Study on cellulose nanofibers (CNF) distribution behaviors and their roles in improving paper property

Recently, cellulose nanofibers (CNF) have gained significant attention as renewable and high-value nano-biomaterial that has the potential to regulate microstructures and enhance the strength properties of paper products. However, the distribution of CNF in paper sheets may impact the physical properties differently, requiring further understanding. In this study, the effects of different CNF distributions on pore sizes and strength properties in paper sheets were investigated. The hypothesis is that the different distributions of CNF within paper sheets can exhibit different functions in improving the physical properties of paper sheets. Three types of paper sheets containing CNF were respectively prepared by mixing with pulp (CNF (mixture)), distribution on the surface of paper sheets (CNF (surface)) and adding in the middle of paper sheets (CNF (middle)). Results show that CNF can narrow the pore size distribution of paper sheets, particularly in samples with CNF (surface) and CNF (middle) that form dense CNF layers. The highest mechanical strength improvement was observed with mixed CNF. X-ray photoelectron spectroscopy (XPS) analysis revealed that this is due to the strong hydrogen bonding between CNF and pulp fibers, resulting from a large bonding area and effective contact with pulp fibers. This study provides a new perspective on CNF distribution within paper sheets for improving wet web strength properties.