Nanocrystalline cellulose (CNC) is a renewable material with high potential in many applications. Due to its unique self-assembly and optical properties, CNC tends to behave as an iridescent pigment. The aim of this research was to explore the potential of CNC as an effect pigment in wood coatings. CNC-based coatings were developed from an aqueous CNC solution, a UV-curable water-based clear coating formulation, several colorants, and specialized additives. In this paper, the morphology of the resulting CNC films was investigated through circular dichroism and optical microscopy under polarized light. The effect of the CNC surface charge changes was monitored through zeta potential measurements. Color changes, or travel, and flop index were used to assess the iridescent effect of the coatings containing CNC. The experimental wood coatings contained CNC showed that the enhancement of the iridescent effect depends on the distribution and alignment of the CNC rod-like particles in order to generate the right pitch in the helical structure and their interaction with the polymer matrix as well with the additives. In conclusion, CNC could be successfully used as effect pigment in finishing systems, which can enhance the attractiveness and bring out the special grain of various types of wood. 1. Introduction Nanocrystalline cellulose (CNC) is a renewable material with high potential in many applications. CNC is generally produced by controlled acid hydrolysis from bleached wood pulp [1, 2] and its production does not pose a significant threat to the environment. The resulting CNC rod-like particles are 100–200？nm in length with cross-sections of 3–5？nm (for an aspect ratio of 30–67) [3]. Favier et al. [4] used CNC as a reinforcing agent in polymer composites. Cao et al. [5] prepared water-based polyurethane films with CNC from flax. With the addition of 10% of CNC (w/w), they obtained modulus in flexure values 16 times greater than for regular polyurethane films without CNC. CNC could therefore be of interest to the paint and coatings industries. New high value-added products based on CNC can be developed in this competitive sector. Gray and coworkers discovered that a unique self-assembled ordered liquid crystal phase was formed when the cellulose crystallites were sufficiently short and uniform (always less than 100？nm) and had a high degree of sulfates esterified onto the surface [3, 6]. When the aqueous CNC suspension reached a critical concentration (called cholesteric phase), chiral nematic ordered structures formed and arranged themselves in a
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