Preparation And Performance Study Of Nano-Silica/Polydimethylsiloxane As Antifoam

During industrial production process,large amount of foams often occurs inevitably,which was harmful to production.Adding antifoams was often used to eliminate these unnecessary foams.At present,the most widely used antifoam was silicone,which adding silica could improve performance of the antifoams,significantly.In this paper,the silica and polydimethylsiloxane?PDMS?were used to prepare the silicone antifoams by blending and in-situ polymerization.The effect of SiO₂ surface polymerization group and the combination mode of silica and polydimethylsiloxane on the performance of antifoam was studied.The main research contents and conclusions are as follows: 1.Study on the preparation and performance of surface modified SiO₂/PDMS silicone paste antifoam.Using liquid-phase in-situ surface modification technology nano-silica containing different organic modifiers such as trimethylsilyl or/and aminopropylsilyl was prepared.The silica paste antifoam was prepared by mixing the nano-silica with silicone oil.The silicone antifoam was investigated by means of shaken method,Ross-Miles method.The results shows that the increase of modifier M-2 could increase the hydrophobicity of silica,enhancing "Pin" effect of silica that improvement in foam film-destroying rate.When the hydrophilic modifier M-A added,the foam inhibition performance of the antifoam was greatly improved.This was because hydrogen atom of the strong polar bond?N-H?in amine propyl can form N-H…O hydrogen bond with the oxygen atom in PDMS,which increases the force between silica and silicone oil.Silica paste with 20% M-2 and 10% M-A co-modified nano-silica as the dispersant shows excellent foam suppression performance,and the time of foam inhibition could reach 63 min.2.Preparation and performance research of surface modified SiO₂/PDMS emulsion antifoam.Span-80 and Tween-80 were used to emulsify silicone paste to prepare emulsion antifoam.The influences of the composite emulsifier with different ratios on the dispersion stability and storage stability of the emulsion antifoam were investigated,and the effects of silica modifiers on the static defoaming properties and antifoaming properties of emulsion antifoam were also probed.The emulsification condition was optimized: silicone paste was made with silicone oil and 5 phr SiO₂ which modified with 20% M-2 and 10%;a compound emulsifier was prepared from Span-80 and Tween-80 in a ratio of 2: 1;silicon paste: composite emulsifier: pure water =2:1:3.In this case,the emulsion antifoam has better defoaming and antifoaming performance.At the same time,through the analysis of the particle size in the emulsion,founding that the dispersed droplets of the emulsion antifoam were smallest in this compounding ratio,and the average particle size was 372 nm.3.Preparation and properties of surface modified SiO₂/PDMS in-situ polymerization antifoamD4 was used as the polymerization monomer to synthesize PDMS by anion ring opening polymerization.In the process of chain propagation of PDMS,hydrophobic nano-SiO₂ was added in the flask to synthesize the inorganic/organic compound.The structure and the synthesis mechanism of the in situ antifoams were analyzed by FTIR and TEM.The inhibition-grafting mechanism of the inorganic/organic compound was proposed: the oligomer PDMS formed by monomer ring-opening polymerization could be grafted on the surface of SiO₂ to form organic/inorganic material,due to the short-chain PDMS grafting on the surface of SiO₂ limited activity of the polymerization ability,the polymerization ability was greatly reduced,so the low viscosity antifoam with a certain grafted structure was obtained.Compared with the blending method antifoams,the in-situ antifoam maintained a good defoaming effect at a lower viscosity.The effects of the ring-opening polymerization time,the amount of silica and the grafting time on the performance of antifoam were investigated.The optimal synthesis condition of the in-situ antifoam was ring-opening polymerization at 105 oC for 20 min,then,addition of 5 phr of hydrophobic SiO₂ for 30 minutes reaction.According to the results of performance tests,the static defoaming time was less than 5 s.Compared with the blending method antifoams,the in-situ antifoam maintained a good defoaming effect at a lower viscosity.The research work on SiO₂/PDMS in-situ preparation of antifoam provides a new structure of low-viscosity and high-efficiency antifoam and its preparation method.