Paper sludge functionalization for achieving fiber-reinforced and low thermal conductivity calcium silicate insulating materials

Paper sludge generated from the paper industry is classified as solid waste, comprising primarily wood fiber and calcium carbonate with low thermal conductivity. This paper is concentrated on the comparison of wood fiber and paper sludge from the structural strength and insulation property of calcium silicate insulating materials (CSIM). Test specimens with wood fiber and two different types of paper sludge were prepared by the compression molding and autoclaved curing, and DSC-TG analysis was used to compare the components and characteristic of different paper sludge. Based on the experimental results, detailed discussions on the strength, water absorption, dry density, correlation and thermal conductivity of CSIM are given. It is noted that the flexural strength of CSIM increases gradually within the increasing amount of two paper sludge from 0 to 7.5% and goes up to the highest value of 16.1 MPa and 15.1 MPa and increases about 14.2% and 7.1%. In addition, paper sludge can replace 0–0.4% of wood fiber under the requirement of the mechanical strength, and the dry density of CSIM with wood fiber is much larger than that with paper sludge. Furthermore, the addition of paper sludge in the CSIM notably decreases the thermal conductivity due to the low thermal conductivity of wood fiber and calcium carbonate. Finally, it can be concluded that the utilization of paper sludge presents a great potential to develop fiber-reinforced and low thermal conductivity CSIM and benefits to the development of waste management in producing sustainable CSIM.