Tài liệu Eco friendly in textile processing

Eco Friendly In Textile Wet Processing By Aravin Prince Periyasamy [email protected] 1 Supercritical Carbon Dioxide [email protected] 2 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. [email protected] 3 Supercritical Fluid of CO2 [email protected] 4 Above 31.10C and 73 atm carbon dioxide behaves as a supercritical fluid and shows properties of both a liquid and a gas It fills the container, like a gas, and dissolves substances like a liquid. [email protected] 5 Supercritical fluid of CO2  With an increase in temperature the meniscus begins to diminish.  The liquid density falls due to expansion and the gas density rises as more of the substance evaporates. [email protected] 6 Supercritical fluid of CO2  Once the critical temperature and pressure have been reached the two distinct phases of liquid and gas are no longer visible. The meniscus can no longer be seen. One homogenous phase called the "supercritical fluid" phase occurs. [email protected] 7 Industrial extraction with supercritical CO2  Decaffeinating coffee and tea  Extracting bitterness to make beer  Defatting cocoa powder  Extracting spices and aromatic plants [email protected] 8 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 [email protected] 9 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. [email protected] 10 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 [email protected] 11 Use of supercritical CO2 in dyeing processes [email protected] 12 Use of supercritical CO2 in dyeing processes [email protected] 13 Enzymes [email protected] 14 [email protected] 15 Electron-ray treatment [email protected] 16 Microwaves Microwaves are electromagnetic waves whose frequency ranges from 1000MHz to10,00,000 MHz. Microwave dyeing takes into account only the dielectric and the thermal properties. The dielectric property refers to the intrinsic electrical properties that affect the dyeing by dipolar rotation of the dye and influences the microwave field upon the dipoles. [email protected] 17  The aqueous solution of dye has two components which are polar, in the high frequency microwave field oscillating at 2450MHz. It influences the vibrational energy in the water molecules and the dye molecules.  The heating mechanism is through ionic conduction, which is a type of resistance heating. Depending on the acceleration of the ions through the dye solution, it results in collision of dye molecules with the molecules of the fiber.  This helps and affects the penetration of the dye and also the depth to which the penetration takes place in the fabric. This makes microwave superior to conventional dyeing techniques [email protected] 18 Ultrasonic Treatments [email protected] 19 Electrochemical dyeing Vat and sulphur dyeing involves both a reducing and an oxidising step, which are carried out with chemical oxidants and reducing agents. The environmental concerns associated with the use of these chemicals are many. An attractive alternative technique is to reduce and oxidise the dye by means of electrochemical methods. With direct electrolysis the dye itself is reduced at the surface of the cathode. In indirect electrolysis the reducing power of the cathode is transferred to the solution by a soluble reversible redox system (e.g. based on antraquinone chemistry or iron complexes). With this reversible redox system the reducing agent is continuously regenerated at the cathode, which thus allows full recycling of the dye bath and the reducing agent. Direct cathodic reduction in an electrochemical cell is applicable to sulphur dyes. Vat dyes are reduced by indirect [email protected] 20 electrolysis.