Bioplastic composite films from cellulose acetate and grape pomace for agricultural mulching: biodegradation and potential contribution to soil fertility

The accumulation of plastic waste from conventional agricultural mulching necessitates the development of sustainable, biodegradable alternatives. However, many biopolymers lack the necessary balance between durability during the crop cycle and efficient biodegradation. This study addressed this gap by adopting a design-by-degradation approach for the development of bioplastic composites based on thermoplastic cellulose acetate (CA) and grape pomace (GP) (from 10 to 50 wt%). To validate the engineering relevance of the materials, a multiscale characterization was performed, integrating mechanical tensile tests and surface wettability analysis with chemical (FT-IR), thermal (TGA, DSC), and morphological (SEM) assessments before and after 120 days of incubation in synthetic and agricultural soils. Results demonstrate that the 30 wt% GP formulation represents the technical optimum: it maintains mechanical properties compatible with industrial requirements (Young’s modulus ∼900 MPa, tensile strength ∼11 MPa, and elongation >10%), ensuring structural integrity during handling and service. Surface wettability analysis revealed that GP loading modulates initial hydrophilicity, facilitating microbial attachment, while a subsequent hydrophobic shift during degradation serves as a marker for plasticizer leaching and matrix deacetylation. While cumulative biodegradation increased with GP content, the degradation mechanism primarily involved enzymatic deacetylation and partial backbone cleavage, ensuring a programmable mechanical failure. Furthermore, bioplastic residues positively enhanced soil enzymatic activity in the short-term period analyzed, suggesting a beneficial role in nutrient cycling. This integrated methodology supports the transformation of standard biodegradation monitoring into a functional engineering protocol for optimizing the lifespan and sustainability of agricultural mulch films.