Surfactant

The  word Surfactant is  coined from  the  expression  " surface  active  agent" . As the  phrase implies, a  surfactant  molecule possesses  surface activity,  a  property associated  with the  chemical structure of  the  molecule. The characteristic feature  of a  surfactant  molecule is  its two  ends attached by a covalent  bond  The  two  ends have diametrically opposed  polarities.  The non - polar  end  is  lyophilic (strongly attracted to  organic  molecules)  while  the  strongly polar  end  is  lyophobic  (having  little attraction  for  organic  molecules)  yet  strongly hydrophilic (water loving).  Duality of
polarity  causes the  molecule to align  itself  with respect  to the  polar  nature of  the surfaces  it  contacts.

Physical  Chemistry  of Surfactant  Solutions

When soap (sodium  oleate) molecules are  added  to pure  water  one  molecule at a  time,  the  first  few  molecules align  at the  air/water  interface and the  hydrocarbon tails  orient  toward  air.  The driving  force  for  this  alignment  is  the  non - polar  tails seeking  to associate  themselves with the  most non - polar interface it  can  find,  in this case air.  As additional  molecules  are  added,  they  too  will  align  at the  water/air interface until all of  the  surface  area is  completely packed.  As more molecules are added, they  are  forced  into the  bulk of  the  water, floating  about  as individual
molecules until  a  saturation  level  is  reached. At this  point,  called  the  Critical Micelle Concentration, soap  molecules  agglomerate  into  water soluble  clumps (Micelles), where  the  lyophobic  tails  are  associated  with themselves  and  the hydrophilic heads are  surrounded  by water  molecules.  This sequence of events are diagrammed  in figure  27.  The first  beaker represents close  packing  of surfactant molecules at the  surface.  The second beaker represents the  condition before micelle formation.  The third  beaker shows the  formation  of  micelles.

Orientation of Surfactant  Molecules in Water 

 

CLASSIFICATION  OF SURFACTANTS 

Surfactants are classified  according  to use,  to ionic  charge and  to chemical structure.

(A) By Use

1.Wetting Agents:  The ability of  a  liquid  to spread on a  smooth  solid  surface  is dependent  on the  polar nature of  the  solid and  the  surface  tension  of  the  liquid. More about  the  thermodynamic relationships will  be brought  up in the  chapter  on water and  oil repellents.  A  non - polar  solid surface  such as paraffin  wax or Teflon will  cause a  drop of  pure water  to bead- up and  not  spread.  Water containing surfactants on the other  hand will  easily  spread on paraffin surfaces  and  have lower  contact  angles on Teflon.  Surfactants used this  way are  called  wetting agents, or penetrating agents when used to wet out repellent fabrics.  This is  illustrated in figure. Penetration  of  fabrics  is  a  function  of  surface  wetting,  however  fabric assemblies have a  volume of  air entrapped  in the  void formed  spaces.  Before a  liquid can  move in,  the  air must move out. Penetrants facilitate this  process.

Spreading  of Water on Smooth Surfaces

 

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  redeposition.

3.Emulsifying Agents: Emulsifying Agentsare  surfactants that convert water- insoluble  oils  into stable, aqueous suspensions.  The lyophilic part of  the  surfactant  molecule is absorbed by the oil droplet and the  lyophobic  head is  oriented  outward, surrounding the  droplet with a  hydrophilic sheath.  Ionic  surfactants add another  dimension  to  the  stability of emulsions, they set  up a  charge - charge  repulsion  field  which  adds to keeping the droplets  separated.

3.Dispersing  Agents: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.  Surfactant molecules  must be  matched  with their intended use.

B. By Ionic  Charge
1.Anionic:  Those  that develop  a  negative charge on the  water  solubilizing  end.
2.Cationic: Those  that  develop  a  positive  charge on the  water  solubilizing  end.
3.Non -Ionic:  Those  that develop  no ionic  charge on the  water  solubilizing  end.
4.Amphoteric:  Those  that have both a positive  and  negative charged  group  on the  molecule.

Denim Manufacturing Process

For manufacturing Denim and Grey Fabric, the process is same up to the level of weaving, but in case of Denim Fabric, dyeing is done at the stage of sizing where as for
Grey Fabric it depends upon the finished product. The details of each process are given below:-

1.   Fabric Weaving 

a. Grey Yarn on Cones

Normally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:

• Warp yarn 
• Weft yarn

Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.



b.  Warping on Sectional/ Direct Warping
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine. 

c. Sizing of yarn in Set/ Beam to Beam Position
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.

d. Drawing–in
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.

e. Beam Gaiting or Knotting on Loom
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length
is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.

f. Weaving 
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:

•  Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
• Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttleless Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms.

Airjet Looms
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.