Physical and Rheological Properties of Toothpaste

Abstract

Toothpastes which are considered to be concentrated suspension, are consisted of fine solid particles (abrasives), water soluble gums (binders), surface active agents, polyol (humectants), water and others. Only a couple of papers on rheological properties of toothpastes have been published so far, furthermore those results have not been used effectively in practical production of toothpastes. The difficulties of rheological studies of toothpastes are that, (1) they belong to quasi-stable system (2) they are highly concentrated suspension and contain a lot of fine solid particles, and (3) they are so-called multi-components suspension system. For present study, rotational coaxial cylinder viscometer (Thixotrometer) was used to characterise the rheological properties of the water soluble gums, such as carboxymethyl cellulose and carrageenan.Their flow curves were analysed by means of power law equation, and the discussions on their flow constants such as K and γ on activation evergy were made. Both samples showed pseudplastic flow, however carrageenan had more complicated flow characteristics than carboxymethyl cellulose. Non newtonian index, γ, of carrageenan ranged 0.19-0.38 and that of carboxymethyl cellulose 0.40-0.66 respectively. The analysis of non-Newtonian index, activation evergy, dynamic modulus and dynamic viscosity indicated that carrageenan had more complicated structure than carboxymethyl cellulose.