What is Silicone Antifoam and Defoamer? Silicone (polydimethylsiloxane，Ref. Wikipedia – Defoamer) has been used as an antifoam for more than 40 years and has been rapidly and extensively used in various fields since the 1980s. Silicone antifoam can effectively remove and suppress foam in the production process.
Antifoam VS defoamer
Even though we call them antifoam, they are used in two ways to help control foam in your system. When used as antifoam, they help prevent foam from developing. When used as defoamer, they help destroy or knock down foam after it has occurred.
Defoaming way
Knockdown refers to the reduction in foam height that occurs when the antifoam is added. Speed of knock down is also important, so is persistence, the length of time the antifoam continues to perform. Different foaming situations require different degrees speed of knock-down, and persistence.
How silicone antifoam agents work?
Silicone has low surface and interfacial tensions (see Fig.1). This enables it to flow easily over the foam wall, and seeks out openings and occupies them, causing the wall to thin and collapse.
To effectively destroy foam, reducing surface tension is key. Silicone antifoaming agent work by lowering the surface tension of liquids, preventing bubbles from forming and enabling them to break apart more easily.
By dispersing smaller bubbles and inhibiting bubble growth, it prevent large foam formations. This ensures stable, long-lasting defoaming, vital in industrial processes where foam control is crucial.
These actions, including surface tension reduction and bubble dispersion, are essential to achieving effective foam destruction and ensuring consistent, high-quality results in various applications.
Surface tension of common liquid
| Liquid surface tension | (mN/m) |
|---|---|
| Water | 73 |
| Alkyd resin | 33 – 60 |
| Butyl glycol ether | 30 |
| Toluene | 29 |
| Isopropyl alcohol | 22 |
| Octane | 21 |
| Trisiloxane | 17 |
| Hexamethylsiloxane | 16 |
Selecting the right silicone antifoam is crucial for optimizing coating performance, it plays an essential role in controlling foam, ensuring a smooth application and preventing defects.
Considered key characteristics included dispersibility, defoaming speed, and persistent foam suppression. These factors help balance efficiency, cost, and appearance, improving overall product quality.
In-depth evaluation of these traits will guide your selection process. Proper testing methods will ensure antifoam meet your specific needs, delivering superior performance in various applications. Below is 3 regular testing method:
| Test method | Explain |
|---|---|
Stirring test | Evaluation of efficiency and separation tendency of defoamer: Complete formulation (include defoamer) is stirred with toothed dissolver at high speed (e.g. 3 min at 4000 rpm), Determined by weight and get density of formulation. Repeat test after storage (e.g. 2 weeks at 50°C) and get defoaming efficiency. |
Bubbling test | (see Fig.1) Add foaming liquid and defoaming agent into cylinder, keep it constant at set temperature, blow air into it at a set flow rate, and record change pattern of foam volume (including volume sum of foam and medium) over time. |
Shake test | Add certain amount of foaming liquid in the cylinder with plug-in, each time under the same number of shake flask, static observation of foam height and defoaming time. |
Silicone based antifoam main active substance is polysiloxanes (see Fig. 1)
SINOSIL offer product in a variety of forms to meet the needs of a wide range of systems and applications. Below is regular type from us:
| Fluids | use in non-aqueous systems. They are inert and not conducive to bacterial growth, available in a wide range of viscosities. |
|---|---|
| Compounds | Scontain a suspension of finely-powdered silica to enhance their defoaming efficiency and designed primarily for non-aqueous systems. |
| Emulsions | ideal for controlling foam in aqueous systems. |
| Dispersions | ideal for controlling foam in aqueous systems. |
| Powder | often used in dry products to help prevent foaming and liquids are added. |
Silicone
defoamer is often diluted to improve application ease, reduce viscosity, and enhance dispersion in foaming systems. Proper dilution(see Fig1: dilute process) ensures faster defoaming without damaging the agent’s effectiveness.
Below we will introduce the dilution method in two cases based on different use
Dilute method #1
- Weigh silicone defoamers
- Add water into antifoam, stir while adding water
- Add an acrylic thickener
- Add 20% NaOH solution until pH7-8
- Add proper amount of fungicide and stir well
Dilute Method #2
- Weigh water and silicone defoamers.
- Add an acrylic thickener to water
- Add 20% NaOH aqueous solution until pH7-8
- Add the thickened water to the antifoam and stir
- Add proper amount of fungicide and stir well
Defoamer section is crucial for effective foam control. Factors like form, content, and application scenario must be carefully evaluated.
In selecting the best type and quantity of silicone defoamer, each application must be assessed separately. lt therefore best to evaluate several antifoams in each system to determine the type and concentration needed to assure optimum results.
Silicone defoamers play a crucial role in eliminating foam in various industries, but several factors affect their performance.
The effectiveness of a silicone defoamer is determined by multiple factors including chemical composition, molecular weight, and solvent choice. Temperature and pH are also key determinants. At higher temperatures, defoamer becomes more active, while pH imbalances can reduce its efficiency. Below is simple explain for each item:
| Application | Technical requirement of silicone antifoam agents |
|---|---|
Resin synthesis | stable; economical; easy to use foam control agents |
Industrial cleaning | alkali-resistant; requires high defoaming efficiency; stable; compatible |
Water treatment | fast defoaming; stable; easy to use |
Metalworking fluid | good compatibility and durability; anti-filter filtration |
Pulping | alkali & high temperature resistant; adaptable to different pulp types (softwood/hardwood) |
Textile printing and dyeing | good compatibility; stable; high temperature resistant |
Acrylic emulsion system | good compatibility, no other adverse effects |
Latex system | excellent dispersibility and compatibility |
Food and beverage processing | safe; efficient; in line with food regulations in China and other countries and regions |
