The effect of sodium hydroxide surface treatment on the tensile strength and elastic modulus of cellulose nanofiber

The use of cellulose nanofibers in the reinforcement of polymers has applications in bio-based building materials. However, one problem observed when using cellulose nanofibers within composites is the difficulty of ensuring their adequate dispersion. The phenomenon of agglomeration is attributed to the high density of polarized hydroxyl groups at the surface of cellulose nanofibers. Initial observations indicate that cellulose nanofiber agglomeration, in a cement matrix at volume fractions larger than 0.1%, are theorized to have contributed to the brittle failure mode of the paste. In order to expand the use of cellulose nanofibers in bio-based building materials, it is necessary to reduce their agglomeration and improve their dispersion within a polymer through surface modifications in an effort to improve their reinforcing capability in composite materials. As such, a mild alkali treatment with sodium hydroxide (NaOH), also known as mercerization, was chosen for use in this study due to its longstanding establishment as a common, low cost, and simple process. Alkali treatment was found to improve the values of tensile strength and modulus, compared to the untreated strips, by 20% and 24%, respectively. These results could be attributed to the rearrangement of fibrils along the direction of tensile deformation, as a result of the dissolution of lignin and hemicelluloses fractions.