Sustainable valorization of recycled cellulose fibers into boric acid/silica modified cementitious composites

Recycled cellulose fibers recovered from paper industry waste were valorized as sustainable reinforcement materials for the development of boric acid/silica-modified cementitious composites with balanced mechanical and thermal performance. A Taguchi-TOPSIS multi-response optimization approach was employed to systematically evaluate the combined effects of cellulose fiber, boric acid, and silica contents on compressive strength, heat capacity, thermal conductivity, and water absorption. Structural characterization by FT-IR, XRD, and SEM-EDX confirmed that the principal cement hydration phases were preserved after modification, while silica-rich formulations exhibited a relatively denser and more homogeneous matrix morphology. Thermogravimetric analysis showed that cellulose incorporation increased the total mass loss from approximately 12-14% for the reference cement to 17-20% for the modified composites, whereas boric acid and silica partially moderated this effect by maintaining residual mass values of 80-85% at elevated temperatures. Among the experimentally evaluated formulations, the Taguchi-TOPSIS multi-response optimization identified the A2B2C3 composition as the optimum formulation, achieving a compressive strength of 38.73 MPa, corresponding to a 52.63% improvement over the reference mixture, together with a 37.06% increase in heat capacity, while simultaneously reducing thermal conductivity and water absorption. These results demonstrate that the combined incorporation of recycled cellulose fibers, boric acid, and silica provides an effective strategy for developing sustainable cementitious composites with improved multifunctional performance while promoting the high-value utilization of paper industry waste.