Scale up coating process of PBAT with modified lignin for paper packaging: Barrier properties, and screening volatile/semi-volatile compounds

To replace fossil-based plastics with circular alternatives, paper packaging requires high-performance functional barriers. This study evaluates coatings composed of poly(butylene adipate-co-terephthalate) (PBAT) and lignin to address this performance gap from paper for food packaging applications. Specifically, paper coatings based on PBAT and esterified lignin (E.Lignin) as compatibilizer were developed and scaled up by extrusion coating. Lignin esterification with propionic acid increased compatibility with the PBAT matrix, as confirmed by FT-IR and ¹ ³C CP/MAS NMR and GC-MS. At laboratory scale, adding 1 wt% E.Lignin to PBAT reduced water and oxygen transmission rates (WVTR and OTR) relative to neat PBAT coatings by 65%. The use of lignosulfonates (LS) as alternative compatibilizer (avoiding esterification) was explored at laboratory scale. Low loadings improved lignin dispersion and comparable moisture-barrier performance was achieved as for the E.Lignin. The selected formulation (PBAT + 1 wt% E.Lignin) was validated by pilot-scale extrusion coating at grammages of 8–24 g/m², achieving WVTR values of 250–150 g/m²·day (23 °C, 50% RH) and OTR values down to 200 cc/m²·day at the highest grammage, achieving the same performance as obtained at lab scale. GC–MS screening of lignin and E.Lignin identified additional volatile/semi-volatile compounds, including Cramer Class III substances, highlighting the need for dedicated migration testing of final coated papers before food-contact use.