Aggregation of Modified Glucuronoxylan in Water and DMSO

Glucuronoxylans are known to be only partly soluble in aqueous media. Chemical modification often aims to improve solubility, yet observations of aggregation even of the modified xylans are not uncommon. We investigated the aggregation of glucuronoxylans of two different molar masses (XS and XM with M_w = 14 and 24 kg/mol, respectively), as well as their derivatives that were modified using periodate oxidation and borohydride reduction. Investigations were carried out in water and dimethyl sulfoxide (DMSO) by means of small angle neutron scattering (SANS). All dispersions of XS and its derivatives were turbid in water and translucent in DMSO. All samples based on XM were translucent in water and transparent in DMSO. In all cases, dispersions showed aggregates at the nanoscale with SANS, even for visually translucent and transparent dispersions with individual chains in a good solvent environment, indicated by the obtained Flory exponent of 0.588. Xylans dispersed in DMSO were less aggregated than xylan dispersed in water. The effect of solvent choice on the dispersibility of the modified xylans depended on the starting material composition. We propose that aggregation on the nanoscale is an intrinsic property of these polysaccharides and must be accounted for in processing, analysis, modification and applications.