What is a temporary defoamer?
The temporary non-aqueous defoamer component is prepared by heating a polymer of a silica filler and a partially hydrolyzed trifunctional silane. The highly dispersed silica filler used is a crushed micropowder raw material, such as precipitated silica and similar silicas. The average particle size of the filler is 7-14 nm, which is calculated based on its surface area.
The hydrolyzable trifunctional silane compound used to prepare the polymer product has the molecular formula RS8 and RSI(OR)3, where is a halogen atom, usually a chlorine atom. R is preferably an alkyl group with 1 to 3 carbon atoms, especially a methyl group. R’ is an alkyl group with 1 to 4 carbon atoms. R’ is preferably a methyl or ethyl group, especially an ethyl group; these hydrolyzable trifunctional silanes include methyltrichlorosilane, methyltrimethoxysilane, methyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, ethyltriethoxysilane, hexyltrichlorosilane and similar compounds.
To prepare the partial hydrolyzates of these trifunctional silanes, any conventional method can be used. For example, in the case of trialkoxysilanes, the partial hydrolyzates can be prepared by mixing silane or a mixture of silanes with water. In the case of trichlorosilane, water or water, ethanol and silane can be mixed and the mixture can be refluxed until the degree of hydrolysis reaches the required level.
The ingredients of the temporary non-aqueous defoamer are prepared by continuous heating at a certain high temperature. It is based on a mixture of highly dispersed silica filler and partially hydrolyzed trifunctional silane polymerization products. The heating temperature is 100-170°C. The minimum heating time is 0.25-5h or longer. It is best to be 0.5-3h. Before heating, it is best to stir the mixture to fully disperse the filler in the polymer. After heating, the mixture does not need to be processed again, but only needs to be cooled to room temperature.
In this example, the operating procedure of the foaming test to detect the defoaming properties of the defoamer is as follows: about 0.1g of the defoamer to be tested is added to 250g of a newly prepared soap solution, which is placed in a stoppered measuring cylinder with a mass fraction of 0.5%. The measuring cylinder is turned upside down and oscillated several times until the defoamer is dispersed in the soap solution. Then, about 100g of the liquid mixture (defoamer and soap solution) is added to a 1000ml measuring cylinder. A nitrogen bubbler with a fine-pore glass tube is installed in the measuring cylinder, and nitrogen is pressed into the liquid mixture. The nitrogen flow rate is the same as the nitrogen flow rate that produces 1000mL of foam every 2 minutes in the soap solution without defoamer. In this way, each group of liquid mixtures (defoamer and soap solution) will produce foam clusters, and the foam height is recorded every 5-10 minutes. By recording the generated foam clusters, the dispersibility and foaming ability of the defoamer can be obtained. The better its dispersibility and defoaming performance, the smaller the height of the foam cluster. These foam clusters can regenerate ±20 mL of foam after 5 min and ±50 mL of foam after 10 min.
