Research progress and development trend of defoamers


Summary:


In this paper, the development background, molecular structure and breakdown mechanism of polyether modified silicone oil defoamer are introduced. The structural characteristics of polyether modified silicone oil defoamer are briefly summarized. The main problems of polyether modified silicone oil defoamer are discussed. At the same time, the future research directions are put forward.


Bubbles exist all the time in people's life and production. Excessive foam will bring inconvenience to production and processing, and even affect the quality of products. At present, defoamer is mainly used in concrete admixture, which is an important component of concrete. Because the polycarboxylic acid mother liquor itself has a large air content, so that concrete produces bubbles. If the defoamer is combined with polycarboxylate superplasticizer, it will eliminate many large bubbles of concrete, effectively alleviate the adverse effects of foam on concrete, and improve production efficiency. These are all concerned issues.


1. Development background of defoamers


There are four stages in the development of defoamers.


The first kind of defoamer is mainly composed of various organic substances, such as fatty acids, mineral oils, aliphatic amides, low alcohols and so on. Most of these defoamers are natural substances, which have little environmental pollution and low price. Because the defoaming property is relatively weak, a large amount of foam can not meet the requirements of production.


The second type is polyether defoamer CnH (2n+1) O (EO) a (PO) bH, polyoxyvinyl chain (EO) is hydrophilic, and polyoxypropylene chain (PO) is lipophilic. The defoamer has good antifoaming property, non-toxicity, no stimulation and good dispersibility. In actual production, the relative molecular weight of polyether and the proportion of EO and PO in polyether chain are adjusted to meet the needs of various production fields. At present, the main polyether Defoamers in the market are straight chain polyether, ether amine, aliphatic alcohol polyether, fatty acid polyoxyethylene ether, and other polyether derivatives.


The third category is organosilicon defoamer, which has better defoaming performance than the former two. Generally, the higher molecular weight silicone oil is insoluble in surfactant solution, while the smaller molecular weight silicone oil is easily solubilized by surfactant molecules, which changes the composition of defoamer and weakens the defoaming performance. For the defoamer of silicone oil, it is insoluble in water and mineral oil, so it has strong foam suppression ability and greatly enhances its foam breaking effect. Because Si-O bond and Si-C bond are relatively stable, they are allowed to be used in systems containing small amounts of acid, alkali and salt. Silicone defoamers commonly used in industrial production are mostly secondary processed products of silicone oil prepared by adding dispersing additives in silicone oil, which belong to liquid mixtures. The mixture is mainly divided into five types: silicon paste type, silicone oil type, emulsion type, solution type and solid type from appearance and fluidity.


The fourth kind of defoamer is polyether modified silicone oil defoamer. On the basis of previous generations of defoamers, we strive to integrate the advantages of polyether and silicone, and introduce polyether segments into silicone oil segments, which has stronger defoaming and anti-foaming properties. Polyether modified silicone oil is a new type of special silicone surfactant. It is a kind of non-ionic silicone surfactant with unique properties, which is formed by addition reaction of polyether containing double bonds and silicone oil containing low hydrogen. It not only retains the high and low temperature resistance, weatherability, demoulding resistance, hydrophobicity and physiological inertia of silicone oil, but also retains the properties of silicone oil. It has the characteristics of polyether non irritation, high surface activity and easy dispersing. Polysiloxane segments are lipophilic and polyether segments are hydrophilic, which makes polyether modified silicone oil both soluble in water and soluble in oil phase, so it can be used as silicone surfactant. Polyether segments can also be used as emulsifiers to make emulsion properties. It can keep stable and has good dispersion performance. Therefore, polyether modified silicone oil has a lasting defoaming effect in water system. Polyether modified silicone oil is widely used because of its good heat resistance, shear resistance, acid and alkaline resistance, non-toxicity, odorless and stable storage, especially when silicone defoamer is difficult to solve.


Transfer from China Admixture Network