Polycaprolactone bionanocomposites reinforced with oxalic acid-esterified microfibrillated cellulose from coffee parchment for sustainable packaging

Biodegradable polycaprolactone (PCL) bionanocomposites reinforced with microfibrillated cellulose (MFC) from coffee parchment were developed via a one-step thermomechanical–chemical process combining steam explosion and in situ oxalic acid esterification. FTIR confirmed ester formation by the appearance of a C O band at 1739 cm⁻¹ . The modified fibers exhibited higher thermal stability (Tonset = 325 °C; Tmax = 377 °C) and increased crystallinity (89.4%) compared to unmodified counterparts. Esterification reduced fiber hydrophilicity and improved interfacial compatibility with PCL, leading to enhanced stress transfer and barrier performance. Composites containing 3 wt% modified MFC showed the best overall performance, with tensile strength of 44.0 MPa (+55%), elongation at break of 1038.7% (+88%), and Young’s modulus of 154.9 MPa (+75%) relative to neat PCL. CO₂ permeability decreased by 10%, while wettability remained unchanged. Morphological analysis revealed a well-dispersed fibrillar network, and DSC indicated no significant changes in PCL crystallization behavior. These results demonstrate that integrating esterification into the steam explosion process provides a scalable and metal-free route to tailor cellulose–polyester interfaces, enabling high-performance biodegradable materials for sustainable packaging applications.