Water based defoamers become water-based after being emulsified by emulsifiers and other fillers, while oil-based defoamers are not emulsified and are composed of mineral oil or polyether.
Foam treatment is a thorny problem in pulp and paper industry when it is used as defoamer. From the pulping unit operation after the ball steaming discharge to the coating process, there are varying degrees of foam, which seriously affects the normal production and paper quality. However, traditional defoamers such as mineral oil, sulfonated vegetable oil, alcohols and other defoamers have poor surface activity, low defoaming efficiency, and narrow application range, which cannot meet user requirements. At present, the domestic and foreign paper industry mainly uses three types of broad-spectrum defoamers: fatty acid amides, polyethers, and organosilicons, which have strong universality, high efficiency, good compatibility, and great market potential. Organosilicon defoamers, as a new type of additive, have attracted widespread attention in the paper industry.
Regarding the mechanism of action of defoamers, it is generally believed that low surface tension defoamers enter the local area of the bimolecular oriented bubble film, disrupting the mechanical equilibrium of the oriented bubble film and leading to bubble rupture or inhibition of foaming. There are many organic compounds suitable for use as defoamers, including silicone oil, polyether, alcohol, fatty acid, phosphate, and metal soap. Structurally speaking, non silicone defoamers are organic compounds or polymers with polar functional groups at one or both ends of their molecules. They are similar to foaming agents, and improper use can have the effect of foaming agents. Their spreading coefficient is large, their defoaming effect is strong, and their anti foaming effect is poor.
The silicone defoamers are mainly divided into four categories according to their physical properties, namely silicone oil type, silicone oil solution type, silicone oil mixture type and silicone oil lotion type. The silicone oil defoamer used in the paper industry can be either silicone oil type or silicone oil lotion type. At present, silicone oil lotion type is mainly used. After emulsification of silicone oil, the surface tension decreases rapidly, so it is easy to be adsorbed on the surface of foam liquid and spread on the liquid surface. The formed surface facial mask has low viscosity and low strength, which can cause local surface tension imbalance on the foam, make the liquid film thin and break, so as to achieve the purpose of defoaming, and also has the role of foam suppression; In addition, lotion defoamer has a large affinity for water, a wide range of pH values, no adverse effect on sizing, and no stain on the paper surface. And using a small amount can achieve strong defoaming and anti foaming effects, making it an important component of defoamers. Silicone oil defoamers generally have high defoaming efficiency, and the key to their use lies in the emulsification of silicone oil. If the emulsification is not complete, it will break the emulsion during use, affecting its effectiveness. The commonly used silicone defoamers are formulated with silicone oil as the basic component, combined with suitable solvents, emulsifiers, or inorganic fillers.
