The influence of hydrocolloid structure on lubrication is investigated using a rheological and tribological study of four polysaccharides that vary in chain expansion from random coil to extended chain and rigid-rod. We show that the conformation that a polysaccharide has in an aqueous solution strongly influences the ability of that fluid to be entrained during lubrication. This is important for the food industry since polysaccharides are typically used to impart thickness, stability and texture to soft-solid and liquid based food products without consideration of their structurally attributable tribological response. Friction coefficients (mu) of random coil solutions in a boundary regime of lubrication significantly increase throughout the concentration range 0.02-0.21 wt%, from 0.19 to 0.28. Rigid-rod and extended-coil polysaccharides, however, reduce boundary mu with an increase in their concentration. In a mixed regime of lubrication, mu decreases linearly with concentration (C) of extended-coil polysaccharide, despite the concentration range passing its C* (coil overlap concentration) value. Mixed regime mu vs. C plots of random coil solutions, however, reveal tribologically critical concentrations (C-T*), where C-T* similar to C*. At C > C-T* the dependence of mu on C reduces, despite pronounced bulk viscosity increases after C*. (C) 2011 Elsevier Ltd. All rights reserved.
- Guar gum
- Friction coefficient
- Critical overlap concentration