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What is supercritical carbon dioxide?
A supercritical fluid is a substance above its
critical temperature and critical pressure.
Under these conditions the distinction
between gases and liquids does not apply
and the substance can only be described as
a fluid.
Above 31.10C and 73 atm carbondioxide behaves as a supercritical fluidand shows properties of both a liquidand a gas
It fills the container, like a gas, anddissolves substances like a liquid.
Supercritical fluid of CO2
With an increase intemperature the meniscusbegins to diminish.
The liquid density falls dueto expansion and the gasdensity rises as more of thesubstance evaporates.
Supercritical fluid of CO2
Once the criticaltemperature and pressurehave been reached the twodistinct phases of liquid andgas are no longer visible.The meniscus can no longerbe seen. One homogenousphase called the"supercritical fluid" phaseoccurs.
Industrial extraction with supercritical CO2
Decaffeinating coffee and tea
Extracting bitterness to make beer
Defatting cocoa powder
Extracting spices and aromatic plants
Significant properties of supercritical fluids
Diffusivity gas > supercritical fluid > liquid
Viscosity gas < supercritical fluid < liquid
Surface tension gas = supercritical fluid < liquid
Density gas < supercritical fluid < or = liquid
Benefits of using supercritical CO2 for extraction
It is having the penetration power of a gas and the extraction power of a liquid.
It acts as a solvent to extract organic compounds with a low molecular weight.
It leaves no residual trace on treated material
It respects the environment.
Supercritical CO2 as solvent
Purification of specialty chemicals and useful natural products
An alternative solvent in coatings industry (replacing 40 - 90% of volatile solvents)
Degreasing and dry cleaning applications
Increasingly applied as a solvents in synthetic industrial processes
Microwaves
Microwaves are electromagnetic waves whosefrequency ranges from 1000MHz to10,00,000MHz.
Microwave dyeing takes into account only thedielectric and the thermal properties.
The dielectric property refers to the intrinsicelectrical properties that affect the dyeing bydipolar rotation of the dye and influences themicrowave field upon the dipoles.
The aqueous solution of dye has two componentswhich are polar, in the high frequency microwavefield oscillating at 2450MHz. It influences thevibrational energy in the water molecules and thedye molecules.
The heating mechanism is through ionicconduction, which is a type of resistance heating.Depending on the acceleration of the ions throughthe dye solution, it results in collision of dyemolecules with the molecules of the fiber.
This helps and affects the penetration of the dyeand also the depth to which the penetration takesplace in the fabric. This makes microwave superiorto conventional dyeing techniques
Electrochemical dyeing
Vat and sulphur dyeing involves both a reducing and anoxidising step, which are carried out with chemical oxidantsand reducing agents. The environmental concerns associatedwith the use of these chemicals are many. An attractivealternative technique is to reduce and oxidise the dye bymeans of electrochemical methods.
With direct electrolysis the dye itself is reduced at the surfaceof the cathode. In indirect electrolysis the reducing power ofthe cathode is transferred to the solution by a solublereversible redox system (e.g. based on antraquinone chemistryor iron complexes). With this reversible redox system thereducing agent is continuously regenerated at the cathode,which thus allows full recycling of the dye bath and thereducing agent.
Direct cathodic reduction in an electrochemical cell is applicable to sulphur dyes. Vat dyes are reduced by indirect electrolysis. [email protected]
Plasma
4th State of Matter
Highly Reactive & Energetic
+ve, -ve Charges,Radicals,Electrons,
Excited molecules, atoms.
Electrically neutral
Thermal Plasma
Thermal
Equilibrium Between
Neutral Particles and
the Charged Particles
> 50,000°[email protected]
Gases Used
Non-polymerizing Gases
He, Ar, Air, Oxygen, Nitrogen, And Mixture Of Gases
Polymerizing Gases
Cf4, C3f6
…..Major Applications
•Soil Release Properties
•Composite Applications
….Synthetic Fibres/films
Deep Shades
…..Major Applications
•Shrinkage resistance
•Dyeability
•Fastness properties
….Natural Fibres
