*2.2. Hydrophobization of CNCs by Grafting Alcohols of Di*ff*erent Chain Lengths onto Their Surfaces*

The CNCs were reacted with TDI following the method of Habibi and Dufresne after minor modifications [40] and the optimum conditions suggested by Abushammala [41,42]. First, 9.6 g of 10.4% CNC suspension (equivalent to 1.0 g of dried CNCs) was solvent-exchanged from water to anhydrous acetone using a washing/precipitation procedure (three times) and then to anhydrous toluene using the same procedure (twice). The precipitation was performed using a Sigma 3-16P centrifuge (5000 rpm for 30 min) (Sigma Laborzentrifugen, Osterode am Harz, Germany). After the final washing with anhydrous toluene, the precipitated CNCs were transferred to a 100 mL round-bottom flask using 46.3 mL of anhydrous toluene. To them, 3.3 g of 2,4-TDI and 3.0 mL of triethylamine (TEA) as catalyst were added. The reaction proceeded at 35 ◦C in a nitrogen environment. After 24 h, the reaction mixture was centrifuged to isolate the TDI-carbamated CNCs (CNCs-TDI) from the unreacted TDI and TEA. Then, the CNCs-TDI were washed three times with anhydrous toluene before transferred to 50 mL of anhydrous ethanol and stirred for 24 h at room temperature to allow a complete grafting of ethanol onto the CNC surface. Then, the CNCs were collected by centrifugation and dried at 60 ◦C under vacuum to a constant mass. The reaction was repeated to assure reproducibility. The reaction was also performed using 1-butanol, 1-hexanol, and 1-octanol instead of ethanol to produced CNCs with different surface properties. The produced CNCs are referred to in this paper as CNCs-TDI-Eth, CNCs-TDI-But, CNCs-TDI-Hex, and CNCs-TDI-Oct, respectively. Following this procedure, almost every CNC surface hydroxyl had an alcohol chain attached to it. This has been confirmed in a previous paper by the authors [19].
