Toward Sustainable Printed Packaging: Surface Properties and Ink Adhesion Behavior of PLA/PCL/Nanosilica Biopolymer Blends

In this study, polylactic acid (PLA) was blended with poly(ε-caprolactone) (PCL) and reinforced with nanosilica (SiO2) to tailor surface characteristics and improve adhesion in biopolymer-based printed packaging applications. The surface microstructure and topography were analyzed using FTIR-ATR, SEM, and surface profilometry. Surface wettability and surface free energy (SFE), along with the adhesion properties of printed ink layers on polymer blends, were assessed, and the optical properties of the substrates and prints were evaluated. SEM revealed that PLA/PCL blends exhibited phase-separated morphologies with PCL droplet domains, whereas incorporation of 3 wt% SiO2 resulted in finer dispersion and reduced surface irregularities. Surface roughness (Ra) increased from 1.92 µm for PLA/SiO2 100/3 to 4.45 µm for PLA/PCL/SiO2 50/50/0, while water contact angle decreased from 70.9° for neat PLA to 43.4° for PLA/SiO2 100/3 surface, reflecting enhanced hydrophilicity. SFE components ranged from 26 to 40.7 mJ/m2 (dispersive) and 3.2 to 21.5 mJ/m2 (polar). Adhesion parameters (interfacial tension ranging from 0.01 to 5.54 mJ/m2, work of adhesion from 76.9 to 97.3 mJ/m2, and wetting coefficient from 3.04 to 11.1 mJ/m2) indicated favorable ink compatibility for most blends, and optical density of the printed layers (1.85–2.35) confirmed potential for good printability. These findings demonstrate that PLA/PCL/SiO2 blends allow controlled tuning of surface morphology, wettability, and adhesion, providing a promising approach for biodegradable and print-ready packaging substrates.