Adsorption of sulphonated lignin-carbohydrate complexes (LCCs) onto cellulose surfaces

Biorefinery side streams have the potential to be utilized for the production of biobased polymers, which can serve as viable substitutes for synthetic and food-based alternatives not only enhancing the sustainability of biorefineries but also contributing to their profitability. One interesting material with potential as barrier coatings for paper and board is the lignin-carbohydrate complex (LCC). However, the chemical structure and molecular weight of the LCCs varies a lot depending on the process conditions and modifications. To be able to optimize their performance it is imperative to obtain a comprehensive understanding of their interactions with cellulosic surfaces and more specifically to correlate these interactions with the chemical structure. For this purpose, we combined adsorption studies using surface-sensitive Quartz Crystal Microbalance with Dissipation (QCM-D) and bulk spray coating of cardboard with detailed structural analysis using 2D HSQC NMR spectroscopy. To elucidate the effect of carbohydrate content and molecular weight, varying LCC samples were compared to lignosulphonate. The QCM-D results revealed that LCCs with higher carbohydrate content adsorbed better on cellulose surface. Increasing the pH from 7 to 10 increased the repulsion leading to lower adsorption. The spray coating results further supported the importance of polymer size and carbohydrate fraction.