Robust thermally insulating carbon-gehlenite composite foams from newspaper waste and sucrose by filter-pressing

Abstract

Carbon composite foams containing 13.6 to 41.8 wt% of gehlenite were obtained by carbonizing newspaper-sucrose composites prepared by filter-pressing of waste newspaper pulps in sucrose solution (0 to 700 g/L) followed by drying. The drying and carbonization shrinkages in the filter-pressing direction depend on the sucrose solution concentration. However, the diametrical shrinkage during drying (marginal) and carbonization were controlled by the newspaper micro-ribbons in the pulp oriented perpendicular to the filter-pressing direction. The newspaper-sucrose composites prepared at sucrose solution concentrations in the range of 400 to 700 g/L were amenable to machining using conventional tools and equipment. The density, compressive strength and Young's modulus of the carbon composite foams increased with an increase in sucrose solution concentration with values observed in the ranges of 0.18 to 0.39 g/cm3, 0.2 to 1.7 MPa and 3.4 to 69.9 MPa, respectively. The carbon composite foams had a hierarchical micro, meso, and macropore structure evidenced by SEM analysis and N2 adsorption-desorption isotherm. The foams showed excellent fire resistance and low thermal conductivity values in the range 0.1 to 0.2 W/m·K. The robust carbon composite foams prepared from the waste newspaper without using any harmful chemicals are a candidate for high temperature thermal insulation. Keywords: Carbon foams, Gehlenite, Filter-pressing, Micro-ribbons