1.6.4 water dispersion of defoamer


Take 5g defoamer into the beaker, add 25g distilled water, shake, and observe the dispersion results. In the case of milky white solution, no white oil phase and no oil spot on the surface of the solution, the water dispersion of defoamer is excellent; in the case of milky white solution, with small white oil phase particles, the water dispersion is good; in the case of milky white transparent solution, with many white oil phase particles and large particles, the water dispersion is general; it can hardly be dispersed in water, and the water dispersion is good It is bad.






2 results and discussion






2.1 structural design of polyether modified polysiloxane


The antifoaming and antifoaming ability of the completely water-soluble substances in the aqueous medium is poor; therefore, the polyoxyalkylene ether modified polysiloxane must have certain hydrophobicity, that is to say, the hydrophobic segment polysiloxane and polyoxypropylene ether in the copolymer must be long enough, while the hydrophilic segment polyoxyethylene ether cannot be too long. When the molar mass of polyether modified polysiloxane is small, the antifoaming ability is strong, but the antifoaming ability is poor; when the molar mass is large, the antifoaming ability is strong, but the antifoaming ability is poor. According to different application targets, the proper ratio of polyoxyene ether and polysiloxane can be set to obtain defoamers with different cloud points. According to this principle, the molar mass of hydrogenated silicone oil is 3000-10000g / mol, active hydrogen content is 0.03-0.12%, and the molar mass of polyether chain segment is 400-1500g / mol.






2.2 hydrophobic treatment of silica


The antifoaming effect of polyether modified polysiloxane can be improved by compounding fumed silica with polyether modified polysiloxane [4]. In this experiment, the white carbon black was treated with hexamethyldisilazane. The feed ratio was 100:20 and treated at 240 ℃ for 6 hours. After the addition of hydrophobic fumed silica, the defoaming time of defoamer can be shortened by 5-7s, and the defoaming time is increased by 7-12min (see Table 1).






2.3 selection of emulsifier


As we all know, polysiloxane is difficult to emulsify, so the selection of emulsifier is very important. Although the ionic emulsifier has excellent stability, it is easy to foam. Therefore, the emulsifier used in the preparation of defoamer is generally non-ionic, and the emulsification effect of composite emulsifier is better than that of single emulsifier [5]. The emulsifying effects of tween-60, Span-60, SS and sse-20 were investigated. According to the principle of composite emulsifier, the four emulsifiers are combined into two pairs, namely Span-60 / tween-60 and SS / sse-20. It was found by experiments that after the dosage of Span-60/Tween-60 system was more than 5%, the emulsion had good stability, good defoaming and anti foaming effect, and adding a small amount of SS/SSE-20 could emulsify silicone oil, so that the emulsifier content in defoamer was small, and the emulsion system was stable. Therefore, SS/SSE-20 was chosen as the compound emulsifier, and its dosage was about 1.5%. The defoamer emulsion was prepared by phase inversion emulsification.






2.4 selection of thickener


In order to obtain better stability of defoamer emulsion, thickener should be added to the formulation as stabilizer of emulsion. The commonly used thickeners are hydroxyethyl cellulose, carboxymethylcellulose, alginate derivatives and polyvinyl alcohol. In this experiment, polyethylene glycol 6000 distearate (HLB is 18.4) was selected as the thickener. The addition of polyethylene glycol 6000 stearic acid ester will change the HLB value of the whole defoaming system. In order to make the performance of the defoamer emulsion good, the total HLB value of the emulsifier and thickener should be consistent with the HLB value of the silicone paste. It was found that when the amount of composite emulsifier was 1.5%, the best amount of thickener was 0.5% - 0.8%.






2.5 performance of defoamer


The defoaming properties of the polyether modified polysiloxane defoamer emulsion and the polyether modified polysiloxane defoamer added with fumed silica were found to be stronger.






The commonly used defoamer in industry are two kinds of polyether defoamer and silicone emulsion defoamer. The results showed that the self-made defoamer was better than the commercial defoamer in defoaming time and inhibiting time.






3 conclusion


In this paper, high hydrogen silicone oil was used as raw material, and low hydrogen silicone oil was prepared by polycondensation method. At the same time, propylene alcohol was used as initiator and NaOH as catalyst to carry out ring opening copolymerization of ethylene oxide and propylene oxide to make allyl terminated polyoxyalkylene ether. Then allyl terminated polyoxyalkylene ether was used to graft low hydrogen silicone oil to obtain polyether modified polysiloxane. The polyether modified polysiloxane was compounded with fumed silica, SS / sse-20 and polyethylene glycol 6000 distearate (1.5% and 0.5% ～ 0.8% respectively) thickener, which was hydrophobically treated by hexamethyldisilazane, to produce a kind of high efficient defoamer. The antifoaming agent has stable emulsifying property, good antifoaming and antifoaming properties, can be dissolved in water rapidly, can be used alone, can also be used in combination with other treatment agents, and is also effective for non-aqueous system. It is a kind of antifoaming agent with good performance and broad application prospect.