Application and characterization of poly(vinyl alcohol) reinforced with cellulose nanofibrils as a coating for wood

Abstract Water solutions of poly(vinyl alcohol) (PVA) at concentrations of 10%, 15%, and 20% were tested as alternatives to traditional wood coatings, with cellulose nanofibrils (CNFs) added to improve their mechanical and physical properties. The indentation hardness of PVA films decreased with higher PVA concentrations but was enhanced by the addition of CNFs. The coatings showed good wood wetting, with contact angles between 51° and 93°. Scanning electron microscopy revealed that the coatings penetrated 100–200 µm into the European beech ( Fagus sylvatica L.) wood, anchoring well within its cellular structure. The coatings reduced wood surface roughness and altered its color (ΔE* ≤ 11.9), while remaining transparent (pure PVA) or semi-transparent (PVA + CNFs). Pure PVA coatings increased the wood gloss by 16 times. All PVA-based coatings made the wood surface more hydrophobic, although hydrolysis of the films was observed. The coatings' elasticity enhanced the resistance to micro-scratching. Photostability tests showed that most color changes were due to chemical alterations in the wood surface. CNFs also exhibited ultraviolet light-blocking properties. The coatings demonstrated excellent adhesion to the wood surface, with pull-off strengths greater than 5 MPa. These results suggest that PVA + CNFs coatings are promising for use as protective treatments for wood, offering improvements in both appearance and durability. Graphical abstract