Search

The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and cristallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapour was also assessed as a function of the air humidity and shown to be lower than that of still liquid water in the case of a saturated atmosphere.

The surface modification of cellulose fibers with trifluoroacetic anhydride (TFAA) was studied using the heterogeneous cellulose/TFAA/pyridine/toluene system. The degree of substitution (DS) of the ensuing trifluoroacetylated fibers ranged from 0.04 to 0.30. This treatment conferred a high degree of both hydrophobicity and lipophobicity on the fibers' surface, even at low DS values. Both the dispersive and the polar contributions to the surface energy were drastically reduced. However, the original cellulose hydrophilicity could be readily restored through hydrolysis, by treating the modified fibers with neutral water.

The topochemistry of the controlled heterogeneous esterification of cellulose fibers with fatty acid chlorides of different chain length, both in swelling and non-swelling media, was assessed by X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and contact angle measurements. On the one hand, the results provided by the combined use of these three powerful techniques showed unambiguously the occurrence of the reaction at the fibers' surface and, on the other hand, the XPS results showed that the surface coverage with the fatty acid moieties increased with their chain length, but was only modestly affected by the degree of substitution (DS), suggesting that when the esterification yield was increased (higher DS values), an in-depth reaction also occurred, particularly when DMF was used as a cellulose swelling medium, involving the OH groups buried below the fibers' surface.