Among the man-made fibres, polyester fibre is widely used because of its certain desirable properties. However, dyeing of polyester fibres with disperse dyes is a complex phenomenon and offers considerable difficulties in dyeing due compact structure and absence of reactive sites. To reduce energy cost, efficient processes such as pretreatment with solvents, have been conceived as a potent route for producing atmospheric pressure dyeable polyester. Extensive research has been carried out on modifying polyesters using solvents. Researchers have established that treatment of polyester with suitable solvent results in molecular rearrangement, giving such morphological structure to polyester, so as to make it more dye receptive. Process to produce low temprature dyeable polyester by methylene chloride pretreatment has been patented15-16. Solvent treatments did not have any adverse effect on the other textile properties of polyester.
The structural modifications of polyester depend upon the extent of interaction between polyester and solvents, associated with their respective solubility parameters. Chemical modification of polyester, by solvent pretreatment, results in changes in the dyeability characteristics. When the polyester is pretreated with a suitable solvent, the internal structure, especially the amorphous region, is changed and thereby more voids, cracks and likes are formed, which facilitate entry of dye molecules in to the polymer structure. Also the solvents break the intermolecular bonds and loosen the fibre structure which in turn increases the segmental mobility of the polymer and thus enhance the dye uptake. The amount of the dye uptake depends upon the degree of interaction between the solvent and the polymer, experimental conditions as well as the extent of structural modification effected by the treatment.
Literature survey shows that treatments with various solvents were carried out at room temperature as well as at elevated temperature and time of treatment is from 2 to 960 min. In these studies, conventional heating techniques were used for treatments at elevated temperature. However, to best of our knowledge no information is available on the use of Microwaves for the solvent pretreatment of polyester, although microwaves are used for the dyeing of polyester.
Therefore the present study was undertaken to investigate the use of microwave heating for solvent pretreatment. The idea behind using microwaves was to reduce the pretreatment time since microwaves are known to give fast and rapid volume heating. This paper deals with the dyeability characteristics and structural changes due to solvent pretreatment in microwave oven.
Published with due permission from Bombay Textile Research Association