Cellulose nanofiber (CNF) produced by enzymatic treatment and wet milling was blended with an acrylic resin emulsion, and waterborne varnish for topcoat and undercoat was prepared. Tensile tests of the film prepared from the varnish for topcoat indicated that elastic modulus, strength, and maximum strain depended on the CNF percentage and dispersion time. In addition, the effect of application of CNF-blended varnish to sugi wood was analyzed. Results showed that the application of CNF-blended varnish for topcoat decreased the gloss of the specimen, whereas the application of CNF-blended varnish for undercoat increased the gloss of the specimen. These findings suggested that the gloss of the coated surface can be modulated by blending CNF. Accelerated weathering tests for 1000 hours revealed that specimens topcoated with CNF-blended varnish had fewer surface defects than specimens topcoated without CNF-blended varnish. Similarly, specimens undercoated with CNF-blended varnish showed fewer surface defects and smaller changes in color than specimens without the undercoat and undercoated without CNF-blended varnish. These results indicated that the CNF-blended varnish prepared in this study can be used to increase the performance of the coating film and the weatherability of coated wood.
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