Selection and use of defoaming agents
There are many types of defoamers, which are mainly divided into five categories: organic siloxane, polyether, silicon and polyether grafting, imine and amide. They have fast defoaming speed, long anti-foaming time, wide range of medium, and even harsh medium environment. How to choose and use defoamers? Let’s follow the editor to learn about it.
Correct use of defoamers: The selection of defoamers should be targeted, and the use environment, temperature, pH value and foaming medium should be understood.
First small test, then pilot test, determine the best product and the best dosage. Stir well after stratification. Even if there is no stratification, stir well before use. Do not dilute at will. If you really need to dilute, please use thick water solution under guidance.
In the process of manufacturing foam ceramics and plastics in life production, such as flotation, fire extinguishing, dust removal, washing, sometimes it is necessary to eliminate the bubble substances generated in the manufacturing process. These bubbles are not allowed to exist in industrial production liquids or solids. They are substances that exist independently on the surface of the film. Common ones are oily bubbles and water-based bubbles. Generally speaking, due to the existence of surface activity, the influence of their own forces in the formation of bubbles, the hydrophilic group and the hydrophobic group are adsorbed by the bubbles and arranged regularly, forming an elastic film on the surface of the bubbles, which is very stable and not easy to break under normal circumstances. Under the influence of the stability of the foam and the surface viscosity and elasticity, electrical repulsion, temperature, and pH, it is not easy to break the harmful bubbles well by themselves, and defoaming agents are needed at this time. In terms of the defoaming effect, factors that can break and inhibit the growth of foam can be used for defoaming. Usually, in order to prevent the formation of foam, foam is needed in the early stage of production to achieve the defoaming effect. Bubbles and surface tension are negatively correlated. To reduce surface tension, chemical defoaming is generally more appropriate and quick, and defoaming agents are important additives in chemical defoaming. There are many varieties of defoaming agents and a wide range of uses. Most of the defoaming agents that inhibit foam on the market are added after the foam is produced to spread on the surface of the foam to form a double film, and the principle of diffusion and penetration replaces the original bubble film to achieve the defoaming effect. In addition, it should be noted that choosing a suitable system of defoaming agents is also an important part of choosing defoaming agents. Defoamers are generally made by compounding multiple components. The performance of the main defoamers can be enhanced by compounding surfactants. Whether an active substance is suitable for defoaming depends on its application conditions. For example, stearic acid is a defoamer under acidic conditions; and a foaming agent under alkaline conditions. It is effective at low temperatures, but ineffective at high temperatures.
Defoamer addition point: In pulp mills, defoamers are generally added in the bleaching and washing sections, generally in the pulp washer, thickener and pulp tank. Defoamers in the papermaking section are generally added to the paper machine headbox, pulp tank, coating and sizing press.
Defoamer addition amount: It is generally more economical and effective to use two defoamers than to use a higher content of one defoamer, and they are added separately at distant locations. For example, one defoamer is added before the beater and the other is added in the headbox.
Solution to the precipitation of defoamers: For example, amide defoamers will cause precipitation and block the sieve plate seam, and will cause fisheye spots and other paper defects due to poor dispersion. Some defoamers will also interfere with sizing, reinforcement and other functions. Therefore, high-emulsion systems have excellent defoaming effects in high- and low-viscosity roughened coatings.
