Defoamer testing common sense

Defoamer Routine Test Method

1. Spray test: spray the bubble solution to make bubbles, and then add a defoaming agent to measure the defoaming effect according to the time taken for defoaming.

2. Shake test: Add the defoamer to the bubble solution, shake it by hand, observe it at regular intervals, and record the defoaming time.

3. Circulating pump test: Put the bubble solution in a closed loop to circulate, add defoamer to stir, and measure the foam height.

4. Densitometer measurement: first measure the density of the solution, then add the solution and the defoamer to test the mixed density, and calculate the density difference.

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Emulsion type defoamer detection method

Appearance: Take a 20ml ~ 50ml sample into a 100ml beaker, and by visual inspection, its color is white or slightly yellow to be qualified.

PH value: Use precise pH test paper to measure the pH value of the emulsion itself.

Determination of solid content: According to the general method of GB / T6284 chemical product moisture content determination, the moisture content in the defoamer is measured. Deducting the moisture content is the solid content of the defoamer product. Use an analytical balance to weigh the weighing bottle M1, add 2 to 3 grams of defoamer sample weight M2, put it in a constant temperature drying box, and bake at a constant temperature of 105 ° C for 1.5 to 2 hours to constant weight weighing The weight is M3, that is, the solid content is [(M3-M1) / (M2-M1)] × 100%.

Defoaming time: Use a 100ml stoppered measuring cylinder to take (50 ± 0.5) ml of 1.0% nonylphenol polyoxyethylene ether (industrial grade), constant temperature to (25 ± 1) ℃, add about 0.2g (accurate to 0.001g) ) Sample, cover the stopper, shake the measuring cylinder up and down 10 times at a frequency of (30 ~ 35) cm at a frequency of 2 times / second, stand still and start timing, record the time it takes for the foam to disappear until the liquid surface appears to defoam. time.

Stability: (centrifuge 800)

Measure 8ml samples in two 10ml centrifuge tubes, place them symmetrically in the centrifuge, and rotate continuously for 15 minutes at a speed of 3000 rpm, and take the test tube to visually check for non-stratification.

Defoaming principle

Foam is a dispersion system in which gas is dispersed in a liquid. Gas is a dispersed phase and liquid is a dispersion medium. A stable state is formed because the gas is insoluble in a surfactant. After the formation of bubbles, due to the intermolecular effect of the foaming system, hydrophilic groups and hydrophobic groups are adsorbed by the bubble wall to form a regular arrangement. The hydrophilic groups face the water phase and the hydrophobic groups face the bubbles, thereby forming an elastic film at the interface of the bubbles. , Its stability is very strong, it is not easy to break under normal conditions. At the same time, foam is a thermodynamically unstable system. Under the action of gravity, the liquid film is continuously flowing down, evaporating, bursting, and draining and permeating between the foam liquid films.

The reasons for defoaming are mainly divided into two aspects: 1) the easy-to-spread and adsorbed defoamer molecules replace the foamer molecules, forming a weak film; 2) the defoamer molecules take away adjacent surfaces during the spreading process Part of the layer solution makes the foam liquid film thin, the foam stability is reduced, and it is easy to be destroyed.

From the above we can know that in order for the defoamer to function, it must first penetrate into the double-layer film of the bubble film, and its penetration capacity can be expressed by the penetration coefficient E. After the defoamer penetrates, it needs to be spread quickly. Its spreading capacity can be expressed by the spreading coefficient S.

In the formula: γF is the surface tension of the foam medium; γDF is the surface tension of the defoamer; γD is the interfacial tension between the foam medium and the defoamer. When E> 0, the defoamer can penetrate into the foam; when E <0, the defoamer cannot penetrate into the foam; when S> 0, the defoamer can expand on the surface of the liquid film; when S <0 The defoamer cannot spread on the surface of the liquid film. Therefore, the defoaming agent has a defoaming effect only when E> 0 and S> 0.

 

 


Post time: Dec-25-2019