Application of MQ silicone resin in defoamer

Ordinary silicone defoamer is usually emulsified with methyl silicone oil and hydrophobic carbon black after high temperature treatment. Silica is dissolved into sodium silicate in strong alkali and high temperature environment soon.And the white carbon black is like a needle tip that punctures the foam,the methyl silicone oil lost the needle tip will inevitably lead to the decrease of the ability to restrain bubbles. On the other hand, the linear molecules of methyl silicone oil breaks gradually in strong alkali and high temperature environment to form small molecules without defoaming ability. At present, there are many reports about the emulsification of silicone defoamer. However, the emulsification process only disperses the active ingrediates of the defoamer in water, which has little effect on the defoaming and antifoaming performance. The active ingrediates of the defoamer are the main decisive factors of defoaming and antifoaming performance.

The network polymers with high degrees of branches is synthesized by adding high viscosity hydroxyl silicone oil and MQ silicone resin, so as to improve the high temperature resistance and strong alkali resistance of defoamer. The MQ silicone resin mass fraction, M / Q ratio, reaction time and catalyst mass fraction will effect on the properties of the defoamer.

The M/Q ratio has a great influence on the foam inhibition performance of the defoamer.

The methyl MQ silicone resin with M / Q = 0.68 can enhance the foam inhibition performance. Under the catalysis of strong alkali, the complex chain breaking and condensation and cross-linking reactions will occur between the residual Si-OH groups of the MQ silicone resin and the hydroxyl silicone oil and the residual Si-OH groups of the partially hydrophobic silica,that will produce the branched polymer with spatial network structures. The structure and molecular weight of MQ silicone resin are determined by the M / Q ratio. The smaller the M / Q ratio is, the more complex its spatial network structure is, and the more conducive it is to improve the foam inhibition performance of the defoamer. However, if the M / Q ratio is too small, it is difficult to dissolve in methyl silicone oil and cannot be used.

When the mass fraction of MQ silicone resin is more than 10%, there is no obvious differences in the foam inhibition performance. If the mass fraction of MQ silicone resin is too much, the foam inhibition performance will not be improved.

If the mass fraction of MQ silicone resin is too little, the contribution to the foam inhibition performance will be small, because the crosslinking degree of the formed polymer is too small, which affects the antifoaming performance of defoamer. Considering the cost factor, 5-10% is appropriate.

References:methyl MQ silicone resin for defoamer