Single-Step Method for the Isolation and Surface Functionalization of Cellulosic Nanowhiskers

Abstract

Surface modification of cellulosic nanowhiskers (CNW) is of great interest, especially to facilitate their use as polymer reinforcements. Generally, alteration of the surface chemistry is performed using multiple reaction steps. In contrast, this study demonstrates that the needed hydrolysis of amorphous cellulose chains can be performed simultaneously with the esterification of accessible hydroxyl groups to produce surface functionalized CNW in a single step. The reaction is carried out in an acid mixture composed of hydrochloric and an organic acid (acetic and butyric are both demonstrated). Resulting CNW are of similar dimensions compared to those obtained by hydrochloric acid hydrolysis alone; sizes are verified by multiangle laser-light scattering and transmission electron microscopy. However, narrower diameter polydispersity indices indicate that surface groups aid the individualization of the nanowhiskers (P x = 2.5 and 2.1 for acetic and butyric acid, P x = 3.0 for hydrochloric acid). More than half of the hydroxyl groups located on the CNW surface are substituted under the employed reaction conditions as determined by quantitative Fourier-transform infrared-spectroscopy. The resulting surface modified CNW are dispersible in ethyl acetate and toluene indicating increased hydrophobicity and thus are presumably more compatible with hydrophobic polymers when used as a reinforcing phase.

Hierarchical Composites Made Entirely from Renewable Resources

“…80 Fischer esterification simultaneously occurring during the hydrolysis of amorphous cellulose chains and acetylation has been used to obtain CNCs with tuned surface energy. 73 It is also possible to conduct esterification in the gasphase, although the CNCs must be dried first. 81 Indeed, CNCs form rigid three-dimensional networks above a certain whisker percolation concentration because of hydrogen bond formation between the individual whiskers.…”

Effects of partial replacement of silica with surface modified nanocrystalline cellulose on properties of natural rubber nanocomposites

“…However, the nature of numerous hydroxyl groups and easy aggregation of NCC make it difficult to disperse NCC finely in a rubber matrix. Surface modification [19][20][21][22] and chemical grafting [23][24][25][26] have been used in the modifications of NCC. The main objectives of the modifications are improving the NCC dispersion and reinforcing the interfacial strength between NCC and rubber.…”

Synthetic Strategies for the Fabrication of Cationic Surface-Modified Cellulose Nanocrystals

“…However, it is crucial to make sure no damage to the original morphology of the nanocrystals occurs during the surface functionalization process and as such, mild chemical methods are required to maintain the integrity of the nanocrystals. A number of surface covalent functionalizations of CNCs has been reported and some common examples include oxidation (tetramethylpiperidinyloxyl radical (TEMPO) oxidation for conversion of the primary hydroxyl groups to carboxylic acids [32] and periodate oxidation of vicinal diols to afford dialdehyde functionalities [33]), esterification [34,35], amidation [36,37], carbamation [38,39], amine functionalized CNCs (conversion of hydroxyl group to a terminated primary amine group) [40,41], radical polymerization [42][43][44][45], etherification, and other chemical modifications [2,29]. Readers are directed to a more detailed and critical review by Eyley and Thielemans on surface modifications of CNCs [29].…”