Stable suspensions of partially silylated cellulose whiskers dispersed in organic solvents

Cellulose whiskers resulting from the acid hydrolysis of tunicin were subjected to partial silylation by the addition in toluene of a series of alkyldimethylchlorosilanes, with alkyl moieties ranging from isopropyl to n-butyl, n-octyl and n-dodecyl. The samples were characterized by elemental composition, X-ray diffraction analysis, FT-IR, transmission electron microcopy, and their dispersion in organic solvents of various polarities was investigated. As the partial silylation resulted essentially in surface derivatization of the whiskers, the extent of their silylation was characterized by their degree of surface substitution (DSs). With DSs of the order of 0.6/1, the whiskers kept their morphological integrity, but due to their surface silylation, they became readily dispersible in solvents of low polarity such as THF. The resulting suspensions, which did not flocculate, were stable and appeared birefringent when viewed between cross polars. With a DSs greater than 1, the core of the whiskers became silylated, leading to the loss of their whisker character. At this level, it was no longer possible to obtain any birefringent suspension.