Progress in Organic Coatings 77 (2014) 813–820 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur na l ho me pa ge: www.elsevier.com/locate/porgcoat Modification of cellulose nanocrystals as reinforcement derivatives for wood coatings Bouddah Poaty a,∗ , Vahe Vardanyan a,b , Luana Wilczak a,c , Gregory Chauve d , Bernard Riedl a a Centre de Recherche sur le Bois, Pavillon G.-H. Kruger, Université Laval, 2425 rue de la Terrasse, Québec, QC G1V 0A6, Canada b Centre d’optique, photonique et laser, Département de Physique, Université Laval, 2375 rue de la Terrasse, Québec, QC G1V 0A6, Canada c École Supérieure du Bois, Atlanpôle, BP 10605, rue Christian Pauc, 44306 Nantes Cedex 3, France d FPInnovations, 570 boul. Saint-Jean, Pointe-Claire, Montréal, QC H9R 3J9, Canada a r t i c l e i n f o Article history: Received 3 May 2013 Received in revised form 9 December 2013 Accepted 9 January 2014 Available online 3 February 2014 Keywords: Cellulose nanocrystal Derivatives synthesis Dispersion Nanocomposites Wood coating Mechanical properties a b s t r a c t Cellulose nanocrystal (CNC), an emerging renewable nanomaterial, was subjected to carbon chains graft- ing in order to improve its dispersion and its ability to transfer its rigidity properties into less polar matrixes, especially acrylic wood coatings. Chemical modifications used to this purpose are required to be simple, not affecting the CNC main structure and compatible or synergistic to oligomer reticulation inside the targeted UV-waterborne formulation. Those modifications were carried out using either alkyl quaternary ammonium bromides or acryloyl chloride. These new chemical functionalities, not induc- ing deep structural changes in modified CNCs, were highlighted through nuclear magnetic resonance, infrared and nitrogen content analyses. CNC derivatives were better dispersed in aqueous acrylic coating as suggested by atomic force microscopy, with a mean surface roughness falling from 9 to 6 nm on the coatings containing unmodified and treated CNCs, respectively. For mechanical evaluations, the coatings including various CNC derivatives were applied on sugar maple wood, a much appreciated material as indoor timber or wooden furniture which requires an efficient surface protection. The abrasion tests indicated that the modified CNCs confer a higher scratch resistance, with an improvement from 24% to 38% for coatings containing CNC derivatives over those with unmodified CNC. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The durability improvement of wood products greatly calls for the development of protective coatings with higher performances. The use of various nanoparticles, including common inorganic metal oxides (ZnO, Al 2 O 3 , TiO 2 , CeO 2 , etc.) as mechanical reinforce- ment additives into coatings, represents a significant approach to reach this end [1–5]. However, difficulties encountered in incor- poration of inorganic nanoparticles in polymer matrixes (organic), such as incomplete dispersion and adhesion, suggest working with organic nanoparticles. That particularly applies to cellulose nanocrystals (CNC), a new renewable non-toxic product obtained after isolation of crystalline domains from cellulose acid hydroly- sis. Indeed, as one of many advantageous characteristics, excellent mechanical reinforcement effects are known with CNC incor- poration which has been the subject of a growing interest in nanocomposite materials with polymers [6–10]. This advantage is ∗ Corresponding author. Tel.: +1 418 656 2131; fax: +1 418 656 2091. E-mail addresses: bouddah.poaty-poaty@ulaval.ca, bouddah.poaty@cegepat.qc.ca (B. Poaty). much more attractive since wood, compared with other natural sources of cellulose (cotton, hemp, bacteria, green algae, etc.), ben- efits from a long process experience of its controlled acid hydrolysis, as pulp, and, moreover, represents the most abundant, renewable and sustainable source of CNC [11–13]. Such CNC diversified appli- cations would also permit to foresee a better development potential in the forest industry [8,14]. Some applications, related to low polarity matrix, appear somewhat limited because of CNC surface hydroxyls and consequent hydrophilic nature, in acrylic water- borne coatings, for instance. Thus, to enhance its dispersion and therefore its mechanical reinforcement in a wide range of matrix polymers, CNC should be submitted to appropriate surface modifi- cations. Thanks to reactive surface of OH side groups, grafting of chem- ical species is possible to achieve in order to functionalize the CNC surface. In addition, the CNC obtained from sulfuric acid hydrolysis exhibits negative charges at the surface at neutral pH [7,9,15,16], which are due to sulfate ester groups which are able to form ionic bonds with a matching reagent. Based on those reactive sites, some modification studies have been described as for the compatibilization of CNC or cellulose with polymer com- posites referring to different application fields, as focused on by 0300-9440/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.porgcoat.2014.01.009