Stephane Jules Jerome Debon

Normal force-controlled tribological measurement of soft drinks and lubrication additives

This paper describes the use of a normal force-controlled tribology device for assessing mouthfeel-related lubrication properties of soft drinks samples and lubrication additives. Samples were sheared between a tribology pair comprised of steel and thermoplastic elastomer surfaces with the 3-contact ball-on-inclined plane tribometer. The boundary lubrication of lemon lime soft drinks was significantly lower than cola soft drinks. The resolution of the instrument was further investigated by measuring the lubrication of confined very dilute non gelling neutral and strongly charged β-1,4 polysaccharides. Poor lubrication was seen with the galactomannans locust bean gum and guar gum. Overall, these experiments demonstrate that tribology yields reproducible results that relate to functional properties of iso-viscous fluids in a dilute regime.

Strong cationic polyelectrolyte adsorption on a water swollen cellulosic biomaterial and its relevance on microstructure and rheological properties

A multiscale approach was taken to study the swelling and viscosifying properties of a cellulose-rich biomaterial as a function of environmental conditions. First, the impact of pH and ionic strength on the surface properties of the fiber was investigated by means of potentiometry and cationic polyelectrolyte adsorption. Three adsorption regimes were identified: the first one occurred in acidic conditions and was related to the ionization of the carboxylic groups of pectin. A very sharp adsorption was then observed in the mild-acidic to neutral region which was most likely related to a conformation change in the plant cell wall architecture. The third adsorption regime happened in the alkaline region and was related to ionization effects. Based on this information, the impact of environmental conditions on the hydrated microstructure was studied in DSC by means of thermoporosimetry. It clearly demonstrated a structural collapse of the hydrated fiber when pH decreased or the amounts of ions increased. This phenomenon was in line with the surface charge measurements. Finally, the link between the wet microstructure and the macroscale behavior of the fiber was demonstrated by studying the flow properties of the reconstituted fiber, below and above its percolation threshold. In line with the surface properties and microstructure data, yield stresses increased when the pH was adjusted from acidic to alkaline conditions. Salt addition resulted in a loss of the texturizing properties.Graphical Abstract