Interfacial interactions between urea formaldehyde and cellulose nanofibrils (CNFs) of varying chemical composition and their impact on particle board (PB) manufacture

Wood-based panels are commonly used as building materials for interior and exterior purposes. Their production and utilization have increased in recent decades due to the useful properties that they present. Adhesive-bonded products comprise up to 80% of the wood alternatives on the global market, and of that, urea–formaldehyde (UF) makes up approximately 81% of the resins used. To improve UF performance, the utilization of microfibrillated cellulose has been demonstrated to be effective. However, further understanding of the mechanisms of the interactions is of relevant importance. In this work, we studied interfacial interactions between UF with bleached (BCNFs) and unbleached (LCNFs) cellulose nanofibrils using Quartz Crystal Microbalance with dissipation monitoring (QCM-D) technique, observing the superior performance of lignin-containing CNFs. Additionally, the surface free energies were investigated using contact angle (CA) measurements, showing a decrease of the values mainly when utilizing LCNFs, which was later correlated with the wettability properties of the PBs. PBs with different adhesive/CNF formulations were produced, showing larger improvements when adding LCNF in terms of modulus of elasticity (MOE), modulus of rupture (MOR), and internal bonding (IB). To gain a better understanding of the interactions between CNFs and UF, both CNFs were fully characterized in terms of morphology, chemical composition, charge density, as well as thermal and colloidal stability.