Defoamers are a wide range of industrial application additives, which are widely used in various fields of the national economy. However, there are many occasions to solve the defoaming problem. In order to solve the defoaming problem of many systems, a variety of defoaming formulations are required. According to the source and structure of raw materials for manufacturing defoamers, they can be divided into the following three categories:
(1) Products based on natural products, such as vegetable oils, mineral oils and compounds, are still in use today due to their many sources and low prices;
(2) Polyether defoamers based on petrochemical products, such as polyoxyethylene, polyoxypropylene polymers or block copolymers of both, have become a major type of defoamers since the 1960s due to the development of petrochemical industry;
(3) Silicone defoamer with polysiloxane as the main raw material is widely used in various fields due to its excellent surface properties.
The selection of defoamer shall comply with the following points:
1. Insoluble or insoluble in foaming liquid
In order to break the foam, the defoamer should be concentrated on the foam film. In the case of foam breaker, it should be concentrated in an instant, and in the case of foam inhibitor, it should always be kept in this state. Therefore, defoamer is in supersaturated state in foaming liquid, and only insoluble or insoluble defoamer is easy to reach supersaturated state. Insoluble or insoluble, it is easy to gather at the gas-liquid interface, it is easy to concentrate on the bubble membrane, and it can play a role at a lower concentration. The defoamer used in the water system and the molecule of the active ingredient must be strong hydrophobic and weak hydrophilic, and the HLB value is in the range of 1.5-3 for good effect.
The printing and dyeing industry is one of the departments that use a large amount of silicone oil for defoaming. Among the eight main processes of fabric processing (i.e. spinning, sizing, weaving, desizing, wool washing, bleaching, dyeing (tie dyeing) and finishing), four processes (sizing, wool washing, dyeing and finishing) require the use of surfactants and other additives, which results in varying degrees of foam trouble. For example, in the process of fabric dyeing, leveling and bleaching, it is often necessary to add penetrant to the dyeing of thick and dense fabrics to improve the dyeing uniformity, and the penetrant is easy to blister and cause color stains, or even waste products; For another example, when printing nylon silk, it is also easy to produce "blisters" that affect product quality. If silicone oil emulsion defoamer is added separately or used together with octanol as defoamer, the problem of foam can be solved, and the leveling effect and stability of color paste can be improved. It should be pointed out that there are strict requirements for the quality of defoamers used in the dyeing and finishing of fiber fabrics. If the stability of defoamer is not good, there may be oil stains or oil spots on the fabric, which will make the product downshift or called waste. Therefore, the properties of defoamer, bath liquid formula, acid and alkali, finishing temperature and mixing conditions should be carefully selected. For general fabrics, silicone oil emulsion defoamer is often used;
