of 90% and an average cell diameter between 170 and 329 μm were obtained. The measured values of compression modulus ranged from 1.8 up to 21.6 MPa and the thermal conductivity was around 40 mW·K−1 m−1. The materials showed also good sound absorption characteristics at medium frequencies with coefficients of 0.5 (500 Hz) and 0.8 (1000 Hz) and at high frequencies with coefficients of 0.7 (2000 Hz) and 0.8 (4000 Hz).