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Introduction


Among the man-made fibres, polyester fibre is widely used becauseof its certain desirable properties. However, dyeing of polyester fibres withdisperse dyes is a complex phenomenon and offers considerable difficulties indyeing due compact structure and absence of reactive sites. To reduce energycost, efficient processes such as pretreatment with solvents, have beenconceived as a potent route for producing atmospheric pressure dyeable polyester. Extensive research has been carried out on modifyingpolyesters using solvents. Researchers have established that treatment of polyesterwith suitable solvent results in molecular rearrangement, giving suchmorphological structure to polyester, so as to make it more dye receptive. Process to produce low tempraturedyeable polyester by methylene chloride pretreatment has been patented15-16. Solvent treatments did not have anyadverse effect on the other textile properties of polyester.


The structural modifications of polyester depend upon the extentof interaction between polyester and solvents, associated with their respectivesolubility parameters. Chemical modification of polyester, bysolvent pretreatment, results in changes in the dyeability characteristics.When the polyester is pretreated with a suitable solvent, the internalstructure, especially the amorphous region, is changed and thereby more voids,cracks and likes are formed, which facilitate entry of dye molecules in to thepolymer structure. Also the solvents break the intermolecular bonds and loosenthe fibre structure which in turn increases the segmental mobility of thepolymer and thus enhance the dye uptake. The amount of the dye uptake dependsupon the degree of interaction between the solvent and the polymer,experimental conditions as well as the extent of structural modificationeffected by the treatment.


Literature survey shows that treatments with various solvents werecarried out at room temperature as well as at elevated temperature and time oftreatment is from 2 to 960 min. In these studies, conventional heatingtechniques were used for treatments at elevated temperature. However, to bestof our knowledge no information is available on the use of Microwaves for thesolvent pretreatment of polyester, although microwaves are used for the dyeingof polyester.


Therefore the present study was undertaken to investigate the useof microwave heating for solvent pretreatment. The idea behind using microwaveswas to reduce the pretreatment time since microwaves are known to give fast andrapid volume heating. This paper deals with the dyeability characteristics andstructural changes due to solvent pretreatment in microwave oven.



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Published with due permission from Bombay Textile ResearchAssociation