Effect of cellulose nanofiber and cellulose nanocrystals reinforcement on the strength and stiffness of PVAc bonded joints

Cellulose nanofiber (CNF) and cellulose nanocrystals (CNC) are strong bio-based materials and have great potential in a reinforcement of the polymeric matrix. This study presents the effect of nanocellulose (CNF and CNC) reinforcement of polyvinyl acetate (PVAc) adhesive. Adhesive formulations with three different concentrations (0.5%, 1%, and 2% w/w) of nanocellulose were prepared by dispersing them in water and mixing the suspension with PVAc adhesive; the other percentages are omitted due to obvious adverse effect. The reinforced adhesive was then used to glue spruce (Picea abies L) and beech (Fagus sylvatica) wood joints to determine joint stiffness and shear strength under static load. Samples were tested at 12% moisture content and after cyclic moisture exposure. Bond line morphology was studied by SEM. FTIR analysis was performed to see the molecular interaction between nanocellulose and PVAc. The addition of nanocellulose to PVAc adhesive significantly improved the elastic stiffness and shear strength of the joints. Optimum elastic stiffness and shear strength values were achieved with a 1% addition of nanocellulose. The general trends are found to be valid for various kind of CNF and CNC.