Foam control is an important factor in textile processing operations.
The main applications of the defoamers are:
- Predefoaming of surfactant concentrates, mainly wetting and scouring agents
- Reliable foam control in aqueous systems
Foam is generated in textile applications mainly by surfactants and surfactant blends which are used as textile auxiliaries during processing. Since foam is disturbing machine runnability, antifoams are currently used. They have to be highly efficient in foam suppression and foam knock down. Defoamer efficiency is dependent on the foaming system. This is why the selection of a suitable defoamer is needed in every specific case. Defoamer efficiency can be determined by preliminary screening tests or a new defoamer has to be developed to match the particular requirements.
When antifoams are used for pre-defoaming of surfactant concentrates, they must be stable and should not separate from the blend during storage. Defoamer stability is especially a problem in textile auxiliaries with a high water content. This is because antifoams must be partially incompatible with the system to be defoamed. If the textile auxiliary already has a high water content, this can result in a negative influence on the stability of the antifoams. Besides the water content, the whole composition of the textile auxiliary is crucial for the stability of the antifoams.
Antifoams are often added in prediluted form to highly diluted aqueous systems in which they have to provide a reliable foam control. In this case, the antifoam has to be stable under several conditions, such as: shear forces, elevated temperatures, presence of electrolytes or high alkalinity.
Antifoams must be free of side-effects, like spotting, and should have minimum impact on possible subsequent treatments (for example printability). Improved dispersability and re-dispersability are beneficial properties.
Antifoam dosage varies in a broad range. Concentrations of 0.005 % up to 0.2 % are currently used and must be optimized by preliminary tests.
Requirements for Antifoams:
- High efficiency
- Stable in concentrates
- No negative side effects
Evonik offers a broad range of defoamers and antifoams in different commercial grades:
- Antifoam concentrates
- Emulsion concentrates
- Ready to use diluted emulsions
which almost completely covers the various needs of the textile industry.
Our antifoams are suitable for pre-defoaming of surfactant concentrates as well as for on line addition in water-containing systems. Depending on the specific requirements of the base materials, our antifoams are carefully selected from our entire product range and different chemistries. We can also modify existing chemistries to meet specific requirements and conditions.
Base materials for our antifoams
- Organic oils
- Silicone oils
- Organomodified siloxanes
- Different hydrophobic solids
Since the range of Evonik antifoams is very large, pre-screening is necessary to select the appropriate antifoam. We provide this service to our customers. By testing your textile auxiliary, we can recommend the suitable antifoam. Of course further field trials are necessary to select individual antifoams. Our Technical Service also provides support for the preparation of ready-to-use defoamers by recommending the best dilution techniques of antifoam concentrates.
Test equipment to run the following lab tests is available within our Technology Centers:
- Sintered glass test
- Modified sintered glas test
- Stirring test
- Shaking test
- Perforated disk beating test (DIN EN 12728)
- Dispersability test
- Dilution techniques
For pre-defoaming of surfactant concentrates with low water content, antifoams can be incorporated at a dosage level of approx. 1 %. This initial dosage level can be optimized by fine-tuning until the optimum performance level is achieved.
Alternatively, antifoams can be added at an early production stage when the water content is as low as possible. After the antifoam has been readily dispersed in the surfactant concentrate, the concentrate can be diluted to the final application concentration.
During textile processing in highly diluted aqueous media,defoamers can be added to provide reliable foam control by itself or in addition with the antifoams already incorporated into the surfactant concentrates.
When applied in systems containing much water, it may be advantageous to use defoamers in low concentration pre-dilutions. Due to many different process conditions encountered in practice, the dosage of antifoams/defoamers in systems with high water content may vary from as low as 0,005 % up to 0,2 %. Preliminary tests are helpful and recommended.
Antifoam concentrates, pre-dilutions and ready-to-use dilutions have to be stored at room temperature and proteced from frost.
Preparation of low concentration antifoam emulsions
Evonik offers various antifoam concentrates which are suitable for the preparation of stable pre-dilutions or ready-to-use low concentration defoamer emulsions.
Stable defoamer dilutions can be produced from concentrates by using thickeners and common dilution techniques. Use of low shear forces is necessary in order to keep the particle size needed for an efficient defoaming performance.
Some examples are shown in the paper "Low concentration emulsions"
Incorporation of an antifoam is often required when producing low-foam textile auxiliaries. TEGO® Antifoam 3062 and TEGO® Antifoam 793, both containing 100 % actives, are designed for pre-defoaming of surfactant concentrates. TEGO® Antifoam 3062 and TEGO® Antifoam 793 are characterized by good compatibility with surfactant concentrates. This leads to stable formulations which, in most cases, are clear or almost clear.
The higher the water content of the surfactant concentrate, the more difficult it is to get a stable incorporation of an antifoam. TEGO® Antifoam 3062, solely based on non-ionic components, is suitable for and efficient at pre-defoaming any surfactant concentrate with a water content below approx. 20 - 30 %. Accordingly, the post-addition of antifoams by the end users may be reduced or even avoided, which results in increased reliability in production processing.
TEGO® Antifoam 3062 provides good foam control at temperatures ranging up to approx. 140 °C and therefore it may be applied to produce pre-defoamed surfactant concentrates for use in various high-temperature processes. As soon as the water content of the surfactant concentrate exceeds approx. 30 %, the incorporation of TEGO® Antifoam 3062 into the surfactants may become more difficult. In several cases the dispersability is somewhat weak as compared with that in the highly concentrated systems.
This may lead to hazy formulations and in the worst case to the separation of the antifoam in the surfactant concentrate. Some solvents (alcohols, glycols) may carefully be used as co-solubilizers in order to improve the dispersability of the organomodified siloxane in the surfactant concentrate. However, these solubilizers have to be added at very low concentrations (not more than 3 %), otherwise the defoaming performance of the antifoam in the surfactant concentrate is adversely effected. TEGO® Antifoam 793 is suitable for surfactant concentrates with a higher water content (up to approx. 35 %).
TEGO® Antifoam 793 and TEGO® Antifoam KE 600, being water-dispersible, can be added to foaming ready-to-use solutions in various process steps. TEGO® Antifoam PS 10, as well as the predilution of TEGO® Antifoam MR 1015, are also suitable for post-addition.
For these applications, pre-dilutions of the defoamers should be prepared as described above. TEGO® Antifoam 3062 can optionally be added to foaming ready-to-use solutions. For these applications a pre-dilution of the defoamer should be prepared. TEGO® Antifoam 3062 is not water-dispersible but can be dispersed in alcohols or glycols.
Test results based on the modified sintered glass test for TEGO® Antifoam MR 1015 and TEGO® Antifoam PS 10
- Surfactant 1: Alkylbenzene sulfonate
- Surfactant 2: Nonylphenol ethoxylate (9 EO) : secondary alkane sulfonate (1: 2) blend
- Surfactant 3: Iso-octylphenol ethoxylate (6.5 EO)
- Surfactant 4: Iso-octylphenol ethoxylate (20 EO)
- Surfactant 5: Iso-tridecyl alcohol ethoxylate (7 EO)
All test results can be found in the paper "Test results based on the modified sintered glass test"