Citric acid-engineered cellulose as a high-performance bio-filler for polyurethane foams: Simultaneous enhancement of acoustic absorption and cushioning properties

As the automotive industry rapidly transitions toward electric vehicles, improving in-cabin noise attenuation and seating comfort has become increasingly important. This study investigates the performance enhancement of polyurethane (PU) composite foams using citric acid-modified cellulose as a bio-based filler. Cellulose particles were chemically esterified with citric acid to improve interfacial compatibility with the PU matrix, as confirmed by FTIR and XPS analyses. The incorporation of modified cellulose induced notable changes in foam morphology, including reduced open porosity and refined cell structures. These morphological improvements significantly enhanced the acoustic properties of the foams, with the formulation containing 0.6 wt% modified cellulose exhibiting the highest sound absorption performance. Compared with the foam containing unmodified filler, the sound absorption coefficient increased by 15%, and the NRC reached 0.35. Mechanical comfort characteristics also improved, as evidenced by increased sag factor and reduced hysteresis loss. Thermogravimetric analysis confirmed that cellulose incorporation and surface modification influenced the thermal degradation behavior of the PU foams, while dynamic mechanical analysis revealed that the modified cellulose increased viscoelastic damping behavior and facilitated greater dissipation of mechanical energy as heat. Overall, the results demonstrate that citric acid-treated cellulose is an effective reinforcement for developing PU foams with superior acoustic and cushioning functionalities, offering a promising pathway toward sustainable, high-performance polyurethane materials.