Cleanability of titanium and stainless steel particles in relation to surface charge aspects

The cleanability of titanium and 316L stainless steel particles was studied in terms of their apparent surface charge density (sigma(app)). Bovine serum albumin (BSA) was used as the model fouling agent. Curves for the sigma(app) of titanium and stainless steel particles showed the apparent points of zero charge (pzc(app)) of 4.6 and 8.5, respectively. Compared with the curve for the sigma(app) of stainless steel, that of titanium was characterized by small positive and large negative sigma(app) values. The isotherms for BSA adsorption and the saturation amount of BSA adsorbed on titanium and stainless steel depended largely on the intrinsic properties of BSA. In continuous cleaning in a plug-flow column fed by a 0.05M NaOH solution, BSA was found to be faster desorbed from titanium than from stainless steel, and smaller amounts of BSA remaining after 120-min cleaning were observed on titanium. Kinetic analysis showed that the two first-order desorption rate constants, reflecting the rate of BSA desorption in the initial and later stages of cleaning, for titanium were respectively 1.7-fold and 1.3-fold higher than those values for stainless steel. It could be suggested that the better cleanability of titanium was probably due to the small binding strength of BSA on slightly negatively-charged titanium surfaces and due to their large negative sigma(app) values under alkaline cleaning conditions.