Application of alcohol defoamers in papermaking
With the development of papermaking industry and the continuous improvement of product quality, the speed of papermaking machines is constantly increasing, and the types of additives added in the wet end are increasing. The generation of foam in the papermaking process and its impact on the quality of paper are becoming more and more important. At present, there are many types of defoamers used in various papermaking applications, with different characteristics, so a defoamer can only be effective for one or several systems.
Methods for eliminating foam
Change the temperature, filter and remove floating objects, make the container open, remove mechanical foaming factors (avoid strong boiling, oscillation, decompression, splashing), remove solutes that are easy to foam, etc.
Add defoaming agent, send defoaming gas, use adsorption, precipitation, chemical reaction to remove foaming substances, adjust pH value and HLB value, add substances that can eliminate foam stability, etc.
The local surface tension of the foam is reduced, resulting in the collapse of the foam. The origin of this mechanism is that higher alcohols or vegetable oils are sprinkled on the foam. When they are dissolved in the foam liquid, the surface tension at that place will be significantly reduced. Because these substances generally have low solubility in water, the reduction of surface tension is limited to the local part of the foam, while the surface tension around the foam has almost no change. The part with reduced surface tension is strongly pulled and extended to the surroundings, and finally breaks.
Defoamers can destroy the elasticity of the membrane and cause the bubbles to burst. When defoamers are added to the foam system, they will diffuse to the gas-liquid interface, making it difficult for the surfactant with foam stabilization to restore the membrane elasticity.
Defoamers can promote the drainage of liquid membranes, thus causing the bubbles to burst. The rate of foam drainage can reflect the stability of the foam. Adding a substance that accelerates the foam drainage can also play a defoaming role.
Hydrophobic solid particles on the surface of bubbles will attract the hydrophobic end of the surfactant, making the hydrophobic particles hydrophilic and entering the water phase, thereby playing a defoaming role.
Certain low-molecular substances that can be fully mixed with the solution can solubilize the foam-assisting surfactant and reduce its effective concentration. Low molecular substances with this effect, such as alcohols such as octanol, ethanol, and propanol, can not only reduce the concentration of surfactants on the surface layer, but also dissolve into the surfactant adsorption layer, reduce the closeness between surfactant molecules, and thus weaken the stability of the foam.
For the foaming liquid that produces stability by the interaction of the double electric layer of the surfactant of the foam, adding ordinary electrolytes can disintegrate the double electric layer of the surfactant to play a defoaming role.
Commonly used defoamers in the papermaking industry
Hydrocarbons are generally not used alone as defoamers, but are used in combination with emulsifiers and waxes to form W/O type emulsions. They have strong diffusion ability and fast defoaming speed, but the anti-foaming effect is general. They are mostly used in the pulping process. If used in combination with hydrophobic particles such as colloidal silica, the effect is better.
Commonly used defoamers are known as “anti-foaming”. In actual applications, these surfactants are often used in combination with silicone oil and mineral oil to reduce costs and achieve a comprehensive effect of anti-foaming and defoaming.
