Hybrid PLA /Thermoplastic Starch Biocomposites Reinforced With Spent Coffee Grounds: Effect of Maleic Anhydride on Interfacial Compatibility, Mechanical Performance, and Biodegradability

ABSTRACT This study developed hybrid poly(lactic acid) (PLA)/thermoplastic starch (TPS) biocomposites reinforced with spent coffee grounds (AK, 0–30 wt%) and compatibilized with maleic anhydride (MA, 5 wt%). The composites were characterized using Fourier‐transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), tensile testing, melt flow rate (MFR), water absorption, and soil‐burial biodegradability. Increasing AK content improved stiffness and biodegradation because of its lignocellulosic structure; however, excessive filler loading caused agglomeration and reduced ductility. MA enhanced interfacial compatibility, filler dispersion, stress transfer, and moisture resistance at low to moderate AK contents. The AK 10% + MA formulation showed the most balanced performance, achieving a tensile strength of 29.86 MPa, low water absorption, favorable melt flow behavior, and 28.03% weight loss after 3 months of soil burial. These results clarify the role of AK and MA in controlling the processing–structure–property–biodegradation relationship of PLA/TPS composites and support the use of spent coffee grounds as sustainable fillers for biodegradable bioplastics.