Precautions for using defoaming agent
In the process of manufacturing foam ceramics and plastics in daily life, such as flotation, fire extinguishing, dust removal, washing, sometimes it is necessary to eliminate the bubbles generated in the manufacturing process. These bubbles are gas-intolerant and exist in industrial 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 formation of bubbles is affected by their own forces. The hydrophilic and hydrophobic groups are adsorbed by the bubbles and arranged regularly to form an elastic film on the surface of the bubbles. The stability is very strong and it is not easy to break under normal circumstances. Under the influence of the stability of the foam and the surface viscosity and elasticity, electrical repulsion, and temperature and pH, it is not easy to break the harmful bubbles well by itself.
At this time, defoaming agents are needed. 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 to achieve the defoaming effect in the early stage of production. 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 types of defoamers with wide applications. Most of the defoamers on the market are added after the foam is produced and spread on the foam surface to form a double film. The principle of diffusion and penetration replaces the original foam film to achieve the defoaming effect.
In addition, it should be noted that choosing a suitable system of defoamers is also an important part of choosing defoamers. 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.
(1) Addition point of defoamer: In pulp mills, defoamers are generally added in the bleaching and washing sections, usually 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.
(2) Defoamer dosage: It is generally more economical and effective to use two defoamers than to use a higher content of one defoamer. They are added separately at distant locations. For example, one defoamer is added before the pulper and the other is added in the headbox.
(3) Solution to defoamer precipitation: For example, amide defoamers will cause precipitation and block the sieve plate seams. Due to poor dispersion, the paper will have fisheye spots and other paper defects. Some defoamers will also interfere with sizing, strengthening and other effects. Therefore, high-emulsion systems have outstanding defoaming effects in high and low viscosity roughened coatings.
