Surface-functionalized microcrystalline cellulose derived from quinoa stalks as a sustainable reinforcing additive...

This study investigates the functionalization of microcrystalline cellulose (MCC) and its application as a sustainable reinforcement for cementitious materials, while promoting the valorization of purified phosphogypsum (PPG) in cementitious materials. MCC was extracted from quinoa stalks and subsequently functionalized through carboxylation, phosphorylation, or sulfonation to modify its surface chemistry while preserving the integrity of the cellulose polymeric backbone. A systematic comparison of the functionalized MCCs enabled direct correlations between macromolecular surface functionality and cement performance. Solid-state ¹³C and ³¹P NMR analyses verified the successful introduction of the functional groups, and elemental quantification confirmed the effective incorporation of carboxyl, phosphorus, and sulfur functionalities with degrees of substitution of 0.033, 0.51, and 0.35, respectively. The functionalized MCC materials were incorporated into PPG-based cement pastes at low contents (0.1-2.0 wt%) as a bio-based macromolecular reinforcing additive. Flowability measurements revealed a progressive decrease with increasing MCC content, while functionalized MCCs improved dispersion and maintained higher workability compared to unmodified MCC. At an optimal content (0.2 wt%), functionalized MCCs significantly enhanced hydration efficiency and mechanical performance, without altering the main hydration phases, as evidenced by XRD, TGA, and FTIR analyses. Carboxylated MCC exhibited the most pronounced effect, increasing the 28-day compressive and flexural strengths by 49.1% and 38.7% respectively compared to CEM II/B-M 32.5. These results highlight the potential of functionalized quinoa-derived MCCs for PPG-based cement materials, thereby supporting the circular use of agro-wastes and phosphogypsum by-products in construction materials.