Types and Mechanism of Defoamers
Types of defoamers:
Defoamer is a commonly used additive in chemical industry. So far, defoamers have undergone four renewals.
1.1 First generation defoamer
There are mainly organic defoamers such as mineral oil and aliphatic group. Most of these defoamers are oil-soluble. Their advantages lie in low production cost of raw materials and mature technology. Their disadvantages lie in poor defoaming effect, narrow application field and poor compatibility with polycarboxylic acid water reducers.
1.2 Second generation defoamer
Polyether defoamer is a polymer with C-O-C as its main chain structure, which has strong defoaming ability. This kind of defoamer is a water-soluble defoamer, which can be used in concrete, exterior wall coatings and other general industries. Polyether defoamers need to be modified, mainly by alkoxysilane, because of their narrow application fields, relatively poor defoaming ability and defoaming rate. In 1967, China successfully developed and invested in the production of polyether defoamers, mainly linear polyethers and polyethers starting from alcohols and ammonia, such as polyoxyethylene, polyoxypropylene and other end-esterified polyether derivatives.
1.3 Third Generation Defoamer
Silicone defoamers have excellent defoaming properties, fast defoaming and non-volatilization. The extension of Si-O bond makes them have good weatherability, high and low temperature resistance and corrosion resistance, low production cost and wide application fields. These defoamers are both water-soluble and oil-soluble, and can be used in industrial production such as concrete, exterior wall coatings and paper making.
1.4 Fourth Generation Defoamer
Silicone modified polyether defoamer is mainly composed of Si-O-Si and C-O-C. Silicone modified polyether defoamer has high defoaming rate and strong adaptability. It is water-soluble and oil-soluble. It can disperse in water quickly. When mixed with concrete admixture, it can quickly reduce a large number of bubbles produced in concrete mixing process. It combines the advantages of silicone and polyether and makes up for the shortcomings of both. It is the direction of future defoamer industrialization development and the main scientific research goal of scientific researchers.
Mechanism of 2 defoamer
Bridging-Spreading puts forward the mechanism of "bridge-laying" from the point of view that the surface tension of defoaming material is relatively low.
In modern concrete processing, sometimes it is necessary to remove foam. Sometimes foam is needed, sometimes two kinds are needed. When polycarboxylic acid water reducer is added to concrete, a large number of air bubbles will be produced during concrete mixing. At the same time, a certain amount of air entraining agent will be added to make concrete produce uniform and stable air bubbles, so as to ensure that concrete meets the relevant mechanical properties of materials in the process of processing. The main process of foam disappearance when the mixture of defoamers and polycarboxylate superplasticizers is added to the concrete is that the defoaming agent spreads quickly on the surface of the foam, the defoamer and the liquid foam form a bilayer membrane, the liquid foam is not balanced by the surface tension of the surface, and the foam gradually thins and eventually breaks
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