Cryogelation of xanthan

摘要: Abstract Xanthan solutions have gel-like properties, including the ability to hold particles in suspension, but network structure breaks down readily, allowing flow freely. These ‘weak gel’ properties are attributed tenuous association of ordered chains, and enhanced by cations, particularly Ca2+. In present work it has been found that much stronger more cohesive networks formed when xanthan frozen thawed. Solutions (0.2–2.0 wt%) were prepared deionised water at 80 °C, rapidly transfer a freezer −20 held °C for 24 h, allowed thaw refrigerator 5 °C. Their rheological then characterised small deformation oscillatory measurements storage loss moduli (G′ G″) The concentration-dependence gel cryogels was unusual, with G′ reaching maximum value ∼100 Pa 0.6 wt% (in comparison ∼4 unfrozen same concentration), decreasing slightly higher concentrations. Gel strength subjecting samples second freeze–thaw cycle, or lowering freezing temperature −80 Melting cryogel occurred over approximate range 20–40 (70 °C) becoming as those samples. Addition sugars (sucrose, glucose, fructose, maltose) concentrations up ∼10 wt% had no effect on cryogels, caused progressive reduction moduli, cryogelation sugar above ∼20 wt%. Incorporation low levels Ca2+ (4 mM) also abolished cryogelation. results interpreted follows. During freezing, chains forced align associate conversion solvent (water) ice crystals. associations survive thawing, give network. restricts liquid ice, thus reducing eliminating formation. Strengthening normal weak high polymer incorporation alignment further during consequent structure.