Detergency

It is a process by which soil is removed from a surface and undergoes solubilization or dispersion.

Result of several physicochemical phenomenons taking place at the interface of three phases : surface/soil/detergent.

The phenomenons are :

– Wetting of surface

– Removal of soil from surface

 – Avoiding re-deposition of soil on surface.

Basic Principal:

1.Wetting of surface: The detergent must come into contact with the surface so that adherence forces of detergent with subtract of surface should be higher than  adherence forces of soil with subtract of surface

          F_{detergent/surface} > F_{soil /surface}   ( Here F = adherence force )

It lower the superficial tension of the detergent solution and the interfacial tensions between aqueous bath, soil and surface

2.Removal of soil:The detergent solution wets the surface, is absorbed by it and lowers the surface’s attraction to allow the soil to separate itself from the surface.

3.Avoiding re-deposition

Chemical reactions

 – lipids undergo saponification

 – mineral soil undergoes solubilization

 – soil undergoes emulsification

 Liquid soil = hydrophobic ; detergent solution = hydrophilic.

Preparation of detergent

During the preparation of detergents, long-chain hydrocarbon obtained from petroleum fractions is converted into an organic aid through a series of steps.  The organic acid is then neutralized with sodium hydroxide, NaOH solution to produce a detergent. Examples are of detergents are: Sodium alkyle sulphate and sodium alkylbenzene sulphonate.

(Above pictures taken from https://image.slidesharecdn.com/soapanddetegents-150725134721-lva1-app6891/95/soap-and-detegents-8-638.jpg?cb=1437832077)

Dispersing Agents (Solid in water):

These are organic compound. A solid material dispersed in a liquid requires an additive to make the dispersion process easier and more stable – this is the role of the dispersing agent, or dispersant. Dispersing Agents function in a manner similar to emulsifying agents. The difference is that solid particulate matter, rather than insoluble oils, is dispersed. The nature of the lyophilic part of the surfactant molecule must be such that it adsorbs onto the particle's surface. These assist the process of dye particles size reduction and help to dissolve dye particles in water. Pigment colour paste one of the most known example in which dispersing agent is used to disperse pigment in water. Disperse dye also contains dispersing agents.

How they work?

When we shake solid (like sand) in water, it seems that solid is dissolved. However after some time solid particles are separated out from water. These solid particles attract each other. That is why they come together and separate out from water. To separate these particles from each other, there is a need of energy. Also, solid particles must be stabilised after they have been separated from each other. The particles will move to each other and glue together again when particle-particle repulsion is insufficient. The spontaneous process of gluing together of solid particles in a liquid is called flocculation. The functionality of a dispersant is to prevent flocculation. Dispersants do their job because the molecules adsorb on the solid-liquid interface and assure repulsion between the particles.

What is the difference between Soaps and Detergent:

Soaps

Soap is made from fat and alkali by specification method. There are not suitable for delicate clothes.  They work well in hot water. They don't produce lather with hard water and are not able to clean the cloth. Lot of water is needed to remove soap from the cloth.

Detergents

Detergents are carbonic compounds which are not alkaline. They are suitable for delicate clothes. They clean both in hot and cold water. They clean the cloth even in hard water. They are removed very easily so less quantity of water is needed.

     3. Emulsifying Agents (Oil in water)

When water and oil are mixed together and vigorously shaken, a dispersion of oil droplets in water - and vice versa - is formed. When shaking stops, the phases start to separate. 

However, when an emulsifier is added to the system, the droplets remain dispersed, and a stable emulsion is obtained.

An emulsifier consists of a water-loving hydrophilic head and an oil-loving hydrophobic tail. The hydrophilic head is directed to the aqueous phase and the hydrophobic tail to the oil phase. 

2. Detergents

Detergents are surfactants that help remove soils from solid surfaces. Over and above reducing water's surface tension, detergents must adsorb onto the soil's surface to aid in spontaneous release. Detergents must also keeps the soil suspended to prevent re-deposition. 

Ø  Detergents are surfactants used  for removal of dirt.

Ø  Detergency involves:

•      Initial wetting of the dirt and the surface to be cleaned.

•      Deflocculation and suspension, emulsification or solubilization of the dirt particles
•      Finally washing away the 

dirt.http://d25smtqkk0nuqw.cloudfront.net/wp-content/uploads/2015/11/biorf11.gif

Following can be understand from the above figure:
1. Dirty Substrate (Any textile material)  come in contact with detergent or surfactant in the presence of water
2. Detergent molecules start coming toward dirt or soil. As the dirt is oily in nature hydrophobic tail come in contact with dirt and hydrophilic head of detergent molecule remain in water.

3. Slowly detergent surrounded dirt particles and pulling them out of substate
4. All the dirt particles removed from the substrate.

a)    Wetting agents: Wetting agent is a surfactant that when dissolved in water, lower the contact angle and reduce the surface tension of a liquid. According to the nature of the liquid and the solid, a drop of liquid placed on a solid surface will adhere to it or no. which is the wettability between liquids and solids. When the forces of adhesion are greater than the forces of cohesion, the liquid tends to wet the surface and vice versa.

To more clarification example of behavior of water and mercury in test tube can be taken. The surface of liquid water (meniscus) has a concave shape because water wets the surface and creeps up the side. The surface of Mercury has a convex shape it does not wet glass because the cohesive forces within the drops are stronger than the adhesive forces between the drops and glass.

Classification of SURFACTANT

Surfactants can be classified in the following ways 

1. According to their uses 

2. According to their ionic nature 

1. According to their uses: These may be classify as given below as per their applications: 

Wetting agents,  Solubilizing agents,  Emulsifying agents, Dispersing agents, Suspending & Deflocculating agents, Foaming and antifoaming agents, Detergents

2. According to their ionic nature : Ionic and Non Ionic
Ionic can further divided in to Anionic, Cationic and Amhoteric or Zwitterionic

Anionic: Those that develop a negative charge on the water solubilizing end.
Cationic: Those that develop a positive charge on the water solubilizing end.
Non-Ionic: Those that develop no ionic charge on the water solubilizing end. 
Amphoteric or Zwitterionic (: Those that have both a positive and negative charged group on the molecule.

Surfactants: Surfactants are surface active agents. Surfactant are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids.

Surface active agent: Certain substances like soaps ,sulphonic acids and organic compounds like methyl alcohol , acetone which when added to the water even in small amount decrease the surface tension of water  to a considerable extent. Such substances which lower the surface tension of water is called surface active agent.

Each surfactant molecule has a hydrophilic (water-loving) head that is attracted to water molecules and a hydrophobic (water-hating) tail that repels water and simultaneously attaches itself to oil and grease in dirt.

(http://slideplayer.com/slide/7682785/)

A surfactant or surface active agent is a substance that, when dissolved in water, gives a product the ability to remove dirt from surfaces such as the human skin, textiles, and other solids.

Principal of Surfactant: Surfactants are also referred to as wetting agents and foamers. Surfactants lower the surface tension of the medium in which it is dissolved. By lowering this interfacial tension between two media or interfaces (e.g. air/water, water/stain, stain/fabric).

Role of Surfactant in wet processing:

All textile processes use water as a process medium. In order to conduct these processes, the textile substrate must be totally wetted out. Surfactants are necessary to lower the surface tension of process solutions for uniform application.

In fibre manufacture of synthetic/regenerated fibres and yarn spinning of cotton, wool, and their blends, surfactants are often sprayed on the fibre and yarn surface to reduce fibre-fibre and fibre-metal friction, referred to as yarn lubricants.

In textile dyeing, surfactants are broadly used as wetting agent, dispersants and leveling agents to help uniform dying and better dye penetration.

Dye fixatives and dye carriers are also surface active although they are not as common as other dyeing assistants.

In textile finishes, surfactants are often used as fabric softeners to improve fabric hand or feel and used as antistatic agents to control static electricity built up on the surface of textile fibres, particularly on synthetic fibre due to their low moisture contents.

Surfactants are also useful to control foam formation during textile processes, referred as antifoaming agents, particularly in dyeing and other processes with high-speed padding. 

Surface tension:

Molecules of the liquid at the surface are in different situation than those in the interior of the liquid. Molecule lying inside the liquid (As shown in figure as 'A') is surrounded by other molecules and so attracted equally in all directions. Hence the net force of attraction acting on the molecule is zero. But a molecule lying at the surface (As shown in figure as 'C') is attracted downwards by the molecules lying in the bulk of the liquid. Thus a molecule lying at the surface experiences a net inward attraction. As a result of this inward pull on all molecules lying at the surface, the surface behaves as if it were under tension. This property of liquid is called surface tension. Unit of surface tension is Dyne per cm. 

Classifications of Chemical Auxiliaries: i) Permanent or Temporary auxiliaries 

ii) Nature of auxiliaries (Surface active/non surface active/soluble/dispersing or emulsifying) 

i) Permanent or Temporary auxiliaries: 

Chemicals which are never remain with textile materials and need to be removed after processing come under Temporary auxiliaries. Examples of these chemicals are sizing chemicals, enzymes, detergents, wetting agents, leveling agents, carriers, dispersing agents, thickeners etc.

In case of permanent auxiliaries the chemicals which permanently fix on the textiles like softeners, water proofing agent, flame retardant chemicals, water repellent chemicals, rot proofing agents, binders, dye fixing agents etc.

ii) Nature of auxiliaries (Surface active/non surface active/soluble/dispersing or emulsifying/Inorganic chemicals) 

a) Surface active agents are those which act on the surface first and then react with the textiles. These are detergents, softeners, wetting agents, water repellent agent, emulsifier, dispersing agents, dyeing assistant etc

b) Non surface active agents are those which mostly not react with the textiles and remain only on the surface. Examples of these are resin, cross linking agents, sizing chemicals, thickener, binder etc.

c) There are some chemical auxiliaries which have non surface active with small amount of surface active agents properties. These are wax emulsions, silicone emulsion, spin finish oils etc.

d) Inorganic chemicals are reducing agents, acids like acetic acid, buffers to maintain pH, bleaching agents, mordants, oxidizing agents, hydrolyzing agents etc

What is Textile Auxiliaries?

At various stages of textile wet processing different types of chemicals and auxiliaries are used. Though all are actually chemicals, in practice the materials without which a process cannot be complete are termed as “chemicals” and the other substances which facilitate or improve the performance of that process are termed as “auxiliaries”. 

Auxiliaries are those chemicals which help processing operation such as preparation, dyeing, printing or finishing to be carried out more effectively. Some of the cases these chemicals are essential if a given effect such as wash & wear, water repellent, flame retardant, aroma finish, anti odour, colour deepening etc. is to be obtained. 

Classifications of Chemical Auxiliaries:

These can be classifies in to two ways:

i)             Permanent or Temporary auxiliaries

ii)           Nature of auxiliaries (Surface active/non surface active/soluble/dispersing or emulsifying)