Effect of water activity and gaseous phase relative humidity on microcrystalline cellulose water contact angle measured by the Washburn technique

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2016-07, Vol.500, p.118-126
• Main Authors: Hammes, Martim Victor, Englert, Alexandre Hahn, Noreña, Caciano Pelayo Zapata, Cardozo, Nilo Sérgio Medeiros
• Format: Article
• Language: English
• Subjects: Capillary rise; Cellulose; Contact angle; Dissolution; GAB model; Mathematical models; Microcrystalline cellulose; Moisture content; Relative humidity; Washburn technique; Water activity; Wettability
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2016.04.018

[Display omitted] •Microcrystalline cellulose (MCC) wettability was assessed by the Washburn technique.•Contact angle (θ) decreased linearly with increasing water activity.•θ showed stronger dependence on the moisture content below monolayer moisture content.•Relative humidity showed to be a relevant parameter when using the Washburn technique.•The Washburn technique was accurate in quantifying the effects of the studied variables. The goal of this work was to examine the effect of water activity (aw) of a material—in this case microcrystalline cellulose (MCC)—on the contact angle obtained by the Washburn technique. The effect of the difference between the relative humidity of the gaseous phase in equilibrium with a sample of a given water activity and the actual relative humidity (RH) of the ambient in which the measurements are being performed was also evaluated. The choice of MCC as case study was based on its importance as component for particulate foods, on the lack of information in the literature regarding its wettability characteristics, and on its low dissolution rate and swelling in water. Eight MCC samples of different aw were prepared and analysed. Additionally, the moisture sorption isotherm of MCC was determined experimentally and fitted to the GAB model. The MCC-water contact angle decreases linearly with aw and nonlinearly with the moisture content, showing more pronounced changes below the monolayer moisture content. Although it was observed that RH does not affect the results obtained during the capillary rise measurement, this parameter is relevant in the determination of the contact angle by the Washburn technique because it affects the moisture content of the sample prepared for analysis. The results here presented show that the Washburn technique has sufficient accuracy to quantify the effects of the considered variables on the wettability of MCC particles.