The construction industry is a major consumer of natural resources and a significant contributor to global CO₂ emissions. To reduce environmental impacts and dependence on resource extraction, waste valorization offers a sustainable alternative. In this study, a green composite was developed using hydrated cement paste and methylcellulose and compared with composites incorporating chitosan and a combination of methylcellulose and chitosan. The composites were fabricated through hot pressing at three temperatures (20 ℃, 60 ℃, and 80 ℃), and their mechanical performance was evaluated through flexural strength tests, while FTIR spectroscopy was employed to investigate potential chemical interactions. Results indicated that the highest flexural strength was observed in the methylcellulose-based composite, with strength increasing proportionally to pressing temperature. The chitosan-based composite exhibited the lowest strength, while the one incorporating methylcellulose and chitosan showed intermediate values. FTIR analysis revealed that no new chemical bonds or interactions occurred between hydrated cement paste and biopolymers. Unlike previous works that mainly explored mechanical strength, this study highlights the FTIR characterization of hydrated cement paste–biopolymer composites. The novelty lies in demonstrating that methylcellulose enhances strength without inducing new chemical bonds, indicating that physical bonding and densification dominate the composite behavior.