Surface properties of xylan and xylan derivatives measured by inverse gas chromatography

Abstract

Xylan (the most common hemicellulose in wood and annual plants) and xylan derivatives have a very wide field of uses for which physico-chemical surface properties play an important role (e.g. in composites or barrier materials). In the present work, for the first time, inverse gas chromatography (at infinite dilution conditions) was used to assess the surface properties of xylan and xylan derivatives. Firstly, carboxymethyl xylan (CMX) and hydroxypropyl xylan (HPX) have been synthesized from commercial xylan (BX) and the presence of substituent groups confirmed by infrared spectroscopy and 1H NMR. Then, the modified and original xylans were analysed for their dispersive component of the surface energy (γsd) and Lewis acid-base properties. It was found that carboxymethylation and hydroxypropylation decreased significantly the γsd value of xylan: from 47.6 mJ m⿿2 in BX to 33.0 mJ m⿿2 and 23.5 mJ m⿿2 in CMX and HPX, respectively. As for the Lewis acid-base properties, HPX showed a perfectly amphoteric behaviour while the surfaces of unmodified xylan and CMX showed a prevalence of Lewis acidic character over the Lewis basic character, being, however, the surface of CMX less acidic than that of the original xylan. These results were interpreted in terms of the effect of the presence of the new substituent groups in the xylan backbone.