Mechanism of deactivation and reactivation of polysiloxane antifoamers

AbstrcatThe phenomena about the deactivation and reactivation of polysiloxane antifoamers,as well as the particle size and distribution of the antifoam dispersion,surface tension of the foam system,contact angle,the thickness of the spreading out layer of silicone oil,and the structure and profile of the foam film in the deactivation process were presented.The deactivation can be resulted in by change of the composition of the silicone oil,separation of the silicone oil and the hydrophobic silica particulate,reduction of the particle size of the antifoaming agent dispersion,the elimination of the spreading out silicone oil and the formation of the white flocculates.Among the above mentioned causes,the separation of the silica (particles) and the silicone oil as well as the elimination of the spreading out silicone oil are the main causes.The addition of (silicone) oil into the deactivated antifoaming agent the antifoaming activity can be resumed.It can be explained by the achieving of optimal ratio of silicone oil to the silica particulate in the antifoam dispersion particles and formation of new silicone oil spreading out layer that has the antifoaming activity.