Shear behaviour of biopolymer suspensions with spheroidal and cylindrical particles

The theological behaviour of suspensions is influenced by many parameters, one of which is the particle shape. For rigid particle suspensions a number of studies demonstrate the effects of the particle aspect ratio. Indeed, f ibres are widely used as theology modifiers in different materials such as synthetic polymers. This work is concerned with testing the hypothesis that regularly shaped particles with aspect ratios larger than one that are mad e of gelled biopolymers could be used as rheology modifiers for biopolymer solutions. Biopolymers, and mixtures thereof are a widely used ingredient i n foods and other products with structure functionality. Tailoring theology modifiers by morphology offers an alternative to using different biopolyme rs. It is demonstrated how biopolymer suspensions with regular spheroidal, or cylindrical particle shapes can be produced by gelling the droplet phase of a liquid two phase biopolymer mixture in a shear field. Biopolymers wer e chosen such that gelation is initiated by cooling. Shear-cooling at const ant stresses leads to the formation of ellipsoidal particles. Cylindrical p articles can be generated by stepping up the sheer stress prior to gelation , i.e., stretching the droplet phase into fibrils, and trapping the shape p rior to break-up through gelation. Morphologies and steady shear theologica l data for suspensions of the two biopolymers gellan and kappa -carrageenan with an internal phase volume of 0.2 are reported. The influence of partic le shape on relative viscosity is pronounced. At high shear stresses partic le orientation leads to decreased viscosity with increasing particle aspect ratio. In the low shear region, higher aspect ratio suspensions show highe r viscosities. Additionally, the material properties, including the interfa cial tension, which influence the suspension morphology are reported.