Structure–Property Relationships in Cellulose Acetate Films from Lignocellulosic Waste: Role of Microalgal Residues in Modulating Microstructure and Mass Transport

The development of bio-based polymeric materials from renewable waste streams represents a key challenge in sustainable material science. In this work, cellulose acetate obtained from grapevine lignocellulosic residues was used as a polymer matrix for composite films incorporating exhausted microalgal biomass of a Chlamydomonas reinhardtii culture as a biofiller. Microalgal residues are proposed to modulate intermolecular interactions and microstructural organization within cellulose acetate matrices, allowing for the tuning of thermal stability and mass transport properties. Films were prepared by solvent casting using glycerol as a plasticizer and investigated to elucidate structure–property relationships. Mechanical analysis shows that microalgal incorporation increases breaking stress while maintaining Young’s modulus and elongation at break. Fourier transform infrared (FTIR) spectroscopy reveals interactions among cellulose acetate, glycerol, and microalgal biomolecules. Differential scanning calorimetry (DSC) analysis indicates enhanced thermal stability, with thermal transitions shifting by more than 50 °C. Scanning electron microscopy (SEM) observations reveal a more compact microstructure. This structural reorganization results in increased surface wettability (contact angle decrease from ∼36° to ∼20°) and a significant reduction in water absorption (–57%), alongside increased mass transport properties. In particular, water vapor permeability increases by ∼40% and oxygen permeability by ∼14%. More broadly, this work establishes a scalable strategy to upcycle complementary bio-waste streams into multifunctional materials with tunable properties. The ability to simultaneously control barrier performance, wettability, and thermal stability highlights the potential of these systems for advanced sustainable packaging and functional coatings. Overall, this approach advances the rational design of high-performance bio-based materials, contributing to the transition toward circular and low-carbon material platforms.