Performance of Spray-Dried Nanofibrillated Cellulose as Wood Varnish Reinforcement in Outdoor Environment

Abstract

The outdoor use of wood can be improved by coating the wood surface with varnish to reduce the effects of natural weathering. However, some varnishes quickly lose their ability to protect wood, and nanoscale additives have been used to mitigate this negative effect, preferably renewable and biodegradable. Therefore, the objective of this study was to evaluate the performance of varnishes reinforced with spray-dried nanofibrillated cellulose (NFC) in a natural weathering test. For this purpose, two varnishes, waterborne and non-waterborne, with 0, 5, and 10% (w/w) NFC addition were applied to Pinus taeda tangential wood samples, which were exposed to natural weathering for half a year, during the period from January to June 2019, in Curitiba, PR, Brazil. Adherence and impact resistance tests were performed to evaluate the surface properties of the varnishes, and the effect of natural weathering on the wood surface was evaluated using quantitative colorimetric analyses (CIELab System). The varnishes did not perform well in the adhesion and impact test. While no significant effects were observed in surface tests, due to the addition of spray-dried NFC, varnishes reinforced with 5% NFC exhibited reduced overall color variation, maintaining yellow and red pigmentation. This suggests that incorporating 5% spray-dried NFC into varnishes did not compromise coating properties and aided in mitigating the impact of natural weathering on wood color variation.

Keywords:
wood preservation; coatings; weathering; nanotechnology; color; biorefinery

HIGHLIGHTS

The addition of nanocellulose showed no effects on the varnish properties.

All changes in color caused by natural weathering were noticeable.

Exposure to natural weathering caused wood color to become gray.

Addition of 5% nanocellulose reduced the variation in wood color.