Synthetic resins play a significant role in the wood composites industry. However, due to environmental concerns such as emissions of harmful contaminants and limited adhesive bond performance, their substitution with biomaterials has been recently considered. In particular, the performance of cellulose nanofibers as a reinforcement agent is dictated by how the fibers and the resin chemically interact. These interactions are currently not fully understood, and they are a key factor for the performance of the reinforced resin. In this research, different types of cellulose nanofibers, bleached (BCNF)  and unbleached (LCNF), were utilized to reinforce and partially replace two commonly used wood composite resins, phenol-resorcinol formaldehyde resin (PRF) and epoxy. The studied PRF resin contains Cascophen PRF and Cascoset catalyst, and the epoxy resin was a type of diglycidyl ether of bisphenol A (Epon 828 or DGEBA) with Jeffamine d-400, diamines of poly(oxypropylene), as a coupling agent. The chemical interactions between cellulose nanofiber and resins were investigated by quartz crystal microbalance with dissipation monitoring (QCMD). Fourier-transform infrared (FTIR) spectroscopy was utilized to understand the composition of the resins before and after nanocellulose addition. Measurements were performed on the cured formulations. In addition, the effect of different concentration of nanocellulose, 0.5, 1, and 2wt% on the rheological behavior of resins was investigated. The results showed that the nanocellulose addition, both BCNF and LCNF, changes the viscosity and chemical composition of both resins because of the favorable interaction between functional groups between BCNF, LCNF, and the resin. However, the effect of BCNF was more pronounced. Based on the QCMD data, nanocellulose from bleached pulp showed favorable chemical interactions with particularly Cascophen and Jeffamin D-400. This indicates that the BCNF can be considered as a reinforcing agent for PRF and epoxy composite materials.

Interfacial interactions and rheological properties of wood adhesives reinforced by cellulose nanofibers

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