foaming and defoaming agent

textile auxiliary chemicals

1. Colorants and Auxiliaries Foaming and De- Foaming agents Course Manager : D.r Abera Kechei By Asnake Ketema & Robel Legesse BAHIR DAR UNIVERSITY (EiTEX ) First Year M.SC In Textile Chemistry

2. Contents Foaming Agent De-Foaming Agent

3. What is foam? Foam is a dispersion of a gas in a liquid . Here the liquid is generally water and the Gas is generally air but it may also be an inert gas. It’s a colloid system . Structure of foam a matrix of foam to transfer chemicals and colorants to textiles

4. Foam-based application in Textile substrate Lubricants stiffening agents size polymers mercerizing liquors durable press resins water/oil repellents Softening agents shrink-resist resins dyes and print pastes.

5. Foaming Agent Definition: A foaming agent is a material that facilitates formation of foam such as a surfactant or blowing agent that helps to maintain it’s integrity by strengthening individual foam bubbles. Example - sodium lauryl sulphate ( C12H25OSO3Na) A foaming agent to give a reasonably stable honeycomb matrix of air cells.

6. The two important steps the foam and applying it to the substrate 1). by high-speed rotors with metered air and liquid flows and monitoring to control the density of the foam. (2) controlled amounts of foam to the substrate is by knife-on roller, floating knife, horizontal pad or furnishing roller with doctor blade.

7. The First Three Being Anionic And The Others Nonionic Sodium lauryl sulphate Ammonium lauryl sulphate Sodium dioctylsulphosuccinate Lauryl alcohol poly( oxyethylene ) Decanol poly( oxyethylene ) Tridecanol poly( oxyethylene ).

8. Requirements of foaming agents: generate consistent foam easily show optimum and uniform wetting It should show little or no effect on color fastness be compatible with the other components be biodegradable

9. Broadly there are 2 types of foam:- 1. Dispersion foam: It is produced by the introduction & mixing of gas from an external source into a liquid phase. In textile field dispersion foam is used. 2. Condensation foam: It results from the generation of a gas within the liquid either by chemical or by a physical change. This type pf foam is not used in textile field. Types of Foam

10. Stabilizer Definition : Foam stabilizer slows down the drainage of liquids from the bubbles & impart workable flow properties. The basic role of a stabilizer in foam is to reinforce the bubble cell wall to a controllable level or stabilize foam from decay. Example :- Hydroxy-ethyl cellulose (HEC) Methyl cellulose Ammonium stearate .

11. Function and Requirements Function:- Slow down drainage. Reinforce bubble cell-wall. Controls life time of foam. Requirements of stabilizer:- Easy solubility. Compatible with a foam finishing system. Effective at low concentration. It should be easily soluble. It should be least affected by fabric handle. Resistance of bacterial attack.

12. De- foaming agents

13. Defoaming agents in Textile Wet-Processing Problems due to foam in textile wet-processing : Dense foam leads to serious entanglements of fabric with consequences of stoppages of machines, uneven absorbency, and patchy dyeing . In the dyeing of hanks and knitted fabrics, foaming of the dye liquor can cause the material to float resulting in uneven application of dye . The foam in printing paste, especially in rotary screen and roller printing machine can cause ‘fish eye’ spots on printed fabrics. D efoamer /anti-foaming agent

14. Defoaming agent The inherent characteristic of a de-foaming agent is that it is surface-active but highly insoluble in water, with an extremely high surface area it is dispersed as tiny droplets in the form of an emulsion. The surface-active components provide it with the ability to spread very rapidly into any air-water interface that it encounters. The spreading action of de- foamer causes a chemical or mechanical shock to the surface, which in turn destabilizes the foam.

15. Mechanism of defoamers : The surface-active nature of the defoamer causes it to spread very rapidly onto any air-water interface that it encounters. The function of hydrophobic silica particles is to pierce the surfaces of foam bubbles, causing them to coalesce when the defoamer spreads at the interface. Depending on the particular antifoam and the foaming system, one can expect differences in the relative importance of these factors:

16. 1. Dispersion of antifoam in the foaming solution 2. Transport of antifoam droplets from bulk to the bubble interface 3. Entry of the droplet into the gas/liquid interface 4. Spreading 5. Bubble rupture

17. Requirements 1. The state of the foaming system, its homogeneity 2. The solution viscosity 3. The surfactant concentration in relationship to the critical micelle concentration (CMC) 4. The surfactant type: ionic, nonionic, or mixed 5. The solution surface tension 6. The operating temperature 7. The solution pH

18. D e- foamers used in textile processing (I ) Non-silicone and (II)Silicone oil-based de-foamers Non-silicone oil de- foamers can be further classified as : a) Mineral oil b) Alkyl phosphate c) Block copolymers of ethylene oxide/propylene oxide a) Mineral oil do not perform at high alkalinity and high temperature, The efficiency is lower inexpensive as compared to silicone-based de- foamers . functional finishes like flame retardants and, in most cases, with water-repellents or fluorochemicals

19. Alkyl phosphate Phosphates are insoluble in water and hence made dispersible by usage of selected surfactants. When such an emulsified product is added in water it rapidly causes displacement of air and allows quick wetting and sinking, thus preventing fabric floatation. They show excellent alkali stability as they are phosphate esters. These foam-control agents are more accurately. c) EO/PO Block Copolymers : EO/PO copolymers normally have good dispersing properties and are often well suited when deposit problems are an issue. These are organic surfactants, which are essentially suitable to formulate no-foaming detergents. They are soluble in aqueous media at room temperature. They can be used as shear-stable antifoams, which are active as foam-control agents above their cloud point

20. Silicone defoamers : Foam is difficult to break down because it is stabilized by the surface elasticity and surface viscosity of its film. Silicones have low surface and interfacial tensions. This enables them to flow easily over the film They seek out openings between the foam-stabilizing surfactants at the liquid-air interface and occupy them. Silicones’ low surface tension and interfacial properties combined with their lack of foam-stabilization properties cause the foam wall to thin and collapse.

21. They are highly efficient antifoams/de- foamers , showing excellent performance even at low dosages; however due to the strong hydrophobic nature of poly-dimethyl siloxane , these emulsions are susceptible to shear, pH and temperature, resulting in difficult-to remove oil stains. Hence these silicone de- foamers are best suited for low-turbulence machines, ambient temperatures and weakly acidic to weakly alkaline aqueous baths. Silicone defoamers :