Gas-Phase Surface Esterification of Cellulose Microfibrils and Whiskers

• Published in: Biomacromolecules Vol. 10; no. 8; pp. 2144 - 2151
• Main Authors: Berlioz, Sophie, Molina-Boisseau, Sonia, Nishiyama, Yoshiharu, Heux, Laurent
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.08.2009
• Subjects: Applied sciences; Calorimetry, Differential Scanning; Cellulose - chemistry; Cellulose and derivatives; Crystallization; Esterification; Exact sciences and technology; Gases - chemistry; Microfibrils - chemistry; Natural polymers; Palmitates - chemistry; Phase Transition; Physicochemistry of polymers; Surface Properties; X-Ray Diffraction; Surface reaction; Gas solid reaction; Cellulose; Microfibril; Experimental study; Esterification; Whisker; Chemical modification; Morphology; Preparation; Supramolecular structure; Acyl chloride; Cellulose organic ester
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm900319k

A new and highly efficient synthetic method has been developed for the surface esterification of model cellulosic substrates of high crystallinity and accessibility, namely, freeze-dried tunicin whiskers and bacterial cellulose microfibrils dried by the critical point method. The reaction, which is based on the gas-phase action of palmitoyl chloride, was monitored by solid-state CP-MAS 13C NMR. It was found that the grafting density not only depended on the experimental conditions, but also on the nature and conditioning of the cellulose samples. The structural and morphological modifications of the substrates at various degrees of grafting were revealed by scanning electron microscopy and X-ray diffraction analysis. These characterizations indicated that the esterification proceeded from the surface of the substrate to their crystalline core. Hence, for moderate degree of substitution, the surface was fully grafted whereas the cellulose core remained unmodified and the original fibrous morphology maintained. An almost total esterification could be achieved under certain conditions, leading to highly substituted cellulose esters, presenting characteristic X-ray diffraction patterns.