Reinforcement of dry and wet paper sheets by cellulose nanofibers

The objective of this study was to evaluate how a wide range (10-100%) of cellulose nanofiber (CNF) addition affects the mechanical properties of paper sheets. Young's modulus and tensile strength in the dry and wet states were measured and compared. In the dry state, the Young's modulus increased with the increase of CNF addition. However, the dry specific Young's modulus was constant for all CNF additions, which was one interesting result. The tensile strength increased as the CNF addition increased to 70%; however, there was no further improvement when the CNF addition was greater than 70%, which was another interesting finding. In the wet state, although the Young's modulus decreased when the CNF addition was greater than 20%, the wet tensile strength of the sheets increased almost linearly with increasing CNF addition up to 50%, followed by a slight decline. The maximum wet strength retention reached nearly 10% with 40% CNF addition, despite the higher water uptake (108%). One of advantages of utilizing CNFs as reinforcement agent in paper is that they can improve the wet strength while making paper sheets maintain a higher moisture content.