CELLULOSE FIBER REINFORCED RF-AEROGELS

Abstract

Cellulose gels were synthesized in which the pore space was filled with resorcinol-formaldehyde (RF) aerogel solution. Three weight percent microcrystalline cellulose was dissolved in an aqueous calcium thiocyanate melt at 110 °C, which gelled on cooling building a nanofibrillar felt structure. The highly concentrated salt solution in the pore space is washed with ethanol until a test with Fe3+ ions does yield a colorless solution. After washing with formaldehyde (24%) the hydrogel was exposed to a resorcinol-formaldehyde solution while gelling. The RF solution had a molar ratio of resorcinol to water (R/W) of 0.04 and of resorcinol to formaldehyde (R/F) of 0.7. The molar ratio of resorcinol to catalyst sodium carbonate (R/C) used was 100, 500, 1000 or 1500. The composite gels prepared were dried supercritically and their nanostructure characterized by SEM. The aerogels were characterized by density, surface area, compression strength and thermal conductivity. Measurements of compression strength showed an anomalous behavior compared to those of pure cellulose aerogels.