Nanofibrillated cellulose in wood coatings: Dispersion and stabilization of ZnO as UV absorber

The effect of nanofibrillated cellulose (NFC) on the dispersion and stabilization of zinc oxide (ZnO) nanoparticles in waterborne wood coatings was examined. Different coating compositions with and without NFC at varying concentrations of unstabilized, powdery or stabilized ZnO were produced. Properties of free coating films prepared via bar coating and wood specimens coated by brush with the coating compositions were evaluated. This included the effects of NFC and ZnO on the coating appearance, film formation, distribution of ZnO in the coatings, tensile properties and UV absorbing properties of free films and the effects of artificial weathering on the coated wood specimens. We showed that NFC significantly improved the distribution of the unstabilized ZnO in the coatings and prevented sedimentation of ZnO. NFC also improved film formation and inhibited crack formation during curing and weathering for more brittle binder materials. NFC had a pronounced matting effect but did not influence the coating colour. Colour stability of coated wood specimens during weathering was affected by the ZnO content, but needs further improvement. The results show that the biopolymer NFC is suitable to stabilize ZnO in coatings for wood, which could be of interest for other applications, as well. (C) 2015 Elsevier B.V. All rights reserved.