Different chemical pretreatments have been studied:carboximethylation (TEMPO oxidation and periodate chlorite oxidation), cationization, and acidic or basic pretreatments [163].Saito and Kimura [164] studied the application of TEMPO-mediated oxidation to the fibers prior to mechanical homogenization (Fig. 5.6) and it resulted in almost transparent and highly viscous dispersions. By the use of this method, crystallinities of 65%95% can be found [164]. The energy required for the homogenization or other mechanical treatment after TEMPO-mediatedoxidation decreases inversely with the increasing carboxylation of primary hydroxyl groups of cellulose [149].Moreover, Li et al. [165] evaluated several lab-scale CNF fabrication routes through cradle-to-gate life cycle assessment and they concluded that this pretreatment resulted in a lower impact than carboxymethylation. The effect of the raw material composition on CNF produced through aTEMPO-mediated oxidation have been studied [48,57,166]. As a result of these investigations, it is concluded that the higher the hemicellulose and the carboxyl content of the fibers, the higher is the yield of CNF and the light transmittance of the CNF [48,57]. This type of CNF can be used to form films with adsorbed cationic surfactants in order to reduce the water wettability, without affecting significantly the tensile index [167]. Li et al. [168] studied the preparation of CNF by oxidation and sonication and they observed that with a higher sonication time, the yield increases [168].