STRUCTURAL RHEOLOGY OF A MODEL OINTMENT

A model ointment consisting of white petrolatum, mineral oil and micro crystalline wax was studied using theology, microscopy and thermal tec hniques. Rheograms studied over a temperature range of 25-40 degrees C indicated that the overall rheogram shape changed little as the tempe rature increased. However, two inflections gradually disappeared as th e temperature increased. Thermal optical analysis showed that the temp erature range over which these inflections disappeared correlated with the melting transition of the components forming the secondary struct ure. Another series of rheograms obtained from ointments with differen t combinations of the raw materials showed the theology of the ointmen t is primarily controlled by the white petrolatum and mineral oil and that the microcrystalline wax acts to build-up the structure by incorp orating itself into the existing white petrolatum structure. Thermal o ptical analysis of comelts of the raw materials proved that the ointme nt network structure is essentially a recombination of the naturally o ccurring components in differing ratios. The knowledge obtained from t hese studies is applied to a discussion of the thermal and mechanical stresses encountered in the filling operation.