Sustainable paper coating suspensions from waste paper: a nanocellulose–lignin based approach

Abstract This study aims to comprehensively evaluate the effects of coating processes employing lignin-reinforced nanocellulose suspensions, derived from various types of waste paper, on the functional and physicochemical properties of packaging papers. In particular, the study focuses on elucidating how the incorporation of lignin within nanocellulose-based coating systems affects key performance characteristics, including mechanical strength, barrier performance, surface properties, and overall paper quality. The results revealed that physical, mechanical, optical, and barrier properties of the papers were significantly influenced by the coating formulation. Papers coated with cellulose nanofiber/lignin (CNF/L) and cellulose nanocrystal/lignin (CNC/L) suspensions exhibited increased thickness and grammage relative to both uncoated and water-coated counterparts. Following the application of nanocellulose/lignin (NC/L) suspensions, a decline in tensile and tear indices was observed, whereas the burst index demonstrated a notable enhancement. Evaluation of optical properties revealed that, except for opacity, all measured optical parameters improved upon coating with CNF- and CNC-based suspensions. In terms of barrier performance, NC-based coatings resulted in higher water absorption values while simultaneously reducing air permeability compared to uncoated papers. To sum up, this study suggests that leveraging CNF and CNC can enhance the quality of low-grammage packaging papers, potentially opening new avenues for their applications.