EFFECTS OF SUSPENDING AGENTS ON THE PROPERTIES OF BARIUM SULFATE SUSPENSIONS

Rheological studies of 10 different natural gums and cellulose derivatives as well as of the suspensions prepared from them were made using the Hoppler's Rheoviscometer, and their flow types have been determined.Suspensions with suspending agents of the plastic flow type (eg PVP, PVA, Acacia, hydroxypropylmethylcellulose, and methyl cellulose) with low viscosity were easy to cake on aging, while those with the pseudoplastic flow type suspending agents were not. Hydroxyethylcellulose (pseudoplastic flow) as a suspending agent produced better fluidity as well as better redispersibility on aging.Most of the barium sulfate suspensions (130%) were of the dilatant flow type. Suspensions containing methylcellulose, hydroxypropylmethylcellulose, tragacanth and sodium carboxymethylcellulose (0.1, 0.2, 0.15 and 0.3%) exhibited thixotropic properties, but did not form thixotropic gels.It was found that proper combined use of electrolytes in suspensions (1% sodium hexametaphosphate 0.8～1.2% sodium citrate)resulted in thixotropic gels, which turn to sols with good fluidity on shaking.Gastric fluid flocculating resistance of barium sulfate suspensions were studied by sedimentation method. Gastric fluids of different pH obtained from patients were mixed with barium sulfate suspensions and sedimentation curves were produced on an automatic recording sedimentation balance (KCY type). The results showed that:1. Suspensions containing sodium hexametaphosphate are more stable than those containing sodium citrate whatever suspending agents were used.2. Gastric fluid of pH 8 (alkalinity due to back-flow of the duodenal fluid) do not cause flucculation, on the other hand the gastric fluid of pH 1～2.5, caused remarkable flocculation.